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rfc:rfc2702

Network Working Group D. Awduche Request for Comments: 2702 J. Malcolm Category: Informational J. Agogbua

                                                              M. O'Dell
                                                             J. McManus
                                                   UUNET (MCI Worldcom)
                                                         September 1999
           Requirements for Traffic Engineering Over MPLS

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (1999).  All Rights Reserved.

Abstract

 This document presents a set of requirements for Traffic Engineering
 over Multiprotocol Label Switching (MPLS). It identifies the
 functional capabilities required to implement policies that
 facilitate efficient and reliable network operations in an MPLS
 domain. These capabilities can be used to optimize the utilization of
 network resources and to enhance traffic oriented performance
 characteristics.

Table of Contents

 1.0   Introduction .............................................  2
 1.1   Terminology ..............................................  3
 1.2   Document Organization ....................................  3
 2.0   Traffic Engineering ......................................  4
 2.1   Traffic Engineering Performance Objectives ...............  4
 2.2   Traffic and Resource Control .............................  6
 2.3   Limitations of Current IGP Control Mechanisms ............  6
 3.0   MPLS and Traffic Engineering .............................  7
 3.1   Induced MPLS Graph .......................................  9
 3.2   The Fundamental Problem of Traffic Engineering Over MPLS .  9
 4.0   Augmented Capabilities for Traffic Engineering Over MPLS . 10
 5.0   Traffic Trunk Attributes and Characteristics   ........... 10
 5.1   Bidirectional Traffic Trunks ............................. 11
 5.2   Basic Operations on Traffic Trunks ....................... 12
 5.3   Accounting and Performance Monitoring .................... 12

Awduche, et al. Informational [Page 1] RFC 2702 MPLS Traffic Engineering September 1999

 5.4   Basic Attributes of Traffic Trunks ....................... 13
 5.5   Traffic Parameter Attributes  ............................ 14
 5.6   Generic Path Selection and Management Attributes ......... 14
 5.6.1 Administratively Specified Explicit Paths ................ 15
 5.6.2 Hierarchy of Preference Rules for Multi-paths ............ 15
 5.6.3 Resource Class Affinity Attributes ....................... 16
 5.6.4 Adaptivity Attribute ..................................... 17
 5.6.5 Load Distribution Across Parallel Traffic Trunks ......... 18
 5.7   Priority Attribute ....................................... 18
 5.8   Preemption Attribute ..................................... 18
 5.9   Resilience Attribute ..................................... 19
 5.10  Policing Attribute  ...................................... 20
 6.0   Resource Attributes ...................................... 21
 6.1   Maximum Allocation Multiplier ............................ 21
 6.2   Resource Class Attribute  ................................ 22
 7.0   Constraint-Based Routing  ................................ 22
 7.1   Basic Features of Constraint-Based Routing ............... 23
 7.2   Implementation Considerations ............................ 24
 8.0   Conclusion   ............................................. 25
 9.0   Security Considerations .................................. 26
 10.0  References   ............................................. 26
 11.0  Acknowledgments .......................................... 27
 12.0  Authors' Addresses ....................................... 28
 13.0  Full Copyright Statement ................................. 29

1.0 Introduction

 Multiprotocol Label Switching (MPLS) [1,2] integrates a label
 swapping framework with network layer routing. The basic idea
 involves assigning short fixed length labels to  packets at the
 ingress to an MPLS cloud (based on the concept of forwarding
 equivalence classes [1,2]). Throughout the interior of the MPLS
 domain, the labels attached to packets are used to make forwarding
 decisions  (usually without recourse to the original packet headers).
 A set of powerful constructs to address many critical issues in the
 emerging differentiated services Internet can be devised from this
 relatively simple paradigm.  One of the most significant initial
 applications of MPLS will be in Traffic Engineering. The importance
 of this application is already well-recognized (see [1,2,3]).
 This manuscript is exclusively focused on the Traffic Engineering
 applications of MPLS. Specifically, the goal of this document is to
 highlight the issues and requirements for Traffic Engineering in a
 large Internet backbone. The expectation is that the MPLS
 specifications, or implementations derived therefrom, will address

Awduche, et al. Informational [Page 2] RFC 2702 MPLS Traffic Engineering September 1999

 the realization of these objectives.  A description of the basic
 capabilities and functionality required of an MPLS implementation to
 accommodate the requirements is also presented.
 It should be noted that even though the focus is on Internet
 backbones, the capabilities described in this document are equally
 applicable to Traffic Engineering in enterprise networks. In general,
 the capabilities can  be applied to any label switched network under
 a single technical administration in which at least two paths exist
 between two nodes.
 Some recent manuscripts have focused on the considerations pertaining
 to Traffic Engineering and Traffic management under MPLS, most
 notably the works of Li and Rekhter [3], and others.  In [3], an
 architecture is proposed which employs MPLS and RSVP to provide
 scalable differentiated services and Traffic Engineering in the
 Internet.  The present manuscript complements the aforementioned and
 similar efforts.  It reflects the authors' operational experience in
 managing a large Internet backbone.

1.1 Terminology

 The reader is assumed to be familiar with the MPLS terminology as
 defined in [1].
 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 RFC 2119 [11].

1.2 Document Organization

 The remainder of this document is organized as follows: Section 2
 discusses the basic functions of Traffic Engineering in the Internet.
 Section 3, provides an overview of the traffic Engineering potentials
 of MPLS. Sections 1 to 3 are essentially background material. Section
 4 presents an overview of the fundamental requirements for Traffic
 Engineering over MPLS. Section 5 describes the desirable attributes
 and characteristics of traffic trunks which are pertinent to Traffic
 Engineering. Section 6 presents a set of attributes which can be
 associated with resources to constrain the routability of traffic
 trunks and LSPs through them. Section 7 advocates the introduction of
 a "constraint-based routing" framework in MPLS domains.  Finally,
 Section 8 contains concluding remarks.

Awduche, et al. Informational [Page 3] RFC 2702 MPLS Traffic Engineering September 1999

2.0 Traffic Engineering

 This section describes the basic functions of Traffic Engineering in
 an Autonomous System in the contemporary Internet. The limitations of
 current IGPs with respect to traffic and resource control are
 highlighted. This section serves as motivation for the requirements
 on MPLS.
 Traffic Engineering (TE) is concerned with performance optimization
 of operational networks. In general, it encompasses the application
 of technology and scientific principles to the measurement, modeling,
 characterization, and control of Internet traffic, and the
 application of such knowledge and techniques to achieve specific
 performance objectives. The aspects of Traffic Engineering that are
 of interest concerning MPLS are measurement and control.
 A major goal of Internet Traffic Engineering is to facilitate
 efficient and reliable network operations while simultaneously
 optimizing network resource utilization and traffic performance.
 Traffic Engineering has become an indispensable function in many
 large Autonomous Systems because of the high cost of network assets
 and the commercial and competitive nature of the Internet. These
 factors emphasize the need for maximal operational efficiency.

