GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc3564

Network Working Group F. Le Faucheur Request for Comments: 3564 Cisco Systems, Inc. Category: Informational W. Lai

                                                                  AT&T
                                                             July 2003
     Requirements for Support of Differentiated Services-aware
                   MPLS Traffic Engineering

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 (2003).  All Rights Reserved.

Abstract

 This document presents Service Provider requirements for support of
 Differentiated Services (Diff-Serv)-aware MPLS Traffic Engineering
 (DS-TE).
 Its objective is to provide guidance for the definition, selection
 and specification of a technical solution addressing these
 requirements.  Specification for this solution itself is outside the
 scope of this document.
 A problem statement is first provided.  Then, the document describes
 example applications scenarios identified by Service Providers where
 existing MPLS Traffic Engineering mechanisms fall short and
 Diff-Serv-aware Traffic Engineering can address the needs.  The
 detailed requirements that need to be addressed by the technical
 solution are also reviewed.  Finally, the document identifies the
 evaluation criteria that should be considered for selection and
 definition of the technical solution.

Le Faucheur & Lai Informational [Page 1] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

Table of Contents

 Specification Requirements .......................................  2
 1.  Introduction .................................................  3
     1.1.  Problem Statement ......................................  3
     1.2.  Definitions ............................................  3
     1.3.  Mapping of traffic to LSPs .............................  5
 2.  Application Scenarios ........................................  6
     2.1.  Scenario 1: Limiting Proportion of Classes on a Link ...  6
     2.2.  Scenario 2: Maintain relative proportion of traffic ....  6
     2.3.  Scenario 3: Guaranteed Bandwidth Services ..............  8
 3.  Detailed Requirements for DS-TE ..............................  9
     3.1.  DS-TE Compatibility ....................................  9
     3.2.  Class-Types ............................................  9
     3.3.  Bandwidth Constraints .................................. 11
     3.4.  Preemption and TE-Classes .............................. 12
     3.5.  Mapping of Traffic to LSPs ............................. 15
     3.6.  Dynamic Adjustment of Diff-Serv PHBs ................... 15
     3.7.  Overbooking ............................................ 16
     3.8.  Restoration ............................................ 16
 4.  Solution Evaluation Criteria ................................. 16
     4.1.  Satisfying detailed requirements ....................... 17
     4.2.  Flexibility ............................................ 17
     4.3.  Extendibility .......................................... 17
     4.4.  Scalability ............................................ 17
     4.5.  Backward compatibility/Migration ....................... 17
     4.6.  Bandwidth Constraints Model ............................ 18
 5.  Security Considerations ...................................... 18
 6.  Acknowledgment ............................................... 18
 7.  Normative References ......................................... 18
 8.  Informative References ....................................... 19
 9.  Contributing Authors ......................................... 20
 10. Editors' Addresses ........................................... 21
 11. Full Copyright Statement ..................................... 22

Specification Requirements

 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 [RFC2119].

Le Faucheur & Lai Informational [Page 2] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

1. Introduction

1.1. Problem Statement

 Diff-Serv is used by some Service Providers to achieve scalable
 network designs supporting multiple classes of services.
 In some such Diff-Serv networks, where optimization of transmission
 resources on a network-wide basis is not sought, MPLS Traffic
 Engineering (TE) mechanisms may not be used.
 In other networks, where optimization of transmission resources is
 sought, Diff-Serv mechanisms [DIFF-MPLS] may be complemented by
 MPLS Traffic Engineering mechanisms [TE-REQ] [ISIS-TE] [OSPF-TE]
 [RSVP-TE] which operate on an aggregate basis across all
 Diff-Serv classes of service.  In this case, Diff-Serv and MPLS TE
 both provide their respective benefits.
 To achieve fine-grained optimization of transmission resources and
 further enhanced network performance and efficiency, as discussed in
 [TEWG-FW], it may be desirable to perform traffic engineering at a
 per-class level instead of at an aggregate level.  By mapping the
 traffic from a given Diff-Serv class of service on a separate LSP, it
 allows this traffic to utilize resources available to the given class
 on both shortest paths and non-shortest paths, and follow paths that
 meet engineering constraints which are specific to the given class.
 This is what we refer to as "Diff-Serv-aware Traffic Engineering
 (DS-TE)".
 This document focuses exclusively on the specific environments which
 would benefit from DS-TE.  Some examples include:
  1. networks where bandwidth is scarce (e.g., transcontinental

networks)

  1. networks with significant amounts of delay-sensitive traffic
  2. networks where the relative proportion of traffic across

classes of service is not uniform

 This document focuses on intra-domain operation.  Inter-domain
 operation is not considered.

1.2. Definitions

 For the convenience of the reader, relevant Diff-Serv ([DIFF-ARCH],
 [DIFF-NEW] and [DIFF-PDB]) definitions are repeated herein.
    Behavior Aggregate (BA): a collection of packets with the same
    (Diff-Serv) codepoint crossing a link in a particular direction.

