GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc2815

Network Working Group M. Seaman Request for Comments: 2815 Telseon Category: Standards Track A. Smith

                                                      Extreme Networks
                                                            E. Crawley
                                                   Unisphere Solutions
                                                         J. Wroclawski
                                                               MIT LCS
                                                              May 2000
          Integrated Service Mappings on IEEE 802 Networks

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 (2000).  All Rights Reserved.

Abstract

 This document describes mappings of IETF Integrated Services over
 LANs built from IEEE 802 network segments which may be interconnected
 by IEEE 802.1D MAC Bridges (switches).  It describes parameter
 mappings for supporting Controlled Load and Guaranteed Service using
 the inherent capabilities of relevant IEEE 802 technologies and, in
 particular, 802.1D-1998 queuing features in switches.
 These mappings are one component of the Integrated Services over IEEE
 802 LANs framework.

Seaman, et al. Standards Track [Page 1] RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000

Table of Contents

 1 Introduction ............................................... 2
 2 Flow Identification and Traffic Class Selection ............ 3
 3 Choosing a flow's IEEE 802 user_priority class ............. 5
 3.1 Context of admission control and delay bounds ............ 6
 3.2 Default service mappings ................................. 7
 3.3 Discussion ............................................... 9
 4 Computation of integrated services characterization parameters
      by IEEE 802 devices .....................................10
 4.1 General characterization parameters ......................10
 4.2 Parameters to implement Guaranteed Service ...............11
 4.3 Parameters to implement Controlled Load ..................11
 4.4 Parameters to implement Best Effort ......................12
 5 Merging of RSVP/SBM objects ................................12
 6 Applicability of these service mappings ....................13
 7 References .................................................14
 8 Security Considerations ....................................15
 9 Acknowledgments ............................................15
 10 Authors' Addresses ........................................16
 11 Full Copyright Statement ..................................17

1. Introduction

 The IEEE 802.1 Interworking Task Group has developed a set of
 enhancements to the basic MAC Service provided in Bridged Local Area
 Networks (a.k.a. "switched LANs"). As a supplement to the original
 IEEE MAC Bridges standard, IEEE 802.1D-1990 [802.1D-ORIG], the
 updated IEEE 802.1D-1998 [802.1D] proposes differential traffic class
 queuing in switches. The IEEE 802.1Q specification [802.1Q] extends
 the capabilities of Ethernet/802.3 media to carry a traffic class
 indicator, or "user_priority" field, within data frames.
 The availability of this differential traffic queuing, together with
 additional mechanisms to provide admission control and signaling,
 allows IEEE 802 networks to support a close approximation of the IETF
 Integrated Services capabilities [CL][GS]. This document describes
 methods for mapping the service classes and parameters of the IETF
 model into IEEE 802.1D network parameters.  A companion document
 [SBM] describes a signaling protocol for use with these mappings.  It
 is recommended that readers be familiar with the overall framework in
 which these mappings and signaling protocol are expected to be used;
 this framework is described fully in [IS802FRAME].
 Within this document, Section 2 describes the method by which end
 systems and routers bordering the IEEE Layer-2 cloud learn what
 traffic class should be used for each data flow's packets.  Section 3
 describes the approach recommended to map IP-level traffic flows to

Seaman, et al. Standards Track [Page 2] RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000

 IEEE traffic classes within the Layer 2 network.  Section 4 describes
 the computation of Characterization Parameters by the layer 2
 network.  The remaining sections discuss some particular issues with
 the use of the RSVP/SBM signaling protocols, and describe the
 applicability of all of the above to different layer 2 network
 topologies.