2.1 Traffic Engineering Performance Objectives

 The key performance objectives associated with traffic engineering
 can be classified as being either:
  1. traffic oriented or
  2. resource oriented.
 Traffic oriented performance objectives include the aspects that
 enhance the QoS of traffic streams. In a single class, best effort
 Internet service model, the key traffic oriented performance
 objectives include: minimization of packet loss, minimization of
 delay, maximization of throughput, and enforcement of service level
 agreements. Under a single class best effort Internet service model,
 minimization of packet loss is one of the most important traffic
 oriented performance objectives. Statistically bounded traffic
 oriented performance objectives (such as peak to peak packet delay
 variation, loss ratio, and maximum packet transfer delay) might
 become useful in the forthcoming differentiated services Internet.
 Resource oriented performance objectives include the aspects
 pertaining to the optimization of resource utilization. Efficient
 management of network resources is the vehicle for the attainment of

Awduche, et al. Informational [Page 4] RFC 2702 MPLS Traffic Engineering September 1999

 resource oriented performance objectives. In particular, it is
 generally desirable to ensure that subsets of network resources do
 not become over utilized and congested while other subsets along
 alternate feasible paths remain underutilized. Bandwidth is a crucial
 resource in contemporary networks.  Therefore, a central function of
 Traffic Engineering is to efficiently manage bandwidth resources.
 Minimizing congestion is a primary traffic and resource oriented
 performance objective.  The interest here is on congestion problems
 that are prolonged rather than on transient congestion resulting from
 instantaneous bursts.  Congestion typically manifests under two
 scenarios:
 1. When network resources are insufficient or inadequate to
    accommodate offered load.
 2. When traffic streams are inefficiently mapped onto available
    resources; causing subsets of network resources to become
    over-utilized while others remain underutilized.
 The first type of congestion problem can be addressed by either: (i)
 expansion of capacity, or (ii) application of classical congestion
 control techniques, or (iii) both. Classical congestion control
 techniques attempt to regulate the demand so that the traffic fits
 onto available resources. Classical techniques for congestion control
 include: rate limiting, window flow control, router queue management,
 schedule-based control, and others; (see [8] and the references
 therein).
 The second type of congestion problems, namely those resulting from
 inefficient resource allocation, can usually be addressed through
 Traffic Engineering.
 In general, congestion resulting from inefficient resource allocation
 can be reduced by adopting load balancing policies. The objective of
 such strategies is to minimize maximum congestion or alternatively to
 minimize maximum resource utilization, through efficient resource
 allocation. When congestion is minimized through efficient resource
 allocation, packet loss decreases, transit delay decreases, and
 aggregate throughput increases. Thereby, the perception of network
 service quality experienced by end users becomes significantly
 enhanced.
 Clearly, load balancing is an important network performance
 optimization policy. Nevertheless, the capabilities provided for
 Traffic Engineering should be flexible enough so that network
 administrators can implement other policies which take into account
 the prevailing cost structure and the utility or revenue model.

Awduche, et al. Informational [Page 5] RFC 2702 MPLS Traffic Engineering September 1999

2.2 Traffic and Resource Control

 Performance optimization of operational networks is fundamentally a
 control problem. In the traffic engineering process model, the
 Traffic Engineer, or a suitable automaton, acts as the controller in
 an adaptive feedback control system. This system includes a set of
 interconnected network elements, a network performance monitoring
 system, and a set of network configuration management tools. The
 Traffic Engineer formulates a control policy, observes the state of
 the network through the monitoring system, characterizes the traffic,
 and applies control actions to drive the network to a desired state,
 in accordance with the control policy.  This can be accomplished
 reactively by taking action in response to the current state of the
 network, or pro-actively by using forecasting techniques to
 anticipate future trends and applying action to obviate the predicted
 undesirable future states.
 Ideally, control actions should involve:
 1. Modification of traffic management parameters,
 2. Modification of parameters associated with routing, and
 3. Modification of attributes and constraints associated with
    resources.
 The level of manual intervention involved in the traffic engineering
 process should be minimized whenever possible.  This can be
 accomplished by automating aspects of the control actions described
 above, in a distributed and scalable fashion.

2.3 Limitations of Current IGP Control Mechanisms

 This subsection reviews some of the well known limitations of current
 IGPs with regard to Traffic Engineering.
 The control capabilities offered by existing Internet interior
 gateway protocols are not adequate for Traffic Engineering.  This
 makes it difficult to actualize effective policies to address network
 performance problems.  Indeed, IGPs based on shortest path algorithms
 contribute significantly to congestion problems in Autonomous Systems
 within the Internet. SPF algorithms generally optimize based on a
 simple additive metric. These protocols are topology driven, so
 bandwidth availability and traffic characteristics are not factors
 considered in routing decisions. Consequently, congestion frequently
 occurs when:

Awduche, et al. Informational [Page 6] RFC 2702 MPLS Traffic Engineering September 1999

 1. the shortest paths of multiple traffic streams converge on
    specific links or router interfaces, or
 2. a given traffic stream is routed through a link or router
    interface which does not have enough bandwidth to accommodate
    it.
 These scenarios manifest even when feasible alternate paths with
 excess capacity exist. It is this aspect of congestion problems (-- a
 symptom of suboptimal resource allocation) that Traffic Engineering
 aims to vigorously obviate.  Equal cost path load sharing can be used
 to address the second cause for congestion listed above with some
 degree of success, however it is generally not helpful in alleviating
 congestion due to the first cause listed above and particularly not
 in large networks with dense topology.
 A popular approach to circumvent the inadequacies of current IGPs is
 through the use of an overlay model, such as IP over ATM or IP over
 frame relay. The overlay model extends the design space by enabling
 arbitrary virtual topologies to be provisioned atop the network's
 physical topology. The virtual topology is constructed from virtual
 circuits which appear as physical links to the IGP routing protocols.
 The overlay model provides additional important services to support
 traffic and resource control, including: (1) constraint-based routing
 at the VC level, (2) support for administratively configurable
 explicit VC paths, (3) path compression, (4) call admission control
 functions, (5) traffic shaping and traffic policing functions, and
 (6) survivability of VCs. These capabilities enable the actualization
 of a variety of Traffic Engineering policies. For example, virtual
 circuits can easily be rerouted to move traffic from over-utilized
 resources onto relatively underutilized ones.
 For Traffic Engineering in large dense networks, it is desirable to
 equip MPLS with a level of functionality at least commensurate with
 current overlay models. Fortunately, this can be done in a fairly
 straight forward manner.

