6.0 Recommendations for Internet Traffic Engineering

   This section describes high level recommendations for traffic
   engineering in the Internet.  These recommendations are presented in
   general terms.

   The recommendations describe the capabilities needed to solve a
   traffic engineering problem or to achieve a traffic engineering
   objective.  Broadly speaking, these recommendations can be
   categorized as either functional and non-functional recommendations.

   Functional recommendations for Internet traffic engineering describe
   the functions that a traffic engineering system should perform.
   These functions are needed to realize traffic engineering objectives
   by addressing traffic engineering problems.

   Non-functional recommendations for Internet traffic engineering
   relate to the quality attributes or state characteristics of a
   traffic engineering system.  These recommendations may contain
   conflicting assertions and may sometimes be difficult to quantify
   precisely.

6.1 Generic Non-functional Recommendations

   The generic non-functional recommendations for Internet traffic
   engineering include: usability, automation, scalability, stability,
   visibility, simplicity, efficiency, reliability, correctness,
   maintainability, extensibility, interoperability, and security.  In a
   given context, some of these recommendations may be critical while
   others may be optional.  Therefore, prioritization may be required
   during the development phase of a traffic engineering system (or
   components thereof) to tailor it to a specific operational context.

   In the following paragraphs, some of the aspects of the non-
   functional recommendations for Internet traffic engineering are
   summarized.

   Usability: Usability is a human factor aspect of traffic engineering
   systems.  Usability refers to the ease with which a traffic
   engineering system can be deployed and operated.  In general, it is
   desirable to have a TE system that can be readily deployed in an
   existing network.  It is also desirable to have a TE system that is
   easy to operate and maintain.

   Automation: Whenever feasible, a traffic engineering system should
   automate as many traffic engineering functions as possible to
   minimize the amount of human effort needed to control and analyze
   operational networks.  Automation is particularly imperative in large
   scale public networks because of the high cost of the human aspects
   of network operations and the high risk of network problems caused by
   human errors.  Automation may entail the incorporation of automatic
   feedback and intelligence into some components of the traffic
   engineering system.

   Scalability: Contemporary public networks are growing very fast with
   respect to network size and traffic volume.  Therefore, a TE system
   should be scalable to remain applicable as the network evolves.  In
   particular, a TE system should remain functional as the network
   expands with regard to the number of routers and links, and with

   respect to the traffic volume.  A TE system should have a scalable
   architecture, should not adversely impair other functions and
   processes in a network element, and should not consume too much
   network resources when collecting and distributing state information
   or when exerting control.

   Stability: Stability is a very important consideration in traffic
   engineering systems that respond to changes in the state of the
   network.  State-dependent traffic engineering methodologies typically
   mandate a tradeoff between responsiveness and stability.  It is
   strongly recommended that when tradeoffs are warranted between
   responsiveness and stability, that the tradeoff should be made in
   favor of stability (especially in public IP backbone networks).

   Flexibility: A TE system should be flexible to allow for changes in
   optimization policy.  In particular, a TE system should provide
   sufficient configuration options so that a network administrator can
   tailor the TE system to a particular environment.  It may also be
   desirable to have both online and offline TE subsystems which can be
   independently enabled and disabled.  TE systems that are used in
   multi-class networks should also have options to support class based
   performance evaluation and optimization.

   Visibility: As part of the TE system, mechanisms should exist to
   collect statistics from the network and to analyze these statistics
   to determine how well the network is functioning.  Derived statistics
   such as traffic matrices, link utilization, latency, packet loss, and
   other performance measures of interest which are determined from
   network measurements can be used as indicators of prevailing network
   conditions.  Other examples of status information which should be
   observed include existing functional routing information
   (additionally, in the context of MPLS existing LSP routes), etc.

   Simplicity: Generally, a TE system should be as simple as possible.
   More importantly, the TE system should be relatively easy to use
   (i.e., clean, convenient, and intuitive user interfaces).  Simplicity
   in user interface does not necessarily imply that the TE system will
   use naive algorithms.  When complex algorithms and internal
   structures are used, such complexities should be hidden as much as
   possible from the network administrator through the user interface.

   Interoperability: Whenever feasible, traffic engineering systems and
   their components should be developed with open standards based
   interfaces to allow interoperation with other systems and components.

   Security: Security is a critical consideration in traffic engineering
   systems.  Such traffic engineering systems typically exert control
   over certain functional aspects of the network to achieve the desired

   performance objectives.  Therefore, adequate measures must be taken
   to safeguard the integrity of the traffic engineering system.
   Adequate measures must also be taken to protect the network from
   vulnerabilities that originate from security breaches and other
   impairments within the traffic engineering system.

   The remainder of this section will focus on some of the high level
   functional recommendations for traffic engineering.

6.2 Routing Recommendations

   Routing control is a significant aspect of Internet traffic
   engineering.  Routing impacts many of the key performance measures
   associated with networks, such as throughput, delay, and utilization.
   Generally, it is very difficult to provide good service quality in a
   wide area network without effective routing control.  A desirable
   routing system is one that takes traffic characteristics and network
   constraints into account during route selection while maintaining
   stability.

   Traditional shortest path first (SPF) interior gateway protocols are
   based on shortest path algorithms and have limited control
   capabilities for traffic engineering [RFC-2702, AWD2].  These
   limitations include :

   1. The well known issues with pure SPF protocols, which do not take
      network constraints and traffic characteristics into account
      during route selection.  For example, since IGPs always use the
      shortest paths (based on administratively assigned link metrics)
      to forward traffic, load sharing cannot be accomplished among
      paths of different costs.  Using shortest paths to forward traffic
      conserves network resources, but may cause the following problems:
      1) If traffic from a source to a destination exceeds the capacity
      of a link along the shortest path, the link (hence the shortest
      path) becomes congested while a longer path between these two
      nodes may be under-utilized; 2) the shortest paths from different
      sources can overlap at some links.  If the total traffic from the
      sources exceeds the capacity of any of these links, congestion
      will occur.  Problems can also occur because traffic demand
      changes over time but network topology and routing configuration
      cannot be changed as rapidly.  This causes the network topology
      and routing configuration to become sub-optimal over time, which
      may result in persistent congestion problems.

   2. The Equal-Cost Multi-Path (ECMP) capability of SPF IGPs supports
      sharing of traffic among equal cost paths between two nodes.
      However, ECMP attempts to divide the traffic as equally as
      possible among the equal cost shortest paths.  Generally, ECMP

      does not support configurable load sharing ratios among equal cost
      paths.  The result is that one of the paths may carry
      significantly more traffic than other paths because it may also
      carry traffic from other sources.  This situation can result in
      congestion along the path that carries more traffic.

   3. Modifying IGP metrics to control traffic routing tends to have
      network-wide effect.  Consequently, undesirable and unanticipated
      traffic shifts can be triggered as a result.  Recent work
      described in Section 8.0 may be capable of better control [FT00,
      FT01].

   Because of these limitations, new capabilities are needed to enhance
   the routing function in IP networks.  Some of these capabilities have
   been described elsewhere and are summarized below.