Le Faucheur & Lai Informational [Page 3] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

    Per-Hop-Behavior (PHB): the externally observable forwarding
    behavior applied at a DS-compliant node to a Diff-Serv behavior
    aggregate.
    PHB Scheduling Class (PSC): A PHB group for which a common
    constraint is that ordering of at least those packets belonging to
    the same microflow must be preserved.
    Ordered Aggregate (OA): a set of BAs that share an ordering
    constraint.  The set of PHBs that are applied to this set of
    Behavior Aggregates constitutes a PHB scheduling class.
    Traffic Aggregate (TA): a collection of packets with a codepoint
    that maps to the same PHB, usually in a DS domain or some subset
    of a DS domain.  A traffic aggregate marked for the foo PHB is
    referred to as the "foo traffic aggregate" or "foo aggregate"
    interchangeably.  This generalizes the concept of Behavior
    Aggregate from a link to a network.
    Per-Domain Behavior (PDB): the expected treatment that an
    identifiable or target group of packets will receive from
    "edge-to-edge" of a DS domain.  A particular PHB (or, if
    applicable, list of PHBs) and traffic conditioning requirements
    are associated with each PDB.
 We also repeat the following definition from [TE-REQ]:
    Traffic Trunk: an aggregation of traffic flows of the same class
    which are placed inside a Label Switched Path.
 In the context of the present document, "flows of the same class" is
 to be interpreted as "flows from the same Forwarding Equivalence
 Class which are to be treated equivalently from the DS-TE
 perspective".
    We refer to the set of TAs corresponding to the set of PHBs of a
    given PSC, as a {TA}PSC.  A given {TA}PSC will receive the
    treatment of the PDB associated with the corresponding PSC.  In
    this document, we also loosely refer to a {TA}PSC as a "Diff-Serv
    class of service", or a "class of service".  As an example, the
    set of packets within a DS domain with a codepoint that maps to
    the EF PHB may form one {TA}PSC in that domain.  As another
    example, the set of packets within a DS domain with a codepoint
    that maps to the AF11 or AF12 or AF13 PHB may form another {TA}PSC
    in that domain.

Le Faucheur & Lai Informational [Page 4] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

 We refer to the collection of packets which belong to a given Traffic
 Aggregate and are associated with a given MPLS Forwarding Equivalence
 Class (FEC) ([MPLS-ARCH]) as a <FEC/TA>.
 We refer to the set of <FEC/TA> whose TAs belong to a given {TA}PSC
 as a <FEC/{TA}PSC>.

1.3. Mapping of traffic to LSPs

 A network may have multiple Traffic Aggregates (TAs) it wishes to
 service.  Recalling from [DIFF-MPLS], there are several options on
 how the set of <FEC/{TA}PSC> of a given FEC can be split into Traffic
 Trunks for mapping onto LSPs when running MPLS Traffic Engineering.
 One option is to not split this set of <FEC/{TA}PSC> so that each
 Traffic Trunk comprises traffic from all the {TA}/PSC.  This option
 is typically used when aggregate traffic engineering is deployed
 using current MPLS TE mechanisms.  In that case, all the
 <FEC/{TA}PSC> of a given FEC are routed collectively according to a
 single shared set of constraints and will follow the same path.  Note
 that the LSP transporting such a Traffic Trunk is, by definition, an
 E-LSP as defined in [DIFF-MPLS].
 Another option is to split the different <FEC/{TA}PSC> of a given FEC
 into multiple Traffic Trunks on the basis of the {TA}PSC.  In other
 words, traffic, from one given node to another, is split, based on
 the "classes of service", into multiple Traffic Trunks which are
 transported over separate LSP and can potentially follow different
 paths through the network.  DS-TE takes advantage of this and
 computes a separate path for each LSP.  In so doing, DS-TE can take
 into account the specific requirements of the Traffic Trunk
 transported on each LSP (e.g., bandwidth requirement, preemption
 priority).  Moreover DS-TE can take into account the specific
 engineering constraints to be enforced for these sets of Traffic
 Trunks (e.g., limit all Traffic Trunks transporting a particular
 {TA}PSC to x% of link capacity).  DS-TE achieves per LSP constraint
 based routing with paths that match specific objectives of the
 traffic while forming the corresponding Traffic Trunk.
 For simplicity, and because this is the specific topic of this
 document, the above paragraphs in this section only considered
 splitting traffic of a given FEC into multiple Traffic Aggregates on
 the basis of {TA}PSC.  However, it should be noted that, in addition
 to this, traffic from every {TA}PSC may also be split into multiple
 Traffic Trunks for load balancing purposes.

Le Faucheur & Lai Informational [Page 5] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

2. Application Scenarios

2.1. Scenario 1: Limiting Proportion of Classes on a Link

 An IP/MPLS network may need to carry a significant amount of VoIP
 traffic compared to its link capacity.  For example, 10,000
 uncompressed calls at 20ms packetization result in about 1Gbps of IP
 traffic, which is significant on an OC-48c based network.  In case of
 topology changes such as link/node failure, VoIP traffic levels can
 even approach the full bandwidth on certain links.
 For delay/jitter reasons, some network administrators see it as
 undesirable to carry more than a certain percentage of VoIP traffic
 on any link.  The rest of the available link bandwidth can be used to
 route other "classes of service" corresponding to delay/jitter
 insensitive traffic (e.g.,  Best Effort Internet traffic).  The exact
 determination of this "certain" percentage is outside the scope of
 this requirements document.
 During normal operations, the VoIP traffic should be able to preempt
 other "classes of service" (if these other classes are designated as
 preemptable and they have lower preemption priority), so that it will
 be able to use the shortest available path, only constrained by the
 maximum defined link utilization ratio/percentage of the VoIP class.
 Existing TE mechanisms only allow constraint based routing of traffic
 based on a single bandwidth constraint common to all "classes of
 service", which does not satisfy the needs described here.  This
 leads to the requirement for DS-TE to be able to enforce a different
 bandwidth constraint for different "classes of service".  In the
 above example, the bandwidth constraint to be enforced for VoIP
 traffic may be the "certain" percentage of each link capacity, while
 the bandwidth constraint to be enforced for the rest of the "classes
 of service" might have their own constraints or have access to the
 rest of the link capacity.