3.0 MPLS and Traffic Engineering

 This section provides an overview of the applicability of MPLS to
 Traffic Engineering. Subsequent sections discuss the set of
 capabilities required to meet the Traffic Engineering requirements.
 MPLS is strategically significant for Traffic Engineering because it
 can potentially provide most of the functionality available from the
 overlay model, in an integrated manner, and at a lower cost than the
 currently competing alternatives. Equally importantly, MPLS offers

Awduche, et al. Informational [Page 7] RFC 2702 MPLS Traffic Engineering September 1999

 the possibility to automate aspects of the Traffic Engineering
 function. This last consideration requires further investigation and
 is beyond the scope of this manuscript.
 A note on terminology: The concept of MPLS traffic trunks is used
 extensively in the remainder of this document. According to Li and
 Rekhter [3], a traffic trunk is an aggregation of traffic flows of
 the same class which are placed inside a Label Switched Path.
 Essentially, a traffic trunk is an abstract representation of traffic
 to which specific characteristics can be associated. It is useful to
 view traffic trunks as objects that can be routed; that is, the path
 through which a traffic trunk traverses can be changed. In this
 respect, traffic trunks are similar to virtual circuits in ATM and
 Frame Relay networks.  It is important, however, to emphasize that
 there is a fundamental distinction between a traffic trunk and the
 path, and indeed the LSP, through which it traverses. An LSP is a
 specification of the label switched path through which the traffic
 traverses. In practice, the terms LSP and traffic trunk are often
 used synonymously. Additional characteristics of traffic trunks as
 used in this manuscript are summarized in section 5.0.
 The attractiveness of  MPLS for Traffic Engineering can be attributed
 to the following factors: (1) explicit label switched paths which are
 not constrained by the destination based forwarding paradigm can be
 easily created through manual administrative action or through
 automated action by the underlying protocols, (2) LSPs can
 potentially be efficiently maintained, (3) traffic trunks can be
 instantiated and mapped onto LSPs, (4) a set of attributes can be
 associated with traffic trunks which modulate their behavioral
 characteristics, (5) a set of attributes can be associated with
 resources which constrain the placement of LSPs and traffic trunks
 across them, (6) MPLS allows for both traffic aggregation and
 disaggregation whereas classical destination only based IP forwarding
 permits only aggregation, (7) it is relatively easy to integrate a
 "constraint-based routing" framework with MPLS, (8) a good
 implementation of MPLS can offer significantly lower overhead than
 competing alternatives for Traffic Engineering.
 Additionally, through explicit label switched paths, MPLS permits a
 quasi circuit switching capability to be superimposed on the current
 Internet routing model.  Many of the existing proposals for Traffic
 Engineering over MPLS focus only on the potential to create explicit
 LSPs. Although this capability is fundamental for Traffic
 Engineering, it is not really sufficient.  Additional augmentations
 are required to foster the actualization of policies leading to
 performance optimization of large operational networks. Some of the
 necessary augmentations are described in this manuscript.

Awduche, et al. Informational [Page 8] RFC 2702 MPLS Traffic Engineering September 1999

3.1 Induced MPLS Graph

 This subsection introduces the concept of an "induced MPLS graph"
 which is central to Traffic Engineering in MPLS domains. An induced
 MPLS graph is analogous to a virtual topology in an overlay model. It
 is logically mapped onto the physical network through the selection
 of LSPs for traffic trunks.
 An induced MPLS graph consists of a set of LSRs which comprise the
 nodes of the graph and a set of LSPs which provide logical point to
 point connectivity between the LSRs, and hence serve as the links of
 the induced graph. it may be possible to construct hierarchical
 induced MPLS graphs based on the concept of label stacks (see [1]).
 Induced MPLS graphs are important because the basic problem of
 bandwidth management in an MPLS domain is the issue of how to
 efficiently map an induced MPLS graph onto the physical network
 topology.  The induced MPLS graph abstraction is formalized below.
 Let G = (V, E, c) be a capacitated graph depicting the physical
 topology of the network. Here, V is the set of nodes in the network
 and E is the set of links; that is, for v and w in V, the object
 (v,w) is in E if v and w are directly connected under G. The
 parameter "c" is a set of capacity and other constraints associated
 with E and V. We will refer to G as the "base" network topology.
 Let H = (U, F, d) be  the induced MPLS graph, where U is a subset of
 V representing the set of LSRs in the network, or more precisely the
 set of LSRs that are the endpoints of at least one LSP. Here, F is
 the set of LSPs, so that for x and y in U, the object (x, y) is in F
 if there is an LSP with x and y as endpoints. The parameter "d" is
 the set of demands and restrictions associated with F. Evidently, H
 is a directed graph. It can be seen that H depends on the
 transitivity characteristics of G.

3.2 The Fundamental Problem of Traffic Engineering Over MPLS

 There are basically three fundamental problems that relate to Traffic
 Engineering over MPLS.
  1. The first problem concerns how to map packets onto forwarding

equivalence classes.

  1. The second problem concerns how to map forwarding equivalence

classes onto traffic trunks.

  1. The third problem concerns how to map traffic trunks onto the

physical network topology through label switched paths.

Awduche, et al. Informational [Page 9] RFC 2702 MPLS Traffic Engineering September 1999

 This document is not focusing on the first two problems listed.
 (even-though they are quite important). Instead, the remainder of
 this manuscript will focus on the capabilities that permit the third
 mapping function to be performed in a manner resulting in efficient
 and reliable network operations. This is really the problem of
 mapping an induced MPLS graph (H) onto the "base" network topology
 (G).

4.0 Augmented Capabilities for Traffic Engineering Over MPLS

 The previous sections reviewed the basic functions of Traffic
 Engineering in the contemporary Internet. The applicability of MPLS
 to that activity was also discussed. The remaining sections of this
 manuscript describe the functional capabilities required to fully
 support Traffic Engineering over MPLS in large networks.
 The proposed capabilities consist of:
 1. A set of attributes associated with traffic trunks which
    collectively specify their behavioral characteristics.
 2. A set of attributes associated with resources which constrain
    the placement of traffic trunks through them. These can also be
    viewed as topology attribute constraints.
 3. A "constraint-based routing" framework which is used to select
    paths for traffic trunks subject to constraints imposed by items
    1) and 2) above. The constraint-based routing framework does not
    have to be part of MPLS. However, the two need to be tightly
    integrated together.
 The attributes associated with traffic trunks and resources, as well
 as parameters associated with routing, collectively represent the
 control variables which can be modified either through administrative
 action or through automated agents to drive the network to a desired
 state.
 In an operational network, it is highly desirable that these
 attributes can be dynamically modified online by an operator without
 adversely disrupting network operations.