2. Flow Identification and Traffic Class Selection

 One model for supporting integrated services over specific link
 layers treats layer-2 devices very much as a special case of routers.
 In this model, switches and other devices along the data path make
 packet handling decisions based on the RSVP flow and filter
 specifications, and use these specifications to classify the
 corresponding data packets. The specifications could either be used
 directly, or could be used indirectly by mapping each RSVP session
 onto a layer-2 construct such as an ATM virtual circuit.
 This approach is inappropriate for use in the IEEE 802 environment.
 Filtering to the per-flow level becomes expensive with increasing
 switch speed; devices with such filtering capabilities are likely to
 have a very similar implementation complexity to IP routers, and may
 not make use of simpler mechanisms such as 802.1D user priority.
 The Integrated Services over IEEE 802 LANs framework [IS802FRAME] and
 this document use an "aggregated flow" approach based on use of
 layer-2 traffic classes. In this model, each arriving flow is
 assigned to one of the available classes for the duration of the flow
 and traverses the 802 cloud in this class.  Traffic flows requiring
 similar service are grouped together into a single class, while the
 system's admission control and class selection rules ensure that the
 service requirements for flows in each of the classes are met.  In
 many situations this is a viable intermediate point between no QoS
 control and full router-type integrated services. The approach can
 work effectively even with switches implementing only the simplest
 differential traffic classification capability specified in the
 802.1D model.  In the aggregated flow model, traffic arriving at the
 boundary of a layer-2 cloud is tagged by the boundary device (end
 host or border router) with an appropriate traffic class, represented
 as an 802.1D "user_priority" value. Two fundamental questions are
 "who determines the correspondence between IP-level traffic flows and
 link-level classes?" and  "how is this correspondence conveyed to the
 boundary devices that must mark the data frames?"
 One approach to answering these questions would be for the meanings
 of the classes to be universally defined. This document would then
 standardize the meanings of a set of classes; e.g., 1 = best effort,
 2 = 100 ms peak delay target, 3 = 10 ms peak delay target, 4 = 1 ms

Seaman, et al. Standards Track [Page 3] RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000

 peak delay target, etc. The meanings of these universally defined
 classes could then be encoded directly in end stations, and the
 flow-to-class mappings computed directly in these devices.
 This universal definition approach would be simple to implement, but
 is too rigid to map the wide range of possible user requirements onto
 the limited number of available 802.1D classes. The model described
 in [IS802FRAME] uses a more flexible mapping: clients ask "the
 network" which user_priority traffic class to use for a given traffic
 flow, as categorized by its flow-spec and layer-2 endpoints. The
 network provides a value back to the requester that is appropriate
 considering the current network topology, load conditions, other
 admitted flows, etc.  The task of configuring switches with this
 mapping (e.g., through network management, a switch-switch protocol
 or via some network-wide QoS-mapping directory service) is an order
 of magnitude less complex than performing the same function in end
 stations. Also, when new services (or other network reconfigurations)
 are added to such a network, the network elements will typically be
 the ones to be upgraded with new queuing algorithms etc. and can be
 provided with new mappings at this time.
 In the current model it is assumed that all data packets of a flow
 are assigned to the same traffic class for the duration of the flow:
 the characteristics of the MAC service, as defined by Clause 6 of
 [802.1D], then ensure the ordering of the data packets of the flow
 between adjacent Layer 3 routers. This is usually desirable to avoid
 potential re-ordering problems as discussed in [IS802FRAME] and [CL].
 Note that there are some scenarios where it might be desirable to
 send conforming data traffic in one traffic class and non-conforming
 traffic for the same flow in a different, lower traffic class: such a
 division into separate traffic classes is for future study.  When a
 new session or "flow" requiring QoS support is created, a client must
 ask "the network" which traffic class (IEEE 802 user_priority) to use
 for a given traffic flow, so that it can label the packets of the
 flow as it places them into the network.  A request/response protocol
 is needed between client and network to return this information. The
 request can be piggy-backed onto an admission control request and the
 response can be piggy-backed onto an admission control
 acknowledgment. This "one pass" assignment has the benefit of
 completing the admission control transaction in a timely way and
 reducing the exposure to changing conditions that could occur if
 clients cached the knowledge for extensive periods. A set of
 extensions to the RSVP protocol for communicating this information
 have been defined [SBM].
 The network (i.e., the first network element encountered downstream
 from the client) must then answer the following questions:

