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Versions: (draft-wu-mpls-diff-ext) 00 01 02 03 04 05 06 07 08 RFC 3270

                                                    Francois Le Faucheur
                                                                Liwen Wu
                                                             Bruce Davie
                                                           Cisco Systems

                                                          Shahram Davari
                                                         PMC-Sierra Inc.

                                                           Pasi Vaananen
                                                                   Nokia

                                                            Ram Krishnan
                                                     Lucent Technologies

                                                         Pierrick Cheval
                                                                 Alcatel

                                                           Juha Heinanen
                                                           Telia Finland

IETF Internet Draft
Expires: August, 2001
Document: draft-ietf-mpls-diff-ext-08.txt              February, 2001


                MPLS Support of Differentiated Services


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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Le Faucheur, et. al                                                  1
                      MPLS Support of Diff-Serv          February 2001

Abstract

   This document defines a flexible solution for support of
   Differentiated Services (Diff-Serv) over Multi-Protocol Label
   Switching (MPLS) networks.

   This solution allows the MPLS network administrator to select how
   Diff-Serv Behavior Aggregates (BAs) are mapped onto Label Switched
   Paths (LSPs) so that he/she can best match the Diff-Serv, Traffic
   Engineering and protection objectives within his/her particular
   network. For instance, this solution allows the network
   administrator to decide whether different sets of BAs are to be
   mapped onto the same LSP or mapped onto separate LSPs.

   This solution relies on combined use of two types of LSPs:
     - LSPs which can transport multiple Ordered Aggregates, so that
       the EXP field of the MPLS Shim Header conveys to the LSR the PHB
       to be applied to the packet (covering both information about the
       packet's scheduling treatment and its drop precedence).
     - LSPs which only transport a single Ordered Aggregate, so that
       the packet's scheduling treatment is inferred by the LSR
       exclusively from the packet's label value while the packet's
       drop precedence is conveyed in the EXP field of the MPLS Shim
       Header or in the encapsulating link layer specific selective
       drop mechanism (ATM, Frame Relay, 802.1).


1. Introduction

   In an MPLS domain [MPLS_ARCH], when a stream of data traverses a
   common path, a Label Switched Path (LSP) can be established using
   MPLS signaling protocols. At the ingress Label Switch Router (LSR),
   each packet is assigned a label and is transmitted downstream. At
   each LSR along the LSP, the label is used to forward the packet to
   the next hop.

   In a Differentiated Service (Diff-Serv) domain [DIFF_ARCH] all the
   IP packets crossing a link and requiring the same Diff-Serv behavior
   are said to constitute a Behavior Aggregate (BA). At the ingress
   node of the Diff-Serv domain the packets are classified and marked
   with a Diff-Serv Code Point (DSCP) which corresponds to their
   Behavior Aggregate. At each transit node, the DSCP is used to select
   the Per Hop Behavior (PHB) that determines the scheduling treatment
   and, in some cases, drop probability for each packet.

   This document specifies a solution for supporting the Diff-Serv
   Behavior Aggregates whose corresponding PHBs are currently defined
   (in [DIFF_HEADER], [DIFF_AF], [DIFF_EF]) over an MPLS network. This
   solution also offers flexibility for easy support of PHBs that may
   be defined in the future.

   As mentioned in [DIFF_HEADER], "Service providers are not required

 Le Faucheur et. al                                                  2
                      MPLS Support of Diff-Serv          February 2001

   to use the same node mechanisms or configurations to enable service
   differentiation within their networks, and are free to configure the
   node parameters in whatever way that is appropriate for their
   service offerings and traffic engineering objectives". Thus, the
   solution defined in this document gives Service Providers
   flexibility in selecting how Diff-Serv classes of service are Routed
   or Traffic Engineered within their domain (e.g. separate classes of
   services supported via separate LSPs and Routed separately, all
   classes of service supported on the same LSP and Routed together).

   Because MPLS is path-oriented it can potentially provide faster and
   more predictable protection and restoration capabilities in the face
   of topology changes than conventional hop by hop routed IP systems.
   In this document we refer to such capabilities as "MPLS protection".
   Although such capabilities and associated mechanisms are outside the
   scope of this specification, we note that they may offer different
   levels of protection to different LSPs. Since the solution presented
   here allow Service Providers to choose how Diff-Serv classes of
   services are mapped onto LSPs, the solution also gives Service
   Providers flexibility in the level of protection provided to
   different Diff-Serv classes of service (e.g. some classes of service
   can be supported by LSPs which are protected while some other
   classes of service are supported by LSPs which are not protected).

   Furthermore, the solution specified in this document achieves label
   space conservation and reduces the volume of label set-up/tear-down
   signaling where possible by only resorting to multiple LSPs for a
   given Forwarding Equivalent Class (FEC) [MPLS_ARCH] when useful or
   required.

   This specification allows support of Differentiated Services for
   both IPv4 and IPv6 traffic transported over an MPLS network.
   This document only describes operations for unicast. Multicast
   support is for future study.

   The solution described in this document does not preclude the
   signaled or configured use of the EXP bits to support Explicit
   Congestion Notification [ECN] simultaneously with Diff-Serv over
   MPLS. However, techniques for supporting ECN in an MPLS environment
   are outside the scope of this document.

1.1  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in
   this document are to be interpreted as described in RFC 2119.

   The reader is assumed to be familiar with the terminology of
   [MPLS_ARCH], [MPLS_ENCAPS], [MPLS_ATM] and [MPLS_FR] including the
   following:

     EXP        EXPerimental (bits)

 Le Faucheur et. al                                                  3
                      MPLS Support of Diff-Serv          February 2001


     FEC        Forwarding Equivalency Class

     FTN        FEC-To-NHLFE Map

     ILM        Incoming Label Map

     LC-ATM     Label Switching Controlled-ATM (interface)

     LC-FR      Label Switching Controlled-Frame Relay (interface)

     LSP        Label Switched Path

     LSR        Label Switch Router

     MPLS       Multi-Protocol Label Switching

     NHLFE      Next Hop Label Forwarding Entry

   The reader is assumed to be familiar with the terminology of
   [DIFF_ARCH], [DIFF_HEADER], [DIFF_AF] and [DIFF_EF] including the
   following:

     AF         Assured Forwarding

     BA         Behavior Aggregate

     CS         Class Selector

     DF         Default Forwarding

     DSCP       Differentiated Services Code Point

     EF         Expedited Forwarding

     PHB        Per Hop Behavior

   The reader is assumed to be familiar with the terminology of
   [DIFF_NEW] including the following:

     OA        Ordered Aggregate. The set of Behavior Aggregates which
               share an ordering constraint.

     PSC       PHB Scheduling Class. The set of one or more PHB(s) that
               are applied to the Behavior Aggregate(s) belonging to a
               given OA. For example, AF1x is a PSC comprising the
               AF11, AF12 and AF13 PHBs. EF is an example of PSC
               comprising a single PHB, the EF PHB.

   The following acronyms are also used:

     CLP        Cell Loss Priority

 Le Faucheur et. al                                                  4
                      MPLS Support of Diff-Serv          February 2001


     DE         Discard Eligibility

     SNMP       Simple Network Management Protocol

   Finally, the following acronyms are defined in this specification:

     E-LSP      EXP-Inferred-PSC LSP

     L-LSP      Label-Only-Inferred-PSC LSP

1.2 EXP-Inferred-PSC LSPs (E-LSP)

   A single LSP can be used to support up to eight BAs of a given FEC,
   regardless of how many OAs these BAs span. With such LSPs, the EXP
   field of the MPLS Shim Header is used by the LSR to determine the
   PHB to be applied to the packet. This includes both the PSC and the
   drop preference.

   We refer to such LSPs as "EXP-inferred-PSC LSPs" (E-LSP), since the
   PSC of a packet transported on this LSP depends on the EXP field
   value for that packet.

   The mapping from EXP field to PHB (ie to PSC and drop precedence)
   for a given such LSP, is either explicitly signaled at label set-up
   or relies on a pre-configured mapping.

   Detailed operations of E-LSPs are specified in section 3 below.

1.3 Label-Only-Inferred-PSC LSPs (L-LSP)

   A separate LSP can be established for a single <FEC, OA> pair.
   With such LSPs, the PSC is explicitly signaled at label
   establishment time so that, after label establishment, the LSR can
   infer exclusively from the label value the PSC to be applied to a
   labeled packet. When the Shim Header is used, the Drop Precedence to
   be applied by the LSR to the labeled packet, is conveyed inside the
   labeled packet MPLS Shim Header using the EXP field. When the Shim
   Header is not used (e.g. MPLS Over ATM), the Drop Precedence to be
   applied by the LSR to the labeled packet is conveyed inside the link
   layer header encapsulation using link layer specific drop precedence
   fields (e.g. ATM CLP).

   We refer to such LSPs as "Label-Only-Inferred-PSC LSPs" (L-LSP)
   since the PSC can be fully inferred from the label without any other
   information (e.g. regardless of the EXP field value). Detailed
   operations of L-LSPs are specified in section 4 below.

1.4 Overall Operations

   For a given FEC, and unless media specific restrictions apply as
   identified in the sections 7, 8 and 9 below, this specification

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                      MPLS Support of Diff-Serv          February 2001

   allows any one of the following combinations within an MPLS Diff-
   Serv domain:
     - zero or any number of E-LSPs, and
     - zero or any number of L-LSPs.

   The network administrator selects the actual combination of LSPs
   from the set of allowed combinations and selects how the Behavior
   Aggregates are actually transported over this combination of LSPs,
   in order to best match his/her environment and objectives in terms
   of Diff-Serv support, Traffic Engineering and MPLS Protection.
   Criteria for selecting such a combination are outside the scope of
   this specification.

   For a given FEC, there may be more than one LSP carrying the same
   OA, for example for purposes of load balancing of the OA; However in
   order to respect ordering constraints, all packets of a given
   microflow, possibly spanning multiple BAs of a given Ordered
   Aggregate, MUST be transported over the same LSP. Conversely, each
   LSP MUST be capable of supporting all the (active) BAs of a given
   OA.

   Examples of deployment scenarios are provided for information in
   APPENPIX A.

1.5 Relationship between Label and FEC

   [MPLS_ARCH] states in section `2.1. Overview' that:
   `Some routers analyze a packet's network layer header not merely to
   choose the packet's next hop, but also to determine a packet's
   "precedence" or "class of service".  They may then apply different
   discard thresholds or scheduling disciplines to different packets.
   MPLS allows (but does not require) the precedence or class of
   service to be fully or partially inferred from the label.  In this
   case, one may say that the label represents the combination of a FEC
   and a precedence or class of service.'

   In line with this, we observe that:
     - With E-LSPs, the label represents the combination of a FEC and
       the set of BAs transported over the E-LSP). Where all the
       supported BAs are transported over an E-LSP, the label then
       represents the complete FEC.
     - With L-LSPs, the label represents the combination of a FEC and
       an OA.

1.6 Bandwidth Reservation for E-LSPs and L-LSPs

   Regardless of which label binding protocol is used, E-LSPs and
   L-LSPs may be established without bandwidth reservation or with
   bandwidth reservation.

   Establishing an E-LSP or L-LSP with bandwidth reservation means that
   bandwidth requirements for the LSP are signaled at LSP establishment

 Le Faucheur et. al                                                  6
                      MPLS Support of Diff-Serv          February 2001

   time. Such signaled bandwidth requirements may be used by LSRs at
   establishment time to perform admission control of the signaled LSP
   over the Diff-Serv resources provisioned (e.g. via configuration,
   SNMP or policy protocols) for the relevant PSC(s). Such signaled
   bandwidth requirements may also be used by LSRs at establishment
   time to perform adjustment to the Diff-Serv resources associated
   with the relevant PSC(s) (e.g. adjust PSC scheduling weight).

   Note that establishing an E-LSP or L-LSP with bandwidth reservation
   does not mean that per-LSP scheduling is necessarily required. Since
   E-LSPs and L-LSPs are specified in this document for support of
   Differentiated Services, the required forwarding treatment
   (scheduling and drop policy) is defined by the appropriate Diff-Serv
   PHB. This forwarding treatment MUST be applied by the LSR at the
   granularity of the BA and MUST be compliant with the relevant PHB
   specification.

   When bandwidth requirements are signaled at establishment of an
   L-LSP, the signaled bandwidth is obviously associated with the
   L-LSP's PSC. Thus, LSRs which use the signaled bandwidth to perform
   admission control may perform admission control over Diff-Serv
   resources which are dedicated to the PSC (e.g. over the bandwidth
   guaranteed to the PSC through its scheduling weight).

   When bandwidth requirements are signaled at establishment of an
   E-LSP, the signaled bandwidth is associated collectively to the
   whole LSP and therefore to the set of transported PSCs. Thus, LSRs
   which use the signaled bandwidth to perform admission control may
   perform admission control over global resources which are shared by
   the set of PSCs (e.g. over the total bandwidth of the link).

   Examples of scenarios where bandwidth reservation is not used and
   scenarios where bandwidth reservation is used are provided for
   information in APPENDIX B.


2. Label Forwarding Model for Diff-Serv LSRs and Tunneling Models

2.1 Label Forwarding Model for Diff-Serv LSRs

   Since different Ordered Aggregates of a given FEC may be transported
   over different LSPs, the label swapping decision of a Diff-Serv LSR
   clearly depends on the forwarded packet's Behavior Aggregate. Also,
   since the IP DS field of a forwarded packet may not be directly
   visible to an LSR, the way to determine the PHB to be applied to a
   received packet and to encode the PHB into a transmitted packet is
   different than a non-MPLS Diff-Serv Router.

   Thus, in order to describe Label Forwarding by Diff-Serv LSRs, we
   model the LSR Diff-Serv label switching behavior as comprising four
   stages:
     - Incoming PHB Determination (A)

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                      MPLS Support of Diff-Serv          February 2001

     - Outgoing PHB Determination with Optional Traffic Conditioning(B)
     - Label Forwarding (C)
     - Encoding of Diff-Serv information into Encapsulation Layer (EXP,
       CLP, DE, User_Priority)  (D)

   Each stage is described in more details in the following sections.