5.0 Traffic Trunk Attributes and Characteristics

 This section describes the desirable attributes which can be
 associated with traffic trunks to influence their behavioral
 characteristics.

Awduche, et al. Informational [Page 10] RFC 2702 MPLS Traffic Engineering September 1999

 First, the basic properties of traffic trunks (as used in this
 manuscript) are summarized below:
  1. A traffic trunk is an *aggregate* of traffic flows belonging

to the same class. In some contexts, it may be desirable to

    relax this definition and allow traffic trunks to include
    multi-class traffic aggregates.
  1. In a single class service model, such as the current Internet,

a traffic trunk could encapsulate all of the traffic between an

    ingress LSR and an egress LSR, or subsets thereof.
  1. Traffic trunks are routable objects (similar to ATM VCs).
  1. A traffic trunk is distinct from the LSP through which it

traverses. In operational contexts, a traffic trunk can be

    moved from one path onto another.
  1. A traffic trunk is unidirectional.
 In practice, a traffic trunk can be characterized by its ingress and
 egress LSRs, the forwarding equivalence class which is mapped onto
 it, and a set of attributes which determine its behavioral
 characteristics.
 Two basic issues are of particular significance: (1) parameterization
 of traffic trunks and (2) path placement and maintenance rules for
 traffic trunks.

5.1 Bidirectional Traffic Trunks

 Although traffic trunks are conceptually unidirectional, in many
 practical contexts, it is useful to  simultaneously instantiate two
 traffic trunks with the same endpoints, but which carry packets in
 opposite directions. The two traffic trunks are logically coupled
 together.  One trunk, called the forward trunk, carries traffic from
 an originating node to a destination node. The other trunk, called
 the backward trunk, carries traffic from the destination node to the
 originating node. We refer to the amalgamation of two such traffic
 trunks as one bidirectional traffic trunk (BTT) if the following two
 conditions hold:
  1. Both traffic trunks are instantiated through an atomic action at

one LSR, called the originator node, or through an atomic action

   at a network management station.
  1. Neither of the composite traffic trunks can exist without the

other. That is, both are instantiated and destroyed together.

Awduche, et al. Informational [Page 11] RFC 2702 MPLS Traffic Engineering September 1999

 The topological properties of BTTs should also be considered. A BTT
 can be topologically symmetric or topologically asymmetric.  A BTT is
 said to be "topologically symmetric" if its constituent traffic
 trunks are routed through the same physical path, even though they
 operate in opposite directions. If, however, the component traffic
 trunks are routed through different physical paths, then the BTT is
 said to be "topologically asymmetric."
 It should be noted that bidirectional traffic trunks are merely an
 administrative convenience. In practice, most traffic engineering
 functions can be implemented using only unidirectional traffic
 trunks.

5.2 Basic Operations on Traffic Trunks

 The basic operations on traffic trunks significant to Traffic
 Engineering purposes are summarized below.
  1. Establish: To create an instance of a traffic trunk.
  1. Activate: To cause a traffic trunk to start passing traffic.

The establishment and activation of a traffic trunk are

   logically separate events. They may, however, be implemented
   or invoked as one atomic action.
  1. Deactivate: To cause a traffic trunk to stop passing traffic.
  1. Modify Attributes: To cause the attributes of a traffic trunk

to be modified.

  1. Reroute: To cause a traffic trunk to change its route. This

can be done through administrative action or automatically

   by the underlying protocols.
  1. Destroy: To remove an instance of a traffic trunk from the

network and reclaim all resources allocated to it. Such

   resources include label space and possibly available bandwidth.
 The above are considered the basic operations on traffic trunks.
 Additional operations are also possible such as policing and traffic
 shaping.

5.3 Accounting and Performance Monitoring

 Accounting and performance monitoring capabilities are very important
 to the billing and traffic characterization functions.  Performance
 statistics obtained from accounting and performance monitoring

Awduche, et al. Informational [Page 12] RFC 2702 MPLS Traffic Engineering September 1999

 systems can be used for traffic characterization, performance
 optimization, and capacity planning within the Traffic Engineering
 realm..
 The capability to obtain statistics at the traffic trunk level is so
 important that it should be considered an essential requirement for
 Traffic Engineering over MPLS.

5.4 Basic Traffic Engineering Attributes of Traffic Trunks

 An attribute of a traffic trunk is a parameter assigned to it which
 influences its behavioral characteristics.
 Attributes can be explicitly assigned to traffic trunks through
 administration action or they can be implicitly assigned by the
 underlying protocols when packets are classified and mapped into
 equivalence classes at the ingress to an MPLS domain. Regardless of
 how the attributes were originally assigned, for Traffic Engineering
 purposes, it should be possible to administratively modify such
 attributes.
 The basic attributes of traffic trunks  particularly significant for
 Traffic Engineering are itemized below.
  1. Traffic parameter attributes
  1. Generic Path selection and maintenance attributes
  1. Priority attribute
  1. Preemption attribute
  1. Resilience attribute
  1. Policing attribute
 The combination of traffic parameters and policing attributes is
 analogous to usage parameter control in ATM networks. Most of the
 attributes listed above have analogs in well established
 technologies.  Consequently, it should be relatively straight forward
 to map the traffic trunk attributes onto many existing switching and
 routing architectures.
 Priority and preemption can be regarded as relational attributes
 because they express certain binary relations between traffic trunks.
 Conceptually, these binary relations determine the manner in which
 traffic trunks interact with each other as they compete for network
 resources during path establishment and path maintenance.

Awduche, et al. Informational [Page 13] RFC 2702 MPLS Traffic Engineering September 1999

5.5 Traffic parameter attributes

 Traffic parameters can be used to capture the characteristics of the
 traffic streams (or more precisely the forwarding equivalence class)
 to be transported through the traffic trunk. Such characteristics may
 include peak rates, average rates, permissible burst size, etc.  From
 a traffic engineering perspective, the traffic parameters are
 significant because they indicate the resource requirements of the
 traffic trunk. This is useful for resource allocation and congestion
 avoidance through anticipatory policies.
 For the purpose of bandwidth allocation, a single canonical value of
 bandwidth requirements can be computed from a traffic trunk's traffic
 parameters.  Techniques for performing these computations are well
 known. One example of this is the theory of effective bandwidth.