   Constraint-based routing is desirable to evolve the routing
   architecture of IP networks, especially public IP backbones with
   complex topologies [RFC-2702].  Constraint-based routing computes
   routes to fulfill requirements subject to constraints.  Constraints
   may include bandwidth, hop count, delay, and administrative policy
   instruments such as resource class attributes [RFC-2702, RFC-2386].
   This makes it possible to select routes that satisfy a given set of
   requirements subject to network and administrative policy
   constraints.  Routes computed through constraint-based routing are
   not necessarily the shortest paths.  Constraint-based routing works
   best with path oriented technologies that support explicit routing,
   such as MPLS.

   Constraint-based routing can also be used as a way to redistribute
   traffic onto the infrastructure (even for best effort traffic).  For
   example, if the bandwidth requirements for path selection and
   reservable bandwidth attributes of network links are appropriately
   defined and configured, then congestion problems caused by uneven
   traffic distribution may be avoided or reduced.  In this way, the
   performance and efficiency of the network can be improved.

   A number of enhancements are needed to conventional link state IGPs,
   such as OSPF and IS-IS, to allow them to distribute additional state
   information required for constraint-based routing.  These extensions
   to OSPF were described in [KATZ] and to IS-IS in [SMIT].
   Essentially, these enhancements require the propagation of additional
   information in link state advertisements.  Specifically, in addition
   to normal link-state information, an enhanced IGP is required to
   propagate topology state information needed for constraint-based
   routing.  Some of the additional topology state information include
   link attributes such as reservable bandwidth and link resource class
   attribute (an administratively specified property of the link).  The

   resource class attribute concept was defined in [RFC-2702].  The
   additional topology state information is carried in new TLVs and
   sub-TLVs in IS-IS, or in the Opaque LSA in OSPF [SMIT, KATZ].

   An enhanced link-state IGP may flood information more frequently than
   a normal IGP.  This is because even without changes in topology,
   changes in reservable bandwidth or link affinity can trigger the
   enhanced IGP to initiate flooding.  A tradeoff is typically required
   between the timeliness of the information flooded and the flooding
   frequency to avoid excessive consumption of link bandwidth and
   computational resources, and more importantly, to avoid instability.

   In a TE system, it is also desirable for the routing subsystem to
   make the load splitting ratio among multiple paths (with equal cost
   or different cost) configurable.  This capability gives network
   administrators more flexibility in the control of traffic
   distribution across the network.  It can be very useful for
   avoiding/relieving congestion in certain situations.  Examples can be
   found in [XIAO].

   The routing system should also have the capability to control the
   routes of subsets of traffic without affecting the routes of other
   traffic if sufficient resources exist for this purpose.  This
   capability allows a more refined control over the distribution of
   traffic across the network.  For example, the ability to move traffic
   from a source to a destination away from its original path to another
   path (without affecting other traffic paths) allows traffic to be
   moved from resource-poor network segments to resource-rich segments.
   Path oriented technologies such as MPLS inherently support this
   capability as discussed in [AWD2].

   Additionally, the routing subsystem should be able to select
   different paths for different classes of traffic (or for different
   traffic behavior aggregates) if the network supports multiple classes
   of service (different behavior aggregates).

6.3 Traffic Mapping Recommendations

   Traffic mapping pertains to the assignment of traffic workload onto
   pre-established paths to meet certain requirements.  Thus, while
   constraint-based routing deals with path selection, traffic mapping
   deals with the assignment of traffic to established paths which may
   have been selected by constraint-based routing or by some other
   means.  Traffic mapping can be performed by time-dependent or state-
   dependent mechanisms, as described in Section 5.1.

   An important aspect of the traffic mapping function is the ability to
   establish multiple paths between an originating node and a
   destination node, and the capability to distribute the traffic
   between the two nodes across the paths according to some policies.  A
   pre-condition for this scheme is the existence of flexible mechanisms
   to partition traffic and then assign the traffic partitions onto the
   parallel paths.  This requirement was noted in [RFC-2702].  When
   traffic is assigned to multiple parallel paths, it is recommended
   that special care should be taken to ensure proper ordering of
   packets belonging to the same application (or micro-flow) at the
   destination node of the parallel paths.

   As a general rule, mechanisms that perform the traffic mapping
   functions should aim to map the traffic onto the network
   infrastructure to minimize congestion.  If the total traffic load
   cannot be accommodated, or if the routing and mapping functions
   cannot react fast enough to changing traffic conditions, then a
   traffic mapping system may rely on short time scale congestion
   control mechanisms (such as queue management, scheduling, etc.) to
   mitigate congestion.  Thus, mechanisms that perform the traffic
   mapping functions should complement existing congestion control
   mechanisms.  In an operational network, it is generally desirable to
   map the traffic onto the infrastructure such that intra-class and
   inter-class resource contention are minimized.

   When traffic mapping techniques that depend on dynamic state feedback
   (e.g., MATE and such like) are used, special care must be taken to
   guarantee network stability.

6.4 Measurement Recommendations

   The importance of measurement in traffic engineering has been
   discussed throughout this document.  Mechanisms should be provided to
   measure and collect statistics from the network to support the
   traffic engineering function.  Additional capabilities may be needed
   to help in the analysis of the statistics.  The actions of these
   mechanisms should not adversely affect the accuracy and integrity of
   the statistics collected.  The mechanisms for statistical data
   acquisition should also be able to scale as the network evolves.

   Traffic statistics may be classified according to long-term or
   short-term time scales.  Long-term time scale traffic statistics are
   very useful for traffic engineering.  Long-term time scale traffic
   statistics may capture or reflect periodicity in network workload
   (such as hourly, daily, and weekly variations in traffic profiles) as
   well as traffic trends.  Aspects of the monitored traffic statistics
   may also depict class of service characteristics for a network
   supporting multiple classes of service.  Analysis of the long-term

   traffic statistics MAY yield secondary statistics such as busy hour
   characteristics, traffic growth patterns, persistent congestion
   problems, hot-spot, and imbalances in link utilization caused by
   routing anomalies.

   A mechanism for constructing traffic matrices for both long-term and
   short-term traffic statistics should be in place.  In multi-service
   IP networks, the traffic matrices may be constructed for different
   service classes.  Each element of a traffic matrix represents a
   statistic of traffic flow between a pair of abstract nodes.  An
   abstract node may represent a router, a collection of routers, or a
   site in a VPN.

   Measured traffic statistics should provide reasonable and reliable
   indicators of the current state of the network on the short-term
   scale.  Some short term traffic statistics may reflect link
   utilization and link congestion status.  Examples of congestion
   indicators include excessive packet delay, packet loss, and high
   resource utilization.  Examples of mechanisms for distributing this
   kind of information include SNMP, probing techniques, FTP, IGP link
   state advertisements, etc.

6.5 Network Survivability

   Network survivability refers to the capability of a network to
   maintain service continuity in the presence of faults.  This can be
   accomplished by promptly recovering from network impairments and
   maintaining the required QoS for existing services after recovery.
   Survivability has become an issue of great concern within the
   Internet community due to the increasing demands to carry mission
   critical traffic, real-time traffic, and other high priority traffic
   over the Internet.  Survivability can be addressed at the device
   level by developing network elements that are more reliable; and at
   the network level by incorporating redundancy into the architecture,
   design, and operation of networks.  It is recommended that a
   philosophy of robustness and survivability should be adopted in the
   architecture, design, and operation of traffic engineering that
   control IP networks (especially public IP networks).  Because
   different contexts may demand different levels of survivability, the
   mechanisms developed to support network survivability should be
   flexible so that they can be tailored to different needs.

   Failure protection and restoration capabilities have become available
   from multiple layers as network technologies have continued to
   improve.  At the bottom of the layered stack, optical networks are
   now capable of providing dynamic ring and mesh restoration
   functionality at the wavelength level as well as traditional
   protection functionality.  At the SONET/SDH layer survivability

   capability is provided with Automatic Protection Switching (APS) as
   well as self-healing ring and mesh architectures.  Similar
   functionality is provided by layer 2 technologies such as ATM
   (generally with slower mean restoration times).  Rerouting is
   traditionally used at the IP layer to restore service following link
   and node outages.  Rerouting at the IP layer occurs after a period of
   routing convergence which may require seconds to minutes to complete.
   Some new developments in the MPLS context make it possible to achieve
   recovery at the IP layer prior to convergence [SHAR].

   To support advanced survivability requirements, path-oriented
   technologies such a MPLS can be used to enhance the survivability of
   IP networks in a potentially cost effective manner.  The advantages
   of path oriented technologies such as MPLS for IP restoration becomes
   even more evident when class based protection and restoration
   capabilities are required.

   Recently, a common suite of control plane protocols has been proposed
   for both MPLS and optical transport networks under the acronym
   Multi-protocol Lambda Switching [AWD1].  This new paradigm of Multi-
   protocol Lambda Switching will support even more sophisticated mesh
   restoration capabilities at the optical layer for the emerging IP
   over WDM network architectures.

   Another important aspect regarding multi-layer survivability is that
   technologies at different layers provide protection and restoration
   capabilities at different temporal granularities (in terms of time
   scales) and at different bandwidth granularity (from packet-level to
   wavelength level).  Protection and restoration capabilities can also
   be sensitive to different service classes and different network
   utility models.

   The impact of service outages varies significantly for different
   service classes depending upon the effective duration of the outage.
   The duration of an outage can vary from milliseconds (with minor
   service impact) to seconds (with possible call drops for IP telephony
   and session time-outs for connection oriented transactions) to
   minutes and hours (with potentially considerable social and business
   impact).

   Coordinating different protection and restoration capabilities across
   multiple layers in a cohesive manner to ensure network survivability
   is maintained at reasonable cost is a challenging task.  Protection
   and restoration coordination across layers may not always be
   feasible, because networks at different layers may belong to
   different administrative domains.

   The following paragraphs present some of the general recommendations
   for protection and restoration coordination.

   -  Protection and restoration capabilities from different layers
   should be coordinated whenever feasible and appropriate to provide
   network survivability in a flexible and cost effective manner.
   Minimization of function duplication across layers is one way to
   achieve the coordination.  Escalation of alarms and other fault
   indicators from lower to higher layers may also be performed in a
   coordinated manner.  A temporal order of restoration trigger timing
   at different layers is another way to coordinate multi-layer
   protection/restoration.

   -  Spare capacity at higher layers is often regarded as working
   traffic at lower layers.  Placing protection/restoration functions in
   many layers may increase redundancy and robustness, but it should not
   result in significant and avoidable inefficiencies in network
   resource utilization.

   -  It is generally desirable to have protection and restoration
   schemes that are bandwidth efficient.

   -  Failure notification throughout the network should be timely and
   reliable.

   -  Alarms and other fault monitoring and reporting capabilities
   should be provided at appropriate layers.

6.5.1 Survivability in MPLS Based Networks

   MPLS is an important emerging technology that enhances IP networks in
   terms of features, capabilities, and services.  Because MPLS is
   path-oriented, it can potentially provide faster and more predictable
   protection and restoration capabilities than conventional hop by hop
   routed IP systems.  This subsection describes some of the basic
   aspects and recommendations for MPLS networks regarding protection
   and restoration.  See [SHAR] for a more comprehensive discussion on
   MPLS based recovery.

   Protection types for MPLS networks can be categorized as link
   protection, node protection, path protection, and segment protection.

   -  Link Protection: The objective for link protection is to protect
      an LSP from a given link failure.  Under link protection, the path
      of the protection or backup LSP (the secondary LSP) is disjoint
      from the path of the working or operational LSP at the particular
      link over which protection is required.  When the protected link
      fails, traffic on the working LSP is switched over to the

      protection LSP at the head-end of the failed link.  This is a
      local repair method which can be fast.  It might be more
      appropriate in situations where some network elements along a
      given path are less reliable than others.

   -  Node Protection: The objective of LSP node protection is to
      protect an LSP from a given node failure.  Under node protection,
      the path of the protection LSP is disjoint from the path of the
      working LSP at the particular node to be protected.  The secondary
      path is also disjoint from the primary path at all links
      associated with the node to be protected.  When the node fails,
      traffic on the working LSP is switched over to the protection LSP
      at the upstream LSR directly connected to the failed node.

   -  Path Protection: The goal of LSP path protection is to protect an
      LSP from failure at any point along its routed path.  Under path
      protection, the path of the protection LSP is completely disjoint
      from the path of the working LSP.  The advantage of path
      protection is that the backup LSP protects the working LSP from
      all possible link and node failures along the path, except for
      failures that might occur at the ingress and egress LSRs, or for
      correlated failures that might impact both working and backup
      paths simultaneously.  Additionally, since the path selection is
      end-to-end, path protection might be more efficient in terms of
      resource usage than link or node protection.  However, path
      protection may be slower than link and node protection in general.

   -  Segment Protection: An MPLS domain may be partitioned into
      multiple protection domains whereby a failure in a protection
      domain is rectified within that domain.  In cases where an LSP
      traverses multiple protection domains, a protection mechanism
      within a domain only needs to protect the segment of the LSP that
      lies within the domain.  Segment protection will generally be
      faster than path protection because recovery generally occurs
      closer to the fault.

6.5.2 Protection Option

   Another issue to consider is the concept of protection options.  The
   protection option uses the notation m:n protection, where m is the
   number of protection LSPs used to protect n working LSPs.  Feasible
   protection options follow.

   -  1:1: one working LSP is protected/restored by one protection LSP.

   -  1:n: one protection LSP is used to protect/restore n working LSPs.

   -  n:1: one working LSP is protected/restored by n protection LSPs,
      possibly with configurable load splitting ratio.  When more than
      one protection LSP is used, it may be desirable to share the
      traffic across the protection LSPs when the working LSP fails to
      satisfy the bandwidth requirement of the traffic trunk associated
      with the working LSP.  This may be especially useful when it is
      not feasible to find one path that can satisfy the bandwidth
      requirement of the primary LSP.

   -  1+1: traffic is sent concurrently on both the working LSP and the
      protection LSP.  In this case, the egress LSR selects one of the
      two LSPs based on a local traffic integrity decision process,
      which compares the traffic received from both the working and the
      protection LSP and identifies discrepancies.  It is unlikely that
      this option would be used extensively in IP networks due to its
      resource utilization inefficiency.  However, if bandwidth becomes
      plentiful and cheap, then this option might become quite viable
      and attractive in IP networks.

6.6 Traffic Engineering in Diffserv Environments

   This section provides an overview of the traffic engineering features
   and recommendations that are specifically pertinent to Differentiated
   Services (Diffserv) [RFC-2475] capable IP networks.

   Increasing requirements to support multiple classes of traffic, such
   as best effort and mission critical data, in the Internet calls for
   IP networks to differentiate traffic according to some criteria, and
   to accord preferential treatment to certain types of traffic.  Large
   numbers of flows can be aggregated into a few behavior aggregates
   based on some criteria in terms of common performance requirements in
   terms of packet loss ratio, delay, and jitter; or in terms of common
   fields within the IP packet headers.

   As Diffserv evolves and becomes deployed in operational networks,
   traffic engineering will be critical to ensuring that SLAs defined
   within a given Diffserv service model are met.  Classes of service
   (CoS) can be supported in a Diffserv environment by concatenating
   per-hop behaviors (PHBs) along the routing path, using service
   provisioning mechanisms, and by appropriately configuring edge
   functionality such as traffic classification, marking, policing, and
   shaping.  PHB is the forwarding behavior that a packet receives at a
   DS node (a Diffserv-compliant node).  This is accomplished by means
   of buffer management and packet scheduling mechanisms.  In this
   context, packets belonging to a class are those that are members of a
   corresponding ordering aggregate.

   Traffic engineering can be used as a compliment to Diffserv
   mechanisms to improve utilization of network resources, but not as a
   necessary element in general.  When traffic engineering is used, it
   can be operated on an aggregated basis across all service classes
   [RFC-3270] or on a per service class basis.  The former is used to
   provide better distribution of the aggregate traffic load over the
   network resources.  (See [RFC-3270] for detailed mechanisms to
   support aggregate traffic engineering.)  The latter case is discussed
   below since it is specific to the Diffserv environment, with so
   called Diffserv-aware traffic engineering [DIFF_TE].

   For some Diffserv networks, it may be desirable to control the
   performance of some service classes by enforcing certain
   relationships between the traffic workload contributed by each
   service class and the amount of network resources allocated or
   provisioned for that service class.  Such relationships between
   demand and resource allocation can be enforced using a combination
   of, for example: (1) traffic engineering mechanisms on a per service
   class basis that enforce the desired relationship between the amount
   of traffic contributed by a given service class and the resources
   allocated to that class, and (2) mechanisms that dynamically adjust
   the resources allocated to a given service class to relate to the
   amount of traffic contributed by that service class.

   It may also be desirable to limit the performance impact of high
   priority traffic on relatively low priority traffic.  This can be
   achieved by, for example, controlling the percentage of high priority
   traffic that is routed through a given link.  Another way to
   accomplish this is to increase link capacities appropriately so that
   lower priority traffic can still enjoy adequate service quality.
   When the ratio of traffic workload contributed by different service
   classes vary significantly from router to router, it may not suffice
   to rely exclusively on conventional IGP routing protocols or on
   traffic engineering mechanisms that are insensitive to different
   service classes.  Instead, it may be desirable to perform traffic
   engineering, especially routing control and mapping functions, on a
   per service class basis.  One way to accomplish this in a domain that
   supports both MPLS and Diffserv is to define class specific LSPs and
   to map traffic from each class onto one or more LSPs that correspond
   to that service class.  An LSP corresponding to a given service class
   can then be routed and protected/restored in a class dependent
   manner, according to specific policies.

   Performing traffic engineering on a per class basis may require
   certain per-class parameters to be distributed.  Note that it is
   common to have some classes share some aggregate constraint (e.g.,
   maximum bandwidth requirement) without enforcing the constraint on
   each individual class.  These classes then can be grouped into a

   class-type and per-class-type parameters can be distributed instead
   to improve scalability.  It also allows better bandwidth sharing
   between classes in the same class-type.  A class-type is a set of
   classes that satisfy the following two conditions:

   1) Classes in the same class-type have common aggregate requirements
   to satisfy required performance levels.

   2) There is no requirement to be enforced at the level of individual
   class in the class-type.  Note that it is still possible,
   nevertheless, to implement some priority policies for classes in the
   same class-type to permit preferential access to the class-type
   bandwidth through the use of preemption priorities.

   An example of the class-type can be a low-loss class-type that
   includes both AF1-based and AF2-based Ordering Aggregates.  With such
   a class-type, one may implement some priority policy which assigns
   higher preemption priority to AF1-based traffic trunks over AF2-based
   ones, vice versa, or the same priority.

   See [DIFF-TE] for detailed requirements on Diffserv-aware traffic
   engineering.

6.7 Network Controllability

   Off-line (and on-line) traffic engineering considerations would be of
   limited utility if the network could not be controlled effectively to
   implement the results of TE decisions and to achieve desired network
   performance objectives.  Capacity augmentation is a coarse grained
   solution to traffic engineering issues.  However, it is simple and
   may be advantageous if bandwidth is abundant and cheap or if the
   current or expected network workload demands it.  However, bandwidth
   is not always abundant and cheap, and the workload may not always
   demand additional capacity.  Adjustments of administrative weights
   and other parameters associated with routing protocols provide finer
   grained control, but is difficult to use and imprecise because of the
   routing interactions that occur across the network.  In certain
   network contexts, more flexible, finer grained approaches which
   provide more precise control over the mapping of traffic to routes
   and over the selection and placement of routes may be appropriate and
   useful.

   Control mechanisms can be manual (e.g., administrative
   configuration), partially-automated (e.g., scripts) or fully-
   automated (e.g., policy based management systems).  Automated
   mechanisms are particularly required in large scale networks.
   Multi-vendor interoperability can be facilitated by developing and
   deploying standardized management

   systems (e.g., standard MIBs) and policies (PIBs) to support the
   control functions required to address traffic engineering objectives
   such as load distribution and protection/restoration.

   Network control functions should be secure, reliable, and stable as
   these are often needed to operate correctly in times of network
   impairments (e.g., during network congestion or security attacks).

7.0 Inter-Domain Considerations

   Inter-domain traffic engineering is concerned with the performance
   optimization for traffic that originates in one administrative domain
   and terminates in a different one.

   Traffic exchange between autonomous systems in the Internet occurs
   through exterior gateway protocols.  Currently, BGP [BGP4] is the
   standard exterior gateway protocol for the Internet.  BGP provides a
   number of attributes and capabilities (e.g., route filtering) that
   can be used for inter-domain traffic engineering.  More specifically,
   BGP permits the control of routing information and traffic exchange
   between Autonomous Systems (AS's) in the Internet.  BGP incorporates
   a sequential decision process which calculates the degree of
   preference for various routes to a given destination network.  There
   are two fundamental aspects to inter-domain traffic engineering using
   BGP:

   -  Route Redistribution: controlling the import and export of routes
      between AS's, and controlling the redistribution of routes between
      BGP and other protocols within an AS.

   -  Best path selection: selecting the best path when there are
      multiple candidate paths to a given destination network.  Best
      path selection is performed by the BGP decision process based on a
      sequential procedure, taking a number of different considerations
      into account.  Ultimately, best path selection under BGP boils
      down to selecting preferred exit points out of an AS towards
      specific destination networks.  The BGP path selection process can
      be influenced by manipulating the attributes associated with the
      BGP decision process.  These attributes include: NEXT-HOP, WEIGHT
      (Cisco proprietary which is also implemented by some other
      vendors), LOCAL-PREFERENCE, AS-PATH, ROUTE-ORIGIN, MULTI-EXIT-
      DESCRIMINATOR (MED), IGP METRIC, etc.

   Route-maps provide the flexibility to implement complex BGP policies
   based on pre-configured logical conditions.  In particular, Route-
   maps can be used to control import and export policies for incoming
   and outgoing routes, control the redistribution of routes between BGP
   and other protocols, and influence the selection of best paths by

   manipulating the attributes associated with the BGP decision process.
   Very complex logical expressions that implement various types of
   policies can be implemented using a combination of Route-maps, BGP-
   attributes, Access-lists, and Community attributes.

   When looking at possible strategies for inter-domain TE with BGP, it
   must be noted that the outbound traffic exit point is controllable,
   whereas the interconnection point where inbound traffic is received
   from an EBGP peer typically is not, unless a special arrangement is
   made with the peer sending the traffic.  Therefore, it is up to each
   individual network to implement sound TE strategies that deal with
   the efficient delivery of outbound traffic from one's customers to
   one's peering points.  The vast majority of TE policy is based upon a
   "closest exit" strategy, which offloads interdomain traffic at the
   nearest outbound peer point towards the destination autonomous
   system.  Most methods of manipulating the point at which inbound
   traffic enters a network from an EBGP peer (inconsistent route
   announcements between peering points, AS pre-pending, and sending
   MEDs) are either ineffective, or not accepted in the peering
   community.

   Inter-domain TE with BGP is generally effective, but it is usually
   applied in a trial-and-error fashion.  A systematic approach for
   inter-domain traffic engineering is yet to be devised.

   Inter-domain TE is inherently more difficult than intra-domain TE
   under the current Internet architecture.  The reasons for this are
   both technical and administrative.  Technically, while topology and
   link state information are helpful for mapping traffic more
   effectively, BGP does not propagate such information across domain
   boundaries for stability and scalability reasons.  Administratively,
   there are differences in operating costs and network capacities
   between domains.  Generally, what may be considered a good solution
   in one domain may not necessarily be a good solution in another
   domain.  Moreover, it would generally be considered inadvisable for
   one domain to permit another domain to influence the routing and
   management of traffic in its network.

   MPLS TE-tunnels (explicit LSPs) can potentially add a degree of
   flexibility in the selection of exit points for inter-domain routing.
   The concept of relative and absolute metrics can be applied to this
   purpose.  The idea is that if BGP attributes are defined such that
   the BGP decision process depends on IGP metrics to select exit points
   for inter-domain traffic, then some inter-domain traffic destined to
   a given peer network can be made to prefer a specific exit point by
   establishing a TE-tunnel between the router making the selection to
   the peering point via a TE-tunnel and assigning the TE-tunnel a
   metric which is smaller than the IGP cost to all other peering

   points.  If a peer accepts and processes MEDs, then a similar MPLS
   TE-tunnel based scheme can be applied to cause certain entrance
   points to be preferred by setting MED to be an IGP cost, which has
   been modified by the tunnel metric.

   Similar to intra-domain TE, inter-domain TE is best accomplished when
   a traffic matrix can be derived to depict the volume of traffic from
   one autonomous system to another.

   Generally, redistribution of inter-domain traffic requires
   coordination between peering partners.  An export policy in one
   domain that results in load redistribution across peer points with
   another domain can significantly affect the local traffic matrix
   inside the domain of the peering partner.  This, in turn, will affect
   the intra-domain TE due to changes in the spatial distribution of
   traffic.  Therefore, it is mutually beneficial for peering partners
   to coordinate with each other before attempting any policy changes
   that may result in significant shifts in inter-domain traffic.  In
   certain contexts, this coordination can be quite challenging due to
   technical and non- technical reasons.

   It is a matter of speculation as to whether MPLS, or similar
   technologies, can be extended to allow selection of constrained paths
   across domain boundaries.

8.0 Overview of Contemporary TE Practices in Operational IP Networks

   This section provides an overview of some contemporary traffic
   engineering practices in IP networks.  The focus is primarily on the
   aspects that pertain to the control of the routing function in
   operational contexts.  The intent here is to provide an overview of
   the commonly used practices.  The discussion is not intended to be
   exhaustive.

   Currently, service providers apply many of the traffic engineering
   mechanisms discussed in this document to optimize the performance of
   their IP networks.  These techniques include capacity planning for
   long time scales, routing control using IGP metrics and MPLS for
   medium time scales, the overlay model also for medium time scales,
   and traffic management mechanisms for short time scale.

   When a service provider plans to build an IP network, or expand the
   capacity of an existing network, effective capacity planning should
   be an important component of the process.  Such plans may take the
   following aspects into account: location of new nodes if any,
   existing and predicted traffic patterns, costs, link capacity,
   topology, routing design, and survivability.

   Performance optimization of operational networks is usually an
   ongoing process in which traffic statistics, performance parameters,
   and fault indicators are continually collected from the network.
   This empirical data is then analyzed and used to trigger various
   traffic engineering mechanisms.  Tools that perform what-if analysis
   can also be used to assist the TE process by allowing various
   scenarios to be reviewed before a new set of configurations are
   implemented in the operational network.

   Traditionally, intra-domain real-time TE with IGP is done by
   increasing the OSPF or IS-IS metric of a congested link until enough
   traffic has been diverted from that link.  This approach has some
   limitations as discussed in Section 6.2.  Recently, some new intra-
   domain TE approaches/tools have been proposed
   [RR94][FT00][FT01][WANG].  Such approaches/tools take traffic matrix,
   network topology, and network performance objective(s) as input, and
   produce some link metrics and possibly some unequal load-sharing
   ratios to be set at the head-end routers of some ECMPs as output.
   These new progresses open new possibility for intra-domain TE with
   IGP to be done in a more systematic way.

   The overlay model (IP over ATM or IP over Frame relay) is another
   approach which is commonly used in practice [AWD2].  The IP over ATM
   technique is no longer viewed favorably due to recent advances in
   MPLS and router hardware technology.

   Deployment of MPLS for traffic engineering applications has commenced
   in some service provider networks.  One operational scenario is to
   deploy MPLS in conjunction with an IGP (IS-IS-TE or OSPF-TE) that
   supports the traffic engineering extensions, in conjunction with
   constraint-based routing for explicit route computations, and a
   signaling protocol (e.g., RSVP-TE or CRLDP) for LSP instantiation.

   In contemporary MPLS traffic engineering contexts, network
   administrators specify and configure link attributes and resource
   constraints such as maximum reservable bandwidth and resource class
   attributes for links (interfaces) within the MPLS domain.  A link
   state protocol that supports TE extensions (IS-IS-TE or OSPF-TE) is
   used to propagate information about network topology and link
   attribute to all routers in the routing area.  Network administrators
   also specify all the LSPs that are to originate each router.  For
   each LSP, the network administrator specifies the destination node
   and the attributes of the LSP which indicate the requirements that to
   be satisfied during the path selection process.  Each router then
   uses a local constraint-based routing process to compute explicit
   paths for all LSPs originating from it.  Subsequently, a signaling

   protocol is used to instantiate the LSPs.  By assigning proper
   bandwidth values to links and LSPs, congestion caused by uneven
   traffic distribution can generally be avoided or mitigated.

   The bandwidth attributes of LSPs used for traffic engineering can be
   updated periodically.  The basic concept is that the bandwidth
   assigned to an LSP should relate in some manner to the bandwidth
   requirements of traffic that actually flows through the LSP.  The
   traffic attribute of an LSP can be modified to accommodate traffic
   growth and persistent traffic shifts.  If network congestion occurs
   due to some unexpected events, existing LSPs can be rerouted to
   alleviate the situation or network administrator can configure new
   LSPs to divert some traffic to alternative paths.  The reservable
   bandwidth of the congested links can also be reduced to force some
   LSPs to be rerouted to other paths.

   In an MPLS domain, a traffic matrix can also be estimated by
   monitoring the traffic on LSPs.  Such traffic statistics can be used
   for a variety of purposes including network planning and network
   optimization.  Current practice suggests that deploying an MPLS
   network consisting of hundreds of routers and thousands of LSPs is
   feasible.  In summary, recent deployment experience suggests that
   MPLS approach is very effective for traffic engineering in IP
   networks [XIAO].

   As mentioned previously in Section 7.0, one usually has no direct
   control over the distribution of inbound traffic.  Therefore, the
   main goal of contemporary inter-domain TE is to optimize the
   distribution of outbound traffic between multiple inter-domain links.
   When operating a global network, maintaining the ability to operate
   the network in a regional fashion where desired, while continuing to
   take advantage of the benefits of a global network, also becomes an
   important objective.

   Inter-domain TE with BGP usually begins with the placement of
   multiple peering interconnection points in locations that have high
   peer density, are in close proximity to originating/terminating
   traffic locations on one's own network, and are lowest in cost.
   There are generally several locations in each region of the world
   where the vast majority of major networks congregate and
   interconnect.  Some location-decision problems that arise in
   association with inter-domain routing are discussed in [AWD5].

   Once the locations of the interconnects are determined, and circuits
   are implemented, one decides how best to handle the routes heard from
   the peer, as well as how to propagate the peers' routes within one's
   own network.  One way to engineer outbound traffic flows on a network
   with many EBGP peers is to create a hierarchy of peers.  Generally,

   the Local Preferences of all peers are set to the same value so that
   the shortest AS paths will be chosen to forward traffic.  Then, by
   over-writing the inbound MED metric (Multi-exit-discriminator metric,
   also referred to as "BGP metric".  Both terms are used
   interchangeably in this document) with BGP metrics to routes received
   at different peers, the hierarchy can be formed.  For example, all
   Local Preferences can be set to 200, preferred private peers can be
   assigned a BGP metric of 50, the rest of the private peers can be
   assigned a BGP metric of 100, and public peers can be assigned a BGP
   metric of 600.  "Preferred" peers might be defined as those peers
   with whom the most available capacity exists, whose customer base is
   larger in comparison to other peers, whose interconnection costs are
   the lowest, and with whom upgrading existing capacity is the easiest.
   In a network with low utilization at the edge, this works well.  The
   same concept could be applied to a network with higher edge
   utilization by creating more levels of BGP metrics between peers,
   allowing for more granularity in selecting the exit points for
   traffic bound for a dual homed customer on a peer's network.

   By only replacing inbound MED metrics with BGP metrics, only equal
   AS-Path length routes' exit points are being changed.  (The BGP
   decision considers Local Preference first, then AS-Path length, and
   then BGP metric).  For example, assume a network has two possible
   egress points, peer A and peer B.  Each peer has 40% of the
   Internet's routes exclusively on its network, while the remaining 20%
   of the Internet's routes are from customers who dual home between A
   and B.  Assume that both peers have a Local Preference of 200 and a
   BGP metric of 100.  If the link to peer A is congested, increasing
   its BGP metric while leaving the Local Preference at 200 will ensure
   that the 20% of total routes belonging to dual homed customers will
   prefer peer B as the exit point.  The previous example would be used
   in a situation where all exit points to a given peer were close to
   congestion levels, and traffic needed to be shifted away from that
   peer entirely.

   When there are multiple exit points to a given peer, and only one of
   them is congested, it is not necessary to shift traffic away from the
   peer entirely, but only from the one congested circuit.  This can be
   achieved by using passive IGP-metrics, AS-path filtering, or prefix
   filtering.

   Occasionally, more drastic changes are needed, for example, in
   dealing with a "problem peer" who is difficult to work with on
   upgrades or is charging high prices for connectivity to their
   network.  In that case, the Local Preference to that peer can be
   reduced below the level of other peers.  This effectively reduces the
   amount of traffic sent to that peer to only originating traffic

   (assuming no transit providers are involved).  This type of change
   can affect a large amount of traffic, and is only used after other
   methods have failed to provide the desired results.

   Although it is not much of an issue in regional networks, the
   propagation of a peer's routes back through the network must be
   considered when a network is peering on a global scale.  Sometimes,
   business considerations can influence the choice of BGP policies in a
   given context.  For example, it may be imprudent, from a business
   perspective, to operate a global network and provide full access to
   the global customer base to a small network in a particular country.
   However, for the purpose of providing one's own customers with
   quality service in a particular region, good connectivity to that
   in-country network may still be necessary.  This can be achieved by
   assigning a set of communities at the edge of the network, which have
   a known behavior when routes tagged with those communities are
   propagating back through the core.  Routes heard from local peers
   will be prevented from propagating back to the global network,
   whereas routes learned from larger peers may be allowed to propagate
   freely throughout the entire global network.  By implementing a
   flexible community strategy, the benefits of using a single global AS
   Number (ASN) can be realized, while the benefits of operating
   regional networks can also be taken advantage of.  An alternative to
   doing this is to use different ASNs in different regions, with the
   consequence that the AS path length for routes announced by that
   service provider will increase.

9.0 Conclusion

   This document described principles for traffic engineering in the
   Internet.  It presented an overview of some of the basic issues
   surrounding traffic engineering in IP networks.  The context of TE
   was described, a TE process models and a taxonomy of TE styles were
   presented.  A brief historical review of pertinent developments
   related to traffic engineering was provided.  A survey of
   contemporary TE techniques in operational networks was presented.
   Additionally, the document specified a set of generic requirements,
   recommendations, and options for Internet traffic engineering.

10.0 Security Considerations

   This document does not introduce new security issues.

11.0 Acknowledgments

   The authors would like to thank Jim Boyle for inputs on the
   recommendations section, Francois Le Faucheur for inputs on Diffserv
   aspects, Blaine Christian for inputs on measurement, Gerald Ash for

   inputs on routing in telephone networks and for text on event-
   dependent TE methods, Steven Wright for inputs on network
   controllability, and Jonathan Aufderheide for inputs on inter-domain
   TE with BGP.  Special thanks to Randy Bush for proposing the TE
   taxonomy based on "tactical vs strategic" methods.  The subsection
   describing an "Overview of ITU Activities Related to Traffic
   Engineering" was adapted from a contribution by Waisum Lai.  Useful
   feedback and pointers to relevant materials were provided by J. Noel
   Chiappa.  Additional comments were provided by Glenn Grotefeld during
   the working last call process.  Finally, the authors would like to
   thank Ed Kern, the TEWG co-chair, for his comments and support.

12.0 References

   [ASH2]      J. Ash, Dynamic Routing in Telecommunications Networks,
               McGraw Hill, 1998.

   [ASH3]      Ash, J., "TE & QoS Methods for IP-, ATM-, & TDM-Based
               Networks", Work in Progress, March 2001.

   [AWD1]      D. Awduche and Y. Rekhter, "Multiprocotol Lambda
               Switching:  Combining MPLS Traffic Engineering Control
               with Optical Crossconnects", IEEE Communications
               Magazine, March 2001.

   [AWD2]      D. Awduche, "MPLS and Traffic Engineering in IP
               Networks", IEEE Communications Magazine, Dec. 1999.

   [AWD5]      D. Awduche et al, "An Approach to Optimal Peering Between
               Autonomous Systems in the Internet", International
               Conference on Computer Communications and Networks
               (ICCCN'98), Oct. 1998.

   [CRUZ]      R. L. Cruz, "A Calculus for Network Delay, Part II:
               Network Analysis", IEEE Transactions on Information
               Theory, vol. 37, pp.  132-141, 1991.

   [DIFF-TE]   Le Faucheur, F., Nadeau, T., Tatham, M., Telkamp, T.,
               Cooper, D., Boyle, J., Lai, W., Fang, L., Ash, J., Hicks,
               P., Chui, A., Townsend, W. and D. Skalecki, "Requirements
               for support of Diff-Serv-aware MPLS Traffic Engineering",
               Work in Progress, May 2001.

   [ELW95]     A. Elwalid, D. Mitra and R.H. Wentworth, "A New Approach
               for Allocating Buffers and Bandwidth to Heterogeneous,
               Regulated Traffic in an ATM Node", IEEE IEEE Journal on
               Selected Areas in Communications, 13:6, pp. 1115-1127,
               Aug. 1995.

   [FGLR]      A. Feldmann, A. Greenberg, C. Lund, N. Reingold, and J.
               Rexford, "NetScope: Traffic Engineering for IP Networks",
               IEEE Network Magazine, 2000.

   [FLJA93]    S. Floyd and V. Jacobson, "Random Early Detection
               Gateways for Congestion Avoidance", IEEE/ACM Transactions
               on Networking, Vol. 1 Nov. 4., p. 387-413, Aug. 1993.

   [FLOY94]    S. Floyd, "TCP and Explicit Congestion Notification", ACM
               Computer Communication Review, V. 24, No. 5, p. 10-23,
               Oct. 1994.

   [FT00]      B. Fortz and M. Thorup, "Internet Traffic Engineering by
               Optimizing OSPF Weights", IEEE INFOCOM 2000, Mar. 2000.

   [FT01]      B. Fortz and M. Thorup, "Optimizing OSPF/IS-IS Weights in
               a Changing World",
               www.research.att.com/~mthorup/PAPERS/papers.html.

   [HUSS87]    B.R. Hurley, C.J.R. Seidl and W.F. Sewel, "A Survey of
               Dynamic Routing Methods for Circuit-Switched Traffic",
               IEEE Communication Magazine, Sep. 1987.

   [ITU-E600]  ITU-T Recommendation E.600, "Terms and Definitions of
               Traffic Engineering", Mar. 1993.

   [ITU-E701]  ITU-T Recommendation E.701, "Reference Connections for
               Traffic Engineering", Oct. 1993.

   [ITU-E801]  ITU-T Recommendation E.801, "Framework for Service
               Quality Agreement", Oct. 1996.

   [JAM]       Jamoussi, B., Editior, Andersson, L., Collon, R. and R.
               Dantu, "Constraint-Based LSP Setup using LDP", RFC 3212,
               January 2002.

   [KATZ]      Katz, D., Yeung, D. and K. Kompella, "Traffic Engineering
               Extensions to OSPF", Work in Progress, February 2001.

   [LNO96]     T. Lakshman, A. Neidhardt, and T. Ott, "The Drop from
               Front Strategy in TCP over ATM and its Interworking with
               other Control Features", Proc. INFOCOM'96, p. 1242-1250,
               1996.

   [MA]        Q. Ma, "Quality of Service Routing in Integrated Services
               Networks", PhD Dissertation, CMU-CS-98-138, CMU, 1998.

   [MATE]      A. Elwalid, C. Jin, S. Low, and I. Widjaja, "MATE: MPLS
               Adaptive Traffic Engineering", Proc. INFOCOM'01, Apr.
               2001.

   [MCQ80]     J.M. McQuillan, I. Richer, and E.C. Rosen, "The New
               Routing Algorithm for the ARPANET", IEEE.  Trans. on
               Communications, vol. 28, no. 5, pp. 711-719, May 1980.

   [MR99]      D. Mitra and K.G. Ramakrishnan, "A Case Study of
               Multiservice, Multipriority Traffic Engineering Design
               for Data Networks", Proc. Globecom'99, Dec 1999.

   [RFC-1458]  Braudes, R. and S. Zabele, "Requirements for Multicast
               Protocols", RFC 1458, May 1993.

   [RFC-1771]  Rekhter, Y. and T. Li, "A Border Gateway Protocol 4
               (BGP-4)", RFC 1771, March 1995.

   [RFC-1812]  Baker, F., "Requirements for IP Version 4 Routers", STD
               4, RFC 1812, June 1995.

   [RFC-1992]  Castineyra, I., Chiappa, N. and M. Steenstrup, "The
               Nimrod Routing Architecture", RFC 1992, August 1996.

   [RFC-1997]  Chandra, R., Traina, P. and T. Li, "BGP Community
               Attributes", RFC 1997, August 1996.

   [RFC-1998]  Chen, E. and T. Bates, "An Application of the BGP
               Community Attribute in Multi-home Routing", RFC 1998,
               August 1996.

   [RFC-2205]  Braden, R., Zhang, L., Berson, S., Herzog, S. and S.
               Jamin, "Resource Reservation Protocol (RSVP) - Version 1
               Functional Specification", RFC 2205, September 1997.

   [RFC-2211]  Wroclawski, J., "Specification of the Controlled-Load
               Network Element Service", RFC 2211, September 1997.

   [RFC-2212]  Shenker, S., Partridge, C. and R. Guerin, "Specification
               of Guaranteed Quality of Service", RFC 2212, September
               1997.

   [RFC-2215]  Shenker, S. and J. Wroclawski, "General Characterization
               Parameters for Integrated Service Network Elements", RFC
               2215, September 1997.

   [RFC-2216]  Shenker, S. and J. Wroclawski, "Network Element Service
               Specification Template", RFC 2216, September 1997.

   [RFC-2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328, July 1997.

   [RFC-2330]  Paxson, V., Almes, G., Mahdavi, J. and M. Mathis,
               "Framework for IP Performance Metrics", RFC 2330, May
               1998.

   [RFC-2386]  Crawley, E., Nair, R., Rajagopalan, B. and H. Sandick, "A
               Framework for QoS-based Routing in the Internet", RFC
               2386, August 1998.

   [RFC-2474]  Nichols, K., Blake, S., Baker, F. and D. Black,
               "Definition of the Differentiated Services Field (DS
               Field) in the IPv4 and IPv6 Headers", RFC 2474, December
               1998.

   [RFC-2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.
               and W. Weiss, "An Architecture for Differentiated
               Services", RFC 2475, December 1998.

   [RFC-2597]  Heinanen, J., Baker, F., Weiss, W. and J. Wroclawski,
               "Assured Forwarding PHB Group", RFC 2597, June 1999.

   [RFC-2678]  Mahdavi, J. and V. Paxson, "IPPM Metrics for Measuring
               Connectivity", RFC 2678, September 1999.

   [RFC-2679]  Almes, G., Kalidindi, S. and M. Zekauskas, "A One-way
               Delay Metric for IPPM", RFC 2679, September 1999.

   [RFC-2680]  Almes, G., Kalidindi, S. and M. Zekauskas, "A One-way
               Packet Loss Metric for IPPM", RFC 2680, September 1999.

   [RFC-2702]  Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M. and J.
               McManus, "Requirements for Traffic Engineering over
               MPLS", RFC 2702, September 1999.

   [RFC-2722]  Brownlee, N., Mills, C. and G. Ruth, "Traffic Flow
               Measurement: Architecture", RFC 2722, October 1999.

   [RFC-2753]  Yavatkar, R., Pendarakis, D. and R. Guerin, "A Framework
               for Policy-based Admission Control", RFC 2753, January
               2000.

   [RFC-2961]  Berger, L., Gan, D., Swallow, G., Pan, P., Tommasi, F.
               and S. Molendini, "RSVP Refresh Overhead Reduction
               Extensions", RFC 2961, April 2000.

   [RFC-2998]  Bernet, Y., Ford, P., Yavatkar, R., Baker, F., Zhang, L.,
               Speer, M., Braden, R., Davie, B., Wroclawski, J. and E.
               Felstaine, "A Framework for Integrated Services Operation
               over Diffserv Networks", RFC 2998, November 2000.

   [RFC-3031]  Rosen, E., Viswanathan, A. and R. Callon, "Multiprotocol
               Label Switching Architecture", RFC 3031, January 2001.

   [RFC-3086]  Nichols, K. and B. Carpenter, "Definition of
               Differentiated Services Per Domain Behaviors and Rules
               for their Specification", RFC 3086, April 2001.

   [RFC-3124]  Balakrishnan, H. and S. Seshan, "The Congestion Manager",
               RFC 3124, June 2001.

   [RFC-3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.
               and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
               Tunnels", RFC 3209, December 2001.

   [RFC-3210]  Awduche, D., Hannan, A. and X. Xiao, "Applicability
               Statement for Extensions to RSVP for LSP-Tunnels", RFC
               3210, December 2001.

   [RFC-3213]  Ash, J., Girish, M., Gray, E., Jamoussi, B. and G.
               Wright, "Applicability Statement for CR-LDP", RFC 3213,
               January 2002.

   [RFC-3270]  Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaahanen,
               P., Krishnan, R., Cheval, P. and J. Heinanen, "Multi-
               Protocol Label Switching (MPLS) Support of Differentiated
               Services", RFC 3270, April 2002.

   [RR94]      M.A. Rodrigues and K.G. Ramakrishnan, "Optimal Routing in
               Shortest Path Networks", ITS'94, Rio de Janeiro, Brazil.

   [SHAR]      Sharma, V., Crane, B., Owens, K., Huang, C., Hellstrand,
               F., Weil, J., Anderson, L., Jamoussi, B., Cain, B.,
               Civanlar, S. and A. Chui, "Framework for MPLS Based
               Recovery", Work in Progress.

   [SLDC98]    B. Suter, T. Lakshman, D. Stiliadis, and A. Choudhury,
               "Design Considerations for Supporting TCP with Per-flow
               Queueing", Proc. INFOCOM'98, p. 299-306, 1998.

   [SMIT]      Smit, H. and T. Li, "IS-IS extensions for Traffic
               Engineering", Work in Progress.

   [WANG]      Y. Wang, Z. Wang, L. Zhang, "Internet traffic engineering
               without full mesh overlaying", Proceedings of
               INFOCOM'2001, April 2001.

   [XIAO]      X. Xiao, A. Hannan, B. Bailey, L. Ni, "Traffic
               Engineering with MPLS in the Internet", IEEE Network
               magazine, Mar. 2000.

   [YARE95]    C. Yang and A. Reddy, "A Taxonomy for Congestion Control
               Algorithms in Packet Switching Networks", IEEE Network
               Magazine, p.  34-45, 1995.

13.0 Authors' Addresses

   Daniel O. Awduche
   Movaz Networks
   7926 Jones Branch Drive, Suite 615
   McLean, VA 22102

   Phone: 703-298-5291
   EMail: awduche@movaz.com


   Angela Chiu
   Celion Networks
   1 Sheila Dr., Suite 2
   Tinton Falls, NJ 07724

   Phone: 732-747-9987
   EMail: angela.chiu@celion.com


   Anwar Elwalid
   Lucent Technologies
   Murray Hill, NJ 07974

   Phone: 908 582-7589
   EMail: anwar@lucent.com


   Indra Widjaja
   Bell Labs, Lucent Technologies
   600 Mountain Avenue
   Murray Hill, NJ 07974

   Phone: 908 582-0435
   EMail: iwidjaja@research.bell-labs.com


   XiPeng Xiao
   Redback Networks
   300 Holger Way
   San Jose, CA 95134

   Phone: 408-750-5217
   EMail: xipeng@redback.com

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