   Obviously, to enforce the Diff-Serv service differentiation the LSR
   MUST also apply the forwarding treatment corresponding to the
   Outgoing PHB.

   This model is illustrated below:

   --Inc_label(s)(*)------------------------>I===I--Outg_label(s)(&)-->
     \                                       I   I \
      \---->I===I                            I C I  \-->I===I--Encaps->
            I A I           I===I--Outg_PHB->I===I      I D I   (&)
   -Encaps->I===I--Inc_PHB->I B I         \          /->I===I
      (*)                   I===I          \--------+
                                                     \----Forwarding-->
                                                           Treatment
                                                             (PHB)

   "Encaps" designates the Diff-Serv related information encoded in the
   MPLS Encapsulation layer (eg EXP field, ATM CLP, Frame Relay DE,
   802.1 User_Priority)

   (*) when the LSR behaves as an MPLS ingress node, the incoming
   packet may be received unlabelled.

   (&) when the LSR behaves as an MPLS egress node, the outgoing packet
   may be transmitted unlabelled.

   This model is presented here to describe the functional operations
   of Diff-Serv LSRs and does not constrain actual implementation.

2.2 Incoming PHB Determination

   This stage determines which Behavior Aggregate the received packet
   belongs to.

2.2.1 Incoming PHB Determination Considering a Label Stack Entry

   Sections 3.3 and 4.3 provide the details on how to perform incoming
   PHB Determination considering a given received label stack entry
   and/or received incoming MPLS encapsulation information depending on
   the incoming LSP type and depending on the incoming MPLS
   encapsulation.

   Section 2.6 provides the details of which label stack entry to
   consider for the Incoming PHB Determination depending on the
   supported Diff-Serv tunneling mode.

 Le Faucheur et. al                                                  8
                      MPLS Support of Diff-Serv          February 2001


2.2.2 Incoming PHB Determination Considering IP Header

   Section 2.6 provides the details of when the IP Header is to be
   considered for incoming PHB determination depending on the supported
   Diff-Serv tunneling model. In those cases where the IP header is to
   be used, this stage operates exactly as with a non-MPLS IP Diff-Serv
   Router and uses the DS field to determine incoming PHB.

2.3 Outgoing PHB Determination With Optional Traffic Conditioning

   The traffic conditioning stage is optional and may be used on an LSR
   to perform traffic conditioning including Behavior Aggregate
   demotion or promotion. It is outside the scope of this
   specification. For the purpose of specifying Diff-Serv over MPLS
   forwarding, we simply note that the PHB to be actually enforced, and
   conveyed to downstream LSRs, by an LSR (referred to as "outgoing
   PHB") may be different to the PHB which had been associated with the
   packet by the previous LSR (referred to as "incoming PHB").

   When the traffic conditioning stage is not present, the "outgoing
   PHB" is simply identical to the "incoming PHB".

2.4 Label Forwarding

   [MPLS_ARCH] describes how label swapping is performed by LSRs on
   incoming labeled packets using an Incoming Label Map (ILM), where
   each incoming label is mapped to one or multiple NHLFEs. [MPLS_ARCH]
   also describes how label imposition is performed by LSRs on incoming
   unlabelled packets using a FEC-to-NHLFEs Map (FTN), where each
   incoming FEC is mapped to one or multiple NHLFEs.

   A Diff-Serv Context for a label is defined as comprising:
     - `LSP type (ie E-LSP or L-LSP)'
     - `supported PHBs'
     - `Encaps-->PHB mapping' for an incoming label
     - `Set of PHB-->Encaps mappings' for an outgoing label

   The present specification defines that a Diff-Serv Context is stored
   in the ILM for each incoming label.

   [MPLS_ARCH] states that the `NHLFE may also contain any other
   information needed in order to properly dispose of the packet'. In
   accordance with this, the present specification defines that a Diff-
   Serv Context is stored in the NHLFE for each outgoing label which is
   swapped or pushed.

   This Diff-Serv Context information is populated into the ILM and the
   FTN at label establishment time.

   If the label corresponds to an E-LSP for which no EXP<-->PHB mapping
   has been explicitly signaled at LSP setup, the `supported PHBs' is

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                      MPLS Support of Diff-Serv          February 2001

   populated with the set of PHBs of the preconfigured
   EXP<-->PHB Mapping, which is discussed below in section 3.2.1.

   If the label corresponds to an E-LSP for which an EXP<-->PHB mapping
   has been explicitly signaled at LSP setup, the `supported PHBs' is
   populated with the set of PHBs of the signaled EXP<-->PHB mapping.

   If the label corresponds to an L-LSP, the `supported PHBs' is
   populated with the set of PHBs forming the PSC that is signaled at
   LSP set-up.

   The details of how the `Encaps-->PHB mapping' or `Set of
   PHB-->Encaps mappings' are populated are defined below in sections 3
   and 4.

   [MPLS_ARCH] also states that:
   "If the ILM [respectively, FTN] maps a particular label to a set of
   NHLFEs that contains more than one element, exactly one element of
   the set must be chosen before the packet is forwarded.  The
   procedures for choosing an element from the set are beyond the scope
   of this document.  Having the ILM [respectively, FTN] map a label
   [respectively, a FEC] to a set containing more than one NHLFE may be
   useful if, e.g., it is desired to do load balancing over multiple
   equal-cost paths."

   In accordance with this, the present specification allows that an
   incoming label [respectively FEC] may be mapped, for Diff-Serv
   purposes, to multiple NHLFEs (for instance where different NHLFEs
   correspond to egress labels supporting different sets of PHBs). When
   a label [respectively FEC] maps to multiple NHLFEs, the Diff-Serv
   LSR MUST choose one of the NHLFEs whose Diff-Serv Context indicates
   that it supports the Outgoing PHB of the forwarded packet.

   When a label [respectively FEC] maps to multiple NHLFEs which
   supports the Outgoing PHB, the procedure for choosing one among
   those is outside the scope of this document. This situation may be
   encountered where it is desired to do load balancing of a Behavior
   Aggregate over multiple LSPs. In such situations, in order to
   respect ordering constraints, all packets of a given microflow MUST
   be transported over the same LSP.

2.5 Encoding Diff-Serv Information Into Encapsulation Layer

   This stage determines how to encode the fields which convey Diff-
   Serv information in the transmitted packet (e.g. MPLS Shim EXP, ATM
   CLP, Frame Relay DE, 802.1 User_Priority).

2.5.1 Encoding Diff-Serv Information Into Transmitted Label Entry

   Sections 3.5 and 4.5 provide the details on how to perform Diff-Serv
   information encoding into a given transmitted label stack entry
   and/or transmitted MPLS encapsulation information depending on the

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                      MPLS Support of Diff-Serv          February 2001

   corresponding outgoing LSP type and depending on the MPLS
   encapsulation.

   Section 2.6 provides the details of which label stack entry to
   perform Diff-Serv information encoding into depending on the
   supported Diff-Serv tunneling mode.

2.5.2 Encoding Diff-Serv Information Into Transmitted IP Header

   To perform Diff-Serv Information Encoding into the transmitted
   packet IP header, this stage operates exactly as with a non-MPLS IP
   Diff-Serv Router and encodes the DSCP of the Outgoing PHB into the
   DS field.

   Section 2.6 provides the details of when Diff-Serv Information
   Encoding is to be performed into transmitted IP header depending on
   the supported Diff-Serv tunneling mode.

2.6 Diff-Serv Tunneling Models over MPLS

2.6.1 Diff-Serv Tunneling Models

   [DIFF_TUNNEL] considers the interaction of Differentiated Services
   with IP tunnels of various forms. MPLS LSPs are not a form of "IP
   tunnels" since the MPLS encapsulating header does not contain an IP
   header and thus MPLS LSPs are not considered in [DIFF_TUNNEL].
   However, although not a form of "IP tunnel", MPLS LSPs are a form of
   "tunnel".

   From the Diff-Serv standpoint, LSPs share a lot of characteristics
   with IP Tunnels:
     - Intermediate nodes (i.e. Nodes somewhere along the LSP span)
       only see and operate on the "outer" Diff-Serv information.
     - LSPs are unidirectional.
     - The "outer" Diff-Serv information can be modified at any
       intermediate nodes.

   However, from the Diff-Serv standpoint, LSPs also have a
   distinctive property compared to IP Tunnels:
     - There is generally no behavior analogous to Penultimate Hop
       Popping (PHP) used with IP Tunnels. Furthermore, PHP results in
       the "outer" Diff-Serv information associated with the LSP not
       being visible to the LSP egress. In situations where this
       information is not meaningful at the LSP Egress, this is
       obviously not an issue at all. In situations where this
       information is meaningful at the LSP Egress, then it must
       somehow be carried in some other means.

   The two conceptual models for Diff-Serv tunneling over IP Tunnels
   defined in [DIFF_TUNNEL] are applicable and useful to Diff-Serv over
   MPLS but their respective detailed operations is somewhat different
   over MPLS. These two models are the Pipe Model and the Uniform

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                      MPLS Support of Diff-Serv          February 2001

   Model. Their operations over MPLS are specified in the following
   sections. Discussion and definition of alternative tunneling models
   are outside the scope of this specification.

2.6.2 Pipe Model

   With the Pipe Model, MPLS tunnels (aka LSPs) are used to hide the
   intermediate MPLS nodes between LSP Ingress and Egress from the
   Diff-Serv perspective.

   In this model, tunneled packets must convey two meaningful pieces of
   Diff-Serv information:
     - the Diff-Serv information which is meaningful to intermediate
       nodes along the LSP span including the LSP Egress (which we
       refer to as the "LSP Diff-Serv Information"). This LSP Diff-Serv
       Information is not meaningful beyond the LSP Egress: Whether
       Traffic Conditioning at intermediate nodes on the LSP span
       affects the LSP Diff-Serv information or not, this updated Diff-
       Serv information is not considered meaningful beyond the LSP
       Egress and is ignored.
     - the Diff-Serv information which is meaningful beyond the LSP
       Egress (which we refer to as the "Tunneled Diff-Serv
       Information"). This information is to be conveyed by the LSP
       Ingress to the LSP Egress. This Diff-Serv information is not
       meaningful to the intermediate nodes on the LSP span.


   Operation of the Pipe Model without PHP is illustrated below:

            ========== LSP =============================>

                ---Swap--(M)--...--Swap--(M)--Swap----
               /        (outer header)                \
             (M)                                      (M)
             /                                          \
   >--(m)-Push.................(m).....................Pop--(m)-->
            I             (inner header)                E   (M*)

   (M) represents the "LSP Diff-Serv information"
   (m) represents the "Tunneled Diff-Serv information"
   (*) The LSP Egress considers the LSP Diff-Serv information received
      in the outer header (i.e. before the pop) in order to apply its
      Diff-Serv forwarding treatment (i.e. actual PHB)
    I represents the LSP ingress node
    E represents the LSP egress node


   With the Pipe Model, the "LSP Diff-Serv Information" needs to be
   conveyed to LSP Egress so that it applies its forwarding treatment
   based on it. The "Tunneled Diff-Serv information" also needs to be
   conveyed to the LSP Egress so it can be conveyed further downstream.


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                      MPLS Support of Diff-Serv          February 2001

   Since both Diff-Serv information need to be conveyed to the LSP
   Egress, the Pipe Model operates only without PHP.

   The Pipe Model is particularly appropriate to environments in which:
     - the cloud upstream of the incoming interface of the LSP Ingress
       and the cloud downstream of the outgoing interface of the LSP
       Egress are in Diff-Serv domains which use a common set of Diff-
       Serv service provisioning policies and PHB definitions, while
       the LSP spans one (or more) Diff-Serv domain(s) which use(s) a
       different set of Diff-Serv service provisioning policies and PHB
       definitions
     - the outgoing interface of the LSP Egress is in the (last) Diff-
       Serv domain spanned by the LSP.

   As an example, consider the case where a service provider is
   offering an MPLS VPN service (see [MPLS_VPN] for an example of MPLS
   VPN architecture) including Diff-Serv differentiation. Say that a
   collection of sites are interconnected via such an MPLS VPN service.
   Now say that this collection of sites are managed under a common
   administration and are also supporting Diff-Serv service
   differentiation. If the VPN site administration and the Service
   Provider are not sharing the exact same Diff-Serv policy (for
   instance not supporting the same number of PHBs), then operation of
   Diff-Serv in the Pipe Model over the MPLS VPN service would allow
   the VPN Sites Diff-Serv policy to operate consistently throughout
   the ingress VPN Site and Egress VPN Site and transparently over the
   Service Provider Diff-Serv domain. It may be useful to view such
   LSPs as linking the Diff-Serv domains at their endpoints into a
   single Diff-Serv region by making these endpoints virtually
   contiguous even though they may be physically separated by
   intermediate network nodes.

   The Pipe Model MUST be supported.

   For support of the Pipe Model over a given LSP without PHP, an LSR
   performs the Incoming PHB Determination and the Diff-Serv
   information Encoding in the following manner:
     - when receiving an unlabelled packet, the LSR performs Incoming
       PHB Determination considering the received IP Header.
     - when receiving a labeled packet, the LSR performs Incoming PHB
       Determination considering the outer label entry in the received
       label stack. In particular, when a pop operation is to be
       performed for the considered LSP, the LSR performs Incoming PHB
       Determination BEFORE the pop.
     - when performing a push operation for the considered LSP, the
       LSR:
           o encodes Diff-Serv Information corresponding to the
             OUTGOING PHB in the transmitted label entry corresponding
             to the pushed label.
           o encodes Diff-Serv Information corresponding to the
             INCOMING PHB in the encapsulated header (swapped label
             entry or IP header).

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                      MPLS Support of Diff-Serv          February 2001

     - when performing a swap-only operation for the considered LSP,
       the LSR encodes Diff-Serv Information in the transmitted label
       entry that contains the swapped label
     - when performing a pop operation for the considered LSP, the LSR
       does not perform Encoding of Diff-Serv Information into the
       header exposed by the pop operation (i.e. the LSR leaves the
       exposed header "as is").

2.6.2.1 Short Pipe Model

   The Short Pipe Model is an optional variation over the Pipe Model
   described above. The only difference is that, with the Short Pipe
   Model, the Diff-Serv forwarding treatment at the LSP Egress is
   applied based on the "Tunneled Diff-Serv Information" (i.e. Diff-
   Serv information conveyed in the encapsulated header) rather than on
   the "LSP Diff-Serv information" (i.e. Diff-Serv information conveyed
   in the encapsulating header).


   Operation of the Short Pipe Model without PHP is illustrated below:

            ========== LSP =============================>

                ---Swap--(M)--...--Swap--(M)--Swap----
               /        (outer header)                \
             (M)                                      (M)
             /                                          \
   >--(m)-Push.................(m).....................Pop--(m)-->
            I             (inner header)                E

   (M) represents the "LSP Diff-Serv information"
   (m) represents the "Tunneled Diff-Serv information"
    I represents the LSP ingress node
    E represents the LSP egress node


   Since the LSP Egress applies its forwarding treatment based on the
   "Tunneled Diff-Serv Information", the "LSP Diff-Serv information"
   does not need to be conveyed by the penultimate node to the LSP
   Egress. Thus the Short Pipe Model can also operate with PHP.

   Operation of the Short Pipe Model with PHP is illustrated below:

            =========== LSP ============================>

                 ---Swap--(M)--...--Swap------
                /       (outer header)        \
              (M)                             (M)
              /                                 \
    >--(m)-Push.................(m).............Pop-(m)--E--(m)-->
            I           (inner header)           P (M*)


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                      MPLS Support of Diff-Serv          February 2001

   (M) represents the "LSP Diff-Serv information"
   (m) represents the "Tunneled Diff-Serv information"
   (*) The Penultimate LSR considers the LSP Diff-Serv information
      received in the outer header (i.e. before the pop) in order to
      apply its Diff-Serv forwarding treatment (i.e. actual PHB)
    I represents the LSP ingress node
    P represents the LSP penultimate node
    E represents the LSP egress node


   The Short Pipe Model is particularly appropriate to environments in
   which:
     - the cloud upstream of the incoming interface of the LSP Ingress
       and the cloud downstream of the outgoing interface of the LSP
       Egress are in Diff-Serv domains which use a common set of Diff-
       Serv service provisioning policies and PHB definitions, while
       the LSP spans one (or more) Diff-Serv domain(s) which use(s) a
       different set of Diff-Serv service provisioning policies and PHB
       definitions
     - the outgoing interface of the LSP Egress is in the same Diff-
       Serv domain as the cloud downstream of it.

   Since each outgoing interface of the LSP Egress is in the same Diff-
   Serv domain as the cloud downstream of it, each outgoing interface
   may potentially be in a different Diff-Serv domain, and the LSP
   Egress needs to be configured with awareness of every corresponding
   Diff-Serv policy. This operational overhead is justified in some
   situations where the respective downstream Diff-Serv policies are
   better suited to offering service differentiation over each egress
   interface than the common Diff-Serv policy used on the LSP span. An
   example of such a situation is where a Service Provider offers an
   MPLS VPN service and where some VPN users request that their own VPN
   Diff-Serv policy be applied to control service differentiation on
   the dedicated link from the LSP Egress to the destination VPN site,
   rather than the Service Provider's Diff-Serv policy.

   The Short Pipe Model MAY be supported.

   For support of the Short Pipe Model over a given LSP without PHP, an
   LSR performs the Incoming PHB Determination and the Diff-Serv
   information Encoding in the same manner as with the Pipe Model with
   the following exception:
     - when receiving a labeled packet, the LSR performs Incoming PHB
       Determination considering the header (label entry or IP header)
       which is used to do the actual forwarding. In particular, when a
       pop operation is to be performed for the considered LSP, the LSR
       performs Incoming PHB Determination AFTER the pop.

   For support of the Short Pipe Model over a given LSP with PHP, an
   LSR performs Incoming PHB Determination and Diff-Serv information
   Encoding in the same manner as without PHP with the following
   exceptions:

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                      MPLS Support of Diff-Serv          February 2001

     - the Penultimate LSR performs Incoming PHB Determination
       considering the outer label entry in the received label stack.
       In other words, when a pop operation is to be performed for the
       considered LSP, the Penultimate LSR performs Incoming PHB
       Determination BEFORE the pop.
   Note that the behavior of the Penultimate LSR in the Short Pipe Mode
   with PHP, is identical to the behavior of the LSP Egress in the Pipe
   Mode (necessarily without PHP).

2.6.3 Uniform Model

   With the Uniform Model, MPLS tunnels (aka LSPs) are viewed as
   artifacts of the end-to-end path from the Diff-Serv standpoint. MPLS
   Tunnels may be used for forwarding purposes but have no significant
   impact on Diff-Serv. In this model, any packet contains exactly one
   piece of Diff-Serv information which is meaningful and is always
   encoded in the outer most label entry (or in the IP DSCP where the
   IP packet is transmitted unlabelled for instance at the egress of
   the LSP). Any Diff-Serv information encoded somewhere else (e.g. in
   deeper label entries) is of no significance to intermediate nodes or
   to the tunnel egress and is ignored. If Traffic Conditioning at
   intermediate nodes on the LSP span affects the "outer" Diff-Serv
   information, the updated Diff-Serv information is the one considered
   meaningful at the egress of the LSP.


   Operation of the Uniform Model without PHP is illustrated below:

             ========== LSP =============================>

                 ---Swap--(M)--...-Swap--(M)--Swap----
                /         (outer header)              \
              (M)                                     (M)
              /                                         \
   >--(M)--Push...............(x).......................Pop--(M)->
            I            (inner header)                  E

   (M) represents the Meaningful Diff-Serv information encoded in the
   corresponding header.
   (x) represents non-meaningful Diff-Serv information.
    I represents the LSP ingress node
    E represents the LSP egress node


   Operation of the Uniform Model with PHP is illustrated below :

             ========== LSP =========================>

                 ---Swap-(M)-...-Swap------
                /        (outer header)    \
              (M)                          (M)
              /                              \

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                      MPLS Support of Diff-Serv          February 2001

   >--(M)--Push..............(x)............Pop-(M)--E--(M)->
             I          (inner header)       P

   (M) represents the Meaningful Diff-Serv information encoded in the
   corresponding header.
   (x) represents non-meaningful Diff-Serv information.
    I represents the LSP ingress node
    P represents the LSP penultimate node
    E represents the LSP egress node


   The Uniform Model for Diff-Serv over MPLS is such that, from the
   Diff-Serv perspective, operations are exactly identical to the
   operations if MPLS was not used. In other words, MPLS is entirely
   transparent to the Diff-Serv operations.

   Use of the Uniform Model allows LSPs to span Diff-Serv domain
   boundaries without any other measure in place than an inter-domain
   Traffic Conditioning Agreement at the physical boundary between the
   Diff-Serv domains and operating exclusively on the "outer" header,
   since the meaningful Diff-Serv information is always visible and
   modifiable in the outmost label entry.

   The Uniform Model MAY be supported.

   For support of the Uniform Model over a given LSP, an LSR performs
   Incoming PHB Determination and Diff-Serv information Encoding in the
   following manner:
     - when receiving an unlabelled packet, the LSR performs Incoming
       PHB Determination considering the received IP Header.
     - when receiving a labeled packet, the LSR performs Incoming PHB
       Determination considering the outer label entry in the received
       label stack. In particular, when a pop operation is to be
       performed for the considered LSP, the LSR performs Incoming PHB
       Determination BEFORE the pop.
     - when performing a push operation for the considered LSP, the LSR
       encodes Diff-Serv Information in the transmitted label entry
       corresponding to the pushed label. The Diff-Serv Information
       encoded in the encapsulated header (swapped label entry or IP
       Header) is of no importance.
     - when performing a swap-only operation for the considered LSP,
       the LSR encodes Diff-Serv Information in the transmitted label
       entry that contains the swapped label.
     - when PHP is used, the Penultimate LSR needs to be aware of the
       "Set of PHB-->Encaps mappings" for the label corresponding to
       the exposed header (or the PHB-->DSCP mapping) in order to
       perform Diff-Serv Information Encoding. Methods for providing
       this mapping awareness are outside the scope of this
       specification. As an example, the "PHB-->DSCP mapping" may be
       locally configured. As another example, in some environments, it
       may be appropriate for the Penultimate LSR to assume that the
       "Set of PHB-->Encaps mappings" to be used for the outgoing label

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                      MPLS Support of Diff-Serv          February 2001

       in the exposed header is the "Set of PHB-->Encaps mappings" that
       would be used by the LSR if the LSR was not doing PHP.
       Note also that this specification assumes that the Penultimate
       LSR does not perform label swapping over the label entry exposed
       by the pop operation (and in fact that it does not even look at
       the exposed label). Consequently, restrictions may apply to the
       Diff-Serv Information Encoding that can be performed by the
       Penultimate LSR. For example, this specification does not allow
       situations where the Penultimate LSR pops a label corresponding
       to an E-LSP supporting two PSCs, while the header exposed by the
       pop contains label values for two L-LSPs each supporting one
       PSC, since the Diff-Serv Information Encoding would require
       selecting one label or the other.

   Note that LSR behaviors for the Pipe , the Short Pipe and  the
   Uniform Model only differ when doing a push or a pop. Thus,
   Intermediate LSRs which perform swap only operations for an LSP,
   behave exactly in the same way regardless of whether they are
   behaving in the Pipe, Short Pipe or the Uniform model. With a Diff-
   Serv implementation supporting multiple Tunneling Models, only LSRs
   behaving as LSP Ingress, Penultimate LSR or LSP Egress need to be
   configured to operate in a particular Model. Signaling to associate
   a Diff-Serv tunneling model on a per-LSP basis is out of the scope
   of this specification.

2.6.4 Hierarchy

   Through the label stack mechanism, MPLS allows LSP tunneling to nest
   to any depth. We observe that with such nesting, the push of level
   N+1 takes place on a subsequent (or the same) LSR to the LSR doing
   the push for level N, while the pop of level N+1 takes place on a
   previous (or the same) LSR to the LSR doing the pop of level N. For
   a given level N LSP, the Ingress LSR doing the push and the LSR
   doing the pop (Penultimate LSR or LSP Egress) must operate in the
   same Tunneling Model (i.e. Pipe, Short Pipe or Uniform). However,
   there is no requirement for consistent tunneling models across
   levels so that LSPs at different levels may be operating in
   different Tunneling Models.

   Hierarchical operations is illustrated below in the case of two
   levels of tunnels:

               +--------Swap--...---+
              /    (outmost header)  \
             /                        \
           Push(2).................(2)Pop
           / (outer header)             \
          /                              \
   >>---Push(1)........................(1)Pop-->>
             (inner header)

   (1) Tunneling Model 1

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                      MPLS Support of Diff-Serv          February 2001

   (2) Tunneling Model 2
   Tunneling Model 2 may be the same as or may be different to
   Tunneling Model 1.


   For a given LSP of level N, the LSR must perform the Incoming PHB
   Determination and the Diff-Serv information Encoding as specified in
   section 2.6.2, 2.6.2.1 and 2.6.3 according to the Tunneling Model of
   this level N LSP and independently of the Tunneling Model of other
   level LSPs.


3. Detailed Operations of E-LSPs

3.1 E-LSP Definition

   E-LSPs are defined in section 1.2.

   Within a given MPLS Diff-Serv domain, all the E-LSPs relying on the
   pre-configured mapping are capable of transporting the same common
   set of 8, or fewer, BAs. Each of those E-LSPs may actually transport
   this full set of BAs or any arbitrary subset of it.

   For a given FEC, two given E-LSPs using signaled EXP<-->PHB mapping
   can support the same or different sets of Ordered Aggregates.

3.2 Populating the `Encaps-->PHB mapping' for an incoming E-LSP

   This section defines how the `Encaps-->PHB mapping' of the Diff-Serv
   Context is populated for an incoming E-LSP in order to allow
   Incoming PHB determination.

   The `Encaps-->PHB mapping' for an E-LSP is always of the form
   `EXP-->PHB mapping'.

   If the label corresponds to an E-LSP for which no EXP<-->PHB mapping
   has been explicitly signaled at LSP setup, the `EXP-->PHB mapping'
   is populated based on the Preconfigured EXP<-->PHB Mapping which is
   discussed below in section 3.2.1.

   If the label corresponds to an E-LSP for which an EXP<-->PHB mapping
   has been explicitly signaled at LSP setup, the `EXP-->PHB mapping'
   is populated as per the signaled EXP<-->PHB mapping.

3.2.1 Preconfigured EXP<-->PHB mapping

   LSRs supporting E-LSPs which use the preconfigured EXP<-->PHB
   mapping must allow local configuration of this EXP<-->PHB mapping.
   This mapping applies to all the E-LSPs established on this LSR
   without a mapping explicitly signaled at set-up time.



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                      MPLS Support of Diff-Serv          February 2001

   The preconfigured EXP<-->PHB mapping must either be consistent at
   every E-LSP hop throughout the MPLS Diff-Serv domain spanned by the
   LSP or appropriate remarking of the EXP field must be performed by
   the LSR whenever a different preconfigured mapping is used on the
   ingress and egress interfaces.

   In case, the preconfigured EXP<-->PHB mapping has not actually been
   configured by the Network Administrator, the LSR should use a
   default preconfigured EXP<-->PHB mapping which maps all EXP values
   to the Default PHB.

3.3 Incoming PHB Determination On Incoming E-LSP

   This section defines how Incoming PHB Determination is carried out
   when the considered label entry in the received label stack
   corresponds to an E-LSP. This requires that the `Encaps-->PHB
   mapping' is populated as defined in section 3.2.

   When considering a label entry corresponding to an incoming E-LSP
   for Incoming PHB Determination, the LSR:
     - determines the EXP-->PHB mapping by looking up the
       `Encaps-->PHB mapping' of the Diff-Serv Context associated in
       the ILM with the considered incoming E-LSP label.
     - determines the incoming PHB by looking up the EXP field of the
       considered label entry in the EXP-->PHB mapping table.

3.4 Populating the `Set of PHB-->Encaps mappings' for an outgoing E-LSP

   This section defines how the `Set of PHB-->Encaps mappings' of the
   Diff-Serv Context is populated at label setup for an outgoing E-LSP
   in order to allow Encoding of Diff-Serv information in the
   Encapsulation Layer.

3.4.1 `PHB-->EXP mapping'

   An outgoing E-LSP must always have a `PHB-->EXP mapping' as part of
   the `Set of PHB-->Encaps mappings' of its Diff-Serv Context.

   If the label corresponds to an E-LSP for which no EXP<-->PHB mapping
   has been explicitly signaled at LSP setup, this `PHB-->EXP mapping'
   is populated based on the Preconfigured EXP<-->PHB Mapping which is
   discussed above in section 3.2.1.

   If the label corresponds to an E-LSP for which an EXP<-->PHB mapping
   has been explicitly signaled at LSP setup, the `PHB-->EXP mapping'
   is populated as per the signaled EXP<-->PHB mapping.

3.4.2 `PHB-->CLP mapping'

   If the LSP is egressing over an ATM interface which is not label
   switching controlled, then one `PHB-->CLP mapping' is added to the


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                      MPLS Support of Diff-Serv          February 2001

   `Set of PHB-->Encaps mappings' for this outgoing LSP. This
   `PHB-->CLP mapping' is populated in the following way:
     - it is a function of the PHBs supported on this LSP, and may use
       the relevant mapping entries for these PHBs from the
       Default PHB-->CLP Mapping defined in section 3.4.2.1. Other
       mappings than the one defined in section 3.4.2.1 may be used. In
       particular, if a mapping from PHBs to CLP is standardized in the
       future for operations of Diff-Serv over ATM, such standardized
       mapping may then be used.

   For example if the outgoing label corresponds to an LSP supporting
   the AF1 PSC , then the `PHB-->CLP mapping' may be populated with:

        PHB                CLP Field

        AF11       ---->      0
        AF12       ---->      1
        AF13       ---->      1
        EF         ---->      0

   Notice that in this case the `Set of PHB-->Encaps mappings' contains
   both a `PHB-->EXP mapping' and a `PHB-->CLP mapping'.

3.4.2.1 Default PHB-->CLP Mapping

        PHB                CLP Bit

        DF         ---->      0
        CSn        ---->      0
        AFn1       ---->      0
        AFn2       ---->      1
        AFn3       ---->      1
        EF         ---->      0

3.4.3 `PHB-->DE mapping'

   If the LSP is egressing over a Frame Relay interface which is not
   label switching controlled, one `PHB-->DE mapping' is added to the
   `Set of PHB-->Encaps mappings' for this outgoing LSP and is
   populated in the following way:
     - it is a function of the PHBs supported on this LSP, and may use
       the relevant mapping entries for these PHBs from the Default
       PHB-->DE Mapping defined in section 3.4.3.1. Other mappings than
       the one defined in section 3.4.3.1 may be used. In particular,
       if a mapping from PHBs to DE is standardized in the future for
       operations of Diff-Serv over Frame Relay, such standardized
       mapping may then be used.

   Notice that in this case the `Set of PHB-->Encaps mappings' contains
   both a `PHB-->EXP mapping' and a `PHB-->DE mapping'.

3.4.3.1 Default PHB-->DE Mapping

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                      MPLS Support of Diff-Serv          February 2001


        PHB                 DE Bit

         DF       ---->       0
         CSn      ---->       0
         AFn1     ---->       0
         AFn2     ---->       1
         AFn3     ---->       1
         EF       ---->       0

3.4.4 `PHB-->802.1 mapping'

   If the LSP is egressing over a LAN interface on which multiple 802.1
   Traffic Classes are supported as per [IEEE_802.1], then one
   `PHB-->802.1 mapping' is added to the `Set of PHB-->Encaps mappings'
   for this outgoing LSP. This `PHB-->802.1 mapping' is populated in
   the following way:
     - it is a function of the PHBs supported on this LSP, an uses the
       relevant mapping entries for these PHBs from the Preconfigured
       PHB-->802.1 Mapping defined in section 3.4.4.1.

   Notice that the `Set of PHB-->Encaps mappings' then contains both a
   `PHB-->EXP mapping' and a `PHB-->802.1 mapping'.

3.4.4.1 Preconfigured `PHB-->802.1 Mapping'

   At the time of producing this specification, there are no
   standardized mapping from PHBs to 802.1 Traffic Classes.
   Consequently, an LSR supporting multiple 802.1 Traffic Classes over
   LAN interfaces must allow local configuration of a `PHB-->802.1
   Mapping'. This mapping applies to all the outgoing LSPs established
   by the LSR on such LAN interfaces.

3.5 Encoding Diff-Serv information into Encapsulation Layer On Outgoing
E-LSP

   This section defines how to encode Diff-Serv information into the
   MPLS encapsulation Layer for a given transmitted label entry
   corresponding to an outgoing E-LSP. This requires that the `Set of
   PHB-->Encaps mappings' is populated as defined in section 3.4.

   The LSR first determines the `Set of PHB-->Encaps mappings' of the
   Diff-Serv Context associated with the corresponding label in the
   NHLFE.

3.5.1 `PHB-->EXP mapping'

   If the `Set of PHB-->Encaps mappings' contains a mapping of the form
   `PHB-->EXP mapping', then the LSR:
      - determines the value to be written in the EXP field of the
       corresponding level label entry by looking up the "outgoing PHB"
       in this PHB-->EXP mapping table.

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                      MPLS Support of Diff-Serv          February 2001


3.5.2 `PHB-->CLP mapping'

   If the `Set of PHB-->Encaps mappings' contains a mapping of the form
   `PHB-->CLP mapping', then the LSR:
     - determines the value to be written in the CLP field of the ATM
       encapsulation header, by looking up the "outgoing PHB" in this
       PHB-->CLP mapping table.

3.5.3 `PHB-->DE mapping'

   If the `Set of PHB-->Encaps mappings' contains a mapping of the form
   `PHB-->DE mapping', then the LSR:
     - determines the value to be written in the DE field of the Frame
       Relay encapsulation header, by looking up the "outgoing PHB" in
       this PHB-->DE mapping table.

3.5.4 `PHB-->802.1 mapping'

   If the `Set of PHB-->Encaps mappings' contains a mapping of the form
   `PHB-->802.1 mapping', then the LSR:
     - determines the value to be written in the User_Priority field of
       the Tag Control Information of the 802.1 encapsulation header
       [IEEE_802.1], by looking up the "outgoing PHB" in this
       PHB-->802.1 mapping table.

3.6 E-LSP Merging

   In an MPLS domain, two or more LSPs can be merged into one LSP at
   one LSR. E-LSPs are compatible with LSP Merging under the following
   condition:

        E-LSPs can only be merged into one LSP if they support the
        exact same set of BAs.

   For E-LSPs using signaled EXP<-->PHB mapping, the above merge
   condition MUST be enforced by LSRs through explicit checking at
   label setup that the exact same set of PHBs is supported on the
   merged LSPs.

   For E-LSPs using the preconfigured EXP<-->PHB mapping, since the
   PHBs supported over an E-LSP is not signaled at establishment time,
   an LSR can not rely on signaling information to enforce the above
   merge. However all E-LSPs using the preconfigured EXP<-->PHB mapping
   are required to support the same set of Behavior Aggregates within a
   given MPLS Diff-Serv domain. Thus, merging of E-LSPs using the
   preconfigured EXP<-->PHB mapping is allowed within a given MPLS
   Diff-Serv domain.


4.  Detailed Operation of L-LSPs


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                      MPLS Support of Diff-Serv          February 2001

4.1 L-LSP Definition

   L-LSPs are defined in section 1.3.

4.2 Populating the `Encaps-->PHB mapping' for an incoming L-LSP

   This section defines how the `Encaps-->PHB mapping' of the Diff-Serv
   Context is populated at label setup for an incoming L-LSP in order
   to allow Incoming PHB determination.

4.2.1 `EXP-->PHB mapping'

   If the LSR terminates the MPLS Shim Layer over this incoming L-LSP
   and the L-LSP ingresses on an interface which is not ATM nor Frame
   Relay, then the `Encaps-->PHB mapping' is populated in the following
   way:
     - it is actually a `EXP-->PHB mapping'
     - this mapping is a function of the PSC which is carried on this
       LSP, and must use the relevant mapping entries for this PSC from
       the Mandatory EXP/PSC-->PHB Mapping defined in Section 4.2.1.1.

   For example if the incoming label corresponds to an L-LSP supporting
   the AF1 PSC, then the `Encaps-->PHB mapping' will be populated with:

      EXP Field              PHB

        000        ---->    AF11
        001        ---->    AF12
        011        ---->    AF13

   An LSR supporting L-LSPs over PPP interfaces and LAN interfaces is
   an example of LSR terminating the Shim layer over ingress interfaces
   which are not ATM nor Frame Relay.

   If the LSR terminates the MPLS Shim Layer over this incoming L-LSP
   and the L-LSP ingresses on an ATM or Frame Relay interface, then the
   `Encaps-->PHB mapping' is populated in the following way:
     - it should actually be a `EXP-->PHB mapping'. Alternative
       optional ways of populating the `Encaps-->PHB mapping' might be
       defined in the future (e.g., using a 'CLP/EXP--> PHB mapping' or
       a 'DE/EXP-->PHB mapping') but are outside the scope of this
       document.
     - when the `Encaps-->PHB mapping' is an `EXP-->PHB mapping', this
       `EXP-->PHB mapping' mapping is a function of the PSC which is
       carried on the L-LSP, and must use the relevant mapping entries
       for this PSC from the Mandatory EXP/PSC-->PHB Mapping defined in
       Section 4.2.1.1.

   An Edge-LSR of an ATM-MPLS domain or of a FR-MPLS domain is an
   example of LSR terminating the shim layer over an ingress ATM/FR
   interface.


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                      MPLS Support of Diff-Serv          February 2001

4.2.1.1 Mandatory EXP/PSC --> PHB mapping

      EXP Field      PSC             PHB

        000          DF    ---->    DF
        000          CSn   ---->    CSn
        000          AFn   ---->    AFn1
        001          AFn   ---->    AFn2
        011          AFn   ---->    AFn3
        000          EF    ---->    EF

4.2.2 `CLP-->PHB mapping'

   If the LSR does not terminate an MPLS Shim Layer over this incoming
   label and uses ATM encapsulation (i.e. it is an ATM-LSR), then the
   `Encaps-->PHB mapping' for this incoming L-LSP is populated in the
   following way:
     - it is actually a `CLP-->PHB mapping'
     - the mapping is a function of the PSC which is carried on this
       LSP, and should use the relevant mapping entries for this PSC
       from the Default CLP/PSC-->PHB Mapping defined in Section
       4.2.2.1.

   For example if the incoming label corresponds to an L-LSP supporting
   the AF1 PSC, then the `Encaps-->PHB mapping' should be populated
   with:

      CLP Field              PHB

        0          ---->    AF11
        1          ---->    AF12

4.2.2.1 Default CLP/PSC --> PHB Mapping

      CLP Bit      PSC             PHB

         0          DF    ---->    DF
         0          CSn   ---->    CSn
         0          AFn   ---->    AFn1
         1          AFn   ---->    AFn2
         0          EF    ---->    EF

4.2.3 `DE-->PHB mapping'

   If the LSR does not terminate an MPLS Shim Layer over this incoming
   label and uses Frame Relay encapsulation (i.e. it is a FR-LSR), then
   the `Encaps-->PHB mapping' for this incoming L-LSP is populated in
   the following way:
     - it is actually a `DE-->PHB mapping'
     - the mapping is a function of the PSC which is carried on this
       LSP, and should use the relevant mapping entries for this PSC


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                      MPLS Support of Diff-Serv          February 2001

       from the Default DE/PSC-->PHB Mapping defined in Section
       4.2.3.1.

4.2.3.1 Default DE/PSC --> PHB Mapping

      DE Bit      PSC             PHB

         0          DF    ---->    DF
         0          CSn   ---->    CSn
         0          AFn   ---->    AFn1
         1          AFn   ---->    AFn2
         0          EF    ---->    EF

4.3 Incoming PHB Determination On Incoming L-LSP

   This section defines how Incoming PHB determination is carried out
   when the considered label entry in the received label stack
   corresponds to an L-LSP. This requires that the `Encaps-->PHB
   mapping' is populated as defined in section 4.2.

   When considering a label entry corresponding to an incoming L-LSP
   for Incoming PHB Determination, the LSR first determines the
   `Encaps-->PHB mapping' associated with -corresponding label.

4.3.1 `EXP-->PHB mapping'

   If the `Encaps-->PHB mapping' is of the form `EXP-->PHB mapping',
   then the LSR:
     - determines the incoming PHB by looking at the EXP field of the
       considered label entry and by using the EXP-->PHB mapping.

4.3.2 `CLP-->PHB mapping'

   If the `Encaps-->PHB mapping' is of the form `CLP-->PHB mapping',
   then the LSR:
     - determines the incoming PHB by looking at the CLP field of the
       ATM Layer encapsulation and by using the CLP-->PHB mapping.

4.3.3 `DE-->PHB mapping'

   If the `Encaps-->PHB mapping' is of the form `DE-->PHB mapping',
   then the LSR:
     - determines the incoming PHB by looking at the DE field of the
       Frame Relay encapsulation and by using the DE-->PHB mapping.

4.4 Populating the `Set of PHB-->Encaps mappings' for an outgoing L-LSP

   This section defines how the `Set of PHB-->Encaps mappings' of the
   Diff-Serv Context is populated at label setup for an outgoing L-LSP
   in order to allow Encoding of Diff-Serv Information.

4.4.1 `PHB-->EXP mapping'

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                      MPLS Support of Diff-Serv          February 2001


   If the LSR uses an MPLS Shim Layer over this outgoing L-LSP, then
   one `PHB-->EXP mapping' is added to the `Set of
   PHB-->Encaps mappings' for this outgoing
   L-LSP. This `PHB-->EXP mapping' is populated in the following way:
     - it is a function of the PSC supported on this LSP, and must use
       the mapping entries relevant for this PSC from the Mandatory
       PHB-->EXP Mapping defined in section 4.4.1.1.

   For example if the outgoing label corresponds to an L-LSP supporting
   the AF1 PSC, then the following `PHB-->EXP mapping' is added into
   the `Set of PHB-->Encaps mappings':

        PHB                EXP Field

        AF11       ---->      000
        AF12       ---->      001
        AF13       ---->      011

4.4.1.1 Mandatory PHB-->EXP Mapping

        PHB                EXP Field

        DF         ---->      000
        CSn        ---->      000
        AFn1       ---->      000
        AFn2       ---->      001
        AFn3       ---->      011
        EF         ---->      000

4.4.2 `PHB-->CLP mapping'

   If the L-LSP is egressing on an ATM interface (i.e. it is an ATM-LSR
   or it is a frame-based LSR sending packets on an LC-ATM interface or
   on an ATM interface which is not label switching controlled), then
   one `PHB-->CLP mapping' is added to the `Set of PHB-->Encaps
   mappings' for this outgoing L-LSP.

   If the L-LSP is egressing over an ATM interface which is not label-
   controlled, the `PHB-->CLP mapping' is populated as per section
   3.4.2.

   If the L-LSP is egressing over an LC-ATM interface, the `PHB-->CLP
   mapping' is populated in the following way:
     - it is a function of the PSC supported on this LSP, and should
       use the relevant mapping entries for this PSC from the Default
       PHB-->CLP Mapping defined in section 3.4.2.1.

   Notice that if the LSR is a frame-based LSR supporting an L-LSP
   egressing over an ATM interface, then the `Set of PHB-->Encaps
   mappings' contains both a `PHB-->EXP mapping' and a `PHB-->CLP


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                      MPLS Support of Diff-Serv          February 2001

   mapping'. If the LSR is an ATM-LSR supporting an L-LSP, then the
   `Set of PHB-->Encaps mappings' only contains a `PHB-->CLP mapping'.

4.4.3 `PHB-->DE mapping'

   If the L-LSP is egressing over a Frame Relay interface (i.e. it is
   an LSR sending packets on an LC-FR interface or on a Frame Relay
   interface which is not label switching controlled), one `PHB-->DE
   mapping' is added to the `Set of PHB-->Encaps mappings' for this
   outgoing L-LSP.

   If the L-LSP is egressing over a FR interface which is not label
   switching controlled, the `PHB-->DE mapping' is populated as per
   section 3.4.3.

   If the L-LSP is egressing over an LC-FR interface, the `PHB-->DE
   mapping' is populated in the following way:
     - it is a function of the PSC supported on this LSP, and should
       use the relevant mapping entries for this PSC from the Default
       PHB-->DE Mapping defined in section 3.4.3.1.

   Notice that if the LSR is an Edge-LSR supporting an L-LSP egressing
   over a LC-FR interface, then the `Set of PHB-->Encaps mappings'
   contains both a `PHB-->EXP mapping' and a `PHB-->DE mapping'. If the
   LSR is a FR-LSR supporting an L-LSP, then the `Set of PHB-->Encaps
   mappings' only contains a `PHB-->DE mapping'.

4.4.4 `PHB-->802.1 mapping'

   If the LSP is egressing over a LAN interface on which multiple 802.1
   Traffic Classes are supported as defined in [IEEE_802.1], then one
   `PHB-->802.1 mapping' is added as per section 3.4.4.

4.5 Encoding Diff-Serv Information into Encapsulation Layer on Outgoing
L-LSP

   This section defines how to encode Diff-Serv information into the
   MPLS encapsulation Layer for a transmitted label entry corresponding
   to an outgoing L-LSP. This requires that the `Set of PHB-->Encaps
   mappings' is populated as defined in section 4.4.

   The LSR first determines the `Set of PHB-->Encaps mappings' of the
   Diff-Serv Context associated with the corresponding label in the
   NHLFE and then performs corresponding encoding as specified in
   sections 3.5.1, 3.5.2, 3.5.3 and 3.5.4.

4.6 L-LSP Merging

   In an MPLS domain, two or more LSPs can be merged into one LSP at
   one LSR. L-LSPs are compatible with LSP Merging under the following
   condition:


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                      MPLS Support of Diff-Serv          February 2001

        L-LSPs can only be merged into one L-LSP if they support the
        same PSC.

   The above merge condition MUST be enforced by LSRs through explicit
   checking at label setup that the same PSC is supported on the merged
   LSPs.

   Note that when L-LSPs merge, the bandwidth that is available for the
   PSC downstream of the merge point must be sufficient to carry the
   sum of the merged traffic. This is particularly important in the
   case of EF traffic. This can be ensured in multiple ways (for
   instance via provisioning, or via bandwidth signaling and explicit
   admission control).


5. RSVP Extension for Diff-Serv Support

   The MPLS architecture does not assume a single label distribution
   protocol. [RSVP_MPLS_TE] defines the extension to RSVP for
   establishing label switched paths (LSPs) in MPLS networks. This
   section specifies the extensions to RSVP, beyond those defined in
   [RSVP_MPLS_TE], to establish label switched path (LSPs) supporting
   Differentiated Services in MPLS networks.

5.1 Diff-Serv related RSVP Messages Format

   One new RSVP Object is defined in this document: the DIFFSERV
   Object. Detailed description of this Object is provided below. This
   new Object is applicable to Path messages. This specification only
   defines the use of the DIFFSERV Object in Path messages used to
   establish LSP Tunnels in accordance with [RSVP_MPLS_TE] and thus
   containing a Session Object with a C-Type equal to LSP_TUNNEL_IPv4
   and containing a LABEL_REQUEST object.

   Restrictions defined in [RSVP_MPLS_TE] for support of establishment
   of LSP Tunnels via RSVP are also applicable to the establishment of
   LSP Tunnels supporting Diff-Serv: for instance, only unicast LSPs
   are supported and Multicast LSPs are for further study.

   This new DIFFSERV object is optional with respect to RSVP so that
   general RSVP implementations not concerned with MPLS LSP set up do
   not have to support this object.

   The DIFFSERV Object is optional for support of LSP Tunnels as
   defined in [RSVP_MPLS_TE]. A Diff-Serv capable LSR supporting E-LSPs
   using the preconfigured EXP<-->PHB mapping in compliance with this
   specification MAY support the DIFFSERV Object. A Diff-Serv capable
   LSR supporting E-LSPs using a signaled EXP<-->PHB mapping in
   compliance with this specification MUST support the DIFFSERV Object.
   A Diff-Serv capable LSR supporting L-LSPs in compliance with this
   specification MUST support the DIFFSERV Object.


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                      MPLS Support of Diff-Serv          February 2001

5.1.1 Path Message Format

   The format of the Path message is as follows:

         <Path Message> ::=       <Common Header> [ <INTEGRITY> ]
                                  <SESSION> <RSVP_HOP>
                                  <TIME_VALUES>
                                  [ <EXPLICIT_ROUTE> ]
                                  <LABEL_REQUEST>
                                  [ <SESSION_ATTRIBUTE> ]
                                  [ <DIFFSERV> ]
                                  [ <POLICY_DATA> ... ]
                                  [ <sender descriptor> ]

         <sender descriptor> ::=  <SENDER_TEMPLATE> [ <SENDER_TSPEC> ]
                                  [ <ADSPEC> ]
                                  [ <RECORD_ROUTE> ]

5.2 DIFFSERV Object

   The DIFFSERV object formats are shown below. Currently there are two
   possible C_Types. Type 1 is a DIFFSERV object for an E-LSP. Type 2
   is a DIFFSERV object for an L-LSP.

5.2.1. DIFFSERV object for an E-LSP:

   class = TBD, C_Type = 1  (need to get an official class num from the
   IANA with the form 0bbbbbbb)

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        Reserved                                       | MAPnb |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                            MAP (1)                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    //                               ...                            //
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                            MAP (MAPnb)                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Reserved : 28 bits
       This field is reserved. It must be set to zero on transmission
       and must be ignored on receipt.

     MAPnb : 4 bits
       Indicates the number of MAP entries included in the DIFFSERV
       Object. This can be set to any value from 0 to 8.

     MAP : 32 bits

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                      MPLS Support of Diff-Serv          February 2001

       Each MAP entry defines the mapping between one EXP field value
       and one PHB. The MAP entry has the following format:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |            Reserved     | EXP |             PHBID             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Reserved : 13 bits
               This field is reserved. It must be set to zero on
               transmission and must be ignored on receipt.

           EXP : 3 bits
               This field contains the value of the EXP field for the
               EXP<-->PHB mapping defined in this MAP entry.

           PHBID : 16 bits
               This field contains the PHBID of the PHB for the
               EXP<-->PHB mapping defined in this MAP entry. The PHBID
               is encoded as specified in section 2 of [PHBID].

5.2.2 DIFFSERV object for an L-LSP:

   class = TBD, C_Type = 2  (class num is the same as DIFFSERV object
   for E-LSP))

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        Reserved               |             PSC               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Reserved : 16 bits
       This field is reserved. It must be set to zero on transmission
       and must be ignored on receipt.

     PSC : 16 bits
        The PSC indicates a PHB Scheduling Class to be supported by the
        LSP. The PSC is encoded as specified in section 2 of [PHBID]:
            - Where the PSC comprises a single PHB defined by standards
        action, the encoding for the PSC is the encoding for this
        single PHB. It is the recommended DSCP value for that PHB,
        left-justified in the 16-bit field, with bits 6 through 15 set
        to zero.
           - Where the PSC comprises multiple PHBs defined by standards
        action, the PSC encoding is the encoding for this set of PHB.
        It is the smallest numerical value of the recommended DSCP for
        the various PHBs in the PSC, left-justified in the 16 bit
        field, with bits 6 through 13 and bit 15 set to zero and with
        bit 14 set to one.


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                      MPLS Support of Diff-Serv          February 2001

       For instance, the encoding of the EF PSC is :
              0                   1
              0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             |1 0 1 1 1 0|0 0 0 0 0 0 0 0 0 0|
             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       For instance, the encoding of the AF1 PSC is :
              0                   1
              0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             |0 0 1 0 1 0|0 0 0 0 0 0 0 0 1 0|
             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.3 Handling DIFFSERV Object

   To establish an LSP tunnel with RSVP, the sender creates a Path
   message with a session type of LSP_Tunnel_IPv4 and with a
   LABEL_REQUEST object as per [RSVP_MPLS_TE].

   To establish with RSVP an E-LSP tunnel which uses the Preconfigured
   EXP<-->PHB mapping, the sender creates a Path message:
     - with a session type of LSP_Tunnel_IPv4,
     - with the LABEL_REQUEST object, and
     - without the DIFFSERV object.

   To establish with RSVP an E-LSP tunnel which uses the Preconfigured
   EXP<-->PHB mapping, the sender MAY alternatively create a Path
   message:
     - with a session type of LSP_Tunnel_IPv4,
     - with the LABEL_REQUEST object, and
     - with the DIFFSERV object for an E-LSP containing no MAP entries.

   To establish with RSVP an E-LSP tunnel which uses a signaled EXP<--
   >PHB mapping, the sender creates a Path message :
     - with a session type of LSP_Tunnel_IPv4,
     - with the LABEL_REQUEST object,
     - with the DIFFSERV object for an E-LSP containing one MAP entry
       for each EXP value to be supported on this E-LSP.

   To establish with RSVP an L-LSP tunnel, the sender creates a Path
   message:
     - with a session type of LSP_Tunnel_IPv4,
     - with the LABEL_REQUEST object,
     - with the DIFFSERV object for an L-LSP containing the PHB
       Scheduling Class (PSC) supported on this L-LSP.

   If a path message contains multiple DIFFSERV objects, only the first
   one is meaningful; subsequent DIFFSERV object(s) must be ignored and
   not forwarded.



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                      MPLS Support of Diff-Serv          February 2001

   Each LSR along the path records the DIFFSERV object, when present,
   in its path state block.

   If a DIFFSERV object is not present in the Path message, the LSR
   SHOULD interpret this as a request for an E-LSP using the
   Preconfigured EXP<-->PHB Mapping. However, for backward
   compatibility purposes with other non-Diff-Serv Quality of Service
   options allowed by [RSVP_MPLS_TE] such as Integrated Services
   Controlled Load or Guaranteed Services, the LSR MAY support a
   configurable "override option". When this "override option" is
   configured, the LSR interprets a path message without a Diff-Serv
   object as a request for an LSP with such non-Diff-Serv Quality of
   Service.

   If a DIFFSERV object for an E-LSP containing no MAP entry is present
   in the Path message, the LSR MUST interpret this as a request for an
   E-LSP using the Preconfigured EXP<-->PHB Mapping. In particular,
   this allows an LSR with the "override option" configured to support
   E-LSPs with Preconfigured EXP<-->PHB Mapping simultaneously with
   LSPs with non-Diff-Serv Quality of Service.

   If a DIFFSERV object for an E-LSP containing at least one MAP entry
   is present in the Path message, the LSR MUST interpret this as a
   request for an E-LSP with signaled EXP<-->PHB Mapping.

   If a DIFFSERV object for an L-LSP is present in the Path message,
   the LSR MUST interpret this as a request for an L-LSP.

   The destination LSR of an E-LSP or L-LSP responds to the Path
   message containing the LABEL_REQUEST object by sending a Resv
   message:
     - with the LABEL object
     - without a DIFFSERV object.

   Assuming the label request is accepted and a label is allocated, the
   Diff-Serv LSRs (sender, destination, intermediate nodes) must:
     - update the Diff-Serv Context associated with the established
       LSPs in their ILM/FTN as specified in previous sections
       (incoming and outgoing label),
     - install the required Diff-Serv forwarding treatment (scheduling
       and dropping behavior) for this NHLFE (outgoing label).

   An LSR that recognizes the DIFFSERV object and that receives a path
   message which contains the DIFFSERV object but which does not
   contain a LABEL_REQUEST object or which does not have a session type
   of LSP_Tunnel_IPv4, sends a PathErr towards the sender with the
   error code `Diff-Serv Error' and an error value of `Unexpected
   DIFFSERV object'. Those are defined below in section 5.5.

   An LSR receiving a Path message with the DIFFSERV object for E-LSP,
   which recognizes the DIFFSERV object but does not support the
   particular PHB encoded in one, or more, of the MAP entries, sends a

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                      MPLS Support of Diff-Serv          February 2001

   PathErr towards the sender with the error code `Diff-Serv Error' and
   an error value of `Unsupported PHB'. Those are defined below in
   section 5.5.

   An LSR receiving a Path message with the DIFFSERV object for E-LSP,
   which recognizes the DIFFSERV object but determines that the
   signaled EXP<-->PHB mapping is invalid, sends a PathErr towards the
   sender with the error code `Diff-Serv Error' and an error value of
   `Invalid EXP<-->PHB mapping'. Those are defined below in section
   5.5. The EXP<-->PHB mapping signaled in the DIFFSERV Object for an
   E-LSP is invalid when:
     - the MAPnb field is not within the range 0 to 8 or
     - a given EXP value appears in more than one MAP entry, or
     - the PHBID encoding is invalid.

   An LSR receiving a Path message with the DIFFSERV object for L-LSP,
   which recognizes the DIFFSERV object but does not support the
   particular PSC encoded in the PSC field, sends a PathErr towards the
   sender with the error code `Diff-Serv Error' and an error value of
   `Unsupported PSC'. Those are defined below in section 5.5.

   An LSR receiving a Path message with the DIFFSERV object, which
   recognizes the DIFFSERV object but that is unable to allocate the
   required per-LSP Diff-Serv context sends a PathErr with the error
   code "Diff-Serv Error" and the error value "Per-LSP context
   allocation failure". Those are defined below in section 5.5.

   A Diff-Serv LSR MUST handle the situations where the label request
   can not be accepted for other reasons than those already discussed
   in this section, in accordance with [RSVP_MPLS_TE] (e.g. reservation
   rejected by admission control, a label can not be associated).

5.4 Non-support of the DIFFSERV Object

   An LSR that does not recognize the DIFFSERV object Class-Num must
   behave in accordance with the procedures specified in [RSVP] for an
   unknown Class-Num whose format is 0bbbbbbb i.e. it must send a
   PathErr with the error code `Unknown object class' toward the
   sender.

   An LSR that recognize the DIFFSERV object Class-Num but does not
   recognize the DIFFSERV object C-Type, must behave in accordance with
   the procedures specified in [RSVP] for an unknown C-type i.e. It
   must send a PathErr with the error code `Unknown object C-Type'
   toward the sender.

   In both situations, this causes the path set-up to fail. The sender
   should notify management that a L-LSP cannot be established and
   possibly take action to retry LSP establishment without the DIFFSERV
   object (e.g. attempt to use E-LSPs with Preconfigured EXP<-->PHB
   mapping as a fall-back strategy).


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                      MPLS Support of Diff-Serv          February 2001

5.5 Error Codes For Diff-Serv

   In the procedures described above, certain errors must be reported
   as a `Diff-Serv Error'. The value of the `Diff-Serv Error' error
   code is TBD (number to be allocated by IANA)).

   The following defines error values for the Diff-Serv Error:

       Value    Error

        1       Unexpected DIFFSERV object
        2       Unsupported PHB
        3       Invalid EXP<-->PHB mapping
        4       Unsupported PSC
        5       Per-LSP context allocation failure

5.6 Use of COS Service with E-LSPs and L-LSPs

   Both E-LSPs and L-LSPs can be established with bandwidth reservation
   or without bandwidth reservation.

   To establish an E-LSP or an L-LSP with bandwidth reservation, Int-
   Serv's Controlled Load service (or possibly Guaranteed Service) is
   used and the bandwidth is signaled in the SENDER_TSPEC (respectively
   FLOWSPEC) of the path (respectively Resv) message.

   To establish an E-LSP or an L-LSP without bandwidth reservation, the
   Class of Service service defined in [RSVP_MPLS_TE] is used.

   Note that this specification defines usage of E-LSPs and L-LSPs
   for support of the Diff-Serv service only. Regardless of whether the
   signaling messages actually indicate an Int-Serv service of COS, GS
   or CL and regardless of whether the signaling messages contain a
   signaled bandwidth reservation or not, E-LSPs and L-LSPs are defined
   here for support of Diff-Serv services. Support of Int-Serv services
   over an MPLS Diff-Serv backbone is outside the scope of this
   specification.

   A Path message containing a COS SENDER_TSPEC and not containing a
   DIFFSERV object indicates to a Diff-Serv capable LSR that the LSP to
   be established is an E-LSP using the Preconfigured mapping and
   without any bandwidth reservation.

   A Path message containing a COS SENDER_TSPEC and containing a
   DIFFSERV object for E-LSP indicates to a Diff-Serv capable LSR that
   the LSP to be established is an E-LSP using a signaled mapping and
   without any bandwidth reservation.

   A Path message containing a COS SENDER_TSPEC and containing a
   DIFFSERV object for L-LSP indicates to a Diff-Serv capable LSR that
   the LSP to be established is an L-LSP without any bandwidth
   reservation.

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                      MPLS Support of Diff-Serv          February 2001


   The above is summarized in the following table:

           Path Message  LSP type
    Service  DIFFSERV
              Object

     GS/CL     No        E-LSP + preconf mapping + bandw reservation
     GS/CL   Yes/E-LSP   E-LSP + signaled mapping + bandw reservation
     GS/CL   Yes/L-LSP   L-LSP + bandw reservation
     COS       No        E-LSP + preconf mapping + no bandw reservation
     COS     Yes/E-LSP   E-LSP + signaled mapping + no band reservation
     COS     Yes/L-LSP   L-LSP + no bandw reservation

   Where:
        - GS stands for Guaranteed Service
        - CL stands for Controlled Load
        - COS stands for COS service

   When processing a path (respectively Resv) message for an E-LSP or
   an L-LSP using the COS service, a Diff-Serv capable LSR must ignore
   the value of the COS field within a COS SENDER_TSPEC (respectively a
   COS FLOWSPEC).


6. LDP Extensions for Diff-Serv Support

   The MPLS architecture does not assume a single label distribution
   protocol. [LDP] defines the Label Distribution Protocol and its
   usage for establishment of label switched paths (LSPs) in MPLS
   networks. This section specifies the extensions to LDP to establish
   label switched path (LSPs) supporting Differentiated Services in
   MPLS networks.

   One new LDP TLV is defined in this document:
        - the Diff-Serv TLV
   Detailed description of this TLV is provided below.

   The new Diff-Serv TLV is optional with respect to LDP. A Diff-Serv
   capable LSR supporting E-LSPs which uses the Preconfigured
   EXP<-->PHB mapping in compliance with this specification MAY support
   the Diff-Serv TLV. A Diff-Serv capable LSR supporting E-LSPs which
   uses the signaled EXP<-->PHB mapping in compliance with this
   specification MUST support the Diff-Serv TLV. A Diff-Serv capable
   LSR supporting L-LSPs in compliance with this specification MUST
   support the Diff-Serv TLV.

6.1 Diff-Serv TLV

   The Diff-Serv TLV has the following formats:
   Diff-Serv TLV for an E-LSP:


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                      MPLS Support of Diff-Serv          February 2001

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F|  Diff-Serv (0x901)        |      Length                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |T|        Reserved                                     | MAPnb |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            MAP (1)                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                    ...

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            MAP (MAPnb)                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     T:1 bit
       LSP Type. This is set to 0 for an E-LSP

     Reserved : 27 bits
       This field is reserved. It must be set to zero on transmission
       and must be ignored on receipt.

     MAPnb : 4 bits
       Indicates the number of MAP entries included in the DIFFSERV
       Object. This can be set to any value from 1 to 8.

     MAP : 32 bits
       Each MAP entry defines the mapping between one EXP field value
       and one PHB. The MAP entry has the following format:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |            Reserved     | EXP |             PHBID             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Reserved : 13 bits
               This field is reserved. It must be set to zero on
               transmission and must be ignored on receipt.

           EXP : 3 bits
               This field contains the value of the EXP field for the
               EXP<-->PHB mapping defined in this MAP entry.

           PHBID : 16 bits
               This field contains the PHBID of the PHB for the
               EXP<-->PHB mapping defined in this MAP entry. The PHBID
               is encoded as specified in section 2 of [PHBID].


   Diff-Serv TLV for an L-LSP:


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                      MPLS Support of Diff-Serv          February 2001

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F| Type = PSC (0x901)        |      Length                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |T|        Reserved             |              PSC              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     T:1 bit
       LSP Type. This is set to 1 for an L-LSP

     Reserved : 15 bits
       This field is reserved. It must be set to zero on transmission
       and must be ignored on receipt.

     PSC : 16 bits
        The PSC indicates a PHB Scheduling Class to be supported by the
        LSP. The PSC is encoded as specified in section 2 of [PHBID]:
            - Where the PSC comprises a single PHB defined by standards
        action, the encoding for the PSC is the encoding for this
        single PHB. It is the recommended DSCP value for that PHB,
        left-justified in the 16-bit field, with bits 6 through 15 set
        to zero.
           - Where the PSC comprises multiple PHBs defined by standards
        action, the PSC encoding is the encoding for this set of PHB.
        It is the smallest numerical value of the recommended DSCP for
        the various PHBs in the PSC, left-justified in the 16 bit
        field, with bits 6 through 13 and bit 15 set to zero and with
        bit 14 set to one.

       For instance, the encoding of the EF PSC is :
              0                   1
              0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             |1 0 1 1 1 0|0 0 0 0 0 0 0 0 0 0|
             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       For instance, the encoding of the AF1 PSC is :
              0                   1
              0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             |0 0 1 0 1 0|0 0 0 0 0 0 0 0 1 0|
             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

6.2 Diff-Serv Status Code Values

   The following values are defined for the Status Code field of the
   Status TLV:

        Status Code                             E   Status Data

        Unexpected Diff-Serv TLV                0   0x01000001

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                      MPLS Support of Diff-Serv          February 2001

        Unsupported PHB                         0   0x01000002
        Invalid EXP<-->PHB mapping              0   0x01000003
        Unsupported PSC                         0   0x01000004
        Per-LSP context allocation failure      0   0x01000005

6.3 Diff-Serv Related LDP Messages

6.3.1 Label Request Message

   The format of the Label Request message is extended as follows, to
   optionally include the Diff-Serv TLV:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|   Label Request (0x0401)    |      Message Length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Message ID                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     FEC TLV                                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Diff-Serv TLV (optional)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

6.3.2 Label Mapping Message

   The format of the Label Mapping message is extended as follows, to
   optionally include the Diff-Serv TLV:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|   Label Mapping (0x0400)    |      Message Length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Message ID                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     FEC TLV                                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Label TLV                                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Diff-Serv TLV (optional)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

6.3.3 Label Release Message

   The format of the Label Release message is extended as follows, to
   optionally include the Status TLV:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |0|   Label Release (0x0403)   |      Message Length            |

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                      MPLS Support of Diff-Serv          February 2001

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Message ID                                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     FEC TLV                                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Label TLV (optional)                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Status TLV (optional)                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

6.3.4 Notification Message

   The format of the Notification message is extended as follows, to
   optionally include the Diff-Serv TLV:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|   Notification (0x0001)     |      Message Length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Message ID                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Status TLV                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Optional Parameters                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Diff-Serv TLV (optional)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

6.4 Handling of the Diff-Serv TLV

6.4.1 Handling of the Diff-Serv TLV in Downstream Unsolicited Mode

   This section describes operations when the Downstream Unsolicited
   Mode is used.

   When allocating a label for an E-LSP which is to use the
   preconfigured EXP<-->PHB mapping, a downstream Diff-Serv LSR issues
   a Label Mapping message without the Diff-Serv TLV.

   When allocating a label for an E-LSP which is to use a signaled
   EXP<-->PHB mapping, a downstream Diff-Serv LSR issues a Label
   Mapping message with the Diff-Serv TLV for an E-LSP which contains
   one MAP entry for each EXP value to be supported on this E-LSP.

   When allocating a label for an L-LSP, a downstream Diff-Serv LSR
   issues a Label Mapping message with the Diff-Serv TLV for an L-LSP
   which contains the PHB Scheduling Class (PSC) to be supported on
   this L-LSP.

   Assuming the label set-up is successful, the downstream and upstream
   LSRs must:

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                      MPLS Support of Diff-Serv          February 2001

     - update the Diff-Serv Context associated with the established
       LSPs in their ILM/FTN as specified in previous sections
       (incoming and outgoing label),
     - install the required Diff-Serv forwarding treatment (scheduling
       and dropping behavior) for this NHLFE (outgoing label).

   An upstream Diff-Serv LSR receiving a Label Mapping message with
   multiple Diff-Serv TLVs only considers the first one as meaningful.
   The LSR must ignore and not forward the subsequent Diff-Serv TLV(s).

   An upstream Diff-Serv LSR which receives a Label Mapping message
   with the Diff-Serv TLV for an E-LSP and does not support the
   particular PHB encoded in one, or more, of the MAP entries, must
   reject the mapping by sending a Label Release message which includes
   the Label TLV and the Status TLV with a Status Code of `Unsupported
   PHB'.

   An upstream Diff-Serv LSR receiving a Label Mapping message with the
   Diff-Serv TLV for an E-LSP and determining that the signaled
   EXP<-->PHB mapping is invalid, must reject the mapping by sending a
   Label Release message which includes the Label TLV and the Status
   TLV with a Status Code of `Invalid EXP<-->PHB Mapping'. The
   EXP<-->PHB mapping signaled in the DIFFSERV Object for an E-LSP is
   invalid when:
     - the MAPnb field is not within the range 1 to 8, or
     - a given EXP value appears in more than one MAP entry, or
     - the PHBID encoding is invalid

   An upstream Diff-Serv LSR receiving a Label Mapping message with the
   Diff-Serv TLV for an L-LSP containing a PSC value which is not
   supported, must reject the mapping by sending a Label Release
   message which includes the Label TLV and the Status TLV with a
   Status Code of `Unsupported PSC'.

6.4.2 Handling of the Diff-Serv TLV in Downstream on Demand Mode

   This section describes operations when the Downstream on Demand Mode
   is used.

   When requesting a label for an E-LSP which is to use the
   preconfigured EXP<-->PHB mapping, an upstream Diff-Serv LSR sends a
   Label Request message without the Diff-Serv TLV.

   When requesting a label for an E-LSP which is to use a signaled
   EXP<-->PHB mapping, an upstream Diff-Serv LSR sends a Label Request
   message with the Diff-Serv TLV for an E-LSP which contains one MAP
   entry for each EXP value to be supported on this E-LSP.

   When requesting a label for an L-LSP, an upstream Diff-Serv LSR
   sends a Label Request message with the Diff-Serv TLV for an L-LSP
   which contains the PSC to be supported on this L-LSP.


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                      MPLS Support of Diff-Serv          February 2001

   A downstream Diff-Serv LSR sending a Label Mapping message in
   response to a Label Request message for an E-LSP or an L-LSP must
   not include a Diff-Serv TLV in this Label Mapping message.
   Assuming the label set-up is successful, the downstream and upstream
   LSRs must:
     - update the Diff-Serv Context associated with the established
       LSPs in their ILM/FTN as specified in previous sections
       (incoming and outgoing label),
     - install the required Diff-Serv forwarding treatment (scheduling
       and dropping behavior) for this NHLFE (outgoing label).

   An upstream Diff-Serv LSR receiving a Label Mapping message
   containing a Diff-Serv TLV in response to its Label Request message,
   must reject the label mapping by sending a Label Release message
   which includes the Label TLV and the Status TLV with a Status Code
   of `Unexpected Diff-Serv TLV'.

   A downstream Diff-Serv LSR receiving a Label Request message with
   multiple Diff-Serv TLVs only considers the first one as meaningful.
   The LSR must ignore and not forward the subsequent Diff-Serv TLV(s).

   A downstream Diff-Serv LSR which receives a Label Request message
   with the Diff-Serv TLV for an E-LSP and does not support the
   particular PHB encoded in one (or more) of the MAP entries, must
   reject the request by sending a Notification message which includes
   the Status TLV with a Status Code of `Unsupported PHB'.

   A downstream Diff-Serv LSR receiving a Label Request message with
   the Diff-Serv TLV for an E-LSP and determining that the signaled
   EXP<-->PHB mapping is invalid, must reject the request by sending a
   Notification message which includes the Status TLV with a Status
   Code of `Invalid EXP<-->PHB Mapping'. The EXP<-->PHB mapping
   signaled in the DIFFSERV TLV for an E-LSP is invalid when:
     - the MAPnb field is not within the range 1 to 8, or
     - a given EXP value appears in more than one MAP entry, or
     - the PHBID encoding is invalid

   A downstream Diff-Serv LSR receiving a Label Request message with
   the Diff-Serv TLV for an L-LSP containing a PSC value which is not
   supported, must reject the request by sending a Notification message
   which includes the Status TLV with a Status Code of `Unsupported
   PSC'.

   A downstream Diff-Serv LSR that recognizes the Diff-Serv TLV Type in
   a Label Request message but is unable to allocate the required
   per-LSP context information, must reject the request sending a
   Notification message which includes the Status TLV with a Status
   Code of `Per-LSP context allocation failure'.

   A downstream Diff-Serv LSR that recognizes the Diff-Serv TLV Type in
   a Label Request message and supports the requested PSC but is not
   able to satisfy the label request for other reasons (e.g. no label

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                      MPLS Support of Diff-Serv          February 2001

   available), must send a Notification message in accordance with
   existing LDP procedures [LDP] (e.g. with a `No Label Resource'
   Status Code). This Notification message must include the requested
   Diff-Serv TLV.

6.5 Non-Handling of the Diff-Serv TLV

   An LSR that does not recognize the Diff-Serv TLV Type, on receipt of
   a Label Request message or a Label Mapping message containing the
   Diff-Serv TLV, must behave in accordance with the procedures
   specified in [LDP] for an unknown TLV whose U Bit and F Bit are set
   to 0 i.e. it must ignore the message, return a Notification message
   with `Unknown TLV' Status.

6.6 Bandwidth Information

   Bandwidth information may also be signaled at establishment time of
   E-LSP and L-LSP, for instance for the purpose of Traffic
   Engineering, using the Traffic Parameters TLV as described in
   [MPLS CR LDP].


7. MPLS Support of Diff-Serv over PPP, LAN, Non-LC-ATM and Non-LC-FR
Interfaces

   The general operations for MPLS support of Diff-Serv, including
   label forwarding and LSP setup operations are specified in the
   previous sections. This section describes the specific operations
   required for MPLS support of Diff-Serv over PPP interfaces, LAN
   interfaces, ATM Interfaces which are not label controlled and Frame
   Relay interfaces which are not label controlled.

   On these interfaces, this specification allows any of the following
   LSP combinations per FEC:

     - Zero or any number of E-LSP, and
     - Zero or any number of L-LSPs.

   A Diff-Serv capable LSR MUST support E-LSPs which use pre-configured
   EXP<-->PHB mapping over these interfaces.

   A Diff-Serv capable LSR MAY support E-LSPs which use signaled
   EXP<-->PHB mapping and L-LSPs over these interfaces.


8. MPLS Support of Diff-Serv over LC-ATM Interfaces

   This section describes the specific operations required for MPLS
   support of Diff-Serv over label switching controlled ATM (LC-ATM)
   interfaces.



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                      MPLS Support of Diff-Serv          February 2001

   This document allows any number of L-LSPs per FEC within an MPLS ATM
   Diff-Serv domain. E-LSPs are not supported over LC-ATM interfaces.

8.1 Use of ATM Traffic Classes and Traffic Management mechanisms

   The use of the ATM traffic classes as specified by ITU-T and ATM-
   Forum or of vendor specific ATM traffic classes is outside of the
   scope of this specification. The only requirement for compliant
   implementation is that the forwarding behavior experienced by a
   Behavior Aggregate forwarded over an L-LSP by the ATM LSR MUST be
   compliant with the corresponding Diff-Serv PHB specifications.

   Since there is only one bit (CLP) for encoding the PHB drop
   precedence value over ATM links, only two different drop precedence
   levels are supported in ATM LSRs. Sections 4.2.2 and 4.4.2 define
   how the three drop precedence levels of the AFn Ordered Aggregates
   are mapped to these two ATM drop precedence levels. This mapping is
   in accordance with the requirements specified in [DIFF_AF] for the
   case when only two drop precedence levels are supported.

   To avoid discarding parts of the packets, frame discard mechanisms,
   such as Early Packet Discard (EPD) SHOULD be enabled in the ATM-LSRs
   for all PHBs described in this document.

8.2 LSR Implementation With LC-ATM Interfaces

   A Diff-Serv capable LSR MUST support L-LSPs over LC-ATM interfaces.

   This specification assumes that Edge-LSRs of the ATM-LSR domain use
   the "shim header" encapsulation method defined in [MPLS_ATM].
   Operations without the "shim header" encapsulation is outside the
   scope of this specification.


9. MPLS Support of Diff-Serv over LC-FR Interfaces

   This section describes the specific operations required for MPLS
   support of Diff-Serv over label switching controlled Frame Relay
   (LC-FR) interfaces.

   This document allows any number of L-LSPs per FEC within an MPLS
   Frame Relay Diff-Serv domain. E-LSPs are not supported over LC-FR
   interfaces.

9.1 Use of Frame Relay Traffic parameters and Traffic Management
mechanisms

   The use of the Frame Relay traffic parameters as specified by ITU-T
   and Frame Relay-Forum or of vendor specific Frame Relay traffic
   management mechanisms is outside of the scope of this specification.
   The only requirement for compliant implementation is that the
   forwarding behavior experienced by a Behavior Aggregate forwarded

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                      MPLS Support of Diff-Serv          February 2001

   over an L-LSP by the Frame Relay LSR MUST be compliant with the
   corresponding Diff-Serv PHB specifications.

   Since there is only one bit (DE) for encoding the PHB drop
   precedence value over Frame Relay links, only two different drop
   precedence levels are supported in Frame Relay LSRs. Sections 4.2.3
   and 4.4.3 define how the three drop precedence levels of the AFn
   Ordered Aggregates are mapped to these two Frame Relay drop
   precedence levels. This mapping is in accordance with the
   requirements specified in [DIFF_AF] for the case when only two drop
   precedence levels are supported.

9.2 LSR Implementation With LC-FR Interfaces

   A Diff-Serv capable LSR MUST support L-LSPs over LC-Frame Relay
   interfaces.

   This specification assumes that Edge-LSRs of the FR-LSR domain use
   the "generic encapsulation" method as recommended in [MPLS_FR].
   Operations without the "generic encapsulation" is outside the scope
   of this specification.


10. IANA Considerations.

   This document defines a number of objects with implications for
   IANA.

   This document defines in section 5.2 a new RSVP object, the Diffserv
   object. This object requires a number to be assigned from the space
   defined in [RSVP] for those objects which, if not understood, cause
   the entire RSVP message to be rejected with an error code of
   "Unknown Object Class". Such objects are identified by a zero in the
   most significant bit of the class number. Within that space, this
   object should be assigned a number from the "IETF Consensus" space.

   This document defines in section 5.5 a new RSVP error code,
   "Diffserv Error". This error code should be assigned by IANA. This
   document defines values 1 through 5 of the value field to be used
   within the ERROR_SPEC object for this error code. Future allocations
   of values in this space should be handled by IANA using the First
   Come First Served policy defined in [IANA].

   This document defines in section 6.1 a new LDP TLV, the Diffserv
   TLV. The number for this TLV has been assigned by working group
   consensus according to the policies defined in [LDP].

   This document defines in section 6.2 five new LDP Status Code values
   for Diffserv-related error conditions. The values for the Status
   Code have been assigned by working group consensus according to the
   policies defined in [LDP].


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                      MPLS Support of Diff-Serv          February 2001


11. Security Considerations

   This document does not introduce any new security issues beyond
   those inherent in Diff-Serv, MPLS and RSVP, and may use the same
   mechanisms proposed for those technologies.


12. Acknowledgments

   This document has benefited from discussions with Eric Rosen, Angela
   Chiu and Carol Iturralde. It has also borrowed from the work done by
   D. Black regarding Diff-Serv and IP Tunnels interaction.


APPENDIX A. Example Deployment Scenarios

   This section does not provide additional specification and is only
   here to provide examples of how this flexible approach for Diff-Serv
   support over MPLS may be deployed. Pros and cons of various
   deployment options for particular environments are beyond the scope
   of this document.

A.1 Scenario 1: 8 (or fewer) BAs, no Traffic Engineering, no MPLS
Protection

   A Service Provider running 8 (or fewer) BAs over MPLS, not
   performing Traffic engineering, not using MPLS protection and using
   MPLS Shim Header encapsulation in his/her network, may elect to run
   Diff-Serv over MPLS using a single E-LSP per FEC established via
   LDP. Furthermore the Service Provider may elect to use the
   preconfigured EXP<-->PHB mapping.

   Operations can be summarized as follows:
     - the Service Provider configures at every LSR the bi-directional
       mapping between each PHB and a value of the EXP field
       (e.g. 000<-->AF11, 001<-->AF12, 010<-->AF13)
     - the Service Provider configures at every LSR, and for every
       interface, the scheduling behavior for each PSC (eg bandwidth
       allocated to AF1) and the dropping behavior for each PHB (e.g.
       drop profile for AF11, AF12, AF13)
     - LSRs signal establishment of a single E-LSP per FEC using LDP in
       accordance with the specification above (i.e. no Diff-Serv TLV
       in LDP Label Request/Label Mapping messages to implicitly
       indicate that the LSP is an E-LSP and that it uses the
       preconfigured mapping)

A.2 Scenario 2: More than 8 BAs, no Traffic Engineering, no MPLS
Protection

   A Service Provider running more than 8 BAs over MPLS, not performing
   Traffic Engineering, not using MPLS protection and using MPLS Shim

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                      MPLS Support of Diff-Serv          February 2001

   encapsulation in his/her network may elect to run Diff-Serv over
   MPLS using for each FEC:
     - one E-LSP established via LDP and using the preconfigured
       mapping to support a set of 8 (or less) BAs, AND
     - one L-LSP per <FEC,OA> established via LDP for support of the
       other BAs.

   Operations can be summarized as follows:
     - the Service Provider configures at every LSR the bi-directional
       mapping between each PHB and a value of the EXP field for the
       BAs transported over the E-LSP
     - the Service Provider configures at every LSR, and for every
       interface, the scheduling behavior for each PSC supported over
       the E-LSP and the dropping behavior for each corresponding PHB
     - the Service Provider configures at every LSR, and for every
       interface, the scheduling behavior for each PSC supported over
       the L-LSPs and the dropping behavior for each corresponding PHB
     - LSRs signal establishment of a single E-LSP per FEC for the set
       of E-LSP transported BAs using LDP as specified above (i.e. no
       Diff-Serv TLV in LDP Label Request/Label Mapping messages to
       implicitly indicate that the LSP is an E-LSP and that it uses
       the preconfigured mapping)
     - LSRs signal establishment of one L-LSP per <FEC,OA> for the
       other BAs using LDP as specified above (i.e. Diff-Serv TLV in
       LDP Label Request/Label Mapping messages to indicate the L-LSP's
       PSC).

A.3 Scenario 3: 8 (or fewer) BAs, Aggregate Traffic Engineering,
Aggregate MPLS Protection

   A Service Provider running 8 (or fewer) BAs over MPLS, performing
   aggregate Traffic Engineering (i.e. performing a single common path
   selection for all BAs), using aggregate MPLS protection   (i.e.
   restoring service to all PSCs jointly) and using MPLS Shim Header
   encapsulation in his/her network, may elect to run Diff-Serv over
   MPLS using a single E-LSP per FEC established via RSVP
   [RSVP_MPLS_TE] or CR-LDP [CR-LDP_MPLS_TE] and using the
   preconfigured mapping.

   Operations can be summarized as follows:
     - the Service Provider configures at every LSR the bi-directional
       mapping between each PHB and a value of the EXP field
       (e.g. 000<-->AF11, 001<-->AF12, 010<-->AF13)
     - the Service Provider configures at every LSR, and for every
       interface, the scheduling behavior for each PSC (eg bandwidth
       allocated to AF1) and the dropping behavior for each PHB (eg
       drop profile for AF11, AF12, AF13)
     - LSRs signal establishment of a single E-LSP per FEC which will
       use the preconfigured mapping:
           * using the RSVP protocol as specified above (i.e. no
       DIFFSERV RSVP Object in the PATH message containing the
       LABEL_REQUEST Object), OR

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                      MPLS Support of Diff-Serv          February 2001

           * using the CR-LDP protocol as specified above (i.e. no
       Diff-Serv TLV in LDP Label Request/Label Mapping messages).
     - protection is activated on all the E-LSPs in order to achieve
       MPLS protection via mechanisms outside the scope of this
       document.

A.4 Scenario 4: per-OA Traffic Engineering/MPLS Protection

   A Service Provider running any number of BAs over MPLS, performing
   per-OA Traffic Engineering (i.e. performing a separate path
   selection for each OA) and performing per-OA MPLS protection (i.e.
   performing protection with potentially different levels of
   protection for the different OAs) in his/her network, may elect to
   run Diff-Serv over MPLS using one L-LSP per <FEC,OA> pair
   established via RSVP or CR-LDP.

   Operations can be summarized as follows:
     - the Service Provider configures at every LSR, and for every
       interface, the scheduling behavior for each PSC (eg bandwidth
       allocated to AF1) and the dropping behavior for each PHB (eg
       drop profile for AF11, AF12, AF13)
     - LSRs signal establishment of one L-LSP per <FEC,OA>:
                * using the RSVP as specified above to signal the
       L-LSP's PSC (i.e. DIFFSERV RSVP Object in the PATH message
       containing the LABEL_REQUEST), OR
                * using the CR-LDP protocol as specified above to
       signal the L-LSP PSC (i.e. Diff-Serv TLV in LDP Label
       Request/Label Mapping messages).
     - the appropriate level of protection is activated on the
       different L-LSPs (potentially with a different level of
       protection for each PSC)_via mechanisms outside the scope of
       this document.

A.5 Scenario 5: 8 (or fewer) BAs, per-OA Traffic Engineering/MPLS
Protection

   A Service Provider running 8 (or fewer) 8 BAs over MPLS, performing
   per-OA Traffic Engineering (i.e. performing a separate path
   selection for each OA) and performing per-OA MPLS protection (i.e.
   performing protection with potentially different levels of
   protection for the different OAs) in his/her network, may elect to
   run Diff-Serv over MPLS using one E-LSP per <FEC,OA> pair
   established via RSVP or CR-LDP. Furthermore, the Service Provider
   may elect to use the preconfigured mapping on all the E-LSPs.

   Operations can be summarized as follows:
     - the Service Provider configures at every LSR the bi-directional
       mapping between each PHB and a value of the EXP field
       (e.g. 000<-->AF11, 001<-->AF12, 010<-->AF13)
     - the Service Provider configures at every LSR, and for every
       interface, the scheduling behavior for each PSC (eg bandwidth


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                      MPLS Support of Diff-Serv          February 2001

       allocated to AF1) and the dropping behavior for each PHB (eg
       drop profile for AF11, AF12, AF13)
     - LSRs signal establishment of one E-LSP per <FEC,OA>:
                * using the RSVP protocol as specified above to signal
       that the LSP is an E-LSP which uses the preconfigured mapping
       (i.e. no DIFFSERV RSVP Object in the PATH message containing the
       LABEL_REQUEST), OR
                * using the CR-LDP protocol as specified above to
       signal that the LSP is an E-LSP  which uses the preconfigured
       mapping (i.e. no Diff-Serv TLV in LDP Label Request/Label
       Mapping messages)
     - the Service Provider configures, for each E-LSP, at the head-end
       of that E-LSP, a filtering/forwarding criteria so that only the
       packets belonging to a given OA are forwarded on the E-LSP
       established for the corresponding FEC and corresponding OA.
     - the appropriate level of protection is activated on the
       different E-LSPs (potentially with a different level of
       protection depending on the PSC actually transported over each
       E-LSP)_via mechanisms outside the scope of this document.


A.6 Scenario 6: no Traffic Engineering/MPLS Protection on 8 BAs, per-OA
Traffic Engineering/MPLS Protection on other BAs.

   A Service Provider not performing Traffic Engineering/MPLS
   Protection on 8 (or fewer) BAs, performing per-OA Traffic
   Engineering/MPLS Protection on the other BAs (i.e. performing a
   separate path selection for each OA corresponding to the other BAs
   and performing MPLS Protection with a potentially different policy
   for each of these OA) and using the MPLS Shim encapsulation in
   his/her network may elect to run Diff-Serv over MPLS, using for each
   FEC:
     - one E-LSP using the preconfigured mapping established via LDP to
       support the set of 8 (or fewer) non-traffic-engineered/non-
       protected BAs, AND
     - one L-LSP per <FEC,OA> pair established via RSVP or CR-LDP for
       support of the other BAs.

   Operations can be summarized as follows:
     - the Service Provider configures at every LSR the bi-directional
       mapping between each PHB and a value of the EXP field for the
       BAs supported over the E-LSP
     - the Service Provider configures at every LSR, and for every
       interface, the scheduling behavior for each PSC supported over
       the E-LSP and the dropping behavior for each corresponding PHB
     - the Service Provider configures at every LSR, and for every
       interface, the scheduling behavior for each PSC supported over
       the L-LSPs and the dropping behavior for each corresponding PHB
     - LSRs signal establishment of a single E-LSP per FEC for the non-
       traffic engineered BAs using LDP as specified above (i.e. no
       Diff-Serv TLV in LDP Label Request/Label Mapping messages)


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                      MPLS Support of Diff-Serv          February 2001

     - LSRs signal establishment of one L-LSP per <FEC,OA> for the
       other BAs:
                * using the RSVP protocol as specified above to signal
       the L-LSP PSC (i.e. DIFFSERV RSVP Object in the PATH message
       containing the LABEL_REQUEST Object), OR
                * using the CR-LDP protocol as specified above to
       signal the L-LSP PSC (i.e. Diff-Serv TLV in LDP Label
       Request/Label Mapping messages).
     - protection is not activated on the E-LSPs.
     - the appropriate level of protection is activated on the
       different L-LSPs (potentially with a different level of
       protection depending on the L-LSP's PSC)_via mechanisms outside
       the scope of this document.

A.7 Scenario 7: More than 8 BAs, no Traffic Engineering, no MPLS
Protection

   A Service Provider running more than 8 BAs over MPLS, not performing
   Traffic engineering, not performing MPLS protection and using MPLS
   Shim Header encapsulation in his/her network, may elect to run Diff-
   Serv over MPLS using two E-LSPs per FEC established via LDP and
   using signaled EXP<-->PHB mapping.
   Operations can be summarized as follows:
     - the Service Provider configures at every LSR, and for every
       interface, the scheduling behavior for each PSC (eg bandwidth
       allocated to AF1) and the dropping behavior for each PHB (eg
       drop profile for AF11, AF12, AF13)
     - LSRs signal establishment of two E-LSPs per FEC using LDP in
       accordance with the specification above (i.e. Diff-Serv TLV in
       LDP Label Request/Label Mapping messages to explicitly indicate
       that the LSP is an E-LSP and its EXP<--> mapping). The signaled
       mapping will indicate the subset of 8 (or less) BAs to be
       transported on each E-LSP and what EXP values are mapped to each
       BA on each E-LSP.


APPENDIX B. Example Bandwidth Reservation Scenarios

B.1 Scenario 1: No Bandwidth Reservation

   Consider the case where a network administrator elects to:
     - have Diff-Serv resources entirely provisioned off-line (e.g. via
       Command Line Interface, via SNMP, via COPS,...)
     - have Shortest Path Routing used for all the Diff-Serv traffic.

   This is the closest model to provisioned Diff-Serv over non-MPLS IP.
   In that case, E-LSPs and/or L-LSPs would be established without
   signaled bandwidth.

B.2 Scenario 2: Bandwidth Reservation for per-PSC Admission Control

   Consider the case where a network administrator elects to:

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                      MPLS Support of Diff-Serv          February 2001

     - have Diff-Serv resources entirely provisioned off-line (e.g. via
       Command Line Interface, via SNMP, via COPS,...)
     - use L-LSPs
     - have Constraint Based Routing performed separately for each PSC,
       where one of the constraints is availability of bandwidth from
       the bandwidth allocated to the relevant PSC.

   In that case, L-LSPs would be established with signaled bandwidth.
   The bandwidth signaled at L-LSP establishment would be used by LSRs
   to perform admission control at every hop to ensure that the
   constraint on availability of bandwidth for the relevant PSC is met.

B.3 Scenario 3: Bandwidth Reservation for per-PSC Admission Control and
per-PSC Resource Adjustment

   Consider the case where a network administrator elects to:
     - use L-LSPs
     - have Constraint Based Routing performed separately for each PSC,
       where one of the constraints is availability of bandwidth from
       the bandwidth allocated to the relevant PSC.
     - have Diff-Serv resources dynamically adjusted

   In that case, L-LSPs would be established with signaled bandwidth.
   The bandwidth signaled at L-LSP establishment would be used by LSRs
   to attempt to adjust the resources allocated to the relevant PSC
   (e.g. scheduling weight) and then perform admission control to
   ensure that the constraint on availability of bandwidth for the
   relevant PSC is met after the adjustment.


References

   [MPLS_ARCH] Rosen et al., "Multiprotocol label switching
   Architecture", RFC-3031, January 2001.

   [MPLS_ENCAPS] Rosen et al., "MPLS Label Stack Encoding", RFC-3032,
   January 2001.

   [MPLS_ATM] Davie et al., "MPLS using LDP and ATM VC Switching", RFC-
   3035, January 2001.

   [MPLS_FR] Conta et al., "Use of Label Switching on Frame Relay
   Networks Specification", RFC-3034, January 2001.

   [DIFF_ARCH] Blake et al., "An architecture for Differentiated
   Services", RFC-2475, December 1998.

   [DIFF_AF] Heinanen et al., "Assured Forwarding PHB Group", RFC-2597,
   June 1999.

   [DIFF_EF] Jacobson et al., "An Expedited Forwarding PHB", RFC-2598,
   June 1999.

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                      MPLS Support of Diff-Serv          February 2001


   [DIFF_HEADER] Nichols et al., "Definition of the Differentiated
   Services Field (DS Field) in the IPv4 and IPv6 Headers", RFC-2474,
   December 1998.

   [ECN] Ramakrishnan et al., "A Proposal to add Explicit Congestion
   Notification (ECN) to IP", RFC-2481, January 1999.

   [LDP] Andersson et al., "LDP Specification", RFC-3036, January 2001

   [RSVP_MPLS_TE] Awduche et al, "Extensions to RSVP for LSP Tunnels",
   work in progress, draft-ietf-mpls-rsvp-lsp-tunnel-07.txt, August
   2000

   [CR-LDP_MPLS_TE] Jamoussi et al., "Constraint-Based LSP Setup using
   LDP", work in progress, draft-ietf-mpls-cr-ldp-04.txt, July 2000

   [PHBID] Brim et al., "Per Hop Behavior Identification Codes"
   RFC-2836, May 2000

   [DIFF_NEW] Grossman, "New Terminology for Diffserv", work in
   progress, draft-ietf-diffserv-new-terms-03.txt, August 2000

   [IEEE_802.1] ISO/IEC 15802-3: 1998 ANSI/IEEE Std 802.1D, 1998
   Edition (Revision and redesignation of ISO/IEC 10038:98

   [ANSI/IEEE Std 802.1D, 1993 Edition], incorporating IEEE
   supplements P802.1p, 802.1j-1996, 802.6k-1992, 802.11c-1998, and
   P802.12e)

   [DIFF_TUNNEL] Black, "Differentiated Services and Tunnels",
   RFC-2983, October 2000.

   [MPLS_VPN] Rosen et al., "BGP/MPLS VPNs", work in progress, draft-
   rosen-rfc2547bis-02.txt, July 2000.

   [RSVP] Braden et al., "Resource ReSerVation Protocol (RSVP) -
   Version 1 Functional Specification", RFC-2205, September 1997.

   [IANA] T. Narten, H. Alvestrand, "Guidelines for Writing an IANA
   Considerations Section in RFCs", RFC 2434, October 1998.


Authors' Address:

   Francois Le Faucheur
   Cisco Systems
   Village d'Entreprise Green Side - Batiment T3
   400, Avenue de Roumanille
   06410 Biot-Sophia Antipolis
   France
   Phone: +33 4 97 23 26 19

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                      MPLS Support of Diff-Serv          February 2001

   Email: flefauch@cisco.com

   Liwen Wu
   Cisco Systems
   250 Apollo Drive, Chelmsford, MA 01824,
   USA
   Phone: +1 (978) 244-3087
   Email: liwwu@cisco.com

   Bruce Davie
   Cisco Systems
   250 Apollo Drive, Chelmsford, MA 01824
   USA
   Phone: +1 (978) 244-8000
   Email: bsd@cisco.com

   Shahram Davari
   PMC-Sierra Inc.
   555 Legget drive,
   Suit 834, Tower B,
   Ottawa, ON K2K 2X3
   Canada
   Phone: +1 (613) 271-4018
   Email: shahram_davari@pmc-sierra.com

   Pasi Vaananen
   Nokia
   3 Burlington Woods Drive, Suit 250
   Burlington, MA 01803
   USA
   Phone +1 (781) 238-4981
   Email: pasi.vaananen@nokia.com

   Ram Krishnan
   Lucent Technologies
   200 Nickerson Road,
   Marlboro, MA 01752
   USA
   E-mail: ram64@lucent.com

   Pierrick Cheval
   Alcatel
   5 rue Noel-Pons
   92734 Nanterre Cedex
   France
   E-mail:pierrick.cheval@alcatel.fr

   Juha Heinanen
   Telia Finland
   E-mail: jh@lohi.eng.telia.fi



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                      MPLS Support of Diff-Serv          February 2001

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