5.6 Generic Path Selection and Management Attributes

 Generic path selection and management attributes define the rules for
 selecting the route taken by a traffic trunk as well as the rules for
 maintenance of paths that are already established.
 Paths can be computed automatically by the underlying routing
 protocols or they can be defined administratively by a network
 operator. If there are no resource requirements or restrictions
 associated with a traffic trunk, then a topology driven protocol can
 be used to select its path. However, if resource requirements or
 policy restrictions exist, then a constraint-based routing scheme
 should be used for path selection.
 In Section 7, a constraint-based routing framework which can
 automatically compute paths subject to a set of constraints is
 described.  Issues pertaining to explicit paths instantiated through
 administrative action are discussed in Section 5.6.1 below.
 Path management concerns all aspects pertaining to the maintenance of
 paths traversed by traffic trunks.  In some operational contexts, it
 is desirable that an MPLS implementation can dynamically reconfigure
 itself, to adapt to some notion of change in "system state."
 Adaptivity and resilience are aspects of dynamic path management.
 To guide the path selection and management process, a set of
 attributes are required. The basic attributes and behavioral
 characteristics associated with traffic trunk path selection and
 management are described in the remainder of this sub-section.

Awduche, et al. Informational [Page 14] RFC 2702 MPLS Traffic Engineering September 1999

5.6.1 Administratively Specified Explicit Paths

 An administratively specified explicit path for a traffic trunk is
 one which is configured through operator action. An administratively
 specified path can be completely specified or partially specified. A
 path is completely specified if all of the required hops between the
 endpoints are indicated. A path is partially specified if only a
 subset of intermediate hops are indicated. In this case, the
 underlying protocols are required to complete the path. Due to
 operator errors, an administratively specified path can be
 inconsistent or illogical. The underlying protocols should be able to
 detect such inconsistencies and provide appropriate feedback.
 A "path preference rule" attribute should be associated with
 administratively specified explicit paths.  A path preference rule
 attribute is a binary variable which  indicates whether the
 administratively configured explicit path is "mandatory" or "non-
 mandatory."
 If an administratively specified explicit path is selected with a
 "mandatory attribute, then that path (and only that path) must be
 used. If a mandatory path is topological infeasible (e.g. the two
 endpoints are topologically partitioned), or if the path cannot be
 instantiated because the available resources are inadequate, then the
 path setup process fails. In other words, if a path is specified as
 mandatory, then an alternate path cannot be used regardless of
 prevailing circumstance.  A mandatory path which is successfully
 instantiated is also implicitly pinned. Once the path is instantiated
 it cannot be changed except through deletion and instantiation of a
 new path.
 However, if an administratively specified explicit path is selected
 with a "non-mandatory" preference rule attribute value, then the path
 should be used if feasible.  Otherwise, an alternate path can be
 chosen instead by the underlying protocols.

5.6.2 Hierarchy of Preference Rules For Multi-Paths

 In some practical contexts, it can be useful to have the ability to
 administratively specify a set of candidate explicit paths for a
 given traffic trunk and define a hierarchy of preference relations on
 the paths. During path establishment, the preference rules are
 applied to select a suitable path from the candidate list. Also,
 under failure scenarios the preference rules are applied to select an
 alternate path from the candidate list.

Awduche, et al. Informational [Page 15] RFC 2702 MPLS Traffic Engineering September 1999

5.6.3 Resource Class Affinity Attributes

 Resource class affinity attributes associated with a traffic trunk
 can be used to specify the class of resources (see Section 6) which
 are to be explicitly included or excluded from the path of the
 traffic trunk. These are policy attributes which can be used to
 impose additional constraints on the path traversed by a given
 traffic trunk.  Resource class affinity attributes for a traffic can
 be specified as a sequence of tuples:
  <resource-class, affinity>; <resource-class, affinity>; ..
 The resource-class parameter identifies a resource class for which an
 affinity relationship is defined with respect to the traffic trunk.
 The affinity parameter indicates the affinity relationship; that is,
 whether members of the resource class are to be included or excluded
 from the path of the traffic trunk. Specifically, the affinity
 parameter may be a binary variable which takes one of the following
 values: (1) explicit inclusion, and (2) explicit exclusion.
 If the affinity attribute is a binary variable, it may be possible to
 use Boolean expressions to specify the resource class affinities
 associated with a given traffic trunk.
 If no resource class affinity attributes are specified, then a "don't
 care" affinity relationship is assumed to hold between the traffic
 trunk and all resources. That is, there is no requirement to
 explicitly include or exclude any resources from the traffic trunk's
 path. This should be the default in practice.
 Resource class affinity attributes are very useful and powerful
 constructs because they can be used to implement a variety of
 policies. For example, they can be used to contain certain traffic
 trunks within specific topological regions of the network.
 A "constraint-based routing" framework (see section 7.0) can be used
 to compute an explicit path for a traffic trunk subject to resource
 class affinity constraints in the following manner:
 1. For explicit inclusion, prune all resources not belonging
    to the specified classes prior to performing path computation.
 2. For explicit exclusion, prune all resources  belonging to the
    specified classes before performing path placement computations.

Awduche, et al. Informational [Page 16] RFC 2702 MPLS Traffic Engineering September 1999

5.6.4 Adaptivity Attribute

 Network characteristics and state change over time. For example, new
 resources become available, failed resources become reactivated, and
 allocated resources become deallocated. In general, sometimes more
 efficient paths become available.  Therefore, from a Traffic
 Engineering perspective, it is necessary to have administrative
 control parameters that can be used to specify how traffic trunks
 respond to this dynamism. In some scenarios, it might be desirable to
 dynamically change the paths of certain traffic trunks in response to
 changes in network state. This process is called re-optimization.  In
 other scenarios, re-optimization might be very undesirable.
 An Adaptivity attribute is a part of the path maintenance parameters
 associated with traffic trunks. The adaptivity attribute associated
 with a traffic trunk indicates whether the trunk is subject to re-
 optimization.  That is, an adaptivity attribute is a binary variable
 which takes one of the following values: (1) permit re-optimization
 and (2) disable re-optimization.
 If re-optimization is enabled, then a traffic trunk can be rerouted
 through different paths by the underlying protocols in response to
 changes in network state (primarily changes in resource
 availability). Conversely, if re-optimization is disabled, then the
 traffic trunk is "pinned" to its established path and cannot be
 rerouted in response to changes in network state.
 Stability is a major concern when re-optimization is permitted. To
 promote stability, an MPLS implementation should not be too reactive
 to the evolutionary dynamics of the network. At the same time, it
 must adapt fast enough so that optimal use can be made of network
 assets. This implies that the frequency of re-optimization should be
 administratively configurable to allow for tuning.
 It is to be noted that re-optimization is distinct from resilience. A
 different attribute is used to specify the resilience characteristics
 of a traffic trunk (see section 5.9).  In practice, it would seem
 reasonable to expect traffic trunks subject to re-optimization to be
 implicitly resilient to failures along their paths. However, a
 traffic trunk which is not subject to re-optimization and whose path
 is not administratively specified with a "mandatory" attribute can
 also be required to be resilient to link and node failures along its
 established path
 Formally, it can be stated that adaptivity to state evolution through
 re-optimization implies resilience to failures, whereas resilience to
 failures does not imply general adaptivity through re-optimization to
 state changes.

Awduche, et al. Informational [Page 17] RFC 2702 MPLS Traffic Engineering September 1999

5.6.5 Load Distribution Across Parallel Traffic Trunks

 Load distribution across multiple parallel traffic trunks between two
 nodes is an important consideration.  In many practical contexts, the
 aggregate traffic between two nodes may be such that no single link
 (hence no single path) can carry the load. However, the aggregate
 flow might be less than the maximum permissible flow across a "min-
 cut" that partitions the two nodes. In this case, the only feasible
 solution is to appropriately divide the aggregate traffic into sub-
 streams and route the sub-streams through multiple paths between the
 two nodes.
 In an MPLS domain, this problem can be addressed by instantiating
 multiple traffic trunks between the two nodes, such that each traffic
 trunk carries a proportion of the aggregate traffic. Therefore, a
 flexible means of load assignment to multiple parallel traffic trunks
 carrying traffic between a pair of nodes is required.
 Specifically, from an operational perspective, in situations where
 parallel traffic trunks are warranted,  it would be useful to have
 some attribute that can be used to indicate the relative proportion
 of traffic to be carried by each traffic trunk. The underlying
 protocols will then map the load onto the traffic trunks according to
 the specified proportions. It is also, generally desirable to
 maintain packet ordering between packets belong to the same micro-
 flow (same source address, destination address, and port number).

5.7 Priority attribute

 The priority attribute defines the relative importance of traffic
 trunks.  If a constraint-based routing framework is used with MPLS,
 then priorities become very important because they can be used to
 determine the order in which path selection is done for traffic
 trunks at connection establishment and under fault scenarios.
 Priorities are also important in implementations  permitting
 preemption because they can be used to impose a partial order on the
 set of traffic trunks according to which preemptive policies can be
 actualized.

5.8 Preemption attribute

 The preemption attribute determines whether a traffic trunk can
 preempt another traffic trunk from a given path, and whether another
 traffic trunk can preempt a specific traffic trunk.  Preemption is
 useful for both traffic oriented and resource oriented performance

Awduche, et al. Informational [Page 18] RFC 2702 MPLS Traffic Engineering September 1999

 objectives. Preemption can used to assure that high priority traffic
 trunks can always be routed through relatively favorable paths within
 a differentiated services environment.
 Preemption can also be used to implement various prioritized
 restoration policies following fault events.
 The preemption attribute can be used to specify four preempt modes
 for a traffic trunk: (1) preemptor enabled, (2) non-preemptor, (3)
 preemptable, and (4) non-preemptable. A preemptor enabled traffic
 trunk can preempt lower priority traffic trunks designated as
 preemptable. A traffic specified as non-preemptable cannot be
 preempted by any other trunks, regardless of relative priorities. A
 traffic trunk designated as preemptable can be preempted by higher
 priority trunks which are preemptor enabled.
 It is trivial to see that some of the preempt modes are mutually
 exclusive. Using the numbering scheme depicted above, the feasible
 preempt mode combinations for a given traffic trunk are as follows:
 (1, 3), (1, 4), (2, 3), and (2, 4). The (2, 4) combination should be
 the default.
 A traffic trunk, say "A", can preempt another traffic trunk, say "B",
 only if *all* of the following five conditions hold: (i) "A" has a
 relatively higher priority than "B", (ii) "A" contends for a resource
 utilized by "B", (iii) the resource cannot concurrently accommodate
 "A" and "B" based on certain decision criteria, (iv) "A" is preemptor
 enabled, and (v) "B" is preemptable.
 Preemption is not considered a mandatory attribute under the current
 best effort Internet service model although it is useful. However, in
 a differentiated services scenario, the need for preemption becomes
 more compelling. Moreover, in the emerging optical internetworking
 architectures, where some protection and restoration functions may be
 migrated from the optical layer to data network elements (such as
 gigabit and terabit label switching routers) to reduce costs,
 preemptive strategies can be used to reduce the restoration time for
 high priority traffic trunks under fault conditions.

5.9 Resilience Attribute

 The resilience attribute determines the behavior of a traffic trunk
 under fault conditions. That is, when a fault occurs along the path
 through which the traffic trunk traverses. The following basic
 problems need to be addressed under such circumstances: (1) fault
 detection, (2) failure notification, (3) recovery and service
 restoration. Obviously, an MPLS implementation will have to
 incorporate mechanisms to address these issues.

Awduche, et al. Informational [Page 19] RFC 2702 MPLS Traffic Engineering September 1999

 Many recovery policies can be specified for traffic trunks whose
 established paths are impacted by faults. The following are examples
 of feasible schemes:
 1. Do not reroute the traffic trunk. For example, a survivability
    scheme may already be in place, provisioned through an
    alternate mechanism, which guarantees service continuity
    under failure scenarios without the need to reroute traffic
    trunks. An example of such an alternate scheme (certainly
    many others exist), is a situation whereby multiple parallel
    label switched paths are provisioned between two nodes, and
    function in a manner such that failure of one LSP causes the
    traffic trunk placed on it to be mapped onto the remaining LSPs
    according to some well defined policy.
 2. Reroute through a feasible path with enough resources. If none
    exists, then do not reroute.
 3. Reroute through any available path regardless of resource
    constraints.
 4. Many other schemes are possible including some which might be
    combinations of the above.
 A "basic" resilience attribute indicates the recovery procedure to be
 applied to traffic trunks whose paths are impacted by faults.
 Specifically, a "basic" resilience attribute is a binary variable
 which determines whether the target traffic trunk is to be rerouted
 when segments of its path fail. "Extended" resilience attributes can
 be used to specify detailed actions to be taken under fault
 scenarios.  For example, an extended resilience attribute might
 specify a set of alternate paths to use under fault conditions, as
 well as the rules that govern the relative preference of each
 specified path.
 Resilience attributes mandate close interaction between MPLS and
 routing.