Seaman, et al. Standards Track [Page 4] RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000

   1. Which of the available traffic classes would be appropriate for
      this flow?
      In general, a newly arriving flow might be assigned to a number
      of classes. For example, if 10ms of delay is acceptable, the
      flow could potentially be assigned to either a 10ms delay class
      or a 1ms delay class. This packing problem is quite difficult to
      solve if the target parameters of the classes are allowed to
      change dynamically as flows arrive and depart.  It is quite
      simple if the target parameters of each class is held fixed, and
      the class table is simply searched to find a class appropriate
      for the arriving flow.  This document adopts the latter
      approach.
   2. Of the appropriate traffic classes, which if any have enough
      capacity available to accept the new flow?
      This is the admission control problem. It is necessary to
      compare the level of traffic currently assigned to each class
      with the available level of network resources (bandwidth,
      buffers, etc), to ensure that adding the new flow to the class
      will not cause the class's performance to go below its target
      values. This problem is compounded because in a priority queuing
      system adding traffic to a higher-priority class can affect the
      performance of lower-priority classes. The admission control
      algorithm for a system using the default 802 priority behavior
      must be reasonably sophisticated to provide acceptable results.
 If an acceptable class is found, the network returns the chosen
 user_priority value to the client.
 Note that the client may be an end station, a router at the edge of
 the layer 2 network, or a first switch acting as a proxy for a device
 that does not participate in these protocols for whatever reason.
 Note also that a device e.g., a server or router may choose to
 implement both the "client" as well as the "network" portion of this
 model so that it can select its own user_priority values. Such an
 implementation would generally be discouraged unless the device has a
 close tie-in with the network topology and resource allocation
 policies. It may, however, work acceptably in cases where there is
 known over-provisioning of resources.

3. Choosing a flow's IEEE 802 user_priority class

 This section describes the method by which IP-level flows are mapped
 into appropriate IEEE user_priority classes. The IP-level services
 considered are Best Effort, Controlled Load, and Guaranteed Service.

Seaman, et al. Standards Track [Page 5] RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000

 The major issue is that admission control requests and application
 requirements are specified in terms of a multidimensional vector of
 parameters e.g., bandwidth, delay, jitter, service class.  This
 multidimensional space must be mapped onto a set of traffic classes
 whose default behavior in L2 switches is unidimensional (i.e., strict
 priority default queuing). This priority queuing alone can provide
 only relative ordering between traffic classes. It can neither
 enforce an absolute (quantifiable) delay bound for a traffic class,
 nor can it discriminate amongst Int-Serv flows within the aggregate
 in a traffic class. Therefore, it cannot provide the absolute control
 of packet loss and delay required for individual Int-Serv flows.
 To provide absolute control of loss and delay three things must
 occur:
 (1) The amount of bandwidth available to the QoS-controlled flows
     must be known, and the number of flows admitted to the network
     (allowed to use the bandwidth) must be limited.
 (2) A traffic scheduling mechanism is needed to give preferential
     service to flows with lower delay targets.
 (3) Some mechanism must ensure that best-effort flows and QoS
     controlled flows that are exceeding their Tspecs do not damage
     the quality of service delivered to in-Tspec QoS controlled
     flows. This mechanism could be part of the traffic scheduler, or
     it could be a separate policing mechanism.
 For IEEE 802 networks, the first function (admission control) is
 provided by a Subnet Bandwidth Manager, as discussed below. We use
 the link-level user_priority mechanism at each switch and bridge to
 implement the second function (preferential service to flows with
 lower delay targets). Because a simple priority scheduler cannot
 provide policing (function three), policing for IEEE networks is
 generally implemented at the edge of the network by a layer-3 device.
 When this policing is performed only at the edges of the network it
 is of necessity approximate. This issue is discussed further in
 [IS802FRAME].

3.1. Context of admission control and delay bounds

 As described above, it is the combination of priority-based
 scheduling and admission control that creates quantified delay
 bounds. Thus, any attempt to quantify the delay bounds expected by a
 given traffic class has to made in the context of the admission
 control elements. Section 6 of the framework [IS802FRAME] provides
 for two different models of admission control - centralized or
 distributed Bandwidth Allocators.

Seaman, et al. Standards Track [Page 6] RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000

 It is important to note that in this approach it is the admission
 control algorithm that determines which of the Int-Serv services is
 being offered. Given a set of priority classes with delay targets, a
 relatively simple admission control algorithm can place flows into
 classes so that the bandwidth and delay behavior experienced by each
 flow corresponds to the requirements of the Controlled-Load service,
 but cannot offer the higher assurance of the Guaranteed service. To
 offer the Guaranteed service, the admission control algorithm must be
 much more stringent in its allocation of resources, and must also
 compute the C and D error terms required of this service.
 A delay bound can only be realized at the admission control element
 itself so any delay numbers attached to a traffic class represent the
 delay that a single element can allow for.  That element may
 represent a whole L2 domain or just a single L2 segment.
 With either admission control model, the delay bound has no scope
 outside of a L2 domain. The only requirement is that it be understood
 by all Bandwidth Allocators in the L2 domain and, for example, be
 exported as C and D terms to L3 devices implementing the Guaranteed
 Service.  Thus, the end-to-end delay experienced by a flow can only
 be characterized by summing along the path using the usual RSVP
 mechanisms.

3.2. Default service mappings

 Table 1 presents the default mapping from delay targets to IEEE 802.1
 user_priority classes. However, these mappings must be viewed as
 defaults, and must be changeable.
 In order to simplify the task of changing mappings, this mapping
 table is held by *switches* (and routers if desired) but generally
 not by end-station hosts.  It is a read-write table. The values
 proposed below are defaults and can be overridden by management
 control so long as all switches agree to some extent (the required
 level of agreement requires further analysis).
 In future networks this mapping table might be adjusted dynamically
 and without human intervention. It is possible that some form of
 network-wide lookup service could be implemented that serviced
 requests from clients e.g., traffic_class = getQoSbyName("H.323
 video") and notified switches of what traffic categories they were
 likely to encounter and how to allocate those requests into traffic
 classes.  Alternatively, the network's admission control mechanisms
 might directly adjust the mapping table to maximize the utilization
 of network resources. Such mechanisms are for further study.

Seaman, et al. Standards Track [Page 7] RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000

 The delay bounds numbers proposed in Table 1 are for per-Bandwidth
 Allocator element delay targets and are derived from a subjective
 analysis of the needs of typical delay-sensitive applications e.g.,
 voice, video. See Annex H of [802.1D] for further discussion of the
 selection of these values. Although these values appear to address
 the needs of current video and voice technology, it should be noted
 that there is no requirement to adhere to these values and no
 dependence of IEEE 802.1 on these values.
          user_priority  Service
               0         Default, assumed to be Best Effort
               1         reserved, "less than" Best Effort
               2         reserved
               3         reserved
               4         Delay Sensitive, no bound
               5         Delay Sensitive, 100ms bound
               6         Delay Sensitive, 10ms bound
               7         Network Control
           Table 1 - Example user_priority to service mappings
    Note: These mappings are believed to be useful defaults but
    further implementation and usage experience is required. The
    mappings may be refined in future editions of this document.
 With this example set of mappings, delay-sensitive, admission
 controlled traffic flows are mapped to user_priority values in
 ascending order of their delay bound requirement. Note that the
 bounds are targets only - see [IS802FRAME] for a discussion of the
 effects of other non-conformant flows on delay bounds of other flows.
 Only by applying admission control to higher-priority classes can any
 promises be made to lower-priority classes.
 This set of mappings also leaves several classes as reserved for
 future definition.
    Note: this mapping does not dictate what mechanisms or algorithms
    a network element (e.g., an Ethernet switch) must perform to
    implement these mappings: this is an implementation choice and
    does not matter so long as the requirements for the particular
    service model are met.
    Note: these mappings apply primarily to networks constructed from
    devices that implement the priority-scheduling behavior defined as
    the default in 802.1D. Some devices may implement more complex
    scheduling behaviors not based only on priority. In that
    circumstance these mappings might still be used, but other, more

Seaman, et al. Standards Track [Page 8] RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000

    specialized mappings may be more appropriate.

3.3. Discussion

 The recommendation of classes 4, 5 and 6 for Delay Sensitive,
 Admission Controlled flows is somewhat arbitrary; any classes with
 priorities greater than that assigned to Best Effort can be used.
 Those proposed here have the advantage that, for transit through
 802.1D switches with only two-level strict priority queuing, all
 delay-sensitive traffic gets "high priority" treatment (the 802.1D
 default split is 0-3 and 4-7 for a device with 2 queues).
 The choice of the delay bound targets is tuned to an average expected
 application mix, and might be retuned by a network manager facing a
 widely different mix of user needs. The choice is potentially very
 significant: wise choice can lead to a much more efficient allocation
 of resources as well as greater (though still not very good)
 isolation between flows.
 Placing Network Control traffic at class 7 is necessary to protect
 important traffic such as route updates and network management.
 Unfortunately, placing this traffic higher in the user_priority
 ordering causes it to have a direct effect on the ability of devices
 to provide assurances to QoS controlled application traffic.
 Therefore, an estimate of the amount of Network Control traffic must
 be made by any device that is performing admission control (e.g.,
 SBMs). This would be in terms of the parameters that are normally
 taken into account by the admission control algorithm. This estimate
 should be used in the admission control decisions for the lower
 classes (the estimate is likely to be a configuration parameter of
 SBMs).
 A traffic class such as class 1 for "less than best effort" might be
 useful for devices that wish to dynamically "penalty tag" all of the
 data of flows that are presently exceeding their allocation or Tspec.
 This provides a way to isolate flows that are exceeding their service
 limits from flows that are not, to avoid reducing the QoS delivered
 to flows that are within their contract. Data from such tagged flows
 might also be preferentially discarded by an overloaded downstream
 device.
 A somewhat simpler approach would be to tag only the portion of a
 flow's packets that actually exceed the Tspec at any given instant as
 low priority. However, it is often considered to be a bad idea to
 treat flows in this way as it will likely cause significant re-
 ordering of the flow's packets, which is not desirable. Note that the
 default 802.1D treatment of user_priorities 1 and 2 is "less than"
 the default class 0.

Seaman, et al. Standards Track [Page 9] RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000

4. Computation of integrated services characterization parameters by

  IEEE 802 devices
 The integrated service model requires that each network element that
 supports integrated services compute and make available certain
 "characterization parameters" describing the element's behavior.
 These parameters may be either generally applicable or specific to a
 particular QoS control service.  These parameters may be computed by
 calculation, measurement, or estimation. When a network element
 cannot compute its own parameters (for example, a simple link), we
 assume that the device sending onto or receiving data from the link
 will compute the link's parameters as well as it's own.  The accuracy
 of calculation of these parameters may not be very critical; in some
 cases loose estimates are all that is required to provide a useful
 service. This is important in the IEEE 802 case, where it will be
 virtually impossible to compute parameters accurately for certain
 topologies and switch technologies.  Indeed, it is an assumption of
 the use of this model by relatively simple switches (see [IS802FRAME]
 for a discussion of the different types of switch functionality that
 might be expected) that they merely provide values to describe the
 device and admit flows conservatively.  The discussion below presents
 a general outline for the computation of these parameters, and points
 out some cases where the parameters must be computed accurately.
 Further specification of how to export these parameters is for
 further study.

4.1. General characterization parameters

 There are some general parameters [GENCHAR] that a device will need
 to use and/or supply for all service types:
  • Ingress link
  • Egress links and their MTUs, framing overheads and minimum packet

sizes (see media-specific information presented above).

  • Available path bandwidth: updated hop-by-hop by any device along

the path of the flow.

  • Minimum latency
 Of these parameters, the MTU and minimum packet size information must
 be reported accurately. Also, the "break bits" must be set correctly,
 both the overall bit that indicates the existence of QoS control
 support and the individual bits that specify support for a particular
 scheduling service. The available bandwidth should be reported as
 accurately as possible, but very loose estimates are acceptable. The
 minimum latency parameter should be determined and reported as

Seaman, et al. Standards Track [Page 10] RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000

 accurately as possible if the element offers Guaranteed service, but
 may be loosely estimated or reported as zero if the element offers
 only Controlled-Load service.

4.2. Parameters to implement Guaranteed Service

 A network element supporting the Guaranteed Service [GS] must be able
 to determine the following parameters:
  • Constant delay bound through this device (in addition to any value

provided by "minimum latency" above) and up to the receiver at the

    next network element for the packets of this flow if it were to be
    admitted.  This includes any access latency bound to the outgoing
    link as well as propagation delay across that link. This value is
    advertised as the 'C' parameter of the Guaranteed Service.
  • Rate-proportional delay bound through this device and up to the

receiver at the next network element for the packets of this flow

    if it were to be admitted.  This value is advertised as the 'D'
    parameter of the Guaranteed Service.
  • Receive resources that would need to be associated with this flow

(e.g., buffering, bandwidth) if it were to be admitted and not

    suffer packet loss if it kept within its supplied Tspec/Rspec.
    These values are used by the admission control algorithm to decide
    whether a new flow can be accepted by the device.
  • Transmit resources that would need to be associated with this flow

(e.g., buffering, bandwidth, constant- and rate-proportional delay

    bounds) if it were to be admitted. These values are used by the
    admission control algorithm to decide whether a new flow can be
    accepted by the device.
 The exported characterization parameters for this service should be
 reported as accurately as possible. If estimations or approximations
 are used, they should err in whatever direction causes the user to
 receive better performance than requested. For example, the C and D
 error terms should overestimate delay, rather than underestimate it.

4.3. Parameters to implement Controlled Load

 A network element implementing the Controlled Load service [CL] must
 be able to determine the following:
  • Receive resources that would need to be associated with this flow

(e.g., buffering) if it were to be admitted. These values are used

    by the admission control algorithm to decide whether a new flow
    can be accepted by the device.

Seaman, et al. Standards Track [Page 11] RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000

  • Transmit resources that would need to be associated with this flow

(e.g., buffering) if it were to be admitted. These values are used

    by the admission control algorithm to decide whether a new flow
    can be accepted by the device.
 The Controlled Load service does not export any service-specific
 characterization parameters. Internal resource allocation estimates
 should ensure that the service quality remains high when considering
 the statistical aggregation of Controlled Load flows into 802 traffic
 classes.

4.4. Parameters to implement Best Effort

 For a network element that implements only best effort service there
 are no explicit parameters that need to be characterized. Note that
 an integrated services aware network element that implements only
 best effort service will set the "break bit" described in
 [RSVPINTSERV].

5. Merging of RSVP/SBM objects

 Where reservations that use the SBM protocol's TCLASS object [SBM]
 need to be merged, an algorithm needs to be defined that is
 consistent with the mappings to individual user_priority values in
 use in the Layer-2 cloud.  A merged reservation must receive at least
 as good a service as the best of the component reservations.
 There is no single merging rule that can prevent all of the following
 side-effects:
  • If a merger were to demote the existing branch of the flow into a

higher-delay traffic class then this is a denial of service to the

    existing flow which would likely receive worse service than
    before.
  • If a merger were to promote the existing branch of the flow into a

new, lower-delay, traffic class, this might then suffer either

    admission control failures or may cost more in some sense than the
    already-admitted flow. This can also be considered as a denial-
    of-service attack.
  • Promotion of the new branch may lead to rejection of the request

because it has been re-assigned to a traffic class that has not

    enough resources to accommodate it.
 Therefore, such a merger is declared to be illegal and the usual SBM
 admission control failure rules are applied. Traffic class selection
 is performed based on the TSpec information. When the first RESV for

Seaman, et al. Standards Track [Page 12] RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000

 a flow arrives, a traffic class is chosen based on the request, an
 SBM TCLASS object is inserted into the message and admission control
 for that traffic class is done by the SBM. Reservation succeeds or
 fails as usual.
 When a second RESV for the same flow arrives at a different egress
 point of the Layer-2 cloud the process starts to repeat. Eventually
 the SBM-augmented RESV may hit a switch with an existing reservation
 in place for the flow i.e., an L2 branch point for the flow. If so,
 the traffic class chosen for the second reservation is checked
 against the first. If they are the same, the RESV requests are merged
 and passed on towards the sender(s).
 If the second TCLASS would have been different, an RSVP/SBM ResvErr
 error is returned to the Layer-3 device that launched the second RESV
 request into the Layer-2 cloud. This device will then pass on the
 ResvErr to the original requester according to RSVP rules. Detailed
 processing rules are specified in [SBM].

6. Applicability of these service mappings

 Switches using layer-2-only standards (e.g., 802.1D-1990, 802.1D-
 1998) need to inter-operate with routers and layer-3 switches. Wide
 deployment of such 802.1D-1998 switches will occur in a number of
 roles in the network: "desktop switches" provide dedicated 10/100
 Mbps links to end stations and high speed core switches often act as
 central campus switching points for layer-3 devices. Layer-2 devices
 will have to operate in all of the following scenarios:
  • every device along a network path is layer-3 capable and intrusive

into the full data stream

  • only the edge devices are pure layer-2
  • every alternate device lacks layer-3 functionality
  • most devices lack layer-3 functionality except for some key

control points such as router firewalls, for example.

    Where int-serv flows pass through equipment which does not support
    Integrated Services or 802.1D traffic management and which places
    all packets through the same queuing and overload-dropping paths,
    it is obvious that some of a flow's desired service parameters
    become more difficult to support. In particular, the two
    integrated service classes studied here, Controlled Load and
    Guaranteed Service, both assume that flows will be policed and
    kept "insulated" from misbehaving other flows or from best effort
    traffic during their passage through the network. This cannot be

Seaman, et al. Standards Track [Page 13] RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000

    done within an IEEE 802 network using devices with the default
    user_priority function; in this case policing must be approximated
    at the network edges.
    In addition, in order to provide a Guaranteed Service, *all*
    switching elements along the path must participate in special
    treatment for packets in such flows: where there is a "break" in
    guaranteed service, all bets are off. Thus, a network path that
    includes even a single switch transmitting onto a shared or half-
    duplex LAN segment is unlikely to be able to provide a very good
    approximation to Guaranteed Service. For Controlled Load service,
    the requirements on the switches and link types are less stringent
    although it is still necessary to provide differential queuing and
    buffering in switches for CL flows over best effort in order to
    approximate CL service. Note that users receive indication of such
    breaks in the path through the "break bits" described in y
    [RSVPINTSERV]. These bits must be correctly set when IEEE 802
    devices that cannot provide a specific service exist in a network.
    Other approaches might be to pass more information between
    switches about the capabilities of their neighbours and to route
    around non-QoS-capable switches: such methods are for further
    study. And of course the easiest solution of all is to upgrade
    links and switches to higher capacities.

7. References

 [802.1D-ORIG] "MAC Bridges", ISO/IEC 10038, ANSI/IEEE Std 802.1D-1993
 [802.1D]      "Information technology - Telecommunications and
               information exchange between systems - Local and
               metropolitan area networks - Common specifications -
               Part 3: Media Access Control (MAC) Bridges:  Revision.
               This is a revision of ISO/IEC 10038: 1993, 802.1j-1992
               and 802.6k-1992. It incorporates P802.11c, P802.1p and
               P802.12e."  ISO/IEC 15802-3:1998"
 [INTSERV]     Braden, R., Clark, D. and S. Shenker, "Integrated
               Services in the Internet Architecture: an Overview",
               RFC 1633, June 1994.
 [RSVP]        Braden, R., Zhang, L., Berson, S., Herzog, S. and S.
               Jamin, "Resource Reservation Protocol (RSVP) - Version
               1 Functional Specification", RFC 2205, September 1997.
 [CL]          Wroclawski, J., "Specification of the Controlled-Load
               Network Element Service", RFC 2211, September 1997.

Seaman, et al. Standards Track [Page 14] RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000

 [GS]          Schenker, S., Partridge, C. and R. Guerin,
               "Specification of Guaranteed Quality of Service", RFC
               2212 September 1997.
 [802.1Q]      ANSI/IEEE Standard 802.1Q-1998, "IEEE Standards for
               Local and Metropolitan Area Networks: Virtual Bridged
               Local Area Networks", 1998.
 [GENCHAR]     Shenker, S., and J. Wroclawski, "General
               Characterization Parameters for Integrated Service
               Network Elements", RFC 2215, September 1997.
 [IS802FRAME]  Ghanwani, A., Pace, W., Srinivasan, V., Smith, A. and
               M. Seaman, "A Framework for Providing Integrated
               Services Over Shared and Switched LAN Technologies",
               RFC 2816, May 2000.
 [SBM]         Yavatkar, R., Hoffman, D., Bernet, Y., Baker, F. and M.
               Speer, "SBM (Subnet Bandwidth Manager): A Protocol for
               Admission Control over IEEE 802-style Networks", RFC
               2814, May 2000.
 [RSVPINTSERV] Wroclawski, J., "The use of RSVP with IETF Integrated
               Services", RFC 2210, September 1997.
 [PROCESS]     Bradner, S., "The Internet Standards Process --
               Revision 3", BCP 9, RFC 2026, October 1996.

8. Security Considerations

 Any use of QoS requires examination of security considerations
 because it leaves the possibility open for denial of service or theft
 of service attacks. This document introduces no new security issues
 on top of those discussed in the companion ISSLL documents
 [IS802FRAME] and [SBM].  Any use of these service mappings assumes
 that all requests for service are authenticated appropriately.

9. Acknowledgments

 This document draws heavily on the work of the ISSLL WG of the IETF
 and the IEEE P802.1 Interworking Task Group.

Seaman, et al. Standards Track [Page 15] RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000

10. Authors' Addresses

 Mick Seaman
 Telseon
 480 S. California Ave
 Palo Alto, CA 94306
 USA
 Email: mick@telseon.com
 Andrew Smith
 Extreme Networks
 3585 Monroe St.
 Santa Clara, CA 95051
 USA
 Phone: +1 408 579 2821
 EMail: andrew@extremenetworks.com
 Eric Crawley
 Unisphere Solutions
 5 Carlisle Rd.
 Westford, MA 01886
 Phone: +1 978 692 1999
 Email: esc@unispheresolutions.com
 John Wroclawski
 MIT Laboratory for Computer Science
 545 Technology Sq.
 Cambridge, MA  02139
 USA
 Phone: +1 617 253 7885
 EMail: jtw@lcs.mit.edu

Seaman, et al. Standards Track [Page 16] RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000

Full Copyright Statement

 Copyright (C) The Internet Society (2000).  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 assigns.
 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.

Seaman, et al. Standards Track [Page 17]

/data/webs/external/dokuwiki/data/pages/rfc/rfc2815.txt · Last modified: 2000/05/08 16:44 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki