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rfc:rfc3670

Network Working Group B. Moore Request for Comments: 3670 IBM Corporation Category: Standards Track D. Durham

                                                                 Intel
                                                          J. Strassner
                                                      INTELLIDEN, Inc.
                                                         A. Westerinen
                                                         Cisco Systems
                                                              W. Weiss
                                                              Ellacoya
                                                          January 2004
                 Information Model for Describing
              Network Device QoS Datapath Mechanisms

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

 The purpose of this document is to define an information model to
 describe the quality of service (QoS) mechanisms inherent in
 different network devices, including hosts.  Broadly speaking, these
 mechanisms describe the properties common to selecting and
 conditioning traffic through the forwarding path (datapath) of a
 network device.  This selection and conditioning of traffic in the
 datapath spans both major QoS architectures: Differentiated Services
 and Integrated Services.
 This document should be used with the QoS Policy Information Model
 (QPIM) to model how policies can be defined to manage and configure
 the QoS mechanisms (i.e., the classification, marking, metering,
 dropping, queuing, and scheduling functionality) of devices.
 Together, these two documents describe how to write QoS policy rules
 to configure and manage the QoS mechanisms present in the datapaths
 of devices.

Moore, et al. Standards Track [Page 1] RFC 3670 QoS Device Datapath Info Model January 2004

 This document, as well as QPIM, are information models.  That is,
 they represent information independent of a binding to a specific
 type of repository.

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Policy Management Conceptual Model . . . . . . . . . . .  6
     1.2.  Purpose and Relation to Other Policy Work. . . . . . . .  7
     1.3.  Typical Examples of Policy Usage . . . . . . . . . . . .  7
 2.  Approach . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     2.1.  Common Needs Of DiffServ and IntServ . . . . . . . . . .  8
     2.2.  Specific Needs Of DiffServ . . . . . . . . . . . . . . .  9
     2.3.  Specific Needs Of IntServ. . . . . . . . . . . . . . . .  9
 3.  Methodology. . . . . . . . . . . . . . . . . . . . . . . . . . 10
     3.1.  Level of Abstraction for Expressing QoS Policies . . . . 10
     3.2.  Specifying Policy Parameters . . . . . . . . . . . . . . 11
     3.3.  Specifying Policy Services . . . . . . . . . . . . . . . 12
     3.4.  Level of Abstraction for Defining QoS Attributes and
           Classes. . . . . . . . . . . . . . . . . . . . . . . . . 13
     3.5.  Characterization of QoS Properties . . . . . . . . . . . 14
     3.6.  QoS Information Model Derivation . . . . . . . . . . . . 15
     3.7.  Attribute Representation . . . . . . . . . . . . . . . . 16
     3.8.  Mental Model . . . . . . . . . . . . . . . . . . . . . . 17
           3.8.1.  The QoSService Class . . . . . . . . . . . . . . 17
           3.8.2.  The ConditioningService Class. . . . . . . . . . 18
           3.8.3.  Preserving QoS Information from Ingress to
                   Egress . . . . . . . . . . . . . . . . . . . . . 19
     3.9.  Classifiers, FilterLists, and Filter Entries . . . . . . 21
     3.10. Modeling of Droppers . . . . . . . . . . . . . . . . . . 23
           3.10.1. Configuring Head and Tail Droppers . . . . . . . 23
           3.10.2. Configuring RED Droppers . . . . . . . . . . . . 24
     3.11. Modeling of Queues and Schedulers. . . . . . . . . . . . 25
           3.11.1. Simple Hierarchical Scheduler. . . . . . . . . . 25
           3.11.2. Complex Hierarchical Scheduler . . . . . . . . . 27
           3.11.3. Excess Capacity Scheduler. . . . . . . . . . . . 29
           3.11.4. Hierarchical CBQ Scheduler . . . . . . . . . . . 31
 4.  The Class Hierarchy. . . . . . . . . . . . . . . . . . . . . . 33
     4.1.  Associations and Aggregations. . . . . . . . . . . . . . 33
     4.2.  The Structure of the Class Hierarchies . . . . . . . . . 34
     4.3.  Class Definitions. . . . . . . . . . . . . . . . . . . . 38
           4.3.1.  The Abstract Class ManagedElement. . . . . . . . 38
           4.3.2.  The Abstract Class ManagedSystemElement. . . . . 39
           4.3.3.  The Abstract Class LogicalElement. . . . . . . . 39
           4.3.4.  The Abstract Class Service . . . . . . . . . . . 39
           4.3.5.  The Class ConditioningService. . . . . . . . . . 39
           4.3.6.  The Class ClassifierService. . . . . . . . . . . 40
           4.3.7.  The Class ClassifierElement. . . . . . . . . . . 41

Moore, et al. Standards Track [Page 2] RFC 3670 QoS Device Datapath Info Model January 2004

           4.3.8.  The Class MeterService . . . . . . . . . . . . . 42
           4.3.9.  The Class AverageRateMeterService. . . . . . . . 44
           4.3.10. The Class EWMAMeterService . . . . . . . . . . . 44
           4.3.11. The Class TokenBucketMeterService. . . . . . . . 46
           4.3.12. The Class MarkerService. . . . . . . . . . . . . 47
           4.3.13. The Class PreambleMarkerService. . . . . . . . . 47
           4.3.14. The Class ToSMarkerService . . . . . . . . . . . 48
           4.3.15. The Class DSCPMarkerService. . . . . . . . . . . 49
           4.3.16. The Class 8021QMarkerService . . . . . . . . . . 49
           4.3.17. The Class DropperService . . . . . . . . . . . . 50
           4.3.18. The Class HeadTailDropperService . . . . . . . . 52
           4.3.19. The Class REDDropperService. . . . . . . . . . . 52
           4.3.20. The Class QueuingService . . . . . . . . . . . . 54
           4.3.21. The Class PacketSchedulingService. . . . . . . . 55
           4.3.22. The Class NonWorkConservingSchedulingService . . 56
           4.3.23. The Class QoSService . . . . . . . . . . . . . . 57
           4.3.24. The Class DiffServService. . . . . . . . . . . . 58
           4.3.25. The Class AFService. . . . . . . . . . . . . . . 59
           4.3.26. The Class FlowService. . . . . . . . . . . . . . 60
           4.3.27. The Class DropThresholdCalculationService. . . . 60
           4.3.28. The Abstract Class FilterEntryBase . . . . . . . 61
           4.3.29. The Class IPHeaderFilter . . . . . . . . . . . . 62
           4.3.30. The Class 8021Filter . . . . . . . . . . . . . . 62
           4.3.31. The Class PreambleFilter . . . . . . . . . . . . 62
           4.3.32. The Class FilterList . . . . . . . . . . . . . . 63
           4.3.33. The Abstract Class ServiceAccessPoint. . . . . . 63
           4.3.34. The Class ProtocolEndpoint . . . . . . . . . . . 63
           4.3.35. The Abstract Class Collection. . . . . . . . . . 65
           4.3.36. The Abstract Class CollectionOfMSEs. . . . . . . 65
           4.3.37. The Class BufferPool . . . . . . . . . . . . . . 65
           4.3.38. The Abstract Class SchedulingElement . . . . . . 65
           4.3.39. The Class AllocationSchedulingElement. . . . . . 66
           4.3.40. The Class WRRSchedulingElement . . . . . . . . . 67
           4.3.41. The Class PrioritySchedulingElement. . . . . . . 69
           4.3.42. The Class BoundedPrioritySchedulingElement . . . 70
     4.4.  Association Definitions. . . . . . . . . . . . . . . . . 70
           4.4.1.  The Abstract Association Dependency. . . . . . . 71
           4.4.2.  The Association ServiceSAPDependency . . . . . . 71
           4.4.3.  The Association
                   IngressConditioningServiceOnEndpoint . . . . . . 71
           4.4.4.  The Association
                   EgressConditioningServiceOnEndpoint. . . . . . . 72
           4.4.5.  The Association HeadTailDropQueueBinding . . . . 72
           4.4.6.  The Association CalculationBasedOnQueue. . . . . 73
           4.4.7.  The Association ProvidesServiceToElement . . . . 74
           4.4.8.  The Association ServiceServiceDependency . . . . 74
           4.4.9.  The Association CalculationServiceForDropper . . 75
           4.4.10. The Association QueueAllocation. . . . . . . . . 75

Moore, et al. Standards Track [Page 3] RFC 3670 QoS Device Datapath Info Model January 2004

           4.4.11. The Association ClassifierElementUsesFilterList. 76
           4.4.12. The Association AFRelatedServices. . . . . . . . 77
           4.4.13. The Association NextService. . . . . . . . . . . 78
           4.4.14. The Association
                   NextServiceAfterClassifierElement. . . . . . . . 79
           4.4.15. The Association NextScheduler. . . . . . . . . . 80
           4.4.16. The Association FailNextScheduler. . . . . . . . 81
           4.4.17. The Association NextServiceAfterMeter. . . . . . 82
           4.4.18. The Association QueueToSchedule. . . . . . . . . 83
           4.4.19. The Association SchedulingServiceToSchedule. . . 84
           4.4.20. The Aggregation MemberOfCollection . . . . . . . 85
           4.4.21. The Aggregation CollectedBufferPool. . . . . . . 85
           4.4.22. The Abstract Aggregation Component . . . . . . . 86
           4.4.23. The Aggregation ServiceComponent . . . . . . . . 86
           4.4.24. The Aggregation QoSSubService. . . . . . . . . . 86
           4.4.25. The Aggregation QoSConditioningSubService. . . . 87
           4.4.26. The Aggregation
                   ClassifierElementInClassifierService . . . . . . 88
           4.4.27. The Aggregation EntriesInFilterList. . . . . . . 89
           4.4.28. The Aggregation ElementInSchedulingService . . . 90
 5.  Intellectual Property Statement. . . . . . . . . . . . . . . . 91
 6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 91
 7.  Security Considerations. . . . . . . . . . . . . . . . . . . . 91
 8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 92
     8.1. Normative References. . . . . . . . . . . . . . . . . . . 92
     8.2. Informative References  . . . . . . . . . . . . . . . . . 92
 9.  Appendix A:  Naming Instances in a Native CIM Implementation . 94
     9.1. Naming Instances of the Classes Derived from Service. . . 94
     9.2. Naming Instances of Subclasses of FilterEntryBase . . . . 94
     9.3. Naming Instances of ProtocolEndpoint. . . . . . . . . . . 94
     9.4. Naming Instances of BufferPool. . . . . . . . . . . . . . 95
           9.4.1.  The Property CollectionID. . . . . . . . . . . . 95
           9.4.2.  The Property CreationClassName . . . . . . . . . 95
     9.5. Naming Instances of SchedulingElement . . . . . . . . . . 95
 10. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 96
 11. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 97

1. Introduction

 The purpose of this document is to define an information model to
 describe the quality of service (QoS) mechanisms inherent in
 different network devices, including hosts.  Broadly speaking, these
 mechanisms describe the attributes common to selecting and
 conditioning traffic through the forwarding path (datapath) of a
 network device.  This selection and conditioning of traffic in the
 datapath spans both major QoS architectures: Differentiated Services
 (see [R2475]) and Integrated Services (see [R1633]).

Moore, et al. Standards Track [Page 4] RFC 3670 QoS Device Datapath Info Model January 2004

 This document is intended to be used with the QoS Policy Information
 Model [QPIM] to model how policies can be defined to manage and
 configure the QoS mechanisms (i.e., the classification, marking,
 metering, dropping, queuing, and scheduling functionality) of
 devices.  Together, these two documents describe how to write QoS
 policy rules to configure and manage the QoS mechanisms present in
 the datapaths of devices.
 This document, as well as [QPIM], are information models.  That is,
 they represent information independent of a binding to a specific
 type of repository.  A separate document could be written to provide
 a mapping of the data contained in this document to a form suitable
 for implementation in a directory that uses (L)DAP as its access
 protocol.  Similarly, a document could be written to provide a
 mapping of the data in [QPIM] to a directory. Together, these four
 documents (information models and directory schema mappings) would
 then describe how to write QoS policy rules that can be used to store
 information in directories to configure device QoS mechanisms.
 The approach taken in this document defines a common set of classes
 that can be used to model QoS in a device datapath. Vendors can then
 map these classes, either directly or using an intervening format
 like a COP-PR PIB, to their own device-specific implementations.
 Note that the admission control element of Integrated Services is not
 included in the scope of this model.
 The design of the class, association, and aggregation hierarchies
 described in this document is influenced by the Network QoS submodel
 defined by the Distributed Management Task Force (DMTF) - see [CIM].
 These hierarchies are not derived from the Policy Core Information
 Model [PCIM].  This is because the modeling of the QoS mechanisms of
 a device is separate and distinct from the modeling of policies that
 manage those mechanisms.  Hence, there is a need to separate QoS
 mechanisms (this document) from their control (specified using the
 generic policy document [PCIM] augmented by the QoS Policy document
 [QPIM]).
 While it is not a policy model per se, this document does have a
 dependency on the Policy Core Information Model Extensions document
 [PCIME].  The device-level packet filtering, through which a
 Classifier splits a traffic stream into multiple streams, is based on
 the FilterEntryBase and FilterList classes defined in [PCIME].
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in BCP 14, RFC 2119
 [R2119].

Moore, et al. Standards Track [Page 5] RFC 3670 QoS Device Datapath Info Model January 2004

1.1. Policy Management Conceptual Model

 The Policy Core Information Model [PCIM] describes a general
 methodology for constructing policy rules.  PCIM Extensions [PCIME]
 updates and extends the original PCIM.  A policy rule aggregates a
 set of policy conditions and an ordered set of policy actions.  The
 semantics of a policy rule are such that if the set of conditions
 evaluates to TRUE, then the set of actions are executed.
 Policy conditions and actions have two principal components: operands
 and operators.  Operands can be constants or variables. To specify a
 policy, it is necessary to specify:
 o  the operands to be examined (also known as state variables);
 o  the operands to be changed (also known as configuration
    variables);
 o  the relationships between these two sets of operands.
 Operands can be specified at a high-level, such as Joe (a user) or
 Gold (a service).  Operands can also be specified at a much finer
 level of detail, one that is much closer to the operation of the
 device.  Examples of the latter include an IP Address or a queue's
 bandwidth allocation.  Implicit in the use of operands is the binding
 of legal values or ranges of values to an operand.  For example, the
 value of an IP address cannot be an integer.  The concepts of
 operands and their ranges are defined in [PCIME].
 The second component of policy conditions and actions is a set of
 operators.  Operators can express both relationships (greater than,
 member of a set, Boolean OR, etc.) and assignments.  Together,
 operators and operands can express a variety of conditions and
 actions, such as:
    If Bob is an Engineer...
    If the source IP address is in the Marketing Subnet...
    Set Joe's IP address to 192.0.2.100
    Limit the bandwidth of application x to 10 Mb
 We recognize that the definition of operator semantics is critical to
 the definition of policies.  However, the definition of these
 operators is beyond the scope of this document.  Rather, this
 document (with [QPIM]) takes the first steps in identifying and
 standardizing a set of properties (operands) for use in defining
 policies for Differentiated and Integrated Services.

Moore, et al. Standards Track [Page 6] RFC 3670 QoS Device Datapath Info Model January 2004

1.2. Purpose and Relation to Other Policy Work

 This model establishes a canonical model of the QoS mechanisms of a
 network device (e.g., a router, switch, or host) that is independent
 of any specific type of network device.  This enables traffic
 conditioning to be described using a common set of abstractions,
 modeled as a set of services and sub-services.
 When the concepts of this document are used in conjunction with the
 concepts of [QPIM], one is able to define policies that bind the
 services in a network to the needs of applications using that
 network.  In other words, the business requirements of an
 organization can be reflected in one set of policies, and those
 policies can be translated to a lower-level set of policies that
 control and manage the configuration and operation of network
 devices.

1.3. Typical Examples of Policy Usage

 Policies could be implemented as low-level rules using the
 information model described in this specification.  For example, in a
 low-level policy, a condition could be represented as an evaluation
 of a specific attribute from this model.  Therefore, a condition such
 as "If filter = HTTP" would be interpreted as a test determining
 whether any HTTP filters have been defined for the device.  A high-
 level policy, such as "If protocol = HTTP, then mark with
 Differentiated Services Code Point (DSCP) 24," would be expressed as
 a series of actions in a low-level policy using the classes and
 attributes described below:
 1.  Create HTTP filter
 2.  Create DSCP marker with the value of 24
 3.  Bind the HTTP filter to the DSCP marker
 Note that unlike "mark with DSCP 24," these low-level actions are not
 performed on a packet as it passes through the device. Rather, they
 are configuration actions performed on the device itself, to make it
 ready to perform the correct action(s) on the correct packet(s).  The
 act of moving from a high-level policy rule to the correct set of
 low-level device configuration actions is an example of what
 [POLTERM] characterizes as "policy translation" or "policy
 conversion".

Moore, et al. Standards Track [Page 7] RFC 3670 QoS Device Datapath Info Model January 2004

2. Approach

 QoS activities in the IETF have mainly focused in two areas,
 Integrated Services (IntServ) and Differentiated Services (DiffServ)
 (see [POLTERM], [R1633] and [R2475]).  This document focuses on the
 specification of QoS properties and classes for modeling the datapath
 where packet traffic is conditioned. However, the framework defined
 by the classes in this document has been designed with the needs of
 the admission control portion of IntServ in mind as well.

2.1. Common Needs Of DiffServ and IntServ

 First, let us consider IntServ.  IntServ has two principal
 components.  One component is embedded in the datapath of the
 networking device.  Its functions include the classification and
 policing of individual flows, and scheduling admitted packets for the
 outbound link.  The other component of IntServ is admission control,
 which focuses on the management of the signaling protocol (e.g., the
 PATH and RESV messages of RSVP).  This component processes
 reservation requests, manages bandwidth, outsources decision making
 to policy servers, and interacts with the Routing Table manager.
 We will consider RSVP when defining the structure of this information
 model.  As this document focuses on the datapath, elements of RSVP
 applicable to the datapath will be considered in the structure of the
 classes.  The complete IntServ device model will, as we have
 indicated earlier, be addressed in a subsequent document.
 This document models a small subset of the QoS policy problem, in
 hopes of constructing a methodology that can be adapted for other
 aspects of QoS in particular, and of policy construction in general.
 The focus in this document is on QoS for devices that implement
 traffic conditioning in the datapath.
 DiffServ operates exclusively in the datapath.  It has all of the
 same components of the IntServ datapath, with two major differences.
 First, DiffServ classifies packets based solely on their DSCP field,
 whereas IntServ examines a subset of a standard flow's addressing 5-
 tuple.  The exception to this rule occurs in a router or host at the
 boundary of a DiffServ domain.  A device in this position may examine
 a packet's DSCP, its addressing 5-tuple, other fields in the packet,
 or even information wholly outside the packet, in determining the
 DSCP value with which to mark the packet prior to its transfer into
 the DiffServ domain.  However, routers in the interior of a DiffServ
 domain will only need to classify based on the DSCP field.

Moore, et al. Standards Track [Page 8] RFC 3670 QoS Device Datapath Info Model January 2004

 The second difference between IntServ and DiffServ is that the
 signaling protocol used in IntServ (e.g., RSVP) affects the
 configuration of the datapath in a more dynamic fashion.  This is
 because each newly admitted RSVP reservation requires a
 reconfiguration of the datapath.  In contrast, DiffServ requires far
 fewer changes to the datapath after the Per Hop Behaviors (PHBs) have
 been configured.
 The approach advocated in this document for the creation of policies
 that control the various QoS mechanisms of networking devices is to
 first identify the attributes with which policies are to be
 constructed.  These attributes are the parameters used in expressions
 that are necessary to construct policies.  There is also a parallel
 desire to define the operators, relations, and precedence constructs
 necessary to construct the conditions and actions that constitute
 these policies.  However, these efforts are beyond the scope of this
 document.

2.2. Specific Needs Of DiffServ

 DiffServ-specific rules focus on two particular areas: the core and
 the edges of the network.  As explained in the DiffServ Architecture
 document [R2475], devices at the edge of the network classify traffic
 into different traffic streams.  The core of the network then
 forwards traffic from different streams by using a set of Per Hop
 Behaviors (PHBs).  A DSCP identifies each PHB. The DSCP is part of
 the IP header of each packet (as described in [R2474]).  This enables
 multiple traffic streams to be aggregated into a small number of
 aggregated traffic streams, where each aggregate traffic stream is
 identified by a particular DSCP, and forwarded using a particular
 PHB.
 The attributes used to manipulate QoS capabilities in the core of the
 network primarily address the behavioral characteristics of each
 supported PHB.  At the edges of the DiffServ network, the additional
 complexities of flow classification, policing, RSVP mappings,
 remarkings, and other factors have to be considered. Additional
 modeling will be required in this area.  However, first, the
 standards for edges of the DiffServ network need more detail - to
 allow the edges to be incorporated into the policy model.

2.3. Specific Needs Of IntServ

 This document focuses exclusively on the forwarding aspects of
 network QoS.  Therefore, while the forwarding aspects of IntServ are
 considered, the management of IntServ is not considered. This topic
 will be addressed in a future document.

Moore, et al. Standards Track [Page 9] RFC 3670 QoS Device Datapath Info Model January 2004

3. Methodology

 There is a clear need to define attributes and behavior that together
 define how traffic should be conditioned.  This document defines a
 set of classes and relationships that represent the QoS mechanisms
 used to condition traffic; [QPIM] is used to define policies to
 control the QoS mechanisms defined in this document.
 However, some very basic issues need to be considered when combining
 these documents.  Considering these issues should help in
 constructing a schema for managing the operation and configuration of
 network QoS mechanisms through the use of QoS policies.

3.1. Level of Abstraction for Expressing QoS Policies

 The first issue requiring consideration is the level of abstraction
 at which QoS policies should be expressed.  If we consider policies
 as a set of rules used to react to events and manipulate attributes
 or generate new events, we realize that policy represents a continuum
 of specifications that relate business goals and rules to the
 conditioning of traffic done by a device or a set of devices.  An
 example of a business level policy might be: from 1:00 pm PST to 7:00
 am EST, sell off 40% of the network capacity on the open market.  In
 contrast, a device-specific policy might be: if the queue depth grows
 at a geometric rate over a specified duration, trigger a potential
 link failure event.
 A general model for this continuum is shown in Figure 1 below.
 +---------------------+
 | High-Level Business |    Not directly related to device
 |     Policies        |    operation and configuration details
 +---------------------+
           |
           |
 +---------V-----------+
 | Device-Independent  |    Translate high-level policies to
 |       Policies      |    generic device operational and
 +---------------------+    configuration information
           |
           |
 +---------V-----------+
 |   Device-Dependent  |    Translate generic device information
 |       Policies      |    to specify how particular devices
 +---------------------+    should operate and be configured
 Figure 1.  The Policy Continuum

Moore, et al. Standards Track [Page 10] RFC 3670 QoS Device Datapath Info Model January 2004

 High-level business policies are used to express the requirements of
 the different applications, and prioritize which applications get
 "better" treatment when the network is congested.  The goal, then, is
 to use policies to relate the operational and configuration needs of
 a device directly to the business rules that the network
 administrator is trying to implement in the network that the device
 belongs to.
 Device-independent policies translate business policies into a set of
 generalized operational and configuration policies that are
 independent of any specific device, but dependent on a particular set
 of QoS mechanisms, such as random early detection (RED) dropping or
 weighted round robin scheduling.  Not only does this enable different
 types of devices (routers, switches, hosts, etc.) to be controlled by
 QoS policies, it also enables devices made by different vendors that
 use the same types of QoS mechanisms to be controlled.  This enables
 these different devices to each supply the correct relative
 conditioning to the same type of traffic.
 In contrast, device-dependent policies translate device-independent
 policies into ones that are specific for a given device.  The reason
 that a distinction is made between device-independent and device-
 dependent policies is that in a given network, many different devices
 having many different capabilities need to be controlled together.
 Device-independent policies provide a common layer of abstraction for
 managing multiple devices of different capabilities, while device-
 dependent policies implement the specific conditioning that is
 required.  This document provides a common set of abstractions for
 representing QoS mechanisms in a device-independent way.
 This document is focused on the device-independent representation of
 QoS mechanisms.  QoS mechanisms are modeled in sufficient detail to
 provide a common device-independent representation of QoS policies.
 They can also be used to provide a basis for specialization, enabling
 each vendor to derive a set of vendor-specific classes that represent
 how traffic conditioning is done for that vendor's set of devices.

3.2. Specifying Policy Parameters

 Policies are a function of parameters (attributes) and operators
 (boolean, arithmetic, relational, etc.).  Therefore, both need to be
 defined as part of the same policy in order to correctly condition
 the traffic.  If the parameters of the policy are specified too
 narrowly, they will reflect the individual implementations of QoS in
 each device.  As there is currently little consensus in the industry
 on what the correct implementation model for QoS is, most defined
 attributes would only be applicable to the unique characteristics of
 a few individual devices.  Moreover, standardizing all of these

Moore, et al. Standards Track [Page 11] RFC 3670 QoS Device Datapath Info Model January 2004

 potential implementation alternatives would be a never-ending task as
 new implementations continued to appear on the market.
 On the other hand, if the parameters of the policy are specified too
 broadly, it is impossible to develop meaningful policies. For
 example, if we concentrate on the so-called Olympic set of policies,
 a business policy like "Bob gets Gold Service," is clearly
 meaningless to the large majority of existing devices. This is
 because the device has no way of determining who Bob is, or what QoS
 mechanisms should be configured in what way to provide Gold service.
 Furthermore, Gold service may represent a single service, or it may
 identify a set of services that are related to each other. In the
 latter case, these services may have different conditioning
 characteristics.
 This document defines a set of parameters that fit into a canonical
 model for modeling the elements in the forwarding path of a device
 implementing QoS traffic conditioning.  By defining this model in a
 device-independent way, the needed parameters can be appropriately
 abstracted.

3.3. Specifying Policy Services

 Administrators want the flexibility to be able to define traffic
 conditioning without having to have a low-level understanding of the
 different QoS mechanisms that implement that conditioning.
 Furthermore, administrators want the flexibility to group different
 services together, describing a higher-level concept such as "Gold
 Service".  This higher-level service could be viewed as providing the
 processing to deliver "Gold" quality of service.
 These two goals dictate the need for the following set of
 abstractions:
 o  a flexible way to describe a service
 o  must be able to group different services that may use different
    technologies (e.g., DiffServ and IEEE 802.1Q) together
 o  must be able to define a set of sub-services that together make up
    a higher-level service
 o  must be able to associate a service and the set of QoS mechanisms
    that are used to condition traffic for that service
 o  must be able to define policies that manage the QoS mechanisms
    used to implement a service.

Moore, et al. Standards Track [Page 12] RFC 3670 QoS Device Datapath Info Model January 2004

 This document addresses this set of problems by defining a set of
 classes and associations that can represent abstract concepts like
 "Gold Service," and bind each of these abstract services to a
 specific set of QoS mechanisms that implement the conditioning that
 they require.  Furthermore, this document defines the concept of
 "sub-services," to enable Gold Service to be defined either as a
 single service or as a set of services that together should be
 treated as an atomic entity.
 Given these abstractions, policies (as defined in [QPIM]) can be
 written to control the QoS mechanisms and services defined in this
 document.

3.4. Level of Abstraction for Defining QoS Attributes and Classes

 This document defines a set of classes and properties to support
 policies that configure device QoS mechanisms.  This document
 concentrates on the representation of services in the datapath that
 support both DiffServ (for aggregate traffic conditioning) and
 IntServ (for flow-based traffic conditioning).  Classes and
 properties for modeling IntServ admission control services may be
 defined in a future document.
 The classes and properties in this document are designed to be used
 in conjunction with the QoS policy classes and properties defined in
 [QPIM].  For example, to preserve the delay characteristics committed
 to an end-user, a network administrator may wish to create policies
 that monitor the queue depths in a device, and adjust resource
 allocations when delay budgets are at risk (perhaps as a result of a
 network topology change).  The classes and properties in this
 document define the specific services and mechanisms required to
 implement those services. The classes and properties defined in
 [QPIM] provide the overall structure of the policy that manages and
 configures this service.
 This combination of low-level specification (using this document) and
 high-level structuring (using [QPIM]) of network services enables
 network administrators to define new services required of the
 network, that are directly related to business goals, while ensuring
 that such services can be managed.  However, this goal (of creating
 and managing service-oriented policies) can only be realized if
 policies can be constructed that are capable of supporting diverse
 implementations of QoS.  The solution is to model the QoS
 capabilities of devices at the behavioral level. This means that for
 traffic conditioning services realized in the datapath, the model
 must support the following characteristics:
 o  modeling of a generic network service that has QoS capabilities

Moore, et al. Standards Track [Page 13] RFC 3670 QoS Device Datapath Info Model January 2004

 o  modeling of how the traffic conditioning itself is defined
 o  modeling of how statistics are gathered to monitor QoS traffic
    conditioning services - this facet of the model will be added in a
    future document.
 This document models a network service, and associates it with one or
 more QoS mechanisms that are used to implement that service.  It also
 models in a canonical form the various components that are used to
 condition traffic, such that standard as well as custom traffic
 conditioning services may be described.

3.5. Characterization of QoS Properties

 The QoS properties and classes will be described in more detail in
 Section 4.  However, we should consider the basic characteristics of
 these properties, to understand the methodology for representing
 them.
 There are essentially two types of properties, state and
 configuration.  Configuration properties describe the desired state
 of a device, and include properties and classes for representing
 desired or proposed thresholds, bandwidth allocations, and how to
 classify traffic.  State properties describe the actual state of the
 device.  These include properties to represent the current
 operational values of the attributes in devices configured via the
 configuration properties, as well as properties that represent state
 (queue depths, excess capacity consumption, loss rates, and so
 forth).
 In order to be correlated and used together, these two types of
 properties must be modeled using a common information model.  The
 possibility of modeling state properties and their corresponding
 configuration settings is accomplished using the same classes in this
 model - although individual instances of the classes would have to be
 appropriately named or placed in different containers to distinguish
 current state values from desired configuration settings.
 State information is addressed in a very limited fashion by QDDIM.
 Currently, only CurrentQueueDepth is proposed as an attribute on
 QueuingService.  The majority of the model is related to
 configuration.  Given this fact, it is assumed that this model is a
 direct memory map into a device.  All manipulation of model classes
 and properties directly affects the state of the device.  If it is
 desired to also use these classes to represent desired configuration,
 that is left to the discretion of the implementor.

Moore, et al. Standards Track [Page 14] RFC 3670 QoS Device Datapath Info Model January 2004

 It is acknowledged that additional properties are needed to
 completely model current state.  However, many of the properties
 defined in this document represent exactly the state variables that
 will be configured by the configuration properties.  Thus, the
 definition of the configuration properties has an exact
 correspondence with the state properties, and can be used in modeling
 both actual (state) and desired/proposed configuration.

3.6. QoS Information Model Derivation

 The question of context also leads to another question: how does the
 information specified in the core and QoS policy models ([PCIM],
 [PCIME], and [QPIM], respectively) integrate with the information
 defined in this document?  To put it another way, where should
 device-independent concepts that lead to device-specific QoS
 attributes be derived from?
 Past thinking was that QoS was part of the policy model.  This view
 is not completely accurate, and it leads to confusion.  QoS is a set
 of services that can be controlled using policy.  These services are
 represented as device mechanisms.  An important point here is that
 QoS services, as well as other types of services (e.g., security),
 are provided by the mechanisms inherent in a given device.  This
 means that not all devices are indeed created equal.  For example,
 although two devices may have the same type of mechanism (e.g., a
 queue), one may be a simple implementation (i.e., a FIFO queue)
 whereas one may be much more complex and robust (e.g., class-based
 weighted fair queuing (CBWFQ)).  However, both of these devices can
 be used to deliver QoS services, and both need to be controlled by
 policy.  Thus, a device-independent policy can instruct the devices
 to queue certain traffic, and a device-specific policy can be used to
 control the queuing in each device.
 Furthermore, policy is used to control these mechanisms, not to
 represent them.  For example, QoS services are implemented with
 classifiers, meters, markers, droppers, queues, and schedulers.
 Similarly, security is also a characteristic of devices, as
 authentication and encryption capabilities represent services that
 networked devices perform (irrespective of interactions with policy
 servers).  These security services may use some of the same
 mechanisms that are used by QoS services, such as the concepts of
 filters.  However, they will mostly require different mechanisms than
 the ones used by QoS, even though both sets of services are
 implemented in the same devices.
 Thus, the similarity between the QoS model and models for other
 services is not so much that they contain a few common mechanisms.
 Rather, they model how a device implements their respective services.

Moore, et al. Standards Track [Page 15] RFC 3670 QoS Device Datapath Info Model January 2004

 As such, the modeling of QoS should be part of a networking device
 schema rather than a policy schema.  This allows the networking
 device schema to concentrate on modeling device mechanisms, and the
 policy schema to focus on the semantics of representing the policy
 itself (conditions, actions, operators, etc.).  While this document
 concentrates on defining an information model to represent QoS
 services in a device datapath, the ultimate goal is to be able to
 apply policies that control these services in network devices.
 Furthermore, these two schemata (device and policy) must be tightly
 integrated in order to enable policy to control QoS services.

3.7. Attribute Representation

 The last issue to be considered is the question of how attributes are
 represented.  If QoS attributes are represented as absolute numbers
 (e.g., Class AF2 gets 2 Mbs of bandwidth), it is more difficult to
 make them uniform across multiple ports in a device or across
 multiple devices, because of the broad variation in link capacities.
 However, expressing attributes in relative or proportional terms
 (e.g., Class AF2 gets 5% of the total link bandwidth) makes it more
 difficult to express certain types of conditions and actions, such
 as:
    (If ConsumedBandwidth = AssignedBandwidth Then ...)
 There are really three approaches to addressing this problem:
 o  Multiple properties can be defined to express the same value in
    various forms.  This idea has been rejected because of the
    difficulty in keeping these different properties synchronized
    (e.g., when one property changes, the others all have to be
    updated).
 o  Multi-modal properties can be defined to express the same value,
    in different terms, based on the access or assignment mode.  This
    option was rejected because it significantly complicates the model
    and is impossible to express in current directory access protocols
    (e.g., (L)DAP).
 o  Properties can be expressed as "absolutes", but the operators in
    the policy schema would need to be more sophisticated.  Thus, to
    represent a percentage, division and multiplication operators are
    required (e.g., Class AF2 gets .05 * the total link bandwidth).
    This is the approach that has been taken in this document.

Moore, et al. Standards Track [Page 16] RFC 3670 QoS Device Datapath Info Model January 2004

3.8. Mental Model

 The mental model for constructing this schema is based on the work
 done in the Differentiated Services working group.  This schema is
 based on information provided in the current versions of the DiffServ
 Informal Management Model [DSMODEL], the DiffServ MIB [DSMIB], the
 PIB [PIB], as well as on information in the set of RFCs that
 constitute the basic definition of DiffServ itself ([R2475], [R2474],
 [R2597], and [R3246]).  In addition, a common set of terminology is
 available in [POLTERM].
 This model is built around two fundamental class hierarchies that are
 bound together using a set of associations.  The two class
 hierarchies derive from the QoSService and ConditioningService base
 classes.  A set of associations relate lower-level QoSService
 subclasses to higher-level QoS services, relate different types of
 conditioning services together in processing a traffic class, and
 relate a set of conditioning services to a specific QoS service.
 This combination of associations enables us to view the device as
 providing a set of services that can be configured, in a modular
 building block fashion, to construct application-specific services.
 Thus, this document can be used to model existing and future standard
 as well as application-specific network QoS services.

3.8.1. The QoSService Class

 The first of the classes defined here, QoSService, is used to
 represent higher-level network services that require special
 conditioning of their traffic.  An instance of QoSService (or one of
 its subclasses) is used to bring together a group of conditioning
 services that, from the perspective of the system manager, are all
 used to deliver a common service.  Thus, the set of classifiers,
 markers, and related conditioning services that provide premium
 service to the "selected" set of user traffic may be grouped together
 into a premium QoS service.
 QoSService has a set of subclasses that represent different
 approaches to delivering IP services.  The currently defined set of
 subclasses are a FlowService for flow-oriented QoS delivery and a
 DiffServService for DiffServ aggregate-oriented QoS service delivery.
 The QoS services can be related to each other as peers, or they can
 be implemented as subservient services to each other.  The
 QoSSubService aggregation indicates that one or more QoSService
 objects are subservient to a particular QoSService object.  For
 example, this enables us to define Gold Service as a combination of
 two DiffServ services, one for high quality traffic treatment, and
 one for servicing the rest of the traffic.  Each of these

Moore, et al. Standards Track [Page 17] RFC 3670 QoS Device Datapath Info Model January 2004

 DiffServService objects would be associated with a set of
 classifiers, markers, etc, such that the high quality traffic would
 get EF marking and appropriate queuing.
 The DiffServService class itself has an AFService subclass.  This
 subclass is used to represent the specific notion that several
 related markings within the AF PHB Group work together to provide a
 single service.  When other DiffServ PHB Groups are defined that use
 more than one code point, these will be likely candidates for
 additional DiffServService subclasses.
 Technology-specific mappings of these services, representing the
 specific use of PHB marking or 802.1Q marking, are captured within
 the ConditioningService hierarchy, rather than in the subclasses of
 QoSService.
 These concepts are depicted in Figure 2.  Note that both of the
 associations are aggregations: a QoSService object aggregates both
 the set of QoSService objects subservient to it, and the set of
 ConditioningService objects that realize it.  See Section 4 for class
 and association definitions.
              /\______
         0..1 \/      |
 +--------------+     | QoSSubService     +---------------+
 |              |0..n |                   |               |
 |  QoSService  |-----                    | Conditioning  |
 |              |                         |   Service     |
 |              |                         |               |
 |              |0..n                 0..n|               |
 |              | /\______________________|               |
 |              | \/  QoSConditioning     |               |
 +--------------+       SubService        +---------------+
 Figure 2.  QoSService and its Aggregations

3.8.2. The ConditioningService Class

 The goal of the ConditioningService classes is to describe the
 sequence of traffic conditioning that is applied to a given traffic
 stream on the ingress interface through which it enters a device, and
 then on the egress interface through which it leaves the device.
 This is done using a set of classes and relationships.  The routing
 decision in the device core, which selects which egress interface a
 particular packet will use, is not represented in this model.
 A single base class, ConditioningService, is the superclass for a set
 of subclasses representing the mechanisms that condition traffic.

Moore, et al. Standards Track [Page 18] RFC 3670 QoS Device Datapath Info Model January 2004

 These subclasses define device-independent conditioning primitives
 (including classifiers, meters, markers, droppers, queues, and
 schedulers) that together implement the conditioning of traffic on an
 interface.  This model abstracts these services into a common set of
 modular building blocks that can be used, regardless of device
 implementation, to model the traffic conditioning internal to a
 device.
 The different conditioning mechanisms need to be related to each
 other to describe how traffic is conditioned.  Several important
 variations of how these services are related together exist:
 o  A particular ingress or egress interface may not require all the
    types of ConditioningServices.
 o  Multiple instances of the same mechanism may be required on an
    ingress or egress interface.
 o  There is no set order of application for the ConditioningServices
    on an ingress or egress interface.
 Therefore, this model does not dictate a fixed ordering among the
 subclasses of ConditioningService, or identify a subclass of
 ConditioningService that must appear first or last among the
 ConditioningServices on an ingress or egress interface.  Instead,
 this model ties together the various ConditioningService instances on
 an ingress or egress interface using the NextService,
 NextServiceAfterMeter, and NextServiceAfterConditioningElement
 associations.  There are also separate associations, called
 IngressConditioningServiceOnEndpoint and
 EgressConditioningServiceOnEndpoint, which, respectively, tie an
 ingress interface to its first ConditioningService, and tie an egress
 interface to its last ConditioningService(s).

3.8.3. Preserving QoS Information from Ingress to Egress

 There is one important way in which the QDDIM model diverges from the
 [DSMODEL].  In [DSMODEL], traffic passes through a network device in
 three stages:
 o  It comes in on an ingress interface, where it may receive QoS
    conditioning.
 o  It traverses the routing core, where logic outside the scope of
    QoS determines which egress interface it will use to leave the
    device.

Moore, et al. Standards Track [Page 19] RFC 3670 QoS Device Datapath Info Model January 2004

 o  It may receive further QoS conditioning on the selected egress
    interface, and then it leaves the device.
 In this model, no information about the QoS conditioning that a
 packet receives on the ingress interface is communicated with the
 packet across the routing core to the egress interface.
 The QDDIM model relaxes this restriction, to allow information about
 the treatment that a packet received on an ingress interface to be
 communicated along with the packet to the egress interface.  (This
 relaxation adds a capability that is present in many network
 devices.)  QDDIM represents this information transfer in terms of a
 packet preamble, which is how many devices implement it.  But
 implementations are free to use other mechanisms to achieve the same
 result.
     +---------+
     | Meter-A |
  a  |         | b      d
 --->|      In-|---PM-1--->
     |         | c      e
     |     Out-|---PM-2--->
     +---------+
 Figure 3:  Meter Followed by Two Preamble Markers
 Figure 3 shows an example in which meter results are captured in a
 packet preamble.  The arrows labeled with single letters represent
 instances of either the NextService association (a, d, and e), or of
 its peer association NextServiceAfterMeter (b and c).  PreambleMarker
 PM-1 adds to the packet preamble an indication that the packet exited
 Meter A as conforming traffic. Similarly, PreambleMarker PM-2 adds to
 the preambles of packets that come through it indications that they
 exited Meter A as nonconforming traffic.  A PreambleMarker appends
 its information to whatever is already present in a packet preamble,
 as opposed to overwriting what is already there.
 To foster interoperability, the basic format of the information
 captured by a PreambleMarker is specified.  (Implementations, of
 course, are free to represent this information in a different way
 internally - this is just how it is represented in the model.) The
 information is represented by an ordered, multi-valued string
 property FilterItemList, where each individual value of the property
 is of the form "<type>,<value>".  When a PreambleMarker "appends" its
 information to the information that was already present in a packet
 preamble, it does so by adding additional items of the indicated
 format to the end of the list.

Moore, et al. Standards Track [Page 20] RFC 3670 QoS Device Datapath Info Model January 2004

 QDDIM provides a limited set of <type>'s that a PreambleMarker may
 use:
 o  ConformingFromMeter: the value is the name of the meter.
 o  PartConformingFromMeter: the value is the name of the meter.
 o  NonConformingFromMeter: the value is the name of the meter.
 o  VlanId: the value is the virtual LAN identifier (VLAN ID).
 Implementations may recognize other <type>'s in addition to these.
 If collisions of implementation-specific <type>'s become a problem,
 it is possible that <type>'s may become an IANA-administered range in
 a future revision of this document.
 To make use of the information that a PreambleMarker stores in a
 packet preamble, a specific subclass PreambleFilter of
 FilterEntryBase is defined, to match on the "<type>,<value>" strings.
 To simplify the case where there's just a single level of metering in
 a device, but different individual meters on each ingress interface,
 PreambleFilter allows a wildcard "any" for the <value> part of the
 three meter-related filters.  With this wildcard, an administrator
 can specify a Classifier to select all packets that were found to be
 conforming (or partially conforming, or non-conforming) by their
 respective meters, without having to name each meter individually in
 a separate ClassifierElement.
 Once a meter result has been stored in a packet preamble, it is
 available for any subsequent Classifier to use.  So while the
 motivation for this capability has been described in terms of
 preserving QoS conditioning information from an ingress interface to
 an egress interface, a prior meter result may also be used for
 classifying packets later in the datapath on the same interface where
 the meter resides.

3.9. Classifiers, FilterLists, and Filter Entries

 This document uses a number of classes to model the classifiers
 defined in [DSMODEL]: ClassifierService, ClassifierElement,
 FilterList, FilterEntryBase, and various subclasses of
 FilterEntryBase.  There are also two associations involved:
 ClassifierElementUsesFilterList and EntriesInFilterList.  The QDDIM
 model makes no use of CIM's FilterEntry class.
 In [DSMODEL], a single traffic stream coming into a classifier is
 split into multiple traffic streams leaving it, based on which of an
 ordered set of filters each packet in the incoming stream matches.  A

Moore, et al. Standards Track [Page 21] RFC 3670 QoS Device Datapath Info Model January 2004

 filter matches either a field in the packet itself, or possibly other
 attributes associated with the packet.  In the case of a multi-field
 (MF) classifier, packets are assigned to output streams based on the
 contents of multiple fields in the packet header.  For example, an MF
 classifier might assign packets to an output stream based on their
 complete IP-addressing 5-tuple.
 To optimize the representation of MF classifiers, subclasses of
 FilterEntryBase are introduced, which allow multiple related packet
 header fields to be represented in a single object.  These subclasses
 are IPHeaderFilter and 8021Filter.  With IPHeaderFilter, for example,
 criteria for selecting packets based on all five of the IP 5-tuple
 header fields and the DiffServ DSCP can be represented by a
 FilterList containing one IPHeaderFilter object.  Because these two
 classes have applications beyond those considered in this document,
 they, as well as the abstract class FilterEntryBase, are defined in
 the more general document [PCIME] rather than here.
 The FilterList object is always needed, even if it contains only one
 filter entry (that is, one FilterEntryBase subclass) object. This is
 because a ClassifierElement can only be associated with a Filter
 List, as opposed to an individual FilterEntry.  FilterList is also
 defined in [PCIME].
 The EntriesInFilterList aggregation (also defined in [PCIME]) has a
 property EntrySequence, which in the past (in CIM) could be used to
 specify an evaluation order on the filter entries in a FilterList.
 Now, however, the EntrySequence property supports only a single
 value: '0'.  This value indicates that the FilterEntries are ANDed
 together to determine whether a packet matches the MF selector that
 the FilterList represents.
 A ClassifierElement specifies the starting point for a specific
 policy or data path.  Each ClassifierElement uses the
 NextServiceAfterClassifierElement association to determine the next
 conditioning service to apply for packets to.
 A ClassifierService defines a grouping of ClassifierElements. There
 are certain instances where a ClassifierService actually specifies an
 aggregation of ClassifierServices.  One practical case would be where
 each ClassifierService specifies a group of policies associated with
 a particular application and another ClassifierService groups the
 application-specific ClassifierService instances.  In this particular
 case, the application-specific ClassifierService instances are
 specified once, but unique combinations of these ClassifierServices
 are specified, as needed, using other ClassifierService instances.
 ClassifierService instances grouping other ClassifierService
 instances may not specify a FilterList using the

Moore, et al. Standards Track [Page 22] RFC 3670 QoS Device Datapath Info Model January 2004

 ClassifierElementUsesFilterList association.  This special use of
 ClassifierService serves just as a Classifier collecting function.

3.10. Modeling of Droppers

 In [DSMODEL], a distinction is made between absolute droppers and
 algorithmic droppers.  In QDDIM, both of these types of droppers are
 modeled with the DropperService class, or with one of its subclasses.
 In both cases, the queue from which the dropper drops packets is tied
 to the dropper by an instance of the NextService association.  The
 dropper always plays the PrecedingService role in these associations,
 and the queue always plays the FollowingService role.  There is
 always exactly one queue from which a dropper drops packets.
 Since an absolute dropper drops all packets in its queue, it needs no
 configuration beyond a NextService tie to that queue. For an
 algorithmic dropper, however, further configuration is needed:
 o  a specific drop algorithm;
 o  parameters for the algorithm (for example, token bucket size);
 o  the source(s) of input(s) to the algorithm;
 o  possibly per-input parameters for the algorithm.
 The first two of these items are represented by properties of the
 DropperService class, or properties of one of its subclasses. The
 last two, however, involve additional classes and associations.

3.10.1. Configuring Head and Tail Droppers

 The HeadTailDropQueueBinding is the association that identifies the
 inputs for the algorithm executed by a tail dropper.  This
 association is not used for a head dropper, because a head dropper
 always has exactly one input to its drop algorithm, and this input is
 always the queue from which it drops packets.  For a tail dropper,
 this association is defined to have a many-to-many cardinality.
 There are, however, two distinct cases:
 One dropper bound to many queues: This represents the case where the
 drop algorithm for the dropper involves inputs from more than one
 queue.  The dropper still drops from only one queue, the one to which
 it is tied by a NextService association.  But the drop decision may
 be influenced by the state of several queues.  For the classes
 HeadTailDropper and HeadTailDropQueueBinding, the rule for combining
 the multiple inputs is simple addition: if the sum of the lengths of
 the monitored queues exceeds the dropper's QueueThreshold value, then

Moore, et al. Standards Track [Page 23] RFC 3670 QoS Device Datapath Info Model January 2004

 packets are dropped.  This rule for combining inputs may, however, be
 overridden by a different rule in subclasses of one or both of these
 classes.
 One queue bound to many droppers: This represents the case where the
 state of one queue (which is typically also the queue from which
 packets are dropped) provides an input to multiple droppers' drop
 algorithms.  A use case here is a classifier that splits a traffic
 stream into, say, four parts, representing four classes of traffic.
 Each of the parts goes through a separate HeadTailDropper, then
 they're re-merged onto the same queue.  The net is a single queue
 containing packets of four traffic types, with, say, the following
 drop thresholds:
    o    Class 1 - 90% full
    o    Class 2 - 80% full
    o    Class 3 - 70% full
    o    Class 4 - 50% full
 Here the percentages represent the overall state of the queue. With
 this configuration, when the queue in question becomes 50% full,
 Class 4 packets will be dropped rather than joining the queue, when
 it becomes 70% full, Class 3 and 4 packets will be dropped, etc.
 The two cases described here can also occur together, if a dropper
 receives inputs from multiple queues, one or more of which are also
 providing inputs to other droppers.

3.10.2. Configuring RED Droppers

 Like a tail dropper, a RED dropper, represented by an instance of the
 REDDropperService class, may take as its inputs the states of
 multiple queues.  In this case, however, there is an additional step:
 each of these inputs may be smoothed before the RED dropper uses it,
 and the smoothing process itself must be parameterized. Consequently,
 in addition to REDDropperService and QueuingService, a third class,
 DropThresholdCalculationService, is introduced, to represent the
 per-queue parameterization of this smoothing process.

Moore, et al. Standards Track [Page 24] RFC 3670 QoS Device Datapath Info Model January 2004

 The following instance diagram illustrates how these classes work
 with each other:
         RDSvc-A
         |  |  |
   +-----+  |  +-----+
   |        |        |
 DTCS-1   DTCS-2   DTCS-3
   |        |        |
  Q-1      Q-2      Q-3
 Figure 4. Inputs for a RED Dropper
 So REDDropperService-A (RDSvc-A) is using inputs from three queues to
 make its drop decision.  (As always, RDSvc-A is linked to the queue
 from which it drops packets via the NextService association.)  For
 each of these three queues, there is a
 (DropThresholdCalculationService) DTCS instance that represents the
 smoothing weight and time interval to use when looking at that queue.
 Thus each DTCS instance is tied to exactly one queue, although a
 single queue may be examined (with different weight and time values)
 by multiple DTCS instances.  Also, a DTCS instance and the queue
 behind it can be thought of as a "unit of reusability".  So a single
 DTCS can be referred to by multiple RDSvc's.
 Unless it is overridden by a different rule in a subclass of
 REDDropperService, the rule that a RED dropper uses to combine the
 smoothed inputs from the DTCS's to create a value to use in making
 its drop decision is simple addition.

3.11. Modeling of Queues and Schedulers

 In order to appreciate the rationale behind this rather complex model
 for scheduling, we must consider the rather complex nature of
 schedulers, as well as the extreme variations in algorithms and
 implementations.  Although these variations are broad, we have
 identified four examples that serve to test the model and justify its
 complexity.

3.11.1. Simple Hierarchical Scheduler

 A simple, hierarchical scheduler has the following properties. First,
 when a scheduling opportunity is given to a set of queues, a single,
 viable queue is determined based on some scheduling criteria, such as
 bandwidth or priority.  The output of the scheduler is the input to
 another scheduler that treats the first scheduler (and its queues) as
 a single logical queue.  Hence, if the first scheduler determined the
 appropriate packet to release based on a priority assigned to each

Moore, et al. Standards Track [Page 25] RFC 3670 QoS Device Datapath Info Model January 2004

 queue, the second scheduler might specify a bandwidth
 limit/allocation for the entire set of queues aggregated by the first
 scheduler.
 +----------+                              NextService
 |QueuingSvc+----------------------------------------------+
 | Name=EF1 |                                              |
 |          | QueueTo    +--------------+ ElementSched     |
 |          +------------+PrioritySched +---------------+  |
 +----------+ Schedule   |Element       | Service       |  |
                         | Name=EF1-Pri |               |  v
                         | Priority=1   |    +-----------+-+-+
                         +--------------+    |SchedulingSvc  +
                                             | Name=PriSched1+
                         +--------------+    +----------+--+-+
                         |PrioritySched | ElementSched  |  ^
 +----------+            |Element       +---------------+  |
 |QueuingSvc| QueueTo    | Name=AF1x-Pri| Service          |
 | Name=AF1x+------------+ Priority=2   |                  |
 |          | Schedule   +--------------+                  |
 |          |                              NextService     |
 |          +----------------------------------------------+
 +----------+
 :
 +---------------+            NextScheduler
 |SchedulingSvc  +--------------------------------------------+
 | Name=PriSched1|                                            |
 +-------+-------+       +--------------------+ElementSchedSvc|
         | SchedToSched  |AllocationScheduling+--------+      |
         +---------------+Element             |        |      |
                         | Name=PriSched1-Band|        |      |
                         | Units=Bytes        |        |      v
                         | Bandwidth=100      | +------+------+--+
                         +--------------------+ |SchedulingSvc   |
                                                | Name=BandSched1|
                         +--------------------+ +------+------+--+
                         |AllocationScheduling|        |      ^
 +---------------+       |Element             +--------+      |
 |QueuingService |       | Name=BE-Band       |ElementSchedSvc|
 | Name=BE       |QueueTo+ Units=Bytes        |               |
 |               |-------+ Bandwidth=50       |               |
 |               |Sched  +--------------------+               |
 |               |                             NextService    |
 |               +--------------------------------------------+
 +---------------+
 Figure 5. Example 1: Simple Hierarchical Scheduler

Moore, et al. Standards Track [Page 26] RFC 3670 QoS Device Datapath Info Model January 2004

 Figure 5 illustrates the example and how it would be instantiated
 using the model.  In the figure, NextService determines the first
 scheduler after the queue.  NextScheduler determines the
 subsequent ordering of schedulers.  In addition, the
 ElementSchedulingService association determines the set of
 scheduling parameters used by a specific scheduler.  Scheduling
 parameters can be bound either to queues or to schedulers.  In
 the case of the SchedulingElement EF1-Pri, the binding is to a
 queue, so the QueueToSchedule association is used.  In the case
 of the SchedulingElement PriSched1-Band, the binding is to
 another scheduler, so the SchedulerToSchedule association is
 used.  Note that due to space constraints of the document, the
 SchedulingService PRISched1 is represented twice, to show how it
 is connected to all the other objects.

3.11.2. Complex Hierarchical Scheduler

 A complex, hierarchical scheduler has the same characteristics as
 a simple scheduler, except that the criteria for the second
 scheduler are determined on a per queue basis rather than on an
 aggregate basis.  One scenario might be a set of bounded priority
 schedulers.  In this case, each queue is assigned a relative
 priority.  However, each queue is also not allowed to exceed a
 bandwidth allocation that is unique to that queue.  In order to
 support this scenario, the queue must be bound to two separate
 schedulers.  Figure 6 illustrates this situation, by describing
 an EF queue and a best effort (BE) queue both pointing to a
 priority scheduler via the NextService association.  The
 NextScheduler association between the priority scheduler and the
 bandwidth scheduler in turn defines the ordering of the
 scheduling hierarchy.  Also note that each scheduler has a
 distinct set of scheduling parameters that are bound back to each
 queue.  This demonstrates the need to support two or more
 parameter sets on a per queue basis.

Moore, et al. Standards Track [Page 27] RFC 3670 QoS Device Datapath Info Model January 2004

 +----------------+
 |QueuingService  |
 | Name=EF        |
 |                |QueueTo   +----------------+ElementSchedSvc
 |                +----------+AllocationSched +--------+
 ++---+-----------+Schedule  |Element         |        |
  |   |                      | Name=BandEF    |        |
  |   |QueueTo               | Units=Bytes    |        |
  |   |Schedule              | Bandwidth=100  |        |
  |   |                      +----------------+ +------+---------+
  |   |                                         |SchedulingSvc   |
  |   |      +------------------+               | Name=BandSched |
  |   +------+PriorityScheduling|               +------------+--++
  |          |Element           |                            ^  |
  |          | Name=PriEF       |ElementSchedSvc             |  |
  |          | Priority=1       +---------------------+      |  |
  |          +------------------+                     |      |  |
  |NextService                                        |      |  |
  +-------------------------------------------------+ |      |  |
                                                    | |      |  |
   NextService                                      | |      |  |
  +-----------------------------------------------+ | |      |  |
  |                                               | | |      |  |
  |          +------------------+ElementSchedSvc  | | |      |  |
  |          |PriorityScheduling+--------+        | | |      |  |
  |          |Element           |        |        | | |      |  |
  |          | Name=PriBE       |        |        v v |      |  |
  |   +------+ Priority=2       |    +---+--------+-+-+-+Next|  |
  |   |      +------------------+    |SchedulingService +----+  |
  |   |                              | Name=PriSched    |Sched  |
  |   |                              +------------------+       |
  |   |QueueTo                                                  |
  |   |Schedule              +----------------+                 |
  |   |                      |AllocationSched |ElementSchedSvc  |
 +----+---------+            |Element         +-----------------+
 |QueuingService|QueueTo     | Name=BandBE    |
 | Name=BE      +------------+ Units=Bytes    |
 |              |Schedule    | Bandwidth=50   |
 |              |            +----------------+
 +--------------+
 Figure 6. Example 2: Complex Hierarchical Scheduler

Moore, et al. Standards Track [Page 28] RFC 3670 QoS Device Datapath Info Model January 2004

3.11.3. Excess Capacity Scheduler

 An excess capacity scheduler offers a similar requirement to support
 two scheduling parameter sets per queue.  However, in this scenario
 the reasons are a little different.  Suppose a set of queues have
 each been assigned bandwidth limits to ensure that no traffic class
 starves out another traffic class.  The result may be that one or
 more queues have exceeded their allocation while the queues that
 deserve scheduling opportunities are empty.
 The question then is how is the excess (idle) bandwidth allocated.
 Conceivably, the scheduling criteria for excess capacity are
 completely different from the criteria that determine allocations
 under uniform load.  This could be supported with a scheduling
 hierarchy.  However, the problem is that the criteria for using the
 subsequent scheduler are different from those in the last two cases.
 Specifically, the next scheduler should only be used if a scheduling
 opportunity exists that was passed over by the prior scheduler.
 When a scheduler chooses to forgo a scheduling decision, it is
 behaving as a non-work conserving scheduler.  Work conserving
 schedulers, by definition, will always take advantage of a scheduling
 opportunity, irrespective of which queue is being serviced and how
 much bandwidth it has consumed in the past. This point leads to an
 interesting insight.  The semantics of a non-work conserving
 scheduler are equivalent to those of a meter, in that if a packet is
 in profile it is given the scheduling opportunity, and if it is out
 of profile it does not get a scheduling opportunity.  However, with
 meters there are semantics that determine the next action behavior
 when the packet is in profile and when the packet is out of profile.
 Similarly, with the non-work conserving scheduler, there needs to be
 a means for determining the next scheduler when a scheduler chooses
 not to utilize a scheduling opportunity.
 Figure 7 illustrates this last scenario.  It appears very similar to
 Figure 6, except that the binding between the allocation scheduler
 and the WRR scheduler is using a FailNextScheduler association.  This
 association is explicitly indicating the fact that the only time the
 WRR scheduler would be used is when there are non-empty queues that
 the allocation scheduler rejected for scheduling consideration.  Note
 that Figure 7 is incomplete, in that typically there would be several
 more queues that are bound to an allocation scheduler and a WRR
 scheduler.

Moore, et al. Standards Track [Page 29] RFC 3670 QoS Device Datapath Info Model January 2004

 +------------+
 |QueuingSvc  |
 | Name=EF    |
 |            |
 |            |
 ++-+---------+
  | |
  | |QueueTo
  | |Schedule                                     +--------------+
  | |                                             |SchedulingSvc |
  | |      +------------------+                   | Name=WRRSched|
  | +------+AllocationSched   |                   +----------+-+-+
  |        |Element           |                              ^ |
  |        | Name=BandEF      |ElementSchedSvc               | |
  |        | Units=Bytes      +--------------------+         | |
  |        | Bandwidth=100    |                    |         | |
  |        +------------------+                    |         | |
  |NextService                                     |         | |
  +----------------------------------------------+ |         | |
                                                 | |         | |
   NextService                                   | |         | |
  +--------------------------------------------+ | |         | |
  |                                            | | |         | |
  |        +------------------+ElementSchedSvc | | |         | |
  |        |AllocationSched   +--------+       | | |         | |
  |        |Element           |        |       | | |         | |
  |        | Name=BandwidthAF1|        |       | | |         | |
  |        | Units=Bytes      |        |       v v |         | |
  | +------+ Bandwidth=50     |  +--+----------+-+-++FailNext| |
  | |      +------------------+  |SchedulingService +--------+ |
  | |QueueTo                     | Name=BandSched   |Scheduler |
  | |Schedule                    +------------------+          |
  | |                                                          |
  | |                       +---------------------+            |
 ++-+-----------+           | WRRSchedulingElement|            |
 |QueuingService|QueueTo    | Name=WRRBE          +------------+
 | Name=BE      +-----------+ Weight=30           |ElementSchedSvc
 +--------------+Schedule   +---------------------+
 Figure 7.  Example 3: Excess Capacity Scheduler

Moore, et al. Standards Track [Page 30] RFC 3670 QoS Device Datapath Info Model January 2004

3.11.4. Hierarchical CBQ Scheduler

 A hierarchical class-based queuing (CBQ) scheduler is the fourth
 scenario to be considered.  In hierarchical CBQ, each queue is
 allocated a specific bandwidth allocation.  Queues are grouped
 together into a logical scheduler.  This logical scheduler in turn
 has an aggregate bandwidth allocation that equals the sum of the
 queues it is scheduling.  In turn, logical schedulers can be
 aggregated into higher-level logical schedulers.  Changing
 perspectives and looking top down, the top-most logical scheduler has
 100% of the link capacity.  This allocation is parceled out to
 logical schedulers below it such that the sum of the allocations is
 equal to 100%.  These second tier schedulers may in turn parcel out
 their allocation across a third tier of schedulers and so forth until
 the lowest tier that parcels out their allocations to specific queues
 representing relatively fine-grained classes of traffic.  The unique
 aspect of hierarchical CBQ is that when there is insufficient
 bandwidth for a specific allocation, schedulers higher in the tree
 are tested to see if another portion of the tree has capacity to
 spare.
 Figure 8 demonstrates this example with two tiers.  The example is
 split in half because of space constraints, resulting in the CBQTier1
 scheduling service instance being represented twice. Note that the
 total allocation at the top tier is 50 Mb.  The voice allocation is
 22 Mb.  The remaining 23 Mb is split between FTP and Web.  Hence, if
 Web traffic is actually consuming 20 Mb (5 Mb in excess of the
 allocation).  If FTP is consuming 5 Mb, then it is possible for the
 CBQTier1 scheduler to offer 3Mb of its allocation to Web traffic.
 However, this is not enough, so the FailNextScheduler association
 needs to be traversed to determine if there is any excess capacity
 available from the voice class.  If the voice class is only consuming
 15 Mb of its 22 Mb allocation, there are sufficient resources to
 allow the web traffic through.  Note that FailNextScheduler is used
 as the association.  The reason is because the CBQTier1 scheduler in
 fact failed to schedule a packet because of insufficient resources.
 It is conceivable that a variant of hierarchical CBQ allows a
 hierarchy for successful scheduling as well.  Hence, both
 associations are necessary.
 Note that due to space constraints of the document, the
 SchedulingService CBQTier1 is represented twice, to show how it is
 connected to all the other objects.

Moore, et al. Standards Track [Page 31] RFC 3670 QoS Device Datapath Info Model January 2004

 +-----------+                        NextService
 |QueuingSvc +-------------------------------------------+
 | Name=Web  |                                           |
 |           |QueueTo+----------------+ ElementSchedSvc  |
 |           +-------+AllocationSched +----------------+ |
 +-----------+Sched  |Element         |                | |
                     | Name=Web-Alloc |                | v
                     | Bandwidth=15   |    +-----------+-+-+
                     +----------------+    |SchedulingSvc  +
                                           | Name=CBQTier1 +
                     +----------------+    +-----------+-+-+
                     |AllocationSched | ElementSchedSvc| ^
 +-----------+       |Element         +----------------+ |
 |QueuingSvc |QueueTo| Name=FTP-Alloc |                  |
 | Name=FTP  +-------+ Bandwidth=8    |                  |
 |           |Sched  +----------------+                  |
 |           |                        NextService        |
 |           +-------------------------------------------+
 +-----------+
 :
 +---------------+                    FailNextScheduler
 |SchedulingSvc  +---------------------------------------------+
 | Name=CBQTier1 |                                             |
 +-------+-------+       +---------------------+ElementSchedSvc|
         | SchedToSched  |AllocationScheduling +--------+      |
         +---------------+Element              |        |      |
                         | Name=LowPri-Alloc   |        |      |
                         | Bandwidth=23        |        |      v
                         +---------------------+  +-----+------+-+
                                                  |SchedulingSvc |
                                                  | Name=CBQTop  |
                      +---------------------+     +----------+-+-+
                      |AllocationScheduling |ElementSchedSvc | ^
 +------------+       |Element              +----------------+ |
 |QueuingSvc  |QueueTo| Name=BE-Band        |                  |
 | Name=Voice +-------+ Bandwidth=22        |                  |
 |            |Sched  +---------------------+                  |
 |            |                       NextService              |
 |            +------------------------------------------------+
 +------------+
 Figure 8.  Example 4: Hierarchical CBQ Scheduler

Moore, et al. Standards Track [Page 32] RFC 3670 QoS Device Datapath Info Model January 2004

4. The Class Hierarchy

 The following sections present the class and association hierarchies
 that together comprise the information model for modeling QoS
 capabilities at the device level.

4.1. Associations and Aggregations

 Associations and aggregations are a means of representing
 relationships between two (or theoretically more) objects.
 Dependency, aggregation, and other relationships are modeled as
 classes containing two (or more) object references.  It should be
 noted that aggregations represent either "whole-part" or "collection"
 relationships.  For example, aggregation can be used to represent the
 containment relationship between a system and the components that
 constitute the system.
 Since associations and aggregations are classes, they can benefit
 from all of the object-oriented features that other non-relationship
 classes have.  For example, they can contain properties and methods,
 and inheritance can be used to refine their semantics such that they
 represent more specialized types of their superclasses.
 Note that an association (or an aggregation) object is treated as an
 atomic unit (individual instance), even though it relates/collects/is
 comprised of multiple objects.  This is a defining feature of an
 association (or an aggregation) - although the individual elements
 that are related to other objects have their own identities, the
 association (or aggregation) object that is constructed using these
 objects has its own identity and name as well.
 It is important to note that associations and aggregations form an
 inheritance hierarchy that is separate from the class inheritance
 hierarchy.  Although associations and aggregations are typically bi-
 directional, there is nothing that prevents higher order associations
 or aggregations from being defined. However, such associations and
 aggregations are inherently more complex to define, understand, and
 use.  In practice, associations and aggregations of orders higher
 than binary are rarely used, because of their greatly increased
 complexity and lack of generality.  All of the associations and
 aggregations defined in this model are binary.
 Note also that by definition, associations and aggregations cannot be
 unary.

Moore, et al. Standards Track [Page 33] RFC 3670 QoS Device Datapath Info Model January 2004

 Finally, note that associations and aggregations that are defined
 between two classes do not affect the classes themselves.  That is,
 the addition or deletion of an association or an aggregation does not
 affect the interfaces of the classes that it is connecting.

4.2. The Structure of the Class Hierarchies

 The structure of the class, association, and aggregation class
 inheritance hierarchies for managing the datapaths of QoS devices is
 shown, respectively, in Figure 9, Figure 10, and Figure 11. The
 notation (CIMCORE) identifies a class defined in the CIM Core model.
 Please refer to [CIM] for the definitions of these classes.
 Similarly, the notation [PCIME] identifies a class defined in the
 Policy Core Information Model Extensions document. This model has
 been influenced by [CIM], and is compatible with the Directory
 Enabled Networks (DEN) effort.
 +--ManagedElement (CIMCORE)
    |
    +--ManagedSystemElement (CIMCORE)
    |  |
    |  +--LogicalElement (CIMCORE)
    |     |
    |     +--Service (CIMCORE)
    |     |  |
    |     |  +--ConditioningService
    |     |  |  |
    |     |  |  +--ClassifierService
    |     |  |  |  |
    |     |  |  |  +--ClassifierElement
    |     |  |  |
    |     |  |  +--MeterService
    |     |  |  |  |
    |     |  |  |  +--AverageRateMeterService
    |     |  |  |  |
    |     |  |  |  +--EWMAMeterService
    |     |  |  |  |
    |     |  |  |  +--TokenBucketMeterService
    |     |  |  |
    |     |  |  +--MarkerService
    |     |  |  |  |
    |     |  |  |  +--PreambleMarkerService
    |     |  |  |  |
    |     |  |  |  +--TOSMarkerService
    |     |  |  |  |
    |     |  |  |  +--DSCPMarkerService
    |     |  |  |  |

Moore, et al. Standards Track [Page 34] RFC 3670 QoS Device Datapath Info Model January 2004

 (continued from previous page;
  the first four elements are repeated for convenience)
 +--ManagedElement (CIMCORE)
    |
    +--ManagedSystemElement (CIMCORE)
    |  |
    |  +--LogicalElement (CIMCORE)
    |     |
    |     +--Service (CIMCORE)
    |     |  |  |  +--8021QMarkerService
    |     |  |  |
    |     |  |  +--DropperService
    |     |  |  |  |
    |     |  |  |  +--HeadTailDropperService
    |     |  |  |  |
    |     |  |  |  +--RedDropperService
    |     |  |  |
    |     |  |  +--QueuingService
    |     |  |  |
    |     |  |  +--PacketSchedulingService
    |     |  |     |
    |     |  |     +--NonWorkConservingSchedulingService
    |     |  |
    |     |  +--QoSService
    |     |  |  |
    |     |  |  +--DiffServService
    |     |  |  |   |
    |     |  |  |   +--AFService
    |     |  |  |
    |     |  |  +--FlowService
    |     |  |
    |     |  +--DropThresholdCalculationService
    |     |
    |     +--FilterEntryBase [PCIME]
    |     |  |
    |     |  +--IPHeaderFilter [PCIME]
    |     |  |
    |     |  +--8021Filter [PCIME]
    |     |  |
    |     |  +--PreambleFilter
    |     |
    |     +--FilterList [PCIME]
    |     |
    |     +--ServiceAccessPoint (CIMCORE)
    |        |
    |        +--ProtocolEndpoint

Moore, et al. Standards Track [Page 35] RFC 3670 QoS Device Datapath Info Model January 2004

 (continued from previous page;
  the first four elements are repeated for convenience)
 +--ManagedElement (CIMCORE)
    |
    +--ManagedSystemElement (CIMCORE)
    |  |
    |  +--LogicalElement (CIMCORE)
    |     |
    |     +--Service (CIMCORE)
    |
    +--Collection (CIMCORE)
    |  |
    |  +--CollectionOfMSEs (CIMCORE)
    |     |
    |     +--BufferPool
    |
    +--SchedulingElement
       |
       +--AllocationSchedulingElement
       |
       +--WRRSchedulingElement
       |
       +--PrioritySchedulingElement
          |
          +--BoundedPrioritySchedulingElement
 Figure 9.  Class Inheritance Hierarchy

Moore, et al. Standards Track [Page 36] RFC 3670 QoS Device Datapath Info Model January 2004

 The inheritance hierarchy for the associations defined in this
 document is shown in Figure 10.
 +--Dependency (CIMCORE)
 |  |
 |  +--ServiceSAPDependency (CIMCORE)
 |  |  |
 |  |  +--IngressConditioningServiceOnEndpoint
 |  |  |
 |  |  +--EgressConditioningServiceOnEndpoint
 |  |
 |  +--HeadTailDropQueueBinding
 |  |
 |  +--CalculationBasedOnQueue
 |  |
 |  +--ProvidesServiceToElement (CIMCORE)
 |  |  |
 |  |  +--ServiceServiceDependency (CIMCORE)
 |  |     |
 |  |     +--CalculationServiceForDropper
 |  |
 |  +--QueueAllocation
 |  |
 |  +--ClassifierElementUsesFilterList
 |
 +--AFRelatedServices
 |
 +--NextService
 |  |
 |  +--NextServiceAfterClassifierElement
 |  |
 |  +--NextScheduler
 |    |
 |    +--FailNextScheduler
 |
 +--NextServiceAfterMeter
 |
 +--QueueToSchedule
 |
 +--SchedulingServiceToSchedule
 Figure 10.  Association Class Inheritance Hierarchy

Moore, et al. Standards Track [Page 37] RFC 3670 QoS Device Datapath Info Model January 2004

 The inheritance hierarchy for the aggregations defined in this
 document is shown in Figure 11.
 +--MemberOfCollection (CIMCORE)
 |  |
 |  +--CollectedBufferPool
 |
 +--Component (CIMCORE)
 |  |
 |  +--ServiceComponent (CIMCORE)
 |  |  |
 |  |  +--QoSSubService
 |  |  |
 |  |  +--QoSConditioningSubService
 |  |  |
 |  |  +--ClassifierElementInClassifierService
 |  |
 |  +--EntriesInFilterList [PCIME]
 |
 +--ElementInSchedulingService
 Figure 11.  Aggregation Class Inheritance Hierarchy

4.3. Class Definitions

 This section presents the classes and properties that make up the
 Information Model for describing QoS-related functionality in network
 devices, including hosts.  These definitions are derived from
 definitions in the CIM Core model [CIM].  Only the QoS-related
 classes are defined in this document.  However, other classes drawn
 from the CIM Core model, as well as from [PCIME], are described
 briefly.  The reader is encouraged to look at [CIM] and at [PCIME]
 for further information.  Associations and aggregations are defined
 in Section 4.4.

4.3.1. The Abstract Class ManagedElement

 This is an abstract class defined in the Core Model of CIM.  It is
 the root of the entire class inheritance hierarchy in CIM. Among the
 associations that refer to it are two that are subclassed in this
 document: Dependency and MemberOfCollection, which is an aggregation.
 ManagedElement's properties are Caption and Description.  Both are
 free-form strings to describe an instantiated object.  Please refer
 to [CIM] for the full definition of this class.

Moore, et al. Standards Track [Page 38] RFC 3670 QoS Device Datapath Info Model January 2004

4.3.2. The Abstract Class ManagedSystemElement

 This is an abstract class defined in the Core Model of CIM; it is a
 subclass of ManagedElement.  ManagedSystemElement serves as the base
 class for the PhysicalElement and LogicalElement class hierarchies.
 LogicalElement, in turn, is the base class for a number of important
 CIM hierarchies, including System.  Any distinguishable component of
 a System is a candidate for inclusion in this class hierarchy,
 including physical components (e.g., chips and cards) and logical
 components (e.g., software components, services, and other objects).
 None of the associations in which this class participates is used
 directly in the QoS device state model.  However, the aggregation
 Component, which relates one ManagedSystemElement to another, is the
 base class for the two aggregations that form the core of the QoS
 device state model: QoSSubService and QoSConditioningSubService.
 Similarly, the association ProvidesServiceToElement, which relates a
 ManagedSystemElement to a Service, is the base class for the model's
 CalculationServiceForDropper association.
 Please refer to [CIM] for the full definition of this class.

4.3.3. The Abstract Class LogicalElement

 This is an abstract class defined in the Core Model of CIM.  It is a
 subclass of the ManagedSystemElement class, and is the base class for
 all logical components of a managed System, such as Files, Processes,
 or system capabilities in the form of Logical Devices and Services.
 None of the associations in which this class participates is relevant
 to the QoS device state model. Please refer to [CIM] for the full
 definition of this class.

4.3.4. The Abstract Class Service

 This is an abstract class defined in the Core Model of CIM.  It is a
 subclass of the LogicalElement class, and is the base class for all
 objects that represent a "service" or functionality in a System.  A
 Service is a general-purpose object that is used to configure and
 manage the implementation of functionality.  As noted above in
 section 4.3.2, this class participates in the
 ProvidesServiceToElement association.  Please refer to [CIM] for the
 full definition of this class.

4.3.5. The Class ConditioningService

 This is a concrete subclass of the CIM Core class Service; it
 represents the ability to define how traffic is conditioned in the
 data-forwarding path of a device.  The subclasses of

Moore, et al. Standards Track [Page 39] RFC 3670 QoS Device Datapath Info Model January 2004

 ConditioningService define the particular types of conditioning that
 are done.  Six fundamental types of conditioning are defined in this
 document.  These are the services performed by a classifier, a meter,
 a marker, a dropper, a queue, and a scheduler.  Other, more
 sophisticated types of conditioning may be defined in future
 documents.
 ConditioningService is a concrete class because at the time it was
 defined in CIM, its superclass was concrete.  While this class can be
 instantiated, an instance of it would not accomplish anything,
 because the nature of the conditioning, and the parameters that
 control it, are specified only in the subclasses of
 ConditioningService.
 Two associations in which ConditioningService participates are
 critical to its usage in QoS - QoSConditioningSubService and
 NextService.  QoSConditioningSubService aggregates
 ConditioningServices into a particular QoS service (such as AF), to
 describe the specific conditioning functionality that underlies that
 QoS service in a particular device.  NextService indicates the
 subsequent conditioning service(s) for different traffic streams.
 The class definition is as follows:
    NAME                ConditioningService
    DESCRIPTION         A concrete class to define how traffic
                        is conditioned in the data forwarding
                        path of a host or network device.
    DERIVED FROM        Service
    TYPE                Concrete
    PROPERTIES          (none)

4.3.6. The Class ClassifierService

 The concept of a Classifier comes from [DSMODEL]. ClassifierService
 is a concrete class that represents a logical entity in an ingress or
 egress interface of a device, that takes a single input stream, and
 sorts it into one or more output streams.  The sorting is done by a
 set of filters that select packets based on the packet contents, or
 possibly based on other attributes associated with the packet.  Each
 output stream is the result of matching a particular filter.
 The representation of classifiers in QDDIM is closely related to that
 presented in [DSMIB] and [DSMODEL].  Rather than being linked
 directly to its FilterLists, a classifier is modeled here as an
 aggregation of ClassifierElements.  Each of these ClassifierElements
 is then linked to a single FilterList, by the association
 ClassifierElementUsesFilterList.

Moore, et al. Standards Track [Page 40] RFC 3670 QoS Device Datapath Info Model January 2004

 A Classifier is modeled as a subclass of ConditioningService so that
 it can be aggregated into a QoSService (using the
 QoSConditioningSubService aggregation), and can use the NextService
 association to identify the subsequent ConditioningService objects
 for the different traffic streams.
 ClassifierService is designed to allow hierarchical classification.
 When hierarchical classification is used, a ClassifierElement may
 point to another ClassifierService.  When used for this purpose, the
 ClassifierElement must not use the ClassifierElementUsesFilterList
 association.
 The class definition is as follows:
    NAME                ClassifierService
    DESCRIPTION         A concrete class describing how an input
                        traffic stream is sorted into multiple
                        output streams using one or more
                        filters.
    DERIVED FROM        ConditioningService
    TYPE                Concrete
    PROPERTIES          (none)

4.3.7. The Class ClassifierElement

 The concept of a ClassifierElement comes from [DSMIB].  This concrete
 class represents the linkage, within a single ClassifierService,
 between a FilterList that specifies a set of criteria for selecting
 packets from the stream of packets coming into the ClassifierService,
 and the next ConditioningService to which the selected packets go
 after they leave the ClassifierService.  ClassifierElement has no
 properties of its own.  It is present to serve as the anchor for an
 aggregation with its classifier, and for associations with its
 FilterList and its next ConditioningService.
 When a ClassifierElement is associated with a ClassifierService
 through the NextServiceAfterClassifierElement association, the
 ClassifierElement may not use the ClassifierElementUsesFilterList
 association.  Further, when a ClassifierElement is associated with a
 ClassifierService as described above, the order of processing of the
 associated ClassifierService is a function of the ClassifierOrder
 property of the ClassifierElementInClassifierService aggregation.
 For example, lets assume the following:
 1. ClassifierService (C1) aggregates ClassifierElements (E1), (E2)
    and (E3), with relative ClassifierOrder values of 1, 2, and 3.

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 2. ClassifierElements (E1) and (E3) associations to FilterLists (F1)
    and (F3) respectively using the ClassifierElementUsesFilterList
    association.
 3. (E1) & (E3) are associated with Meters (M1) and (M3) through their
    respective NextServiceAfterClassifierElement associations.
 4. (E2) is associated with ClassifierService (C2) through its
    NextServiceAfterClassifierElement association.
 5. ClassifierService (C2) aggregates ClassifierElements (E4) and (E5)
    with relative ClassifierOrder values of 1 and 2.
 6. ClassifierElements (E4) and (E5) have associations to FilterLists
    (F4) and (F5) respectively using the
    ClassifierElementUsesFilterList association.
 In this example, packet processing would match FilterLists in the
 order of (F1), (F4), (F5), and (F3).
 The class definition is as follows:
    NAME                ClassifierElement
    DESCRIPTION         A concrete class representing
                        the process by which a classifier
                        uses a filter to select packets
                        to forward to a specific next
                        conditioning service.
    DERIVED FROM        ClassifierService
    TYPE                Concrete
    PROPERTIES          (none)

4.3.8. The Class MeterService

 This is a concrete class that represents the metering of network
 traffic.  Metering is the function of monitoring the arrival times of
 packets of a traffic stream, and determining the level of conformance
 of each packet with respect to a pre-established traffic profile.  A
 meter has the ability to invoke different ConditioningServices for
 conforming and non-conforming traffic. Traffic leaving a meter may be
 further conditioned (e.g., dropped or queued) by routing the packet
 to another conditioning element. Please see [DSMODEL] for more
 information on metering.
 This class is the base class for defining different types of meters.
 As such, it contains common properties that all meter subclasses
 share.  It is modeled as a ConditioningService so that it can be
 aggregated into a QoSService (using the QoSConditioningSubService

Moore, et al. Standards Track [Page 42] RFC 3670 QoS Device Datapath Info Model January 2004

 association), to indicate that its functionality underlies that QoS
 service.  MeterService also participates in the NextServiceAfterMeter
 association, to identify the subsequent ConditioningService objects
 for conforming and non-conforming traffic.
 The class definition is as follows:
    NAME                MeterService
    DESCRIPTION         A concrete class describing the
                        monitoring of traffic with respect to a
                        pre-established traffic profile.
    DERIVED FROM        ConditioningService
    TYPE                Concrete
    PROPERTIES          MeterType, OtherMeterType,
                        ConformanceLevels
 Note: The MeterType property and the MeterService subclasses provide
 similar information.  The MeterType property is defined for query
 purposes and for future expansion.  It is possible that not all
 MeterServices will require a subclass to define them.  In these
 cases, MeterService will be instantiated directly, and the MeterType
 property will provide the only way of identifying the type of the
 meter.

4.3.8.1. The Property MeterType

 This property is an enumerated 16-bit unsigned integer that is used
 to specify the particular type of meter represented by an instance of
 MeterService.  The following enumeration values are defined:
    1 - Other
    2 - Average Rate Meter
    3 - Exponentially Weighted Moving Average Meter
    4 - Token Bucket Meter
 Note: if the value of MeterType is not one of these four values, it
 SHOULD be interpreted as if it had the value '1' (Other).

4.3.8.2. The Property OtherMeterType

 This is a string property that defines a vendor-specific description
 of a type of meter.  It is used when the value of the MeterType
 property in the instance is equal to 1.

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4.3.8.3. The Property ConformanceLevels

 This property is a 16-bit unsigned integer.  It indicates the number
 of conformance levels supported by the meter.  For example, when only
 "in profile" versus "out of profile" metering is supported,
 ConformanceLevels is equal to 2.

4.3.9. The Class AverageRateMeterService

 This is a concrete subclass of MeterService that represents a simple
 meter, called an Average Rate Meter.  This type of meter measures the
 average rate at which packets are submitted to it over a specified
 time.  Packets are defined as conformant if their average arrival
 rate does not exceed the specified measuring rate of the meter.  Any
 packet that causes the specified measuring rate to be exceeded is
 defined to be non-conforming.  For more information, please see
 [DSMODEL].
 The class definition is as follows:
    NAME                AverageRateMeterService
    DESCRIPTION         A concrete class classifying traffic as
                        either conforming or non-conforming,
                        depending on whether the arrival of a
                        packet causes the average arrival rate
                        to exceed a pre-determined value.
    DERIVED FROM        MeterService
    TYPE                Concrete
    PROPERTIES          AverageRate, DeltaInterval

4.3.9.1. The Property AverageRate

 This is an unsigned 32-bit integer that defines the rate used to
 determine whether admitted packets are in conformance or not. The
 value is specified in kilobits per second.

4.3.9.2. The Property DeltaInterval

 This is an unsigned 64-bit integer that defines the time period over
 which the average measurement should be taken.  The value is
 specified in microseconds.

4.3.10. The Class EWMAMeterService

 This is a concrete subclass of the MeterService class that represents
 an exponentially weighted moving average meter.  This meter is a
 simple low-pass filter that measures the rate of incoming packets

Moore, et al. Standards Track [Page 44] RFC 3670 QoS Device Datapath Info Model January 2004

 over a small, fixed sampling interval.  Any admitted packet that
 pushes the average rate over a pre-defined limit is defined to be
 non-conforming.  Please see [DSMODEL] for more information.
 The class definition is as follows:
    NAME                EWMAMeterService
    DESCRIPTION         A concrete class classifying admitted
                        traffic as either conforming or non-
                        conforming, depending on whether the
                        arrival of a packet causes the average
                        arrival rate in a small fixed
                        sampling interval to exceed a
                        pre-determined value or not.
    DERIVED FROM        MeterService
    TYPE                Concrete
    PROPERTIES          AverageRate, DeltaInterval, Gain

4.3.10.1. The Property AverageRate

 This property is an unsigned 32-bit integer that defines the average
 rate against which the sampled arrival rate of packets should be
 measured.  Any packet that causes the sampled rate to exceed this
 rate is deemed non-conforming.  The value is specified in kilobits
 per second.

4.3.10.2. The Property DeltaInterval

 This property is an unsigned 64-bit integer that defines the sampling
 interval used to measure the arrival rate.  The calculated rate is
 averaged over this interval and checked against the AverageRate
 property.  All packets whose computed average arrival rate is less
 than the AverageRate are deemed conforming.
 The value is specified in microseconds.

4.3.10.3. The Property Gain

 This property is an unsigned 32-bit integer representing the
 reciprocal of the time constant (e.g., frequency response) of what is
 essentially a simple low-pass filter.  For example, the value 64 for
 this property represents a time constant value of 1/64.

Moore, et al. Standards Track [Page 45] RFC 3670 QoS Device Datapath Info Model January 2004

4.3.11. The Class TokenBucketMeterService

 This is a concrete subclass of the MeterService class that represents
 the metering of network traffic using a token bucket meter.  Two
 types of token bucket meters are defined using this class - a simple,
 two-parameter bucket meter, and a multi-stage meter.
 A simple token bucket usually has two parameters, an average token
 rate and a burst size, and has two conformance levels: "conforming"
 and "non-conforming".  This class also defines an excess burst size,
 which enables the meter to have three conformance levels
 ("conforming", "partially conforming", and "non-conforming").  In
 this case, packets that exceed the excess burst size are deemed non-
 conforming, while packets that exceed the smaller burst size but are
 less than the excess burst size are deemed partially conforming.
 Operation of these meters is described in [DSMODEL].
 The class definition is as follows:
    NAME                TokenBucketMeterService
    DESCRIPTION         A concrete class classifying admitted
                        traffic with respect to a token bucket.
                        Either two or three levels of
                        conformance can be defined.
    DERIVED FROM        MeterService
    TYPE                Concrete
    PROPERTIES          AverageRate, PeakRate,
                        BurstSize, ExcessBurstSize

4.3.11.1. The Property AverageRate

 This property is an unsigned 32-bit integer that specifies the
 committed rate of the meter.  The value is expressed in kilobits per
 second.

4.3.11.2. The Property PeakRate

 This property is an unsigned 32-bit integer that specifies the peak
 rate of the meter.  The value is expressed in kilobits per second.

4.3.11.3. The Property BurstSize

 This property is an unsigned 32-bit integer that specifies the
 maximum number of tokens available for the committed rate (specified
 by the AverageRate property).  The value is expressed in kilobytes.

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4.3.11.4. The Property ExcessBurstSize

 This property is an unsigned 32-bit integer that specifies the
 maximum number of tokens available for the peak rate (specified by
 the PeakRate property).  The value is expressed in kilobytes.

4.3.12. The Class MarkerService

 This is a concrete class that represents the general process of
 marking some field in a network packet with some value. Subclasses of
 MarkerService identify particular fields to be marked, and introduce
 properties to represent the values to be used in marking these
 fields.  Markers are usually invoked as a result of a preceding
 classifier match.  Operation of markers of various types is described
 in [DSMODEL].
 MarkerService is a concrete class because at the time it was defined
 in CIM, its superclass was concrete.  While this class can be
 instantiated, an instance of it would not accomplish anything,
 because both the field to be marked and the value to be used to mark
 it are specified only in subclasses of MarkerService.
 MarkerService is modeled as a ConditioningService so that it can be
 aggregated into a QoSService (using the QoSConditioningSubService
 association) to indicate that its functionality underlies that QoS
 service.  It participates in the NextService association to identify
 the subsequent ConditioningService object that acts on traffic after
 it has been marked by the marker.
 The class definition is as follows:
    NAME                MarkerService
    DESCRIPTION         A concrete class representing the
                        general process of marking a selected
                        field in a packet with a specified
                        value.  Packets are marked in order
                        to control the conditioning that
                        they will subsequently receive.
    DERIVED FROM        ConditioningService
    TYPE                Concrete
    PROPERTIES          (none)

4.3.13. The Class PreambleMarkerService

 This is a concrete class that models the storing of traffic-
 conditioning results in a packet preamble.  See Section 3.8.3 for a
 discussion of how, and why, QDDIM models the capability to store
 these results in a packet preamble.  An instance of

Moore, et al. Standards Track [Page 47] RFC 3670 QoS Device Datapath Info Model January 2004

 PreambleMarkerService appends to a packet preamble a two-part string
 of the form "<type>,<value>".  Section 3.8.3 provides a list of the
 <type> strings defined by QDDIM.  Implementations may support other
 <type>'s in addition to these.
 The class definition is as follows:
    NAME                PreambleMarkerService
    DESCRIPTION         A concrete class representing the saving
                        of traffic-conditioning results in a
                        packet preamble.
    DERIVED FROM        MarkerService
    TYPE                Concrete
    PROPERTIES          FilterItemList[ ]

4.3.13.1. The Multi-valued Property FilterItemList

 This property is an ordered list of strings, where each string has
 the format "<type>,<value>".  See Section 3.8.3 for a list of
 <type>'s defined in QDDIM, and the nature of the associated <value>
 for each of these types.

4.3.14. The Class ToSMarkerService

 This is a concrete class that represents the marking of the ToS field
 in the IPv4 packet header [R791].  Following common practice, the
 value to be written into the field is represented as an unsigned 8-
 bit integer.
 The class definition is as follows:
    NAME                ToSMarkerService
    DESCRIPTION         A concrete class representing the
                        process of marking the type of service
                        (ToS) field in the IPv4 packet header
                        with a specified value.  Packets are
                        marked in order to control the
                        conditioning that they will subsequently
                        receive.
    DERIVED FROM        MarkerService
    TYPE                Concrete
    PROPERTIES          ToSValue

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4.3.14.1. The Property ToSValue

 This property is an unsigned 8-bit integer, representing a value to
 be used for marking the type of service (ToS) field in the IPv4
 packet header.  The ToS field is defined to be a complete octet, so
 the range for this property is 0..255.  Some implementations,
 however, require that the lowest-order bit in the ToS field always be
 '0'.  Such an implementation is consequently unable to support an odd
 TosValue.

4.3.15. The Class DSCPMarkerService

 This is a concrete class that represents the marking of the
 differentiated services codepoint (DSCP) within the DS field in the
 IPv4 and IPv6 packet headers, as defined in [R2474]. Following common
 practice, the value to be written into the field is represented as an
 unsigned 8-bit integer.
 The class definition is as follows:
    NAME                DSCPMarkerService
    DESCRIPTION         A concrete class representing the
                        process of marking the DSCP field
                        in a packet with a specified
                        value.  Packets are marked in order
                        to control the conditioning that
                        they will subsequently receive.
    DERIVED FROM        MarkerService
    TYPE                Concrete
    PROPERTIES          DSCPValue

4.3.15.1. The Property DSCPValue

 This property is an unsigned 8-bit integer, representing a value to
 be used for marking the DSCP within the DS field in an IPv4 or IPv6
 packet header.  Since the DSCP consists of 6 bits, the values for
 this property are limited to the range 0..63.  When the DSCP is
 marked, the remaining two bit in the DS field are left unchanged.

4.3.16. The Class 8021QMarkerService

 This is a concrete class that represents the marking of the user
 priority field defined in the IEEE 802.1Q specification [IEEE802Q].
 Following common practice, the value to be written into the field is
 represented as an unsigned 8-bit integer.

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 The class definition is as follows:
    NAME                8021QMarkerService
    DESCRIPTION         A concrete class representing the
                        process of marking the Priority
                        field in an 802.1Q-compliant frame
                        with a specified value.  Frames are
                        marked in order to control the
                        conditioning that they will
                        subsequently receive.
    DERIVED FROM        MarkerService
    TYPE                Concrete
    PROPERTIES          PriorityValue

4.3.16.1. The Property PriorityValue

 This property is an unsigned 8-bit integer, representing a value to
 be used for marking the Priority field in the 802.1Q header. Since
 the Priority field consists of 3 bits, the values for this property
 are limited to the range 0..7.  When the Priority field is marked,
 the remaining bits in its octet are left unchanged.

4.3.17. The Class DropperService

 This is a concrete class that represents the ability to selectively
 drop network traffic, or to invoke another ConditioningService for
 further processing of traffic that is not dropped.  This is the base
 class for different types of droppers. Droppers are distinguished by
 the algorithm that they use to drop traffic.  Please see [DSMODEL]
 for more information about the various types of droppers.  Note that
 this class encompasses both Absolute Droppers and Algorithmic
 Droppers from [DSMODEL].
 DropperService is modeled as a ConditioningService so that it can be
 aggregated into a QoSService (using the QoSConditioningSubService
 association) to indicate that its functionality underlies that QoS
 service.  It participates in the NextService association to identify
 the subsequent ConditioningService object that acts on any remaining
 traffic that is not dropped.
 NextService has special semantics for droppers, in addition to the
 general "what happens next" semantics that apply to all
 ConditioningServices.  The queue(s) from which a particular dropper
 drops packets are identified by following chain(s) of NextService
 associations "rightwards" from the dropper until they reach a queue.

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 The class definition is as follows:
    NAME                DropperService
    DESCRIPTION         A concrete base class describing the
                        common characteristics of droppers.
    DERIVED FROM        ConditioningService
    TYPE                Concrete
    PROPERTIES          DropperType, OtherDropperType, DropFrom
 Note: The DropperType property and the DropperService subclasses
 provide similar information.  The DropperType property is defined for
 query purposes, as well as for those cases where a subclass of
 DropperService is not needed to model a particular type of dropper.
 For example, the Absolute Dropper defined in [DSMODEL] is modeled as
 an instance of the DropperService class with its DropperType set to
 '4' ("Absolute Dropper").

4.3.17.1. The Property DropperType

 This is an enumerated 16-bit unsigned integer that defines the type
 of dropper.  Values include:
    1 - Other
    2 - Random
    3 - HeadTail
    4 - Absolute Dropper
 Note: if the value of DropperType is not one of these four values, it
 SHOULD be interpreted as if it had the value '1' (Other).

4.3.17.2. The Property OtherDropperType

 This string property is used in conjunction with the DropperType
 property.  When the value of DropperType is '1' (i.e., Other), then
 the name of the type of dropper appears in this property.

4.3.17.3. The Property DropFrom

 This is an unsigned 16-bit integer enumeration that indicates the
 point in the associated queue from which packets should be dropped.
 Defined enumeration values are:
    o  unknown(0)
    o  head(1)
    o  tail(2)

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 Note: if the value of DropFrom is '0' (unknown), or if it is not one
 of the three values listed here, then packets MAY be dropped from any
 location in the associated queue.

4.3.18. The Class HeadTailDropperService

 This is a concrete class that represents the threshold information of
 a head or tail dropper.  The inherited property DropFrom indicates
 whether a particular instance of this class represents a head dropper
 or a tail dropper.
 A head dropper always examines the same queue from which it drops
 packets, and this queue is always related to the dropper as the
 following service in the NextService association.
 The class definition is as follows:
    NAME                HeadTailDropperService
    DESCRIPTION         A concrete class used to describe
                        a head or tail dropper.
    DERIVED FROM        DropperService
    TYPE                Concrete
    PROPERTIES          QueueThreshold

4.3.18.1. The Property QueueThreshold

 This is an unsigned 32-bit integer that indicates the queue depth at
 which traffic will be dropped.  For a tail dropper, all newly
 arriving traffic is dropped.  For a head dropper, packets at the
 front of the queue are dropped to make room for new packets, which
 are added at the end.  The value is expressed in bytes.

4.3.19. The Class REDDropperService

 This is a concrete class that represents the ability to drop network
 traffic using a Random Early Detection (RED) algorithm. This
 algorithm is described in [RED].  The purpose of a RED algorithm is
 to avoid congestion (as opposed to managing congestion).  Instead of
 waiting for the queues to fill up, and then dropping large numbers of
 packets, RED works by monitoring the average queue depth.  When the
 queue depth exceeds a minimum threshold, packets are randomly
 discarded.  These discards cause TCP to slow its transmission rate
 for those connections that experienced the packet discards.  Other
 TCP connections are not affected by these discards.  Please see
 [DSMODEL] for more information about a dropper.

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 A RED dropper always drops packets from a single queue, which is
 related to the dropper as the following service in the NextService
 association.  The queue(s) examined by the drop algorithm are found
 by following the CalculationServiceForDropper association to find the
 dropper's DropThresholdCalculationService, and then following the
 CalculationBasedOnQueue association(s) to find the queue(s) being
 watched.
 The class definition is as follows:
    NAME                REDDropperService
    DESCRIPTION         A concrete class used to describe
                        dropping using the RED algorithm (or
                        one of its variants).
    DERIVED FROM        DropperService
    TYPE                Concrete
    PROPERTIES          MinQueueThreshold, MaxQueueThreshold,
                        ThresholdUnits, StartProbability,
                        StopProbability
 NOTE:  In [DSMIB], there is a single diffServRandomDropTable, which
 represents the general category of random dropping.  (RED is one type
 of random dropping, but there are also types of random dropping
 distinct from RED.)  The REDDropperService class corresponds to the
 columns in the table that apply to the RED algorithm in particular.

4.3.19.1. The Property MinQueueThreshold

 This is an unsigned 32-bit integer that defines the minimum average
 queue depth at which packets are subject to being dropped.  The units
 are identified by the ThresholdUnits property.  The slope of the drop
 probability function is described by the Start/StopProbability
 properties.

4.3.19.2. The Property MaxQueueThreshold

 This is an unsigned 32-bit integer that defines the maximum average
 queue length at which packets are subject to always being dropped,
 regardless of the dropping algorithm and probabilities being used.
 The units are identified by the ThresholdUnits property.

4.3.19.3. The Property ThresholdUnits

 This is an unsigned 16-bit integer enumeration that identifies the
 units for the MinQueueThreshold and MaxQueueThreshold properties.
 Defined enumeration values are:

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    o    bytes(1)
    o    packets(2)
 Note: if the value of ThresholdUnits is not one of these two values,
 it SHOULD be interpreted as if it had the value '1' (bytes).

4.3.19.4. The Property StartProbability

 This is an unsigned 32-bit integer; in conjunction with the
 StopProbability property, it defines the slope of the drop
 probability function.  This function governs the rate at which
 packets are subject to being dropped, as a function of the queue
 length.
 This property expresses a drop probability in drops per thousand
 packets.  For example, the value 100 indicates a drop probability of
 100 per 1000 packets, that is, 10%.  Min and max values are 0 to
 1000.

4.3.19.5. The Property StopProbability

 This is an unsigned 32-bit integer; in conjunction with the
 StartProbability property, it defines the slope of the drop
 probability function.  This function governs the rate at which
 packets are subject to being dropped, as a function of the queue
 length.
 This property expresses a drop probability in drops per thousand
 packets.  For example, the value 100 indicates a drop probability of
 100 per 1000 packets, that is, 10%.  Min and max values are 0 to
 1000.

4.3.20. The Class QueuingService

 This is a concrete class that represents the ability to queue network
 traffic, and to specify the characteristics for determining long-term
 congestion.  Please see [DSMODEL] for more information about queuing
 functionality.
 QueuingService is modeled as a ConditioningService so that it can be
 aggregated into a QoSService (using the QoSConditioningSubService
 association) to indicate that its functionality underlies that QoS
 service.

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 The class definition is as follows:
    NAME                QueuingService
    DESCRIPTION         A concrete class describing the ability
                        to queue network traffic and to specify
                        the characteristics for determining
                        long-term congestion.
    DERIVED FROM        ConditioningService
    TYPE                Concrete
    PROPERTIES          CurrentQueueDepth, DepthUnits

4.3.20.1. The Property CurrentQueueDepth

 This is an unsigned 32-bit integer, which functions as a (read-only)
 gauge representing the current depth of this one queue.  This value
 may be important in diagnosing unexpected behavior by a
 DropThresholdCalculationService.

4.3.20.2. The Property DepthUnits

 This is an unsigned 16-bit integer enumeration that identifies the
 units for the CurrentQueueDepth property.  Defined enumeration values
 are:
    o    bytes(1)
    o    packets(2)
 Note: if the value of DepthUnits is not one of these two values, it
 SHOULD be interpreted as if it had the value '1' (bytes).  The

4.3.21. Class PacketSchedulingService

 This is a concrete class that represents a scheduling service, which
 is a process that determines when a queued packet should be removed
 from a queue and sent to an output interface.  Note that output
 interfaces can be physical network interfaces or interfaces to
 components internal to systems, such as crossbars or back planes.  In
 either case, if multiple queues are involved, schedulers are used to
 provide access to the interface.
 Each instance of a PacketSchedulingService describes a scheduler from
 the perspective of the queues that it is servicing.  Please see
 [DSMODEL] for more information about a scheduler.
 PacketSchedulingService is modeled as a ConditioningService so that
 it can be aggregated into a QoSService (using the
 QoSConditioningSubService association) to indicate that its
 functionality underlies that QoS service.  It participates in the

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 NextService association to identify the subsequent
 ConditioningService object, if any, that acts on traffic after it has
 been processed by the scheduler.
 The class definition is as follows:
    NAME                PacketSchedulingService
    DESCRIPTION         A concrete class used to determine when
                        a packet should be removed from a
                        queue and sent to an output interface.
    DERIVED FROM        ConditioningService
    TYPE                Concrete
    PROPERTIES          SchedulerType, OtherSchedulerType

4.3.21.1. The Property SchedulerType

 This property is an enumerated 16-bit unsigned integer, and defines
 the type of scheduler.  Values are:
    1 - Other
    2 - FIFO
    3 - Priority
    4 - Allocation
    5 - Bounded Priority
    6 - Weighted Round Robin Packet
 Note: if the value of SchedulerType is not one of these six values,
 it SHOULD be interpreted as if it had the value '2' (FIFO).

4.3.21.2. The Property OtherSchedulerType

 This string property is used in conjunction with the SchedulerType
 property.  When the value of SchedulerType is 1 (i.e., Other), then
 the type of scheduler is specified in this property.

4.3.22. The Class NonWorkConservingSchedulingService

 This class does not add any properties beyond those it inherits from
 its superclass, PacketSchedulingService.  It does, however,
 participate in one additional association, FailNextScheduler.

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 The class definition is as follows:
    NAME                NonWorkConservingSchedulingService
    DESCRIPTION         A concrete class representing a
                        scheduler that is capable of operating
                        in a non-work conserving manner.
    DERIVED FROM        PacketSchedulingService
    TYPE                Concrete
    PROPERTIES          (none)

4.3.23. The Class QoSService

 This is a concrete class that represents the ability to conceptualize
 a QoS service as a set of coordinated sub-services. This enables the
 network administrator to map business rules to the network, and the
 network designer to engineer the network such that it can provide
 different functions for different traffic streams.
 This class has two main purposes.  First, it serves as a common base
 class for defining the various sub-services needed to build higher-
 level QoS services.  Second, it serves as a way to consolidate the
 relationships between different types of QoS services and different
 types of ConditioningServices.
 For example, Gold Service may be defined as a QoSService which
 aggregates two QoS services together.  Each of these QoS services
 could be represented by an instance of the class DiffServService, one
 for servicing of very high demand packets (represented by an instance
 of DiffServService itself), and one for the service given to most of
 the packets, represented by an instance of AFService, which is a
 subclass of DiffServService.  The high demand DiffServService
 instance will then use the QoSConditioningSubService aggregation to
 aggregate together the necessary classifiers to indicate which
 traffic it applies to, and the appropriate meters for contract
 limits, the marker to mark the EF PHB in the packets, and the
 queuing-related conditioning services.  The AFService instance will
 also use the QoSConditioningSubService aggregation, to aggregate its
 classifiers and meters, the several markers used to mark the
 different AF PHBs in the packets, and the queuing-related
 conditioning services needed to deliver the packet treatment.
 QoSService is modeled as a type of Service, which is used as the
 anchor point for defining a set of sub-services that implement the
 desired conditioning characteristics for different types of flows.
 It will direct the specific type of conditioning services to be used
 in order to implement this service.

Moore, et al. Standards Track [Page 57] RFC 3670 QoS Device Datapath Info Model January 2004

 The class definition is as follows:
    NAME                QoSService
    DESCRIPTION         A concrete class used to represent a QoS
                        service or set of services, as defined
                        by a network administrator.
    DERIVED FROM        Service
    TYPE                Concrete
    PROPERTIES          (none)

4.3.24. The Class DiffServService

 This is a concrete class representing the use of standard or custom
 DiffServ services to implement a (higher-level) QoS service.  Note
 that a DiffServService object may be just one of a set of coordinated
 QoSSubServices objects that together implement a higher-level QoS
 service.
 DiffServService is modeled as a subclass of QoSService.  This enables
 it to be related to a higher-level QoS service via QoSSubService, as
 well as to specific ConditioningService objects (e.g., metering,
 dropping, queuing, and others) via QoSConditioningSubService.
 The class definition is as follows:
    NAME                DiffServService
    DESCRIPTION         A concrete class used to represent a
                        DiffServ service associated with a
                        particular Per Hop Behavior.
    DERIVED FROM        QoSService
    TYPE                Concrete
    PROPERTIES          PHBID

4.3.24.1. The Property PHBID

 This property is a 16-bit unsigned integer, which identifies a
 particular per hop behavior, or family of per hop behaviors.  The
 value here is a Per Hop Behavior Identification Code, as defined in
 [R3140].  Note that as defined, these identification codes use the
 default, recommended, code points for PHBs as part of their
 structure.  These values may well be different from the actual value
 used in the marker, as the marked value is a domain-dependent value.
 The ability to indicate the PHB Identification Code associated with a
 service is helpful for tying the QoS Service to reference documents,
 and for inter-domain coordination and operation.

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4.3.25. The Class AFService

 This is a concrete class that represents a specialization of the
 general concept of forwarding network traffic, by adding specific
 semantics that characterize the operation of the Assured Forwarding
 (AF) Service ([R2597]).
 [R2597] defines four different AF classes, to represent four
 different treatments of traffic.  A different amount of forwarding
 resources, such as buffer space and bandwidth, are allocated to each
 AF class.  Within each AF class, IP packets are marked with one of
 three possible drop precedence values.  The drop precedence of a
 packet determines the relative importance of that packet compared to
 other packets within the same AF class, if congestion occurs.  A
 congested interface will try to avoid dropping packets marked with a
 lower drop precedence value, by instead discarding packets marked
 with a higher drop precedence value.
 Note that [R2597] defines 12 DSCPs that together represent the AF Per
 Hop Behavior (PHB) group.  Implementations are free to extend this
 (e.g., add more classes and/or drop precedences).
 The AFService class is modeled as a specialization of
 DiffServService, which is in turn a specialization of QoSService.
 This enables it to be related to higher-level QoS services, as well
 as to lower-level conditioning sub-services (e.g., classification,
 metering, dropping, queuing, and others).
 The class definition is as follows:
    NAME                AFService
    DESCRIPTION         A concrete class for describing the
                        common characteristics of differentiated
                        services that are used to affect
                        traffic forwarding, using the AF
                        PHB Group.
    DERIVED FROM        DiffServService
    TYPE                Concrete
    PROPERTIES          ClassNumber, DropperNumber

4.3.25.1. The Property ClassNumber

 This property is an 8-bit unsigned integer that indicates the number
 of AF classes that this AF implementation uses.  Among the instances
 aggregated using the QoSConditioningSubService aggregation with an
 instance of AFService, one SHOULD find markers with as many distinct
 values as the ClassNumber of the AFService instance.

Moore, et al. Standards Track [Page 59] RFC 3670 QoS Device Datapath Info Model January 2004

4.3.25.2. The Property DropperNumber

 This property is an 8-bit unsigned integer that indicates the number
 of drop precedence values that this AF implementation uses.  The
 number of drop precedence values is the number PER AF CLASS.  The
 corresponding droppers will be found in the collection of
 conditioning services aggregated with the QoSConditioningSubService
 aggregation.

4.3.26. The Class FlowService

 This class represents a service that supports a particular microflow.
 The microflow is identified by the string-valued property FlowID.  In
 some implementations, an instance of this class corresponds to an
 entry in the implementation's flow table.
 The class definition is as follows:
    NAME                FlowService
    DESCRIPTION         A concrete class representing a
                        microflow.
    DERIVED FROM        QoSService
    TYPE                Concrete
    PROPERTIES          FlowID

4.3.26.1. The Property FlowID

 This property is a string containing an identifier for a microflow.

4.3.27. The Class DropThresholdCalculationService

 This class represents a logical entity that calculates an average
 queue depth for a queue, based on a smoothing weight and a sampling
 time interval.  It does this calculation on behalf of a RED dropper,
 to allow the dropper to make its decisions whether to drop packets
 based on a smoothed average queue depth for the queue.

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 The class definition is as follows:
    NAME                DropThresholdCalculationService
    DESCRIPTION         A concrete class representing a logical
                        entity that calculates an average queue
                        depth for a queue, based on a smoothing
                        weight and a sampling time interval.
                        The latter are properties of this
                        Service, describing how it operates and
                        its necessary parameters.
    DERIVED FROM        Service
    TYPE                Concrete
    PROPERTIES          SmoothingWeight, TimeInterval

4.3.27.1. The Property SmoothingWeight

 This property is a 32-bit unsigned integer, ranging between 0 and
 100,000 - specified in thousandths.  It defines the weighting of past
 history in affecting the calculation of the current average queue
 depth.  The current queue depth calculation uses the inverse of this
 value as its factor, and one minus that inverse as the factor for the
 historical average.  The calculation takes the form:
    average = (old_average*(1-inverse of SmoothingWeight))
         + (current_queue_depth*inverse of SmoothingWeight)
 Implementations may choose to limit the acceptable set of values to a
 specified set, such as powers of 2.
 Min and max values are 0 and 100000.

4.3.27.2. The Property TimeInterval

 This property is a 32-bit unsigned integer, defining the number of
 nanoseconds between each calculation of average/smoothed queue depth.
 If this property is not specified, the CalculationService may
 determine an appropriate interval.

4.3.28. The Abstract Class FilterEntryBase

 FilterEntryBase is the abstract base class from which all filter
 entry classes are derived.  It serves as the endpoint for the
 EntriesInFilterList aggregation, which groups filter entries into
 filter lists.  Its properties include CIM naming properties and an
 IsNegated boolean property (to easily "NOT" the match information
 specified in an instance of one of its subclasses).

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 Because FilterEntryBase has general applicability, it is defined in
 [PCIME].  See [PCIME] for the definition of this class.

4.3.29. The Class IPHeaderFilter

 This concrete class makes it possible to represent an entire IP
 header filter in a single object.  A property IpVersion identifies
 whether the IP addresses in an instance are IPv4 or IPv6 addresses.
 (Since the source and destination IP addresses come from the same
 packet header, they will always be of the same type.)
 See [PCIME] for the definition of this class.

4.3.30. The Class 8021Filter

 This concrete class allows 802.1.source and destination MAC
 addresses, as well as the 802.1 protocol ID, priority, and VLAN
 identifier fields, to be expressed in a single object
 See [PCIME] for the definition of this class.

4.3.31. The Class PreambleFilter

 This is a concrete class that models classifying packets using
 traffic-conditioning results stored in a packet preamble by a
 PreambleMarkerService.  See Section 3.8.3 for a discussion of how,
 and why, QDDIM models the capability to store these results in a
 packet preamble.  An instance of PreambleFilter is used to select
 packets based on a two-part string identifying a specific result.
 The logic for this match is "at least one".  That is, a packet with
 multiple results in its preamble matches a filter if at least one of
 these results matches the filter.
 The class definition is as follows:
    NAME                PreambleFilter
    DESCRIPTION         A concrete class representing criteria
                        for selecting packets based on prior
                        traffic-conditioning results stored in
                        a packet preamble.
    DERIVED FROM        FilterEntryBase
    TYPE                Concrete
    PROPERTIES          FilterItemList[ ]

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4.3.31.1. The Multi-valued Property FilterItemList

 This property is an ordered list of strings, where each string has
 the format "<type>,<value>".  See Section 3.8.3 for a list of
 <type>'s defined in QDDIM, and the nature of the associated <value>
 for each of these types.
 Note that there are two parallel terminologies for characterizing
 meter results.  The enumeration value "conforming(1)" is sometimes
 described as "in profile," and the value "nonConforming(3)" is
 sometimes described as "out of profile".

4.3.32. The Class FilterList

 This is a concrete class that aggregates instances of (subclasses of)
 FilterEntryBase via the aggregation EntriesInFilterList.  It is
 possible to aggregate different types of filters into a single
 FilterList - for example, packet header filters (represented by the
 IPHeaderFilter class) and security filters (represented by subclasses
 of FilterEntryBase defined by IPsec).
 The aggregation property EntriesInFilterList.EntrySequence is always
 set to 0, to indicate that the aggregated filter entries are ANDed
 together to form a selector for a class of traffic.
 See [PCIME] for the definition of this class.

4.3.33. The Abstract Class ServiceAccessPoint

 This is an abstract class defined in the Core Model of CIM.  It is a
 subclass of the LogicalElement class, and is the base class for all
 objects that manage access to CIM_Services.  It represents the
 management of utilizing or invoking a Service. Please refer to [CIM]
 for the full definition of this class.

4.3.34. The Class ProtocolEndpoint

 This is a concrete class derived from ServiceAccessPoint, which
 describes a communication point from which the services of the
 network or the system's protocol stack may be accessed.  Please refer
 to [CIM] for the full definition of this class.

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4.3.35. The Abstract Class Collection

 This is an abstract class defined in the Core Model of CIM.  It is
 the superclass for all classes that represent groupings or bags, and
 that carry no status or "state".  (The latter would be more correctly
 modeled as ManagedSystemElements.)  Please refer to [CIM] for the
 full definition of this class.

4.3.36. The Abstract Class CollectionOfMSEs

 This is an abstract class defined in the Core Model of CIM.  It is a
 subclass of the Collection superclass, restricting the contents of
 the Collection to ManagedSystemElements.  Please refer to [CIM] for
 the full definition of this class.

4.3.37. The Class BufferPool

 This is a concrete class that represents the collection of buffers
 used by a QueuingService.  (The association QueueAllocation
 represents this usage.)  The existence and management of individual
 buffers may be modeled in a future document.  At the current level of
 abstraction, modeling the existence of the BufferPool is necessary.
 Long term, it is not sufficient.
 In implementations where there are multiple buffer sizes, an instance
 of BufferPool should be defined for each set of buffers with
 identical or similar sizes.  These instances of buffer pools can then
 be grouped together using the CollectedBuffersPool aggregation.
 Note that this class is derived from CollectionOfMSEs, and not from
 Forwarding or ConditioningService.  A BufferPool is only a collection
 of storage, and is NOT a Service.
 The class definition is as follows:
    NAME                BufferPool
    DESCRIPTION         A concrete class representing
                        a collection of buffers.
    DERIVED FROM        CollectionOfMSEs
    TYPE                Concrete
    PROPERTIES          Name, BufferSize, TotalBuffers,
                        AvailableBuffers, SharedBuffers

4.3.37.1. The Property Name

 This property is a string with a maximum length of 256 characters.
 It is the common name or label by which the object is known.

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4.3.37.2. The Property BufferSize

 This property is a 32-bit unsigned integer, identifying the
 approximate number of bytes in each buffer in the buffer pool. An
 implementation will typically group buffers of roughly the same size
 together, to reduce the number of buffer pools it needs to manage.
 This model does not specify the degree to which buffers in the same
 buffer pool may differ in size.

4.3.37.3. The Property TotalBuffers

 This property is a 32-bit unsigned integer, reporting the total
 number of individual buffers in the pool.

4.3.37.4. The Property AvailableBuffers

 This property is a 32-bit unsigned integer, reporting the number of
 buffers in the Pool that are currently not allocated to any instance
 of a QueuingService.  Buffers allocated to a QueuingService could
 either be in use (that is, currently contain packet data), or be
 allocated to a queue pending the arrival of new packet data.

4.3.37.5. The Property SharedBuffers

 This property is a 32-bit unsigned integer, reporting the number of
 buffers in the Pool that have been simultaneously allocated to
 multiple instances of QueuingService.

4.3.38. The Abstract Class SchedulingElement

 This is an abstract class that represents the configuration
 information that a PacketSchedulingService has for one of the
 elements that it is scheduling.  The scheduled element is either a
 QueuingService or another PacketSchedulingService.
 Among the subclasses of this class, some are defined in such a way
 that all of their instances are work conserving.  Other subclasses,
 however, may have instances that either are or are not work
 conserving.  In this class, the boolean property WorkConserving
 indicates whether an instance is or is not work conserving.  The
 range of values for WorkConserving is restricted to TRUE in the
 subclasses that are inherently work conserving, since instances of
 these classes cannot be anything other than work conserving.

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 The class definition is as follows:
    NAME                SchedulingElement
    DESCRIPTION         An abstract class representing the
                        configuration information that a
                        PacketSchedulingService has for one of
                        the elements that it is scheduling.
    DERIVED FROM        ManagedElement
    TYPE                Abstract
    PROPERTIES          WorkConserving

4.3.38.1. The Property WorkConserving

 This boolean property indicates whether the PacketSchedulingService
 tied to this instance by the ElementInSchedulingService aggregation
 is treating the input tied to this instance by the QueueToSchedule or
 SchedulingServiceToSchedule association in a work-conserving manner.
 Note that this property is writable, indicating that an administrator
 can change the behavior of the SchedulingElement - but only for those
 elements that can operate in a non-workconserving mode.

4.3.39. The Class AllocationSchedulingElement

 This class is a subclass of the abstract class SchedulingElement. It
 introduces five new properties to support bandwidth-based scheduling.
 As is the case with all subclasses of SchedulingElement, the input
 associated with an instance of AllocationSchedulingElement is of one
 of two types: either a queue, or another scheduler.
 The class definition is as follows:
    NAME                AllocationSchedulingElement
    DESCRIPTION         A concrete class containing parameters
                        for controlling bandwidth-based
                        scheduling.
    DERIVED FROM        SchedulingElement
    TYPE                Concrete
    PROPERTIES          AllocationUnits, BandwidthAllocation,
                        BurstAllocation, CanShare,
                        WorkFlexible

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4.3.39.1. The Property AllocationUnits

 This property is a 16-bit unsigned integer enumeration that
 identifies the units in which the BandwidthAllocation and
 BurstAllocation properties are expressed.  The following values are
 defined:
    o bytes(1)
    o packets(2)
    o cells(3)       -- fixed-size, for example, ATM
 Note: if the value of AllocationUnits is not one of these three
 values, it SHOULD be interpreted as if it had the value '1' (bytes).

4.3.39.2. The Property BandwidthAllocation

 This property is a 32-bit unsigned integer that defines the number of
 units/second that should be allocated to the associated input.  The
 units are identified by the AllocationUnits property.

4.3.39.3. The Property BurstAllocation

 This property is a 32-bit unsigned integer that specifies the amount
 of temporary or short-term bandwidth (in units per second) that can
 be allocated to an input, beyond the amount of bandwidth allocated
 through the BandwidthAllocation property.  If the maximum actual
 bandwidth allocation for the input were to be measured, it would be
 the sum of the BurstAllocation and the BandwidthAllocation
 properties.  The units are identified by the AllocationUnits
 property.

4.3.39.4. The Property CanShare

 This is a boolean property that, if TRUE, enables unused bandwidth
 from the associated input to be allocated to other inputs serviced by
 the Scheduler.

4.3.39.5. The Property WorkFlexible

 This is a boolean property that, if TRUE, indicates that the behavior
 of the scheduler relative to this input can be altered by changing
 the value of the inherited property WorkConserving.

4.3.40. The Class WRRSchedulingElement

 This class is a subclass of the abstract class SchedulingElement,
 representing a weighted round robin (WRR) scheduling discipline. It
 introduces a new property WeightingFactor, to give some inputs a

Moore, et al. Standards Track [Page 67] RFC 3670 QoS Device Datapath Info Model January 2004

 higher probability of being serviced than other inputs.  It also
 introduces a property Priority, to serve as a tiebreaker to be used
 when inputs have equal weighting factors.  As is the case with all
 subclasses of SchedulingElement, the input associated with an
 instance of WRRSchedulingElement is of one of two types: either a
 queue, or another scheduler.
 Because scheduling of this type is always work conserving, the
 inherited boolean property WorkConserving is restricted to the value
 TRUE in this class.
 The class definition is as follows:
    NAME              WRRSchedulingElement
    DESCRIPTION       This class specializes the
                      SchedulingElement class to add
                      a per-input weight.  This is used
                      by a weighted round robin packet
                      scheduler when it handles its
                      associated inputs.  It also adds a
                      second property to serve as a tie-breaker
                      in the case where multiple inputs have
                      been assigned the same weight.
    DERIVED FROM      SchedulingElement
    TYPE              Concrete
    PROPERTIES        WeightingFactor, Priority

4.3.40.1. The Property WeightingFactor

 This property is a 32-bit unsigned integer, which defines the
 weighting factor that offers some inputs a higher probability of
 being serviced than other inputs.  This property represents this
 probability.  Its minimum value is 0, its maximum value is 100000,
 and its units are in thousandths.

4.3.40.2. The Property Priority

 This property is a 16-bit unsigned integer, which serves as a
 tiebreaker, in the event that two or more inputs have equal weights.
 A larger value represents a higher priority.  If this property is
 specified for any of the WRRSchedulingElements associated with a
 PacketSchedulingService, then it must be specified for all
 WRRSchedulingElements for that PacketSchedulingService, and the
 property values for these WRRSchedulingElements must all be
 different.

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 While this condition may not occur in some implementations of a
 weighted round-robin scheduler, many implementations require a
 priority to resolve an equal-weight condition.  In instances where
 this behavior is not necessary or is undesirable, this property may
 be left unspecified.

4.3.41. The Class PrioritySchedulingElement

 This class is a subclass of the abstract class SchedulingElement. It
 indicates that a scheduler is taking packets from a set of inputs
 using the priority scheduling discipline.  As is the case with all
 subclasses of SchedulingElement, the input associated with an
 instance of PrioritySchedulingElement is of one of two types: either
 a queue, or another scheduler.  The property Priority in
 PrioritySchedulingElement represents the priority for an input,
 relative to the priorities of all the other inputs to which the
 scheduler that aggregates this PrioritySchedulingElement is
 associated.  Inputs to which the scheduler is related via other
 scheduling disciplines do not figure in this prioritization.
 Because scheduling of this type is always work conserving, the
 inherited boolean property WorkConserving is restricted to the value
 TRUE in this class.
 The class definition is as follows:
    NAME             PrioritySchedulingElement
    DESCRIPTION      A concrete class that specializes the
                     SchedulingElement class to add a
                     Priority property.  This property is
                     used by a SchedulingService that is doing
                     priority scheduling for a set of  inputs.
    DERIVED FROM     SchedulingElement
    TYPE             Concrete
    PROPERTIES       Priority

4.3.41.1. The Property Priority

 This property is a 16-bit unsigned integer that indicates the
 priority level of a scheduler input relative to the other inputs
 serviced by this PacketSchedulingService.  A larger value represents
 a higher priority.

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4.3.42. The Class BoundedPrioritySchedulingElement

 This class is a subclass of the class PrioritySchedulingElement,
 which is itself derived from the abstract class SchedulingElement.
 As is the case with all subclasses of SchedulingElement, the input
 associated with an instance of BoundedPrioritySchedulingElement is of
 one of two types: either a queue, or another scheduler.
 BoundedPrioritySchedulingElement adds an upper bound (in kilobits per
 second) on how much traffic can be handled from an input.  This data
 is specific to that one input.  It is needed when bounded strict
 priority scheduling is performed.
 This class inherits from its superclass PrioritySchedulingElement the
 restriction of the inherited boolean property WorkConserving to the
 value TRUE.
 The class definition is as follows:
    NAME              BoundedPrioritySchedulingElement
    DESCRIPTION       This concrete class specializes the
                      PrioritySchedulingElement class to add
                      a BandwidthBound property.  This property
                      bounds the rate at which traffic from the
                      associated input can be handled.
    DERIVED FROM      PrioritySchedulingElement
    TYPE              Concrete
    PROPERTIES        BandwidthBound

4.3.42.1. The Property BandwidthBound

 This property is a 32-bit unsigned integer that defines the upper
 limit on the amount of traffic that can be handled from the input.
 This is not a shaped upper bound, since bursts can occur. It is a
 strict bound, limiting the impact of the input.  The units are
 kilobits per second.

4.4. Association Definitions

 This section details the QoS device datapath associations, including
 the aggregations, which were shown earlier in Figures 4 and 5.  These
 associations are defined as classes in the Information Model.  Each
 of these classes has two properties referring to instances of the two
 classes that the association links.  Some of the association classes
 have additional properties as well.

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4.4.1. The Abstract Association Dependency

 This abstract association defines two object references (named
 Antecedent and Dependent) that establish general dependency
 relationships between different managed objects in the information
 model.  The Antecedent reference identifies the independent object in
 the association, while the Dependent reference identifies the entity
 that IS dependent.
 The association's cardinality is many to many.
 The association is defined in the Core Model of CIM.  Please refer to
 [CIM] for the full definition of this class.

4.4.2. The Association ServiceSAPDependency

 This association defines two object references that establish a
 general dependency relationship between a Service object and a
 ServiceAccessPoint object.  This relationship indicates that the
 referenced Service uses the ServiceAccessPoint of ANOTHER Service.
 The Service is the Dependent reference, relying on the
 ServiceAccessPoint to gain access to another Service.
 The association's cardinality is many to many.
 The association is defined in the Core Model of CIM.  Please refer to
 [CIM] for the full definition of this class.

4.4.3. The Association IngressConditioningServiceOnEndpoint

 This association is derived from the association
 ServiceSAPDependency, and represents the binding, in the ingress
 direction, between a protocol endpoint and the first
 ConditioningService that processes packets received via that protocol
 endpoint.  Since there can only be one "first" ConditioningService
 for a protocol endpoint, the cardinality for the Dependent object
 reference is narrowed from 0..n to 0..1. Since, on the other hand, a
 single ConditioningService can be the first to process packets
 received via multiple protocol endpoints, the cardinality of the
 Antecedent object reference remains 0..n.

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 The class definition is as follows:
    NAME              IngressConditioningServiceOnEndpoint
    DESCRIPTION       An association that establishes a
                      dependency relationship between a protocol
                      endpoint and the first conditioning
                      service that processes traffic arriving
                      via that protocol endpoint.
    DERIVED FROM      ServiceSAPDependency
    ABSTRACT          False
    PROPERTIES        Antecedent[ref ProtocolEndpoint[0..n]],
                      Dependent[ref ConditioningService[0..1]]

4.4.4. The Association EgressConditioningServiceOnEndpoint

 This association is derived from the association
 ServiceSAPDependency, and represents the binding, in the egress
 direction, between a protocol endpoint and the last
 ConditioningService that processes packets before they leave a
 network device via that protocol endpoint.  (This "last"
 ConditioningService is ordinarily a scheduler, but it doesn't have to
 be.)  Since there can be multiple "last" ConditioningServices for a
 protocol endpoint in the case of a fallback scheduler, the
 cardinality for the Dependent object reference remains 0..n.  Since,
 however, a single ConditioningService cannot be the last one to
 process packets for multiple protocol endpoints, the cardinality of
 the Antecedent object reference is narrowed from 0..n to 0..1.
 The class definition is as follows:
    NAME              EgressConditioningServiceOnEndpoint
    DESCRIPTION       An association that establishes a
                      dependency relationship between a protocol
                      endpoint and the last conditioning
                      service(s) that process traffic to be
                      transmitted via that protocol endpoint.
    DERIVED FROM      ServiceSAPDependency
    ABSTRACT          False
    PROPERTIES        Antecedent[ref ProtocolEndpoint[0..1]],
                      Dependent[ref ConditioningService[0..n]]

4.4.5. The Association HeadTailDropQueueBinding

 This association is a subclass of Dependency, describing the
 association between a head or tail dropper and a queue that it
 monitors to determine when to drop traffic.  The referenced queue is
 the one whose queue depth is compared against the Dropper's
 threshold.  The cardinality is 1..n on the queue side, since a

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 head/tail dropper must monitor at least one queue.  For the classes
 HeadTailDropper and HeadTailDropQueueBinding, the rule for combining
 the inputs from multiple queues is simple addition: if the sum of the
 lengths of the monitored queues exceeds the dropper's QueueThreshold
 value, then packets are dropped.  This rule for combining inputs may,
 however, be overridden by a different rule in subclasses of one or
 both of these classes.
 The class definition is as follows:
    NAME              HeadTailDropQueueBinding
    DESCRIPTION       A generic association used to establish a
                      dependency relationship between a
                      head or tail dropper and a queue that it
                      monitors.
    DERIVED FROM      Dependency
    ABSTRACT          False
    PROPERTIES        Antecedent[ref QueuingService[1..n]],
                      Dependent[ref
                         HeadTailDropperService [0..n]]

4.4.6. The Association CalculationBasedOnQueue

 This association is a subclass of Dependency, which defines two
 object references that establish a dependency relationship between a
 QueuingService and an instance of the DropThresholdCalculationService
 class.  The queue's current depth is used by the calculation service
 in calculating an average queue depth.
 The class definition is as follows:
    NAME              CalculationBasedOnQueue
    DESCRIPTION       A generic association used to establish a
                      dependency relationship between a
                      QueuingService object and a
                      DropThresholdCalculationService object.
    DERIVED FROM      ServiceServiceDependency
    ABSTRACT          False
    PROPERTIES        Antecedent[ref QueuingService[1..1]],
                      Dependent[ref
                         DropThresholdCalculationService [0..n]]

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4.4.6.1. The Reference Antecedent

 This property is inherited from the Dependency association, and
 overridden to serve as an object reference to a QueuingService object
 (instead of to the more general ManagedElement).  This reference
 identifies the queue that the DropThresholdCalculationService will
 use in its calculation of average queue depth.

4.4.6.2. The Reference Dependent

 This property is inherited from the Dependency association, and
 overridden to serve as an object reference to a
 DropThresholdCalculationService object (instead of to the more
 general ManagedElement).  This reference identifies a
 DropThresholdCalculationService that uses the referenced queue's
 current depth as one of the inputs to its calculation of average
 queue depth.

4.4.7. The Association ProvidesServiceToElement

 This association defines two object references that establish a
 dependency relationship in which a ManagedSystemElement depends on
 the functionality of one or more Services.  The association's
 cardinality is many to many.
 The association is defined in the Core Model of CIM.  Please refer to
 [CIM] for the full definition of this class.

4.4.8. The Association ServiceServiceDependency

 This association defines two object references that establish a
 dependency relationship between two Service objects.  The particular
 type of dependency is represented by the TypeOfDependency property;
 typical examples include that one Service is required to be present
 or required to have completed for the other Service to operate.
 This association is very similar to the ServiceSAPDependency
 relationship.  For the latter, the Service is dependent on an
 AccessPoint to get at another Service.  In this relationship, it
 directly identifies its Service dependency.  Both relationships
 should not be instantiated, since their information is repetitive.
 The association's cardinality is many to many.
 The association is defined in the Core Model of CIM.  Please refer to
 [CIM] for the full definition of this class.

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4.4.9. The Association CalculationServiceForDropper

 This association is a subclass of ServiceServiceDependency, which
 defines two object references that represent the reliance of a
 REDDropperService on a DropThresholdCalculationService - calculating
 an average queue depth based on the observed depths of one or more
 queues.
 The class definition is as follows:
    NAME              CalculationServiceForDropper
    DESCRIPTION       A generic association used to establish a
                      dependency relationship between a
                      calculation service and a
                      REDDropperSrevice for which it performs
                      average queue depth calculations
    DERIVED FROM      ServiceServiceDependency
    ABSTRACT          False
    PROPERTIES        Antecedent[ref
                         DropThresholdCalculationService[1..n]],
                      Dependent[ref REDDropperService[0..n]]

4.4.9.1. The Reference Antecedent

 This property is inherited from the ServiceServiceDependency
 association, and overridden to serve as an object reference to a
 DropThresholdCalculationService object (instead of to the more
 general Service object).  The cardinality of the object reference is
 1..n, indicating that a RED dropper may be served by one or more
 calculation services.

4.4.9.2. The Reference Dependent

 This property is inherited from the ServiceServiceDependency
 association, and overridden to serve as an object reference to a
 REDDropperService object (instead of to the more general Service
 object).  This reference identifies a RED dropper served by a
 DropThresholdCalculationService.

4.4.10. The Association QueueAllocation

 This association is a subclass of Dependency, which defines two
 object references that establish a dependency relationship between a
 QueuingService and a BufferPool that provides storage space for the
 packets in the queue.

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 The class definition is as follows:
    NAME              QueueAllocation
    DESCRIPTION       A generic association used to establish a
                      dependency relationship between a
                      QueuingService object and a BufferPool
                      object.
    DERIVED FROM      Dependency
    ABSTRACT          False
    PROPERTIES        Antecedent[ref BufferPool[0..n]],
                      Dependent[ref QueuingService[0..n]]
                      AllocationPercentage

4.4.10.1. The Reference Antecedent

 This property is inherited from the Dependency association, and
 overridden to serve as an object reference to a BufferPool object.
 This reference identifies the BufferPool in which packets on the
 QueuingService's queue are stored.

4.4.10.2. The Reference Dependent

 This property is inherited from the Dependency association, and
 overridden to serve as an object reference to a QueuingService
 object.  This reference identifies the QueuingService whose packets
 are being stored in the BufferPool's buffers.

4.4.10.3. The Property AllocationPercentage

 This property is an 8-bit unsigned integer with minimum value of zero
 and maximum value of 100.  It defines the percentage of the
 BufferPool that should be allocated to the referenced QueuingService.
 If absolute sizes are desired, this would be accomplished by defining
 individual BufferPools of the specified sizes, with
 QueueAllocation.AllocationPercentages set to 100.

4.4.11. The Association ClassifierElementUsesFilterList

 This association is a subclass of the Dependency association.  It
 relates one or more ClassifierElements with a FilterList representing
 the criteria for selecting packets for each of the ClassifierElements
 to process.
 In the QDDIM model, a classifier is always modeled as a
 ClassifierService that aggregates a set of ClassifierElements. When
 ClassifierElements use the NextServiceAfterClassifierElement

Moore, et al. Standards Track [Page 76] RFC 3670 QoS Device Datapath Info Model January 2004

 association to bind to another ClassifierService (to construct a
 hierarchical classifier), the ClassifierElementUsesFilterList
 association must not be specified.
 The class definition is as follows:
    NAME              ClassifierElementUsesFilterList
    DESCRIPTION       An association relating a
                      ClassifierElement to the FilterList
                      representing the criteria for selecting
                      packets for that
                      ClassifierElement to process.
    DERIVED FROM      Dependency
    ABSTRACT          False
    PROPERTIES        Antecedent[ref FilterList [0..1]],
                      Dependent[ref ClassifierElement [0..n]]

4.4.11.1. The Reference Antecedent

 This property is inherited from the Dependency association, and
 overridden to serve as an object reference to a FilterList object,
 instead of to the more general ManagedElement object. Also, its
 cardinality is restricted to 0 and 1, indicating that a
 ClassifierElement uses either one FilterList to select packets for it
 or no FilterList when the ClassifierElement uses the
 NextServiceAfterClassifierElement association to bind to another
 ClassifierService to form a hierarchical classifier.

4.4.11.2. The Reference Dependent

 This property is inherited from the Dependency association, and
 overridden to serve as an object reference to a ClassifierElement
 object, instead of to the more general ManagedElement object. This
 reference identifies a ClassifierElement that depends on the
 associated FilterList object to represent its packet-selection
 criteria.

4.4.12. The Association AFRelatedServices

 This association defines two object references that establish a
 dependency relationship between two AFService objects.  This
 dependency is the precedence of the individual AF drop-related
 Services within an AF IP packet-forwarding class.

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 The class definition is as follows:
    NAME              AFRelatedServices
    DESCRIPTION       An association used to establish
                      a dependency relationship between two
                      AFService objects.
    DERIVED FROM      Nothing
    ABSTRACT          False
    PROPERTIES        AFLowerDropPrecedence[ref
                        AFService[0..1]],
                      AFHigherDropPrecedence[ref
                        AFService[0..n]]

4.4.12.1. The Reference AFLowerDropPrecedence

 This property serves as an object reference to an AFService object
 that has the lower probability of dropping packets.

4.4.12.2. The Reference AFHigherDropPrecedence

 This property serves as an object reference to an AFService object
 that has the higher probability of dropping packets.

4.4.13. The Association NextService

 This association defines two object references that establish a
 predecessor-successor relationship between two ConditioningService
 objects.  This association is used to indicate the sequence of
 ConditioningServices required to process a particular type of
 traffic.
 Instances of this dependency describe the various relationships
 between different ConditioningServices (such as classifiers, meters,
 droppers, etc.) that are used collectively to condition traffic.
 Both one-to-one and more complicated fan-in and/or fan-out
 relationships can be described.  The ConditioningServices may feed
 one another directly, or they may be mapped to multiple "next"
 Services based on the characteristics of the packet.

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 The class definition is as follows:
    NAME              NextService
    DESCRIPTION       An association used to establish
                      a predecessor-successor relationship
                      between two ConditioningService objects.
    DERIVED FROM      Nothing
    ABSTRACT          False
    PROPERTIES        PrecedingService[ref
                        ConditioningService[0..n]],
                      FollowingService[ref
                        ConditioningService[0..n]]

4.4.13.1. The Reference PrecedingService

 This property serves as an object reference to a ConditioningService
 object that occurs earlier in the processing sequence for a given
 type of traffic.

4.4.13.2. The Reference FollowingService

 This property serves as an object reference to a ConditioningService
 object that occurs later in the processing sequence for a given type
 of traffic, immediately after the ConditioningService identified by
 the PrecedingService object reference.

4.4.14. The Association NextServiceAfterClassifierElement

 This association refines the definition of its superclass, the
 NextService association, in two ways:
 o  It restricts the PrecedingService object reference to the class
    ClassifierElement.
 o  It restricts the cardinality of the FollowingService object
    reference to exactly 1.
 The class definition is as follows:
    NAME              NextServiceAfterClassifierElement
    DESCRIPTION       An association used to establish
                      a predecessor-successor relationship
                      between a single ClassifierElement within
                      a Classifier and the next
                      ConditioningService object that is
                      responsible for further processing of
                      the traffic selected by that
                      ClassifierElement.

Moore, et al. Standards Track [Page 79] RFC 3670 QoS Device Datapath Info Model January 2004

    DERIVED FROM      NextService
    ABSTRACT          False
    PROPERTIES        PrecedingService
                        [ref ClassifierElement[0..n]],
                      FollowingService
                        [ref ConditioningService[1..1]

4.4.14.1. The Reference PrecedingService

 This property is inherited from the NextService association.  It is
 overridden in this subclass to restrict the object reference to a
 ClassifierElement, as opposed to the more general ConditioningService
 defined in the NextService superclass.
 This property serves as an object reference to a ClassifierElement,
 which is a component of a single ClassifierService.  Packets selected
 by this ClassifierElement are always passed to the
 ConditioningService identified by the FollowingService object
 reference.

4.4.14.2. The Reference FollowingService

 This property is inherited from the NextService association.  It is
 overridden in this subclass to restrict the cardinality of the
 reference to exactly 1.  This reflects the requirement that the
 behavior of a DiffServ classifier must be deterministic: the packets
 selected by a given ClassifierElement in a given ClassifierService
 must always go to one and only one next ConditioningService.

4.4.15. The Association NextScheduler

 This association is a subclass of NextService, and defines two object
 references that establish a predecessor-successor relationship
 between PacketSchedulingServices.  In a hierarchical queuing
 configuration where a second scheduler treats the output of a first
 scheduler as a single, aggregated input, the two schedulers are
 related via the NextScheduler association.
 The class definition is as follows:
    NAME              NextScheduler
    DESCRIPTION       An association used to establish
                      predecessor-successor relationships
                      between PacketSchedulingService objects
                      for simple hierarchical scheduling.
    DERIVED FROM      NextService
    ABSTRACT          False

Moore, et al. Standards Track [Page 80] RFC 3670 QoS Device Datapath Info Model January 2004

    PROPERTIES        PrecedingService[ref
                         PacketSchedulingService[0..n]],
                      FollowingService[ref
                         PacketSchedulingService[0..1]]

4.4.15.1. The Reference PrecedingService

 This property is inherited from the NextService association, and
 overridden to serve as an object reference to a
 PacketSchedulingService object (instead of to the more general
 ConditioningService object).  This reference identifies a scheduler
 whose output is being treated as a single, aggregated input by the
 scheduler identified by the FollowingService reference.  The [0..n]
 cardinality indicates that a single FollowingService scheduler may
 bring together the aggregated outputs of multiple prior schedulers.

4.4.15.2. The Reference FollowingService

 This property is inherited from the NextService association, and
 overridden to serve as an object reference to a
 PacketSchedulingService object (instead of to the more general
 ConditioningService object).  This reference identifies a scheduler
 that includes among its inputs the aggregated outputs of one or more
 PrecedingService schedulers.

4.4.16. The Association FailNextScheduler

 This association is a subclass of the NextScheduler association.
 FailNextScheduler represents the relationship between two schedulers
 when the first scheduler passes up a scheduling opportunity (thereby
 behaving in a non-work conserving manner), and makes the resulting
 bandwidth available to the second scheduler for its use.  See
 Sections 3.11.3 and 3.11.4 for examples of where this association
 might be used.
 The class definition is as follows:
    NAME              FailNextScheduler
    DESCRIPTION       This association specializes the
                      NextScheduler association.  It
                      establishes a relationship between a
                      non-work-conserving scheduler and a
                      second scheduler to which it makes
                      available the bandwidth that it elects
                      not to use.
    DERIVED FROM      NextScheduler
    ABSTRACT          False

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    PROPERTIES        PrecedingService[ref
                       NonWorkConservingSchedulingService[0..n]]

4.4.16.1. The Reference PrecedingService

 This property is inherited from the NextScheduler association, and
 overridden to serve as an object reference to a
 NonWorkConservingSchedulingService object (instead of to the more
 general PacketSchedulingService object).  This reference identifies a
 non-work-conserving scheduler whose excess bandwidth is being made
 available to the scheduler identified by the FollowingService
 reference.  The [0..n] cardinality indicates that a single
 FollowingService scheduler may have the opportunity to use the unused
 bandwidth of multiple prior non-work-conserving schedulers.

4.4.17. The Association NextServiceAfterMeter

 This association describes a predecessor-successor relationship
 between a MeterService and one or more ConditioningService objects
 that process traffic from the meter.  For example, for devices that
 implement preamble marking, the FollowingService reference (after the
 meter) is a PreambleMarkerService, to record the results of the
 metering in the preamble.
 It might be expected that the NextServiceAfterMeter association would
 subclass from NextService.  However, meters are 1:n fan-out elements,
 and require a mechanism to distinguish between the different
 results/outputs of the meter.  Therefore, this association defines a
 new key property, MeterResult, which is used to record the result and
 identify the output through which this traffic left the meter.
 Because of this additional key, NextServiceAfterMeter cannot be a
 subclass of NextService.
 The class definition is as follows:
    NAME              NextServiceAfterMeter
    DESCRIPTION       An association used to establish
                      a predecessor-successor relationship
                      between a particular output of a
                      MeterService and the next
                      ConditioningService object that is
                      responsible for further processing of
                      the traffic.
    DERIVED FROM      Nothing
    ABSTRACT          False

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    PROPERTIES        PrecedingService[ref MeterService[0..n]],
                      FollowingService[ref
                        ConditioningService[0..n]],
                      MeterResult

4.4.17.1. The Reference PrecedingService

 The preceding MeterService, 'earlier' in the processing sequence for
 a packet.  Since Meters are 1:n fan-out devices, this relationship
 associates a particular output of a MeterService (identified by the
 MeterResult property) to the next ConditioningService that is used to
 further process the traffic.

4.4.17.2. The Reference FollowingService

 The 'next' or following ConditioningService.

4.4.17.3. The Property MeterResult

 This property is an enumerated 16-bit unsigned integer, and
 represents information describing the result of the metering. Traffic
 is distinguished as being conforming, non-conforming, or partially
 conforming.  More complicated metering can be built either by
 extending the enumeration or by cascading meters.
 The enumerated values are: "Unknown" (0), "Conforming" (1),
 "PartiallyConforming" (2), "NonConforming" (3).

4.4.18. The Association QueueToSchedule

 This is a top-level association, representing the relationship
 between a queue (QueuingService) and a SchedulingElement.  The
 SchedulingElement, in turn, represents the information in a packet
 scheduling service that is specific to this queue, such as relative
 priority or allocated bandwidth.
 It cannot be expressed formally with the association cardinalities,
 but there is an additional constraint on participation in this
 association.  A particular instance of (a subclass of)
 SchedulingElement always participates either in exactly one instance
 of this association, or in exactly one instance of the association
 SchedulingServiceToSchedule.

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 The class definition is as follows:
    NAME              QueueToSchedule
    DESCRIPTION       This association relates a queue to
                      the SchedulingElement containing
                      information specific to the queue.
    DERIVED FROM      Nothing
    ABSTRACT          False
    PROPERTIES        Queue[ref QueuingService[0..1]],
                      SchedElement[ref
                         SchedulingElement[0..n]]

4.4.18.1. The Reference Queue

 This property serves as an object reference to a QueuingService
 object.  A QueuingService object may be associated 0 or more
 SchedulingElement objects.

4.4.18.2. The Reference SchedElement

 This property serves as an object reference to a SchedulingElement
 object.  A SchedulingElement is always associated either with exactly
 one QueuingService or with exactly one upstream scheduler
 (PacketSchedulingService).

4.4.19. The Association SchedulingServiceToSchedule

 This is a top-level association, representing the relationship
 between a scheduler (PacketSchedulingService) and a
 SchedulingElement, in a configuration involving cascaded schedulers.
 The SchedulingElement, in turn, represents the information in a
 subsequent packet scheduling service that is specific to this
 scheduler, such as relative priority or allocated bandwidth.
 It cannot be expressed formally with the association cardinalities,
 but there is an additional constraint on participation in this
 association.  A particular instance of (a subclass of)
 SchedulingElement always participates either in exactly one instance
 of this association, or in exactly one instance of the association
 QueueToSchedule.
 The class definition is as follows:
    NAME              SchedulingServiceToSchedule
    DESCRIPTION       This association relates a scheduler to
                      the SchedulingElement in a subsequent
                      scheduler containing information specific
                      to this scheduler.

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    DERIVED FROM      Nothing
    ABSTRACT          False
    PROPERTIES        SchedService[ref
                         PacketSchedulingService[0..1]],
                      SchedElement[ref
                         SchedulingElement[0..n]]

4.4.19.1. The Reference SchedService

 This property serves as an object reference to a
 PacketSchedulingService object.  A PacketSchedulingService object may
 be associated 0 or more SchedulingElement objects.

4.4.19.2. The Reference SchedElement

 This property serves as an object reference to a SchedulingElement
 object.  A SchedulingElement is always associated either with exactly
 one QueuingService or with exactly one upstream scheduler
 (PacketSchedulingService).

4.4.20. The Aggregation MemberOfCollection

 This aggregation is a generic relationship used to model the
 aggregation of a set of ManagedElements in a generalized Collection
 object.  The aggregation's cardinality is many to many.
 MemberOfCollection is defined in the Core Model of CIM.  Please refer
 to [CIM] for the full definition of this class.

4.4.21. The Aggregation CollectedBufferPool

 This aggregation models the ability to treat a set of buffers as a
 pool, or collection, that can in turn be contained in a "higher-
 level" buffer pool.  This class overrides the more generic
 MemberOfCollection aggregation to restrict both the aggregate and the
 part component objects to be instances only of the BufferPool class.
 The class definition for the aggregation is as follows:
    NAME              CollectedBufferPool
    DESCRIPTION       A generic association used to aggregate
                      a set of related buffers into a
                      higher-level buffer pool.
    DERIVED FROM      MemberOfCollection
    ABSTRACT          False
    PROPERTIES        Collection[ref BufferPool[0..1]],
                      Member[ref BufferPool[0..n]]

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4.4.21.1. The Reference Collection

 This property represents the parent, or aggregate, object in the
 relationship.  It is a BufferPool object.

4.4.21.2. The Reference Member

 This property represents the child, or lower level pool, in the
 relationship.  It is one of the set of BufferPools that together make
 up the higher-level pool.

4.4.22. The Abstract Aggregation Component

 This abstract aggregation is a generic relationship used to establish
 "part-of" relationships between managed objects (named GroupComponent
 and PartComponent).  The association's cardinality is many to many.
 The association is defined in the Core Model of CIM.  Please refer to
 [CIM] for the full definition of this class.

4.4.23. The Aggregation ServiceComponent

 This aggregation is used to model a set of subordinate Services that
 are aggregated together to form a higher-level Service. This
 aggregation is derived from the more generic Component superclass to
 restrict the types of objects that can participate in this
 relationship.  The association's cardinality is many to many.
 The association is defined in the Core Model of CIM.  Please refer to
 [CIM] for the full definition of this class.

4.4.24. The Aggregation QoSSubService

 This aggregation represents a set of subordinate QoSService objects
 (that is, a set of instances of subclasses of the QoSService class)
 that are aggregated together to form a higher-level QoSService.  A
 QoSService is a specific type of Service that conceptualizes QoS
 functionality as a set of coordinated sub-services.
 This aggregation is derived from the more generic ServiceComponent
 superclass to restrict the types of objects that can participate in
 this relationship to QoSService objects, instead of a more generic
 Service object.  It also restricts the cardinality of the aggregate
 to 0-or-1 (instead of the more generic 0-or-more).

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 The class definition for the aggregation is as follows:
    NAME              QoSSubService
    DESCRIPTION       A generic association used to establish
                      "part-of" relationships between a
                      higher-level QoSService object and the
                      set of lower-level QoSServices that
                      are aggregated to create/form it.
    DERIVED FROM      ServiceComponent
    ABSTRACT          False
    PROPERTIES        GroupComponent[ref QoSService[0..1]],
                      PartComponent[ref QoSService[0..n]]

4.4.24.1. The Reference GroupComponent

 This property is overridden in this aggregation to represent an
 object reference to a QoSService object (instead of to the more
 generic Service object defined in its superclass).  This object
 represents the parent, or aggregate, object in the relationship.

4.4.24.2. The Reference PartComponent

 This property is overridden in this aggregation to represent an
 object reference to a QoSService object (instead of to the more
 generic Service object defined in its superclass).  This object
 represents the child, or "component", object in the relationship.

4.4.25. The Aggregation QoSConditioningSubService

 This aggregation identifies the set of conditioning services that
 together condition traffic for a particular QoS service.
 This aggregation is derived from the more generic ServiceComponent
 superclass; it restricts the types of objects that can participate in
 it to ConditioningService and QoSService objects, instead of the more
 generic Service objects.
 The class definition for the aggregation is as follows:
    NAME              QoSConditioningSubService
    DESCRIPTION       A generic aggregation used to establish
                      "part-of" relationships between a set
                      of ConditioningService objects and the
                      particular QoSService object(s) that they
                      provide traffic conditioning for.
    DERIVED FROM      ServiceComponent
    ABSTRACT          False

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    PROPERTIES        GroupComponent[ref QoSService[0..n]],
                      PartComponent[ref
                        ConditioningService[0..n]]

4.4.25.1. The Reference GroupComponent

 This property is overridden in this aggregation to represent an
 object reference to a QoSService object (instead of to the more
 generic Service object defined in its superclass).  The cardinality
 of the reference remains 0..n, to indicate that a given
 ConditioningService may provide traffic conditioning for 0, 1, or
 more than 1 QoSService objects.
 This object represents the parent, or aggregate, object in the
 association.  In this case, this object represents the QoSService
 that aggregates one or more ConditioningService objects to implement
 the appropriate traffic conditioning for its traffic.

4.4.25.2. The Reference PartComponent

 This property is overridden in this aggregation to represent an
 object reference to a ConditioningService object (instead of to the
 more generic Service object defined in its superclass).  This object
 represents the child, or "component", object in the relationship.  In
 this case, this object represents one or more ConditioningService
 objects that together indicate how traffic for a specific QoSService
 is conditioned.

4.4.26. The Aggregation ClassifierElementInClassifierService

 This aggregation represents the relationship between a classifier and
 the classifier elements that provide the fan-out function for the
 classifier.  A classifier typically aggregates multiple classifier
 elements.  A classifier element, however, is aggregated only by a
 single classifier.  See [DSMODEL] and [DSMIB] for more about
 classifiers and classifier elements.
 The class definition for the aggregation is as follows:
    NAME              ClassifierElementInClassifierService
    DESCRIPTION       An aggregation representing the
                      relationship between a classifier
                      and its classifier elements.
    DERIVED FROM      ServiceComponent
    ABSTRACT          False

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    PROPERTIES        GroupComponent[ref
                         ClassifierService[1..1]],
                      PartComponent[ref
                         ClassifierElement[0..n],
                      ClassifierOrder

4.4.26.1. The Reference GroupComponent

 This property is overridden in this aggregation to represent an
 object reference to a ClassifierService object (instead of to the
 more generic Service object defined in its superclass).  It also
 restricts the cardinality of the aggregate to 1..1 (instead of the
 more generic 0-or-more), representing the fact that a
 ClassifierElement always exists within the context of exactly one
 ClassifierService.

4.4.26.2. The Reference PartComponent

 This property is overridden in this aggregation to represent an
 object reference to a ClassifierElement object (instead of to the
 more generic Service object defined in its superclass).  This object
 represents a single traffic selector for the classifier. A
 ClassifierElement usually has an association to a FilterList that
 provides selection criteria for packets from the traffic stream
 coming into the classifier, and to a ConditioningService to which
 packets selected by these criteria are next forwarded.

4.4.26.3. The Property ClassifierOrder

 Because the filters for a classifier can overlap, it is necessary to
 specify the order in which the ClassifierElements aggregated by a
 ClassifierService are presented with packets coming into the
 classifier.  This property is an unsigned 32-bit integer representing
 this order.  Values are represented in ascending order: first '1',
 then '2', and so on.  Different values MUST be assigned for each of
 the ClassifierElements aggregated by a given ClassifierService.

4.4.27. The Aggregation EntriesInFilterList

 This aggregation is a specialization of the Component aggregation; it
 is used to define a set of filter entries (subclasses of
 FilterEntryBase) that are aggregated by a FilterList.
 The cardinalities of the aggregation itself are 0..1 on the
 FilterList end, and 0..n on the FilterEntryBase end.  Thus in the
 general case, a filter entry can exist without being aggregated into

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 any FilterList.  However, the only way a filter entry can figure in
 the QoS Device model is by being aggregated into a FilterList by this
 aggregation.
 See [PCIME] for the definition of this aggregation.

4.4.28. The Aggregation ElementInSchedulingService

 This concrete aggregation represents the relationship between a
 PacketSchedulingService and the set of SchedulingElements that tie it
 to its inputs.
 The class definition for the aggregation is as follows:
    NAME              ElementInSchedulingService
    DESCRIPTION       An aggregation used to tie a
                      PacketSchedlingService to the
                      configuration information for one of
                      the elements (either a QueuingService or
                      another PacketSchedulingService) that it
                      schedules.
    DERIVED FROM      Component
    ABSTRACT          False
    PROPERTIES        GroupComponent[ref
                        PacketSchedulingService[0..1]],
                      PartComponent[ref
                         SchedulingElement[1..n]

4.4.28.1. The Reference GroupComponent

 This property is overridden in this aggregation to represent an
 object reference to a PacketSchedulingService object (instead of to
 the more generic Service object defined in its superclass). It also
 restricts the cardinality of the aggregate to 0..1 (instead of the
 more generic 0-or-more), representing the fact that a
 SchedulingElement exists within the context of at most one
 PacketSchedulingService.

4.4.28.2. The Reference PartComponent

 This property is overridden in this aggregation to represent an
 object reference to a SchedulingElement object (instead of to the
 more generic Service object defined in its superclass).  This object
 represents a single scheduling element for the scheduler. It also
 restricts the cardinality of the SchedulingElement to 1..n (instead
 of the more generic 0-or-more), representing the fact that a
 PacketSchedulingService always includes at least one
 SchedulingElement.

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5. Intellectual Property Statement

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 intellectual property or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; neither does it represent that it
 has made any effort to identify any such rights. Information on the
 IETF's procedures with respect to rights in standards-track and
 standards-related documentation can be found in BCP-11.
 Copies of claims of rights made available for publication and any
 assurances of licenses to be made available, or the result of an
 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF Secretariat.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights which may cover technology that may be required to practice
 this standard.  Please address the information to the IETF Executive
 Director.

6. Acknowledgements

 The authors wish to thank the participants of the Policy Framework
 and Differentiated Services working groups for their many helpful
 comments and suggestions.  Special thanks to Joel Halpern, who
 provided some key technical direction during the latter stages of the
 document's development.

7. Security Considerations

 Like [PCIM] and [PCIME], this document defines an information model
 that cannot be implemented directly.  Consequently, security issues
 do not arise until it is mapped to an actual, implementable data
 model such as a MIB, PIB, or LDAP schema.  See [PCIM] for a general
 discussion of security considerations for information models.  See
 also [DSMIB] (which in fact is a data model that corresponds to a
 large extent with the QDDIM information model), for a discussion of
 the security implications of specific objects in the model.

Moore, et al. Standards Track [Page 91] RFC 3670 QoS Device Datapath Info Model January 2004

8. References

8.1. Normative References

 [CIM]      Common Information Model (CIM) Schema, version 2.5.
            Distributed Management Task Force, Inc., available at
            http://www.dmtf.org/standards/cim_schema_v25.php.
 [IEEE802Q] Virtual Bridged Local Area Networks, ANSI/IEEE std 802.1Q,
            1998 edition.  Approved December 8, 1998
 [PCIM]     Moore, B., Ellesson, E., Strassner, J. and A. Westerinen,
            "Policy Core Information Model - Version 1 Specification",
            RFC 3060, February 2001.
 [PCIME]    Moore, B., Ed., "Policy Core Information Model (PCIM)
            Extensions", RFC 3460, January 2003.
 [R791]     Postel, J., "Internet Protocol", STD 5, RFC 791, September
            1981.
 [R2119]    Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [R2474]    Nichols, K., Blake, S., Baker, F. and D. Black,
            "Definition of the Differentiated Services Field (DS
            Field) in the IPv4 and IPv6 Headers", RFC 2474, December
            1998.
 [R2597]    Heinanen, J., Baker, F., Weiss, W. and J. Wroclawski,
            "Assured Forwarding PHB Group", RFC 2597, June 1999.
 [R3140]    Black, D., Brim, S., Carpenter, B. and F. Le Faucheur,
            "Per Hop Behavior Identification Codes", RFC 3140, June
            2001.

8.2. Informative References

 [DSMIB]    Baker, F., Chan, K. and A. Smith, "Management Information
            Base for the Differentiated Services Architecture", RFC
            3289, May 2002.
 [DSMODEL]  Bernet, Y., Blake, S., Grossman, D. and A. Smith, "An
            Informal Management Model for DiffServ Routers", RFC 3290,
            May 2002.

Moore, et al. Standards Track [Page 92] RFC 3670 QoS Device Datapath Info Model January 2004

 [PIB]      Chan, K., Sahita, R., Hahn, S. and K. McCloghrie,
            "Differentiated Services Quality of Service Policy
            Information Base", RFC 3317, March 2003.
 [POLTERM]  Westerinen, A., Schnizlein, J., Strassner, J., Scherling,
            M., Quinn, B., Herzog, S., Huynh, A., Carlson, M., Perry,
            J. and S. Waldbusser, "Terminology for Policy-Based
            Management", RFC 3198, November 2001.
 [QPIM]     Snir, Y., Ramberg, Y., Strassner, J., Cohen, R. and B.
            Moore, "Policy Quality of Service (QoS) Information
            Model", RFC 3644, November 2003.
 [R1633]    Braden, R., Clark, D. and S. Shenker, "Integrated Services
            in the Internet Architecture: An Overview",  RFC 1633,
            June 1994.
 [R2475]    Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.
            and W. Weiss, "An Architecture for Differentiated
            Service", RFC 2475, December 1998.
 [R3246]    Davie, B., Charny, A., Bennet, J.C.R., Benson, K., Le
            Boudec, J.Y., Courtney, W., Davari, S., Firoiu, V. and D.
            Stiliadis, "An Expedited Forwarding PHB (Per-Hop
            Behavior)", RFC 3246, March 2002.
 [RED]      See http://www.aciri.org/floyd/red.html

Moore, et al. Standards Track [Page 93] RFC 3670 QoS Device Datapath Info Model January 2004

9. Appendix A: Naming Instances in a Native CIM Implementation

 Following the precedent established in [PCIM], this document has
 placed the details of how to name instances of its classes in a
 native CIM implementation here in an appendix.  Since Appendix A in
 [PCIM] has a lengthy discussion of the general principles of CIM
 naming, this appendix does not repeat that information here.  Readers
 interested in a more global discussion of how instances are named in
 a native CIM implementation should refer to [PCIM].

9.1. Naming Instances of the Classes Derived from Service

 Most of the classes defined in this model are derived from the CIM
 class Service.  Although Service is an abstract class, it
 nevertheless has key properties included as part of its definition.
 The purpose of including key properties in an abstract class is to
 have instances of all of its instantiable subclasses named in the
 same way.  Thus, the majority of the classes in this model name their
 instances in exactly the same way: with the two key properties
 CreationClassName and Name that they inherit from Service.

9.2. Naming Instances of Subclasses of FilterEntryBase

 Like Service, FilterEntryBase (defined in [PCIME]) is an abstract
 class that includes key properties in its definition.
 FilterEntryBase has four key properties.  Two of them,
 SystemCreationClassName and SystemName, are propagated to it via the
 weak association FilterEntryInSystem.  The other two,
 CreationClassName and Name, are native to FilterEntryBase.
 Thus, instances of all of the subclasses of FilterEntryBase,
 including the PreambleFilter class defined here, are named in the
 same way: with the four key properties they inherit from
 FilterEntryBase.

9.3. Naming Instances of ProtocolEndpoint

 The class ProtocolEndpoint inherits its key properties from its
 superclass, ServiceAccessPoint.  These key properties provide the
 same naming structure that we've seen before: two propagated key
 properties SystemCreationClassName and SystemName, plus two native
 key properties CreationClassName and Name.

Moore, et al. Standards Track [Page 94] RFC 3670 QoS Device Datapath Info Model January 2004

9.4. Naming Instances of BufferPool

 Unlike the other classes in this model, BufferPool is not derived
 from Service.  Consequently, it does not inherit its key properties
 from Service.  Instead, it inherits one of its key properties,
 CollectionID, from its superclass Collection, and adds its other key
 property, CreationClassName, in its own definition.

9.4.1. The Property CollectionID

 CollectionID is a string property with a maximum length of 256
 characters.  It identifies the buffer pool.  Note that this property
 is defined in the BufferPool class's superclass, CollectionOfMSEs,
 but not as a key property.  It is overridden in BufferPool, to make
 it part of this class's composite key.

9.4.2. The Property CreationClassName

 This property is a string property of with a maximum length of 256
 characters.  It is set to "CIM_BufferPool" if this class is directly
 instantiated, or to the class name of the BufferPool subclass that is
 created.

9.5. Naming Instances of SchedulingElement

 This class has not yet been incorporated into the CIM model, so it
 does not have any CIM naming properties yet.  If the normal pattern
 is followed, however, instances will be named with two properties
 CreationClassName and Name.

Moore, et al. Standards Track [Page 95] RFC 3670 QoS Device Datapath Info Model January 2004

10. Authors' Addresses

 Bob Moore
 P. O. Box 12195, BRQA/B501/G206
 3039 Cornwallis Rd.
 Research Triangle Park, NC  27709-2195
 Phone: (919) 254-4436
 EMail: remoore@us.ibm.com
 David Durham
 Intel
 2111 NE 25th Avenue
 Hillsboro, OR 97124
 Phone: (503) 264-6232
 EMail: david.durham@intel.com
 John Strassner
 INTELLIDEN, Inc.
 90 South Cascade Avenue
 Colorado Springs, CO  80903
 Phone: (719) 785-0648
 EMail: john.strassner@intelliden.com
 Andrea Westerinen
 Cisco Systems, Bldg 20
 725 Alder Drive
 Milpitas, CA 95035
 EMail: andreaw@cisco.com
 Walter Weiss
 Ellacoya Networks
 7 Henry Clay Dr.
 Merrimack, NH 03054
 Phone: (603) 879-7364
 EMail: walterweiss@attbi.com

Moore, et al. Standards Track [Page 96] RFC 3670 QoS Device Datapath Info Model January 2004

11. Full Copyright Statement

 Copyright (C) The Internet Society (2004).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assignees.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Moore, et al. Standards Track [Page 97]

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