5.10 Policing attribute

 The policing attribute determines the actions that should be taken by
 the underlying protocols when a traffic trunk becomes non-compliant.
 That is, when a traffic trunk exceeds its contract as specified in
 the traffic parameters.  Generally, policing attributes can indicate
 whether a non-conformant traffic trunk is to be rate limited, tagged,
 or simply forwarded without any policing action.  If policing is
 used, then adaptations of established algorithms such as the ATM
 Forum's GCRA [11] can be used to perform this function.

Awduche, et al. Informational [Page 20] RFC 2702 MPLS Traffic Engineering September 1999

 Policing is necessary in many operational scenarios, but is quite
 undesirable in some others. In general, it is usually desirable to
 police at the ingress to a network (to enforce compliance with
 service level agreements) and to minimize policing within the core,
 except when capacity constraints dictate otherwise.
 Therefore, from a Traffic Engineering perspective, it is necessary to
 be able to administratively enable or disable traffic policing for
 each traffic trunk.

6.0 Resource Attributes

 Resource attributes are part of the topology state parameters, which
 are used to constrain the routing of traffic trunks through specific
 resources.

6.1 Maximum Allocation Multiplier

 The maximum allocation multiplier (MAM) of a resource is an
 administratively configurable attribute which determines the
 proportion of the resource that is available for allocation to
 traffic trunks.  This attribute is mostly applicable to link
 bandwidth. However,  it can also be applied to buffer resources on
 LSRs. The concept of MAM is analogous to the concepts of subscription
 and booking factors in frame relay and ATM networks.
 The values of the MAM can be chosen so that a resource can be under-
 allocated or over-allocated. A resource is said  to be under-
 allocated if the aggregate demands of all traffic trunks (as
 expressed in the trunk traffic parameters) that can be allocated to
 it are always less than the capacity of the resource. A resource is
 said to be over-allocated if the aggregate demands of all traffic
 trunks allocated to it can exceed the capacity of the resource.
 Under-allocation can be used to bound the utilization of resources.
 However,the situation under MPLS is more complex than in circuit
 switched schemes because under MPLS, some flows can be routed via
 conventional hop by hop protocols (also via explicit paths) without
 consideration for resource constraints.
 Over-allocation can be used to take advantage of the statistical
 characteristics of traffic in order to implement more efficient
 resource allocation policies. In particular, over-allocation can be
 used in situations where the peak demands of traffic trunks do not
 coincide in time.

Awduche, et al. Informational [Page 21] RFC 2702 MPLS Traffic Engineering September 1999

6.2 Resource Class Attribute

 Resource class attributes are administratively assigned parameters
 which express some notion of "class" for resources. Resource class
 attributes can be viewed as "colors" assigned to resources such that
 the set of resources with the same "color" conceptually belong to the
 same class. Resource class attributes can be used to implement a
 variety of policies. The key resources of interest here are links.
 When applied to links, the resource class attribute effectively
 becomes  an aspect of the "link state" parameters.
 The concept of resource class attributes is a powerful abstraction.
 From a Traffic Engineering perspective, it can be used to implement
 many policies with regard to both traffic and resource oriented
 performance optimization. Specifically, resource class attributes can
 be used to:
 1. Apply uniform policies to a set of resources that do not need
    to be in the same topological region.
 2. Specify the relative preference of sets of resources for
    path placement of traffic trunks.
 3. Explicitly restrict the placement of traffic trunks
    to  specific subsets of resources.
 4. Implement generalized inclusion / exclusion policies.
 5. Enforce traffic locality containment policies. That is,
    policies    that seek to contain local traffic within
    specific topological regions of the network.
 Additionally, resource class attributes can be used for
 identification purposes.
 In general, a resource can be assigned more than one resource class
 attribute. For example, all of the OC-48 links in a given network may
 be assigned a distinguished resource class attribute. The subsets of
 OC-48 links which exist with a given abstraction domain of the
 network may be assigned additional resource class attributes in order
 to implement specific containment policies, or to architect the
 network in a certain manner.

7.0 Constraint-Based Routing

 This section discusses the issues pertaining to constraint-based
 routing in MPLS domains. In contemporary terminology, constraint-
 based routing is often referred to as "QoS Routing" see [5,6,7,10].

Awduche, et al. Informational [Page 22] RFC 2702 MPLS Traffic Engineering September 1999

 This document uses the term "constraint-based routing" however,
 because it better captures the functionality envisioned, which
 generally encompasses QoS routing as a subset.
 constraint-based routing enables a demand driven, resource
 reservation aware, routing paradigm to co-exist with current topology
 driven hop by hop Internet interior gateway protocols.
 A constraint-based routing framework uses the following as input:
  1. The attributes associated with traffic trunks.
  1. The attributes associated with resources.
  1. Other topology state information.
 Based on this information, a constraint-based routing process on each
 node automatically computes explicit routes for each traffic trunk
 originating from the node. In this case, an explicit route for each
 traffic trunk is a specification of a label switched path that
 satisfies the demand requirements expressed in the trunk's
 attributes, subject to constraints imposed by resource availability,
 administrative policy, and other topology state information.
 A constraint-based routing framework can greatly reduce the level of
 manual configuration and intervention required to actualize Traffic
 Engineering policies.
 In practice, the Traffic Engineer, an operator, or even an automaton
 will specify the endpoints of a traffic trunk and assign a set of
 attributes to the trunk which encapsulate the performance
 expectations and behavioral characteristics of the trunk. The
 constraint-based routing framework is then expected to find a
 feasible path to satisfy the expectations.  If necessary, the Traffic
 Engineer or a traffic engineering support system can then use
 administratively configured explicit routes to perform fine grained
 optimization.

7.1 Basic Features of Constraint-Based Routing

 A constraint-based routing framework should at least have the
 capability to automatically obtain a basic feasible solution to the
 traffic trunk path placement problem.
 In general, the constraint-based routing problem is known to be
 intractable for most realistic constraints. However, in practice, a
 very simple well known heuristic (see e.g. [9]) can be used to find a
 feasible path if one exists:

Awduche, et al. Informational [Page 23] RFC 2702 MPLS Traffic Engineering September 1999

  1. First prune resources that do not satisfy the requirements of

the traffic trunk attributes.

  1. Next, run a shortest path algorithm on the residual graph.
 Clearly, if a feasible path exists for a single traffic trunk, then
 the above simple procedure will find it. Additional rules can be
 specified to break ties and perform further optimizations.  In
 general, ties should be broken so that congestion is minimized.  When
 multiple traffic trunks are to be routed, however, it can be shown
 that the above algorithm may not always find a mapping, even when a
 feasible mapping exists.

7.2 Implementation Considerations

 Many commercial implementations of frame relay and ATM switches
 already support some notion of constraint-based routing. For such
 devices or for the novel MPLS centric contraptions devised therefrom,
 it should be relatively easy to extend the current constraint-based
 routing implementations to accommodate the peculiar requirements of
 MPLS.
 For routers that use topology driven hop by hop IGPs, constraint-
 based routing can be incorporated in at least one of two ways:
 1. By extending the current IGP protocols such as OSPF and IS-IS to
    support constraint-based routing. Effort is already underway to
    provide such extensions to OSPF (see [5,7]).
 2. By adding a constraint-based routing process to each router which
    can co-exist with current IGPs. This scenario is depicted
    in Figure 1.
  1. —————————————–

| Management Interface |

  1. —————————————–

| | |

  1. ———– —————— ————–

| MPLS |↔| Constraint-Based | | Conventional |

  |            |   | Routing Process  |  | IGP Process  |
   ------------     ------------------    --------------
                         |                  |
           -----------------------    --------------
          | Resource  Attribute   |  | Link State   |
          | Availability Database |  | Database     |
           -----------------------    --------------
  Figure 1. Constraint-Based Routing Process on Layer 3 LSR

Awduche, et al. Informational [Page 24] RFC 2702 MPLS Traffic Engineering September 1999

 There are many important details associated with implementing
 constraint-based routing on Layer 3 devices which we do not discuss
 here. These include the following:
  1. Mechanisms for exchange of topology state information

(resource availability information, link state information,

   resource attribute information) between constraint-based
   routing processes.
  1. Mechanisms for maintenance of topology state information.
  1. Interaction between constraint-based routing processes and

conventional IGP processes.

  1. Mechanisms to accommodate the adaptivity requirements of

traffic trunks.

  1. Mechanisms to accommodate the resilience and survivability

requirements of traffic trunks.

 In summary, constraint-based routing assists in performance
 optimization of operational networks by automatically finding
 feasible paths that satisfy a set of constraints for traffic trunks.
 It can drastically reduce the amount of administrative explicit path
 configuration and manual intervention required to achieve Traffic
 Engineering objectives.

8.0 Conclusion

 This manuscript presented a set of requirements for Traffic
 Engineering over MPLS. Many capabilities were described aimed at
 enhancing the applicability of MPLS to Traffic Engineering in the
 Internet.
 It should be noted that some of the issues described here can be
 addressed by incorporating a minimal set of building blocks into
 MPLS, and then using a network management superstructure to extend
 the functionality in order to realize the requirements. Also, the
 constraint-based routing framework does not have to be part of the
 core MPLS specifications. However, MPLS does require some interaction
 with a constraint-based routing framework in order to meet the
 requirements.

Awduche, et al. Informational [Page 25] RFC 2702 MPLS Traffic Engineering September 1999

9.0 Security Considerations

 This document does not introduce new security issues beyond those
 inherent in MPLS and may use the same mechanisms proposed for this
 technology. It is, however, specifically important that manipulation
 of administratively configurable parameters be executed in a secure
 manner by authorized entities.

10.0 References

 [1]  Rosen, E., Viswanathan, A. and R. Callon, "A Proposed
      Architecture for MPLS", Work in Progress.
 [2]  Callon, R., Doolan, P., Feldman, N., Fredette, A., Swallow, G.
      and A. Viswanathan, "A Framework for Multiprotocol Label
      Switching", Work in Progress.
 [3]  Li, T. and Y. Rekhter, "Provider Architecture for Differentiated
      Services and Traffic Engineering (PASTE)", RFC 2430, October
      1998.
 [4]  Rekhter, Y., Davie, B., Katz, D., Rosen, E. and  G. Swallow,
      "Cisco Systems' Tag Switching Architecture - Overview", RFC
      2105, February 1997.
 [5]  Zhang, Z., Sanchez, C., Salkewicz, B. and E. Crawley "Quality of
      Service Extensions to OSPF", Work in Progress.
 [6]  Crawley, E., Nair, F., Rajagopalan, B. and H. Sandick, "A
      Framework for QoS Based Routing in the Internet", RFC 2386,
      August 1998.
 [7]  Guerin, R., Kamat, S., Orda, A., Przygienda, T. and D. Williams,
      "QoS Routing Mechanisms and OSPF Extensions", RFC 2676, August
      1999.
 [8]  C. Yang and A. Reddy, "A Taxonomy for Congestion Control
      Algorithms in Packet Switching Networks," IEEE Network Magazine,
      Volume 9, Number 5, July/August 1995.
 [9]  W. Lee, M. Hluchyi, and P. Humblet, "Routing Subject to Quality
      of Service Constraints in Integrated Communication Networks,"
      IEEE Network, July 1995, pp 46-55.
 [10] ATM Forum, "Traffic Management Specification: Version 4.0" April
      1996.

Awduche, et al. Informational [Page 26] RFC 2702 MPLS Traffic Engineering September 1999

11.0 Acknowledgments

 The authors would like to thank Yakov Rekhter for his review of an
 earlier draft of this document. The authors would also like to thank
 Louis Mamakos and Bill Barns for their helpful suggestions, and
 Curtis Villamizar for providing some useful feedback.

Awduche, et al. Informational [Page 27] RFC 2702 MPLS Traffic Engineering September 1999

12.0 Authors' Addresses

 Daniel O. Awduche
 UUNET (MCI Worldcom)
 3060 Williams Drive
 Fairfax, VA 22031
 Phone: +1 703-208-5277
 EMail: awduche@uu.net
 Joe Malcolm
 UUNET  (MCI Worldcom)
 3060 Williams Drive
 Fairfax, VA 22031
 Phone: +1 703-206-5895
 EMail: jmalcolm@uu.net
 Johnson Agogbua
 UUNET  (MCI Worldcom)
 3060 Williams Drive
 Fairfax, VA 22031
 Phone: +1 703-206-5794
 EMail: ja@uu.net
 Mike O'Dell
 UUNET  (MCI Worldcom)
 3060 Williams Drive
 Fairfax, VA 22031
 Phone: +1 703-206-5890
 EMail: mo@uu.net
 Jim McManus
 UUNET  (MCI Worldcom)
 3060 Williams Drive
 Fairfax, VA 22031
 Phone: +1 703-206-5607
 EMail: jmcmanus@uu.net

Awduche, et al. Informational [Page 28] RFC 2702 MPLS Traffic Engineering September 1999

13.0 Full Copyright Statement

 Copyright (C) The Internet Society (1999).  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.

Awduche, et al. Informational [Page 29]

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