2.2. Scenario 2: Maintain relative proportion of traffic

 Suppose an IP/MPLS network supports 3 "classes of service".  The
 network administrator wants to perform Traffic Engineering to
 distribute the traffic load.  Also assume that proportion across
 "classes of service" varies significantly depending on the
 source/destination POPs.

Le Faucheur & Lai Informational [Page 6] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

 With existing TE mechanisms, the proportion of traffic from each
 "class of service" on a given link will vary depending on multiple
 factors including:
  1. in which order the different TE-LSPs are established
  2. the preemption priority associated with the different TE-LSPs
  3. link/node failure situations
 This may make it difficult or impossible for the network
 administrator to configure the Diff-Serv PHBs (e.g., queue bandwidth)
 to ensure that each "class of service" gets the appropriate
 treatment.  This leads again to the requirement for DS-TE to be able
 to enforce a different bandwidth constraint for different "classes of
 service".  This could be used to ensure that, regardless of the order
 in which tunnels are routed, regardless of their preemption priority
 and regardless of the failure situation, the amount of traffic of
 each "class of service" routed over a link matches the Diff-Serv
 scheduler configuration on that link to the corresponding class
 (e.g., queue bandwidth).
 As an illustration of how DS-TE would address this scenario, the
 network administrator may configure the service rate of Diff-Serv
 queues to (45%,35%,20%) for "classes of service" (1,2,3)
 respectively.  The administrator would then split the traffic into
 separate Traffic Trunks for each "class of service" and associate a
 bandwidth to each LSP transporting those Traffic Trunks.  The network
 administrator may also want to configure preemption priorities of
 each LSP in order to give highest restoration priority to the highest
 priority "class of service" and medium priority to the medium "class
 of service".  Then DS-TE could ensure that after a failure, "class of
 service" 1 traffic would be rerouted with first access at link
 capacity without exceeding its service rate of 45% of the link
 bandwidth.  "Class of service" 2 traffic would be rerouted with
 second access at the link capacity without exceeding its allotment.
 Note that where "class of service" 3 is the Best-Effort service, the
 requirement on DS-TE may be to ensure that the total amount of
 traffic routed across all "classes of service" does not exceed the
 total link capacity of 100% (as opposed to separately limiting the
 amount of Best Effort traffic to 20 even if there was little "class
 of service" 1 and "class of service" 2 traffic).
 In this scenario, DS-TE would allow for the maintenance of a more
 steady distribution of "classes of service", even during rerouting.
 This would rely on the required capability of DS-TE to adjust the
 amount of traffic of each "class of service"  routed on a link based
 on the configuration of the scheduler and the amount of bandwidth
 available for each "class of service".

Le Faucheur & Lai Informational [Page 7] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

 Alternatively, some network administrators may want to solve the
 problem by having the scheduler dynamically adjusted based on the
 amount of bandwidth of the LSPs admitted for each "class of service".
 This is an optional additional requirement on the DS-TE solution.

2.3. Scenario 3: Guaranteed Bandwidth Services

 In addition to the Best effort service, an IP/MPLS network operator
 may desire to offer a point-to-point "guaranteed bandwidth" service
 whereby the provider pledges to provide a given level of performance
 (bandwidth/delay/loss...) end-to-end through its network from an
 ingress port to an egress port.  The goal is to ensure that all the
 "guaranteed" traffic under the scope of a subscribed service level
 specification, will be delivered within the tolerances of this
 service level specification.
 One approach for deploying such "guaranteed" service involves:
  1. dedicating a Diff-Serv PHB (or a Diff-Serv PSC as defined in

[DIFF-NEW]) to the "guaranteed" traffic

  1. policing guaranteed traffic on ingress against the traffic contract

and marking the "guaranteed" packets with the corresponding

   DSCP/EXP value
 Where a very high level of performance is targeted for the
 "guaranteed" service, it may be necessary to ensure that the amount
 of "guaranteed" traffic remains below a given percentage of link
 capacity on every link.  Where the proportion of "guaranteed" traffic
 is high, constraint based routing can be used to enforce such a
 constraint.
 However, the network operator may also want to simultaneously perform
 Traffic Engineering for the rest of the traffic (i.e.,
 non-guaranteed traffic) which would require that constraint based
 routing is also capable of enforcing a different bandwidth
 constraint, which would be less stringent than the one for guaranteed
 traffic.
 Again, this combination of requirements can not be addressed with
 existing TE mechanisms.  DS-TE mechanisms allowing enforcement of a
 different bandwidth constraint for guaranteed traffic and for
 non-guaranteed traffic are required.

Le Faucheur & Lai Informational [Page 8] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

3. Detailed Requirements for DS-TE

 This section specifies the functionality that the above scenarios
 require out of the DS-TE solution.  Actual technical protocol
 mechanisms and procedures to achieve such functionality are outside
 the scope of this document.

3.1. DS-TE Compatibility

 Since DS-TE may impact scalability (as discussed later in this
 document) and operational practices, DS-TE is expected to be used
 when existing TE mechanisms combined with Diff-Serv cannot address
 the network design requirements (i.e., where constraint based routing
 is required and where it needs to enforce different bandwidth
 constraints for different "classes of service", such as in the
 scenarios described above in section 2).  Where the benefits of DSTE
 are only required in a topological subset of their network, some
 network operators may wish to only deploy DS-TE in this topological
 subset.
 Thus, the DS-TE solution MUST be developed in such a way that:
 (i)    it raises no interoperability issues with existing deployed TE
        mechanisms.
 (ii)   it allows DS-TE deployment to the required level of
        granularity and scope (e.g., only in a subset of the topology,
        or only for the number of classes required in the considered
        network)

3.2. Class-Types

 The fundamental requirement for DS-TE is to be able to enforce
 different bandwidth constraints for different sets of Traffic Trunks.
 [TEWG-FW] introduces the concept of Class-Types when discussing
 operations of MPLS Traffic Engineering in a Diff-Serv environment.
 We refine this definition into the following:
          Class-Type (CT): the set of Traffic Trunks crossing a link,
          that is governed by a specific set of Bandwidth constraints.
          CT is used for the purposes of link bandwidth allocation,
          constraint based routing and admission control.  A given
          Traffic Trunk belongs to the same CT on all links.
 Note that different LSPs transporting Traffic Trunks from the same CT
 may be using the same or different preemption priorities as explained
 in more details in section 3.4 below.

Le Faucheur & Lai Informational [Page 9] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

 Mapping of {TA}PSC to Class-Types is flexible.  Different {TA}PSC can
 be mapped to different CTs, multiple {TA}PSC can be mapped to the
 same CT and one {TA}PSC can be mapped to multiple CTs.
 For illustration purposes, let's consider the case of a network
 running 4 Diff-Serv PDBs which are respectively based on the EF PHB
 [EF], the AF1x PSC [AF], the AF2x PSC and the Default (i.e.,
 Best-Effort) PHB [DIFF-FIELD].  The network administrator may decide
 to deploy DS-TE in the following way:
       o  from every DS-TE Head-end to every DS-TE Tail-end, split the
          traffic into 4 Traffic Trunks: one for traffic of each
          {TA}PSC
       o  because the QoS objectives for the AF1x PDB and for the AF2x
          PDB may be of similar nature (e.g., both targeting low loss
          albeit at different levels perhaps), the same (set of)
          Bandwidth Constraint(s) may be applied collectively over the
          AF1x Traffic Trunks and the AF2x Traffic Trunks.  Thus, the
          network administrator may only define three CTs: one for the
          EF Traffic Trunks, one for the AF1x and AF2x Traffic Trunks
          and one for the Best Effort Traffic Trunks.
 As another example of mapping of {TA}PSC to CTs, a network operator
 may split the traffic from the {TA}PSC associated with EF into two
 different sets of traffic trunks, so that each set of traffic trunks
 is subject to different constraints on the bandwidth it can access.
 In this case, two distinct CTs are defined for the EF {TA}PSC
 traffic:  one for the traffic subset subject to the first (set of)
 bandwidth constraint(s), the other for the traffic subset subject to
 the second (set of) bandwidth constraint(s).
 The DS-TE solution MUST support up to 8 CTs.  Those are referred to
 as CTc, 0 <= c <= MaxCT-1 = 7.
 The DS-TE solution MUST be able to enforce a different set of
 Bandwidth Constraints for each CT.
 A DS-TE implementation MUST support at least 2 CTs, and MAY support
 up to 8 CTs.
 In a given network, the DS-TE solution MUST NOT require the network
 administrator to always deploy the maximum number of CTs.  The DS-TE
 solution MUST allow the network administrator to deploy only the
 number of CTs actually utilized.

Le Faucheur & Lai Informational [Page 10] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

3.3. Bandwidth Constraints

 We refer to a Bandwidth Constraint Model as the set of rules
 defining:
  1. the maximum number of Bandwidth Constraints; and
  2. which CTs each Bandwidth Constraint applies to and how.
 By definition of CT, each CT is assigned either a Bandwidth
 Constraint, or a set of Bandwidth Constraints.
 We refer to the Bandwidth Constraints as BCb, 0 <= b <= MaxBC-1
 For a given Class-Type CTc, 0 <= c <= MaxCT-1, let us define
 "Reserved(CTc)" as the sum of the bandwidth reserved by all
 established LSPs which belong to CTc.
 Different models of Bandwidth Constraints are conceivable for control
 of the CTs.
 For example, a model with one separate Bandwidth Constraint per CT
 could be defined.  This model is referred to as the "Maximum
 Allocation Model" and is defined by:
  1. MaxBC= MaxCT
  2. for each value of b in the range 0 ⇐ b ⇐ (MaxCT - 1):

Reserved (CTb) ⇐ BCb

 For illustration purposes, on a link of 100 unit of bandwidth where
 three CTs are used, the network administrator might then configure
 BC0=20, BC1= 50, BC2=30 such that:
  1. All LSPs supporting Traffic Trunks from CT2 use no more than 30

(e.g., Voice ⇐ 30)

  1. All LSPs supporting Traffic Trunks from CT1 use no more than 50

(e.g., Premium Data ⇐ 50)

  1. All LSPs supporting Traffic Trunks from CT0 use no more than 20

(e.g., Best Effort ⇐ 20)

 As another example, a "Russian Doll" model of Bandwidth Constraints
 may be defined whereby:
  1. MaxBC= MaxCT
  2. for each value of b in the range 0 ⇐ b ⇐ (MaxCT - 1):

SUM (Reserved (CTc)) ⇐ BCb,

             for all "c" in the range  b <= c <= (MaxCT - 1)

Le Faucheur & Lai Informational [Page 11] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

 For illustration purposes, on a link of 100 units of bandwidth where
 three CTs are used, the network administrator might then configure
 BC0=100, BC1= 80, BC2=60 such that:
  1. All LSPs supporting Traffic Trunks from CT2 use no more than 60

(e.g., Voice ⇐ 60)

  1. All LSPs supporting Traffic Trunks from CT1 or CT2 use no more than

80 (e.g., Voice + Premium Data ⇐ 80)

  1. All LSPs supporting Traffic Trunks from CT0 or CT1 or CT2 use no

more than 100 (e.g., Voice + Premium Data + Best Effort ⇐ 100).

 Other Bandwidth Constraints model can also be conceived.  Those could
 involve arbitrary relationships between BCb and CTc.  Those could
 also involve additional concepts such as associating minimum
 reservable bandwidth to a CT.
 The DS-TE technical solution MUST have the capability to support
 multiple Bandwidth Constraints models.  The DS-TE technical solution
 MUST specify at least one bandwidth constraint model and MAY specify
 multiple Bandwidth Constraints models.  Additional Bandwidth
 Constraints models MAY also be specified at a later stage if deemed
 useful based on operational experience from DS-TE deployments.  The
 choice of which (or which set of) Bandwidth Constraints model(s) is
 to be supported by a given DS-TE implementation, is an implementation
 choice.  For simplicity, a network operator may elect to use the same
 Bandwidth Constraints Model on all the links of his/her network.
 However, if he/she wishes/needs to do so, the network operator may
 elect to use different Bandwidth Constraints models on different
 links in a given network.
 Regardless of the Bandwidth Constraint Model, the DS-TE solution MUST
 allow support for up to 8 BCs.

3.4. Preemption and TE-Classes

 [TEWG-FW] defines the notion of preemption and preemption priority.
 The DS-TE solution MUST retain full support of such preemption.
 However, a network administrator preferring not to use preemption for
 user traffic MUST be able to disable the preemption mechanisms
 described below.
 The preemption attributes defined in [TE-REQ] MUST be retained and
 applicable across all Class Types.  The preemption attributes of
 setup priority and holding priority MUST retain existing semantics,
 and in particular these semantics MUST not be affected by the Ordered
 Aggregate transported by the LSP or by the LSP's Class Type.  This
 means that if LSP1 contends with LSP2 for resources, LSP1 may preempt
 LSP2 if LSP1 has a higher set-up preemption priority (i.e., lower

Le Faucheur & Lai Informational [Page 12] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

 numerical priority value) than LSP2's holding preemption priority
 regardless of LSP1's OA/CT and LSP2's OA/CT.
 We introduce the following definition:
     TE-Class: A pair of:
             (i)    a Class-Type
             (ii)   a preemption priority allowed for that
                    Class-Type.  This means that an LSP transporting a
                    Traffic Trunk from that Class-Type can use that
                    preemption priority as the set-up priority, as the
                    holding priority or both.
 Note that by definition:
  1. for a given Class-Type, there may be one or multiple

TE-classes using that Class-Type, each using a different preemption

   priority
 - for a given preemption priority, there may be one or multiple
   TE-Class(es) using that preemption priority, each using a different
   Class-Type.
 The DS-TE solution MUST allow all LSPs transporting Traffic Trunks of
 a given Class-Type to use the same preemption priority.  In other
 words, the DS-TE solution MUST allow a Class-Type to be used by
 single TE-Class.  This effectively allows the network administrator
 to ensure that no preemption happens within that Class-Type, when so
 desired.
 As an example, the DS-TE solution MUST allow the network
 administrator to define a Class-Type comprising a single TE-class
 using preemption 0.
 The DS-TE solution MUST allow two LSPs transporting Traffic Trunks of
 the same Class-Type to use different preemption priorities, and allow
 the LSP with higher (numerically lower) set-up priority to preempt
 the LSP with lower (numerically higher) holding priority when they
 contend for resources.  In other words, the DS-TE solution MUST allow
 multiple TE-Classes to be defined for a given Class-Type. This
 effectively allows the network administrator to enable preemption
 within a Class-Type, when so desired.
 As an example, the DS-TE solution MUST allow the network
 administrator to define a Class-Type comprising three TE-Classes; one
 using preemption 0, one using preemption 1 and one using preemption
 4.

Le Faucheur & Lai Informational [Page 13] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

 The DS-TE solution MUST allow two LSPs transporting Traffic Trunks
 from different Class-Types to use different preemption priorities,
 and allow the LSP with higher setup priority to preempt the one with
 lower holding priority when they contend for resources.
 As an example, the DS-TE solution MUST allow the network
 administrator to define two Class-Types (CT0 and CT1) each comprising
 two TE-Classes where say:
  1. one TE-Class groups CT0 and preemption 0
  2. one TE-Class groups CT0 and preemption 2
  3. one TE-Class groups CT1 and preemption 1
  4. one TE-Class groups CT1 and preemption 3
 The network administrator would then, in particular, be able to:
  1. transport a CT0 Traffic Trunk over an LSP with setup priority=0 and

holding priority=0

  1. transport a CT0 Traffic Trunk over an LSP with setup priority=2 and

holding priority=0

  1. transport a CT1 Traffic Trunk over an LSP with setup priority=1 and

holding priority=1

  1. transport a CT1 Traffic Trunk over an LSP with setup priority=3 and

holding priority=1.

 The network administrator would then, in particular, NOT be able to:
  1. transport a CT0 Traffic Trunk over an LSP with setup priority=1 and

holding priority=1

  1. transport a CT1 Traffic Trunk over an LSP with setup priority=0 and

holding priority=0

 The DS-TE solution MUST allow two LSPs transporting Traffic Trunks
 from different Class-Types to use the same preemption priority.  In
 other words, the DS-TE solution MUST allow TE-classes using different
 CTs to use the same preemption priority.  This effectively allows the
 network administrator to ensure that no preemption happens across
 Class-Types, if so desired.
 As an example, the DS-TE solution MUST allow the network
 administrator to define three Class-Types (CT0, CT1 and CT2) each
 comprising one TE-Class which uses preemption 0.  In that case, no
 preemption will ever occur.
 Since there are 8 preemption priorities and up to 8 Class-Types,
 there could theoretically be up to 64 TE-Classes in a network.  This
 is felt to be beyond current practical requirements.  The current
 practical requirement is that the DS-TE solution MUST allow support

Le Faucheur & Lai Informational [Page 14] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

 for up to 8 TE-classes.  The DS-TE solution MUST allow these
 TE-classes to comprise any arbitrary subset of 8 (or less) from the
 (64) possible combinations of (8) Class-Types and (8) preemption
 priorities.
 As with existing TE, an LSP which gets preempted is torn down at
 preemption time.  The Head-end of the preempted LSP may then attempt
 to reestablish that LSP, which involves re-computing a path by
 Constraint Based Routing based on updated available bandwidth
 information and then signaling for LSP establishment along the new
 path.  It is to be noted that there may be cases where the preempted
 LSP cannot be reestablished (e.g., no possible path satisfying LSP
 bandwidth constraints as well as other constraints).  In such cases,
 the Head-end behavior is left to implementation.  It may involve
 periodic attempts at reestablishing the LSP, relaxing of the LSP
 constraints, or other behaviors.

3.5. Mapping of Traffic to LSPs

 The DS-TE solution MUST allow operation over E-LSPs onto which a
 single <FEC/{TA}PSC> is transported.
 The DS-TE solution MUST allow operation over L-LSPs.
 The DS-TE solution MAY allow operation over E-LSPs onto which
 multiple <FEC/{TA}PSC> of a given FEC are transported, under the
 condition that those multiple <FEC/{TA}PSC> can effectively be
 treated by DS-TE as a single atomic traffic trunk (in particular this
 means that those multiple <FEC/{TA}PSC> are routed as a whole based
 on a single collective bandwidth requirement, a single affinity
 attribute, a single preemption level, a single Class-Type, etc.).  In
 that case, it is also assumed that the multiple {TA}PSCs are grouped
 together in a consistent manner throughout the DS-TE domain (e.g., if
 <FECx/{TA}PSC1> and <FECx/{TA}PSC2> are transported together on an
 E-LSP, then there will not be any L-LSP transporting <FECy/{TA}PSC1>
 or <FECy/{TA}PSC2> on its own, and there will not be any E-LSP
 transporting <FECz/{TA}PSC1> and/or <FECz/{TA}PSC2> with
 <FECz/{TA}PSC3>).

3.6. Dynamic Adjustment of Diff-Serv PHBs

 As discussed in section 2.2, the DS-TE solution MAY support
 adjustment of Diff-Serv PHBs parameters (e.g., queue bandwidth) based
 on the amount of TE-LSPs established for each OA/Class-Type.  Such
 dynamic adjustment is optional for DS-TE implementations.

Le Faucheur & Lai Informational [Page 15] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

 Where this dynamic adjustment is supported, it MUST allow for
 disabling via configuration (thus reverting to PHB treatment with
 static scheduler configuration independent of DS-TE operations).  It
 MAY involve a number of configurable parameters which are outside the
 scope of this specification.  Those MAY include configurable
 parameters controlling how scheduling resources (e.g., service rates)
 need to be apportioned across multiple OAs when those belong to the
 same Class-Type and are transported together on the same E-LSP.
 Where supported, the dynamic adjustment MUST take account of the
 performance requirements of each PDB when computing required
 adjustments.

3.7. Overbooking

 Existing TE mechanisms allow overbooking to be applied on LSPs for
 Constraint Based Routing and admission control.  Historically, this
 has been achieved in TE deployment through factoring overbooking
 ratios at the time of sizing the LSP bandwidth and/or at the time of
 configuring the Maximum Reservable Bandwidth on links.
 The DS-TE solution MUST also allow overbooking and MUST effectively
 allow different overbooking ratios to be enforced for different CTs.
 The DS-TE solution SHOULD optionally allow the effective overbooking
 ratio of a given CT to be tweaked differently in different parts of
 the network.

3.8. Restoration

 With existing TE, restoration policies use standard priority
 mechanisms such as, for example, the preemption priority to
 effectively control the order/importance of LSPs for restoration
 purposes.
 The DS-TE solution MUST ensure that similar application of the use of
 standard priority mechanisms for implementation of restoration policy
 are not prevented since those are expected to be required for
 achieving the survivability requirements of DS-TE networks.
 Further discussion of restoration requirements are presented in the
 output document of the TEWG Requirements Design Team [SURVIV-REQ].

4. Solution Evaluation Criteria

 A range of solutions is possible for the support of the DS-TE
 requirements discussed above.  For example, some solutions may
 require that all current TE protocols syntax (IGP, RSVP-TE,) be

Le Faucheur & Lai Informational [Page 16] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

 extended in various ways.  For instance, current TE protocols could
 be modified to support multiple bandwidth constraints rather than the
 existing single aggregate bandwidth constraint.  Alternatively, other
 solutions may keep the existing TE protocols syntax unchanged but
 modify their semantics to allow for the multiple bandwidth
 constraints.
 This section identifies the evaluation criteria that MUST be used to
 assess potential DS-TE solutions for selection.

4.1. Satisfying detailed requirements

 The solution MUST address all the scenarios described in section 2
 and satisfy all the requirements listed in section 3.

4.2. Flexibility

  1. number of Class-Types that can be supported, compared to number

identified in Requirements section

  1. number of PDBs within a Class-Type

4.3. Extendibility

  1. how far can the solution be extended in the future if requirements

for more Class-Types are identified in the future.

4.4. Scalability

  1. impact on network scalability in what is propagated, processed,

stored and computed (IGP signaling, IGP processing, IGP database,

    TE-Tunnel signaling ,...).
 -  how does scalability impact evolve with number of
    Class-Types/PDBs actually deployed in a network.  In particular,
    is it possible to keep overhead small for a large networks which
    only use a small number of
    Class-Types/PDBs, while allowing higher number of
    Class-Types/PDBs in smaller networks which can bear higher
    overhead)

4.5. Backward compatibility/Migration

  1. backward compatibility/migration with/from existing TE mechanisms
  2. backward compatibility/migration when increasing/decreasing the

number of Class-Types actually deployed in a given network.

Le Faucheur & Lai Informational [Page 17] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

4.6. Bandwidth Constraints Model

 Work is currently in progress to investigate the performance and
 trade-offs of different operational aspects of Bandwidth Constraints
 models (for example see [BC-MODEL], [BC-CONS] and [MAR]).  In this
 investigation, at least the following criteria are expected to be
 considered:
     (1) addresses the scenarios in Section 2
     (2) works well under both normal and overload conditions
     (3) applies equally when preemption is either enabled or disabled
     (4) minimizes signaling load processing requirements
     (5) maximizes efficient use of the network
     (6) Minimizes implementation and deployment complexity.
 In selection criteria (2), "normal condition" means that the network
 is attempting to establish a volume of DS-TE LSPs for which it is
 designed; "overload condition" means that the network is attempting
 to establish a volume of DS-TE LSPs beyond the one it is designed
 for; "works well" means that under these conditions, the network
 should be able to sustain the expected performance, e.g., under
 overload it is x times worse than its normal performance.

5. Security Considerations

 The solution developed to address the DS-TE requirements defined in
 this document MUST address security aspects.  DS-TE does not raise
 any specific additional security requirements beyond the existing
 security requirements of MPLS TE and Diff-Serv.  The solution MUST
 ensure that the existing security mechanisms (including those
 protecting against DOS attacks) of MPLS TE and Diff-Serv are not
 compromised by the protocol/procedure extensions of the DS-TE
 solution or otherwise MUST provide security mechanisms to address
 this.

6. Acknowledgment

 We thank David Allen for his help in aligning with up-to-date
 Diff-Serv terminology.

7. Normative References

 [AF]         Heinanen, J., Baker, F., Weiss, W. and J. Wroclawski,
              "Assured Forwarding PHB Group", RFC 2597, June 1999.
 [DIFF-ARCH]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.
              and W. Weiss,  "An Architecture for Differentiated
              Services", RFC 2475, December 1998.

Le Faucheur & Lai Informational [Page 18] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

 [DIFF-FIELD] 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.
 [MPLS-ARCH]  Rosen, E., Viswanathan, A. and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031, January 2001.
 [DIFF-MPLS]  Le Faucheur, F., Wu, L., Davie, B., Davari, S.,
              Vaananen, P., Krishnan, R., Cheval, P. and J. Heinanen,
              "Multi-Protocol Label Switching (MPLS) Support of
              Differentiated Services", RFC 3270, May 2002.
 [DIFF-NEW]   Grossman, D., "New Terminology and Clarifications for
              Diffserv", RFC 3260, April 2002.
 [EF]         Davie, B., Charny, A., Bennet, J.C.R., Benson, K., Le
              Boudec, J.Y., Davari, S., Courtney, W., Firioiu, V. and
              D. Stiliadis, "An Expedited Forwarding PHB (Per-Hop
              Behavior)", RFC 3246, March 2002.
 [TEWG-FW]    Awduche, D., Chiu, A., Elwalid, A., Widjaja, I. and X.
              Xiao, "Overview and Principles of Internet Traffic
              Engineering", RFC 3272, May 2002.
 [TE-REQ]     Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M. and J.
              McManus, "Requirements for Traffic Engineering over
              MPLS", RFC 2702, September 1999.
 [RFC2119]    Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

8. Informative References

 [DIFF-PDB]   Nichols, K. and B. Carpenter, "Definition of
              Differentiated Services Per Domain Behaviors and Rules
              for their Specification", RFC 3086, April 2001.
 [ISIS-TE]    Smit, Li, "IS-IS extensions for Traffic Engineering",
              Work in Progress, December 2002.
 [OSPF-TE]    Katz, et al., "Traffic Engineering Extensions to OSPF",
              Work in Progress, October 2002.
 [RSVP-TE]    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.

Le Faucheur & Lai Informational [Page 19] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

 [SURVIV-REQ] Lai, W. and D. McDysan, "Network Hierarchy and
              Multilayer Survivability", RFC 3386, November 2002.
 [BC-MODEL]   Lai, W., "Bandwidth Constraints Models for
              Diffserv-aware MPLS Traffic Engineering: Performance
              Evaluation", Work in Progress, June 2002.
 [BC-CONS]    F. Le Faucheur, "Considerations on Bandwidth Constraints
              Models for DS-TE", Work in Progress, June 2002.
 [MAR]        Ash, J., "Max Allocation with Reservation Bandwidth
              Constraint Model for MPLS/DiffServ TE & Performance
              Comparisons", Work in Progress, May 2003.

9. Contributing Authors

 This document was the collective work of several people.  The text
 and content of this document was contributed by the editors and the
 co-authors listed below.  (The contact information for the editors
 appears below.)
 Martin Tatham                        Thomas Telkamp
 BT                                   Global Crossing
 Adastral Park, Martlesham Heath,     Oudkerkhof 51,  3512 GJ Utrecht
 Ipswich IP5 3RE, UK                  The Netherlands
 Phone: +44-1473-606349               Phone: +31 30 238 1250
 EMail: martin.tatham@bt.com          EMail: telkamp@gblx.net
 David Cooper                         Jim Boyle
 Global Crossing                      Protocol Driven Networks, Inc.
 960 Hamlin Court                     1381 Kildaire Farm Road #288
 Sunnyvale, CA 94089, USA             Cary, NC 27511, USA
 Phone: (916) 415-0437                Phone: (919) 852-5160
 EMail: dcooper@gblx.net              EMail: jboyle@pdnets.com
 Luyuan Fang                          Gerald R. Ash
 AT&T Labs                            AT&T Labs
 200 Laurel Avenue                    200 Laurel Avenue
 Middletown, New Jersey 07748, USA    Middletown, New Jersey 07748,USA
 Phone: (732) 420-1921                Phone: (732) 420-4578
 EMail: luyuanfang@att.com            EMail: gash@att.com

Le Faucheur & Lai Informational [Page 20] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

 Pete Hicks                           Angela Chiu
 CoreExpress, Inc                     AT&T Labs-Research
 12655 Olive Blvd, Suite 500          200 Laurel Ave.  Rm A5-1F13
 St. Louis, MO 63141, USA             Middletown, NJ 07748, USA
 Phone: (314) 317-7504                Phone: (732) 420-9061
 EMail: pete.hicks@coreexpress.net    EMail: chiu@research.att.com
 William Townsend                     Thomas D. Nadeau
 Tenor Networks                       Cisco Systems, Inc.
 100 Nagog Park                       300 Beaver Brook Road
 Acton, MA 01720, USA                 Boxborough, MA  01719
 Phone: +1 978-264-4900               Phone: +1-978-936-1470
 EMail:btownsend@tenornetworks.com    EMail: tnadeau@cisco.com
 Darek Skalecki
 Nortel Networks
 3500 Carling Ave,
 Nepean K2H 8E9,
 Phone: (613) 765-2252
 EMail: dareks@nortelnetworks.com

10. Editors' Addresses

 Francois Le Faucheur
 Cisco Systems, Inc.
 Village d'Entreprise Green Side - Batiment T3
 400, Avenue de Roumanille
 06410 Biot-Sophia Antipolis, France
 Phone: +33 4 97 23 26 19
 EMail: flefauch@cisco.com
 Wai Sum Lai
 AT&T Labs
 200 Laurel Avenue
 Middletown, New Jersey 07748, USA
 Phone: (732) 420-3712
 EMail: wlai@att.com

Le Faucheur & Lai Informational [Page 21] RFC 3564 Requirements for Diff-Serv-aware TE July 2003

11. Full Copyright Statement

 Copyright (C) The Internet Society (2003).  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.

Le Faucheur & Lai Informational [Page 22]

/data/webs/external/dokuwiki/data/pages/rfc/rfc3564.txt · Last modified: 2003/07/23 18:46 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki