Francois Le Faucheur
                                                                Liwen Wu
                                                             Bruce Davie
                                                           Cisco Systems

                                                          Shahram Davari
                                                         PMC-Sierra Inc.

                                                           Pasi Vaananen
                                                                   Nokia

                                                            Ram Krishnan
                                                        Nexabit Networks

                                                         Pierrick Cheval
                                                                 Alcatel

                                                           Juha Heinanen
                                                           Telia Finland

IETF Internet Draft
Expires: September, December, 2000
Document: draft-ietf-mpls-diff-ext-04.txt              March, draft-ietf-mpls-diff-ext-05.txt              June, 2000

                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. Internet-Drafts are
   Working documents of the Internet Engineering Task Force (IETF), its
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     http://www.ietf.org/ietf/1id-abstracts.txt
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Abstract

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

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                      MPLS Support of Diff-Serv               March 00              June 2000

   This solution allows the MPLS network administrator to select how
   Diff-Serv Behavior Aggregates (BAs) are mapped onto Label Switched
   Paths so that he/she can best match the Diff-Serv, Traffic
   Engineering and Fast Restoration 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
   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

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                      MPLS Support of Diff-Serv               March 00              June 2000

   or Traffic Engineered within their domain (eg. separate classes of
   services supported via separate LSPs and Routed separately, all
   classes of service supported on the same LSP and Routed together).
   Similarly, the solution gives Service Providers flexibility in how
   Diff-Serv classes of service can be protected via MPLS Fast
   Restoration (eg. some classes of service supported via LSPs which
   are protected via MPLS Fast Restoration while some other classes of
   service are supported via LSPs which are not protected).

   Beside,

   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 study.

1.1  Ordered Aggregate (OA) and PHB Scheduling Class (PSC)

   The Diff-Serv model defines [DIFF_NEW] the set of Behavior
   Aggregates which share an ordering constraint to constitute an
   "Ordered Aggregate (OA)". It also defines the set of one or more
   PHBs that are applied to this set of Behavior Aggregates to
   constitute a "PHB Scheduling Class (PSC)".

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 [MPLS_ENCAPS] 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 relying 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.

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                      MPLS Support of Diff-Serv               March 00
   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

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                      MPLS Support of Diff-Serv              June 2000

   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 [MPLS_ENCAPS].
   When the Shim Header is not used (eg. 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 (eg. ATM Cell Loss Priority).

   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 (eg. 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, 9 and 10 below, this specification
   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 Fast Restoration.
   Criteria for selecting such a combination are outside the scope of
   this specification; 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) PHBs of a given PSC.

   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.'

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                      MPLS Support of Diff-Serv               March 00

   In line with this, we observe that:
     - With E-LSPs, the label represents the combination of a FEC and
       the set of Behavior Aggregates (BAs) transported over the E-

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                      MPLS Support of Diff-Serv              June 2000

       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 Ordered Aggregate (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
   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 COPS) 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 to be used. 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 PHBs.
   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

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                      MPLS Support of Diff-Serv               March 00              June 2000

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 to a non-MPLS Diff-Serv Router.

   In

   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)
     - Optional Outgoing PHB Determination via Local Policy and Traffic
       Conditioning (B)
     - Label Swapping (C)
     - Encoding of Diff-Serv information into Encapsulation Layer
       (EXP,CLP,DE,User_Priority) (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(*)--------------------------->I===I---Outg_label (**)-->
     \                                       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 performs label imposition, the incoming packet is
   received unlabelled.

   (**) when the LSR performs label disposition, the outgoing packet is
   transmitted unlabelled.

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

2.1

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2.2 Incoming PHB Determination

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

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                      MPLS Support of Diff-Serv               March 00

   2.1.1

2.2.1 Incoming PHB Determination for received labelled packets

   This specification defines one default method for this determination
   which allows for regular support of Diff-Serv over MPLS. This method
   considers only Considering a Label Stack Entry

   Sections 3.3 and 4.3 provide the outer encapsulation (ie outer details on how to perform incoming
   PHB Determination considering a given received label stack entry or ATM
   and/or received incoming MPLS encapsulation or Frame Relay encapsulation) and ignores other label
   entries which may be present in information depending on
   the stack. It combines:
     - incoming LSP type corresponding to the Diff-Serv context associated with considered stack entry
   and depending on the incoming MPLS encapsulation.

   Section 2.6 provides the details of which label and
       stored in stack entry to
   consider for the Incoming Label Map (ILM). See section 2.3 below
       for details PHB Determination depending on information comprising the
   supported Diff-Serv context.
     - tunneling mode.

2.2.2 Incoming PHB Determination Considering IP Header

   Section 2.6 provides the Diff-Serv related information that is encoded in the
       corresponding encapsulation layer (ie in EXP field of MPLS Shim
       layer or in CLP/DE field of the link layer encapsulation) of the
       received label packet.

   The details of this method depend on the incoming LSP type and on when the incoming MPLS encapsulation and are defined below in sections
   3.3 and 4.3.

   Support for this default method IP Header is mandatory for compliance to this
   specification.

   Optionally, other methods be
   considered for Incoming incoming PHB Determination may also be
   supported. Other methods may take into account other information in
   addition to, or instead of, the information used by the mandatory
   method. For instance, other method could take into account the DS
   field of determination depending on the encapsulated packet or supported
   Diff-Serv tunneling mode. In those cases where the EXP field of a label IP header
   deeper in the label stack. Such methods are beyond the scope of this
   specification.

2.1.2 Incoming PHB Determination for received unlabelled packets

   For packets received unlabelled, is to
   be used, this stage operates exactly as with a non-MPLS IP Diff-Serv
   Router and uses the DS field.

2.2 field to determine incoming PHB.

2.3 Optional Outgoing PHB Determination Via Local Policy And Traffic
Conditioning

   This stage of Diff-Serv label switching 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 this stage is not present, the "outgoing PHB" is simply
   identical to the "incoming PHB".

   For packets received unlabelled, this stage operates as with a non-
   MPLS IP Diff-Serv Router.

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                      MPLS Support of Diff-Serv               March 00

2.3

2.4 Label Swapping

   [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'

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                      MPLS Support of Diff-Serv              June 2000

     - `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 Context is stored in the NHLFE for each outgoing label which is
   swapped or pushed.

   This Diff-Serv context 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
   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

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                      MPLS Support of Diff-Serv               March 00
   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] is 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 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

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                      MPLS Support of Diff-Serv              June 2000

   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.

2.4

2.5 Encoding Diff-Serv information into Information Into Encapsulation Layer

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

2.4.1

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 for encoding into a given transmitted labeled packets

   This specification defines one default method for this encoding
   which allows regular support of Diff-Serv over MPLS. This method
   takes into account:
     - the Outgoing PHB
     - the Diff-Serv context associated with each swapped/pushed label
       of the selected NHLFE (`Set of PHB-->Encaps mappings').

   This method defines that the Outgoing PHB is reflected into:
     - the EXP field value of all the swapped or pushed label entries
     - the CLP/DE bit when the packet is encapsulated into ATM/Frame
       Relay,
     - the 802.1 User_Priority field of the 802.1 Tag Control
       Information when the packet is encapsulated into LAN interfaces
       supporting multiple Traffic Classes,

   The details of this method depend stack entry
   and/or transmitted MPLS encapsulation information depending on the
   corresponding outgoing LSP type and depending on the outgoing MPLS encapsulation and are defined below in sections
   3.5 and 4.5.

   Support for this default method is mandatory for compliance
   encapsulation.

   Section 2.6 provides the details of which label stack entry to this
   specification.

   Optionally, other methods for encoding
   perform Diff-Serv information encoding into depending on the Encapsulation layer may also be
   supported to allow for more
   sophisticated Diff-Serv operations over MPLS. Other methods may
   affect encapsulation fields differently.

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                      MPLS Support of Diff-Serv               March 00

2.4.2 tunneling mode.

2.5.2 Encoding Diff-Serv information for transmitted unlabelled packets Information Into Transmitted IP Header

   This specification paragraph defines one default method for this encoding
   which allows regular support of Diff-Serv over MPLS.

   Support for this default method is mandatory for compliance how to this
   specification.

   For packets perform Diff-Serv Information Encoding
   into the transmitted unlabelled (ie LSR performing label
   disposition), packet IP header.

   To perform Diff-Serv Information Encoding into the default encoding method writes 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.

   Optionally, other encoding methods may also be supported to allow
   for more sophisticated

   Section 2.6 provides the details of when Diff-Serv operations 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 Terminology

   As per [MPLS_ARCH],
   "we can speak of the level m LSP for Packet P as the sequence of
   routers:

     1. which begins with an LSR (an "LSP Ingress") that pushes on a
       level m label,
     2. all of whose intermediate LSRs make their forwarding decision
       by label Switching on a level m label,
     3. which ends (at an "LSP Egress") when a forwarding decision is
       made by label Switching on a level m-k label, where k>0, or when

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                      MPLS Support of Diff-Serv              June 2000

       a forwarding decision is made by "ordinary", non-MPLS forwarding
       procedures."

   We note that if Penultimate Hop Popping (PHP) is used on the LSP,
   the label pop for the LSP is not performed by the LSP Egress but
   instead is performed by the Penultimate LSR. If PHP is not used,
   then the label pop for the LSP is performed by the LSP Egress.

   In all the figures below, (I) indicates "LSP Ingress", (P) indicates
   "LSP Penultimate Hop" and (E) indicates "LSP Egress".

2.6.2 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 MPLS LSPs are thus clearly out of the scope of
   [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 (ie. 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 number of
   distinctive properties compared to IP Tunnels:
     - There is no behavior analogous to Penultimate Hop Popping (PHP)
       for 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.
     - Two-level hierarchical LSPs with the two nested LSPs starting on
       the same Ingress LSR and finishing on the same Egress LSR, are
       expected to be commonplace in MPLS networks for applications
       such as MPLS VPNs [MPLS_VPN].

   Based on these considerations, it is clear that the two important
   conceptual models for Diff-Serv tunneling over IP Tunnels defined in
   [DIFF_TUNNEL] are applicable and useful to Diff-Serv over MPLS and
   that their respective detailed operations is somewhat different over
   MPLS. These two models are the Uniform Model and the Pipe Model and
   their operations over MPLS is described in the following sections.

2.6.3 Uniform Model

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                      MPLS Support of Diff-Serv              June 2000

   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 (eg. 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.

   With this Uniform Model:
     - the LSP Ingress, when performing the push operation, encodes the
       meaningful Diff-Serv information in the label entry
       corresponding to the pushed label.
     - Intermediate LSRs only consider and operate on the LSP Diff-Serv
       Information encoded in the "outer" label entry (ie label entry
       on which they perform the label swap).
     - Penultimate Hop Popping (PHP) can be used. In that case, the
       meaningful Diff-Serv information is conveyed by the Penultimate
       LSR to the LSP Egress in the header that is exposed by the pop
       operation (ie. in the header that will be used for actual
       forwarding by the LSP Egress).
       Note that to do so, 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). 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
       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.
     - It is also possible to not use PHP. In that case, the meaningful
       Diff-Serv information is conveyed by the Penultimate LSR to the
       LSP Egress in the "outer" label entry (which corresponds to the
       LSP label).

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                      MPLS Support of Diff-Serv              June 2000

     - When the pop operation is performed (ie. Penultimate hop with
       PHP, LSP Egress without PHP), the incoming Diff-Serv information
       contained in the outmost label entry before the pop is
       considered as the meaningful information.

   Operation of the Uniform Model with PHP is illustrated below :

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

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

   Operation of the Uniform Model without PHP is illustrated below:

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

                 +--Swap--(M)-...-Swap-(M)-swap--(M)--+
                /        (outer header)     (P)        \
              (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.

   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 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. For this reason, the

 Le Faucheur et. al                                                 12
                      MPLS Support of Diff-Serv              June 2000

   Uniform Model has been selected in this specification as the base
   mandatory mode of operations and thus MUST be supported.

   For support of the Uniform Model over an LSP (with and 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 swap-only operation for an LSP, the LSR
       encodes Diff-Serv Information in the transmitted label entry
       corresponding to the swapped label
     - when performing a push operation for an 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.

2.6.4 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, the LSP Egress uses the Diff-
   Serv information conveyed from the LSP Ingress inside the
   encapsulated header (be it an IP Header or an MPLS Header) and
   ignores the Diff-Serv information conveyed in the encapsulating
   header.

   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 (which we refer to as the "LSP Diff-
       Serv Information"). This LSP Diff-Serv Information is not
       meaningful at 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 at the LSP Egress and is ignored.
     - the Diff-Serv information which is meaningful at 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.

   With this Pipe Model:
     - the LSP Ingress, when performing the push operation, encodes the
       LSP Diff-Serv information in the label entry that is pushed
       ("outer label entry") and encodes the Tunneled Diff-Serv

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                      MPLS Support of Diff-Serv              June 2000

       Information in the encapsulated header (IP header or swapped
       label entry).
     - Intermediate LSRs only consider and operate on the LSP Diff-Serv
       Information encoded in the "outer" label entry (ie label entry
       on which they perform the label swap).
     - Penultimate Hop Popping (PHP) can be used. In that case, the LSP
       Diff-Serv Information is simply not conveyed by the Penultimate
       LSR to the LSP Egress. The Penultimate LSR conveys to the LSP
       Egress the Tunneled Diff-Serv Information in the header that is
       exposed by the pop operation (ie. in the header that will be
       used for actual forwarding by the LSP Egress). However, since
       the LSP Diff-Serv Information is the meaningful one over the
       whole LSP including from the Penultimate LSR to the LSP Egress,
       the Penultimate LSR performs Diff-Serv forwarding treatment (ie
       PHB enforcement) based on the LSP Diff-Serv Information (even if
       this information is not actually conveyed in the packet
       transmitted to the LSP Egress).
     - it is also possible to not use PHP. In that case, the LSP Diff-
       Serv Information is conveyed by the Penultimate LSR to the LSP
       Egress in the "outer" label entry (which corresponds to the LSP
       label) where it will simply be ignored.
     - When PHP is used, the LSP Egress directly uses the Diff-Serv
       information received in the outer header (IP header or outer
       label entry) since it carries the Tunneled Diff-Serv
       Information.
     - When PHP is not used, LSP Egress ignores the Diff-Serv
       information contained in the label entry to be popped (since it
       contains the LSP Diff-Serv information) and considers the Diff-
       Serv information conveyed in the header (IP header or MPLS
       header) which is used to do the actual forwarding (since it
       contains the  Tunneled LSP Diff-Serv information). In other
       words, the LSP Egress considers the Diff-Serv information
       conveyed in the header after the pop operation.

   Operation of the Pipe Model with PHP is illustrated below:

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

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

   (M) represents the "LSP Diff-Serv information

   (m) represents the "Tunneled Diff-Serv information"

 Le Faucheur et. al                                                 14
                      MPLS Support of Diff-Serv              June 2000

   (*) The Penultimate LSR considers the LSP Diff-Serv information
   received in the outer header (ie. before the pop) in order to apply
   its Diff-Serv forwarding treatment (ie actual PHB)

   Operation of the Pipe Model without PHP is illustrated below:

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

                +--Swap-(M)-...-Swap-(M)--Swap--(M)--+
               /        (outer header)     (P)        \
             (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"

   The Pipe Model is particularly appropriate to environments in which
   the incoming interface of the LSP Ingress and the outgoing interface
   of the LSP Egress are in the same Diff-Serv domain while the LSP
   spans another (other) Diff-Serv domain(s).

   As an example, consider the case where a service provider is
   offering an MPLS VPN service 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 domain policy to operate consistently
   throughout the ingress VPN Site and Egress VPN Site and
   transparently over the Service Provider Diff-Serv domain.

   Support of the Pipe Model is defined in this specification as a
   recommended option and thus SHOULD be supported.

   For support of the Pipe Model over an 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 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.

 Le Faucheur et. al                                                 15
                      MPLS Support of Diff-Serv              June 2000

     - when performing a swap-only operation for an LSP, the LSR
       encodes Diff-Serv Information in the transmitted label entry
       corresponding to the swapped label
     - when performing a push operation for an 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).

   For support of the Pipe Model over an LSP with PHP, an LSR performs
   Incoming PHB Determination and Diff-Serv information Encoding in the
   same manner as without PHP with the following exception:
     - 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.
     - the Penultimate LSR does not perform Encoding of Diff-Serv
       Information into the header exposed by the pop operation.

   Note that LSR behaviors for the Uniform Model and for the Pipe 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 Uniform
   Model or the Pipe model. With a Diff-Serv implementation supporting
   both the Uniform Model and the Pipe Model, only LSRs behaving as LSP
   Ingress, Penultimate LSR or LSP Egress need to be configured to
   operate in a particular Model.

2.6.5 Other Models

   Other Diff-Serv tunneling models are conceivable over MPLS for
   support of more complex scenarios. For instance, the egress of an
   LSP could conceivably make some complex Diff-Serv decision based on
   both the Diff-Serv information conveyed in the encapsulating header
   and in the encapsulated header. Models beyond the Uniform Model and
   the Pipe Model are outside the scope of this specification and MAY
   be supported as an option.

2.6.6 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) are expected to
   operate in the same Tunneling Model (ie Uniform or Pipe). LSRs at

 Le Faucheur et. al                                                 16
                      MPLS Support of Diff-Serv              June 2000

   different levels of LSPs are expected to operate in the same or in
   different Tunneling Models.

 Le Faucheur et. al                                                 17
                      MPLS Support of Diff-Serv              June 2000

   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 (either Uniform or Pipe)

   (2) Tunneling Model 2 (same as Tunneling Model 1 or different Model)

   For support of M levels of push in the Uniform Model:
     - when performing multiple push operations, the LSR encodes Diff-
       Serv Information in the transmitted label entry corresponding to
       the LAST pushed label (ie the label pushed in the outer label
       entry). The Diff-Serv Information encoded in the encapsulated
       header (swapped label entry or IP Header) as well as the Diff-
       Serv Information encoded in label entries for other pushed
       labels are of no importance.

   For support of M levels of pop in the Uniform Model:
     - when performing multiple pop operations for an LSP, the LSR
       performs Incoming PHB Determination considering the outmost
       label entry in the received label stack. In other words, when
       multiple pop operations are to be performed, the LSR performs
       Incoming PHB Determination BEFORE ANY pop operations.
     - when the multiple pop operations are performed by the
       Penultimate LSR, note that to perform Encoding of Diff-Serv
       Information, the Penultimate LSR needs to be aware of the "Set
       of PHB-->Encaps mappings" for the label corresponding to the
       exposed header after all the pop operations (or the PHB-->DSCP
       mapping). Methods for providing this mapping awareness are
       outside the scope of this specification.
     - when the multiple pop operations are performed by the
       Penultimate LSR, note also that this specification assumes that
       the Penultimate LSR does not perform label swapping over MPLS. Other methods the
       label entry exposed after all the pop operations (and in fact
       that it does not even look at the header exposed after the last
       pop operations). Consequently, restrictions may affect apply to the DS field differently. One example would
       Diff-Serv Information Encoding that can be a method
   where performed by the IP packet's DS field is left unchanged regardless
       Penultimate LSR.

   For support of M levels of push in the
   Outgoing PHB. Such a method would allow `MPLS Pipe Model:
     - when performing multiple push operations, the LSR:
           o encodes Diff-Serv
   Transparency' ie it would allow support of Differentiated Services Information corresponding to the
             Outgoing PHB in the transmitted label entry corresponding

 Le Faucheur et. al                                                 18
                      MPLS backbone based on a Support of Diff-Serv policy which is specific              June 2000

             to the MPLS cloud (and different from LAST pushed label (ie the label pushed in the outer
             label entry).
           o encodes Diff-Serv policy applied Information corresponding to the
             Incoming PHB in the non-MPLS clouds around encapsulated header (swapped label
             entry or IP header) as well as in the MPLS cloud) since label entries for
             all the pushed labels (except the last pushed label).

   For support of M levels of pop in the Pipe Model without PHP:
     - when performing multiple pop operations for an LSP, the LSR
       performs Incoming PHB Determination considering the header
       (label entry or IP DS field
   would header) which is used to do the actual
       forwarding. In other words, when a pop operation is to be transported transparently through
       performed for the MPLS cloud. Details considered LSP, the LSR performs Incoming PHB
       Determination AFTER ALL the pop operations.

   For support of such methods M levels of pop in the Pipe Model with PHP, the
   Penultimate LSR:
     - performs Incoming PHB Determination considering the outmost
       label entry in the received label stack. In other words, when
       multiple pop operations are outside to be performed for the scope considered
       LSP, the LSR performs Incoming PHB Determination BEFORE ANY pop
       operations.
     - does not perform Encoding of this specification. Diff-Serv Information into the
       header that is exposed after all the pop operations

3. Detailed Operations of E-LSPs

3.1 E-LSP Definition

    Recognizing that:
     - Certain MPLS encapsulations (such as PPP and LAN) make use of a
       Shim Header which consists of a label stack with one or more
       entries [MPLS_ENCAPS] each with a 3-bit EXP field;
     - the Differentiated-Service (DS) field is 6-bit long
       [DIFF_HEADER] potentially allowing support of up to 64 Behavior
       Aggregates
     - any subset of 8 (or less) DSCP values can be mapped entirely
       into the 3-bit long EXP field of the MPLS label stack entry;

    We define that:
     - an LSP established for a given Forwarding Equivalent Class (FEC)
       may be used for transport of up to eight BAs of that FEC;
     - the set of transported BAs can span multiple OAs;
     - for a given OA transported over the LSP, all supported BAs of
       this OA are transported over the LSP;

 Le Faucheur et. al                                                 10

                      MPLS Support of Diff-Serv               March 00
     - such an LSP is referred to as an "EXP-inferred-PSC" LSP or
       "E-LSP" because the PSC to be applied to a labeled packet by the
       LSR depends on the EXP field value in the MPLS Shim Header;
     - packets belonging to this given (FEC) FEC and from the corresponding
       set of BAs are sent down this E-LSP.

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                      MPLS Support of Diff-Serv              June 2000

     - multiple BAs belonging to the same FEC and transported over the
       same E-LSP are granted different scheduling treatment and
       different drop precedence by the MPLS LSR based on the EXP field
       which is appropriately encoded to reflect both the PSC and the
       drop precedence of the PHB corresponding to the packet's BA.
     - the mapping between EXP field and PHB to be applied by the LSR
       for a given E-LSP is either explicitly signaled at label set-up
       or relies on a preconfigured mapping.

   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 less, 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.

   For a given FEC, there may be more than one E-LSP carrying the same
   OA, for example for purposes of load balancing of the OA. In that
   case, in order to respect ordering constraints, all packets of a
   given microflow must be transported over the same LSP.

   MPLS specifies how LSPs can be established via multiple signaling
   protocols. Those include the Label Distribution Protocol (LDP),
   RSVP, BGP and PIM. Sections 5 and 6 below specify how RSVP and LDP
   are to be used for establishment of E-LSPs.

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
   Context is populated for an incoming E-LSP in order to support the
   mandatory default method for 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.

 Le Faucheur et. al                                                 11

                      MPLS Support of Diff-Serv               March 00

   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 uses 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.

 Le Faucheur et. al                                                 20
                      MPLS Support of Diff-Serv              June 2000

   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.

3.3 Incoming PHB Determination On Incoming E-LSP

   This section defines the mandatory default method for how Incoming PHB
   determination for a labeled packet Determination is carried out
   when the considered label entry in the received on label stack
   corresponds to an E-LSP. This method requires that the `Encaps-->PHB
   mapping' is populated as defined as defined above 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 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.

   When receiving a labeled packet over 3.2.1.

   If the label corresponds to an E-LSP of for which an MPLS ingress
   interface, EXP<-->PHB mapping
   has been explicitly signaled at LSP setup, the LSR:

     -determines `PHB-->EXP mapping'
   is populated as per the EXP-->PHB mapping by looking up signaled EXP<-->PHB mapping.

3.4.2 `PHB-->CLP mapping'

   If the
       `Encaps-->PHB E-LSP is egressing over an ATM interface which is not label
   switching controlled, then one `PHB-->CLP mapping' is added at label
   setup to the `Set of PHB-->Encaps mappings' in the Diff-Serv context associated with
       the incoming label Context
   for this outgoing E-LSP. This `PHB-->CLP mapping' is populated in
   the ILM. following way:
     - determines the incoming PHB by looking up the EXP field it is a function of the
       top level label entry into PHBs supported on this LSP, and may use
       the EXP-->PHB relevant mapping table.

   If entries for these PHBs from the EXP field value
       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

 Le Faucheur et. al                                                 21
                      MPLS Support of Diff-Serv              June 2000

       particular, if a packet received on an E-LSP mapping from PHBs to CLP is not
   included standardized in the EXP-->PHB
       future for operations of Diff-Serv over ATM, such standardized
       mapping associated with this LSP, this EXP
   value should may then be considered invalid. LSR behavior in such situation
   is a local matter used.

   For example if the outgoing label corresponds to an E-LSP supporting
   the AF1 PSC and is outside the scope of this document.

3.4 Populating EF PHB and egressing over an ATM interface, then
   the `PHB-->CLP mapping' may be populated with:

        PHB                CLP Field

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

   Notice that if the `Set of PHB-->Encaps mappings' for an outgoing E-LSP

   This section defines how is egressing over an ATM interface, then
   the `Set of PHB-->Encaps mappings' of the
   Diff-Serv context is populated for an outgoing E-LSP in order to
   support the mandatory default method for Encoding of Diff-Serv
   information in the Encapsulation Layer.

3.4.1 contains both a `PHB-->EXP
   mapping'

   One `PHB-->EXP 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 E-LSP is egressing over a Frame Relay interface which is not
   label switching controlled, one `PHB-->DE mapping' is always added at label
   setup to the `Set of PHB-->Encaps mappings' of in the Diff-Serv context Context
   for an this outgoing E-LSP.

   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'

 Le Faucheur et. al                                                 12

                      MPLS Support of Diff-Serv               March 00 and is populated based in the following way:
     - it is a function of the PHBs supported on this LSP, and may use
       the Preconfigured EXP<-->PHB relevant mapping entries for these PHBs from the Default
       PHB-->DE Mapping which is
   discussed above defined in section 3.2.1.

   If 3.4.3.1. Other mappings than
       the label corresponds one defined in section 3.4.3.1 may be used. In particular,
       if a mapping from PHBs to an E-LSP DE is standardized in the future for which an EXP<-->PHB
       operations of Diff-Serv over Frame Relay, such standardized
       mapping
   has been explicitly signaled at LSP setup, may then be used.

   Notice that if the E-LSP is egressing over a Frame Relay interface,
   then the `Set of PHB-->Encaps mappings' contains both a `PHB-->EXP
   mapping'
   is populated as per the signaled EXP<-->PHB mapping.

3.4.2 and a `PHB-->DE mapping'.

3.4.3.1 Default PHB-->DE Mapping

        PHB                 DE Bit

 Le Faucheur et. al                                                 22
                      MPLS Support of Diff-Serv              June 2000

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

3.4.4 `PHB-->802.1 mapping'

   If the outgoing interface E-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 at label setup to the `Set of
   PHB-->Encaps mappings' of the Diff-
   Serv context Diff-Serv Context for the this outgoing
   E-LSP. This mapping `PHB-->802.1 mapping' is populated at
   label set-up based 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 Mapping defined
   below in section 3.4.2.1. 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'.

3.4.2.1

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 the mandatory default method for encoding of how to encode Diff-Serv related information into the
   MPLS encapsulation Layer to
   be used when for a packet is given transmitted onto label entry
   corresponding to an outgoing E-LSP. This method requires that the `Set of
   PHB-->Encaps mappings' is populated as defined above in section 3.4.

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

3.5.1 `PHB-->EXP mapping'

   For all the labels which are swapped or pushed, the

   The LSR:
     - determines the PHB-->EXP mapping by looking up the
       `Set of PHB-->Encaps mapping' of the Diff-Serv context
       associated with the corresponding label in Diff-Serv Context
       associated with the corresponding label in the NHLFE.
     - 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              June 2000

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 NHLFE. LSR:
     - determines the value to be written in the EXP DE field of the
       corresponding level label entry Frame
       Relay encapsulation header, by looking up the "outgoing PHB" in
       this PHB-->EXP PHB-->DE mapping table.

3.5.2

3.5.4 `PHB-->802.1 mapping'

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                      MPLS Support of Diff-Serv               March 00

   If the `Set of PHB-->Encaps mapping' of the outer label 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

4.1 L-LSP Definition

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                      MPLS Support of Diff-Serv              June 2000

    Recognizing that:

     - All currently defined MPLS encapsulation methods have a field of
       3 bits or less for Diff-Serv encoding (i.e., 3-bit EXP field in
       case of Shim Header and 1-bit CLP/DE bit in case of ATM/Frame
       Relay).
     - The Differentiated-Services (DS) field is 6-bit long
       [DIFF_HEADER] potentially allowing support of up to 64 Behavior
       Aggregates. So that when more than a certain number of BAs are
       used (i.e., more than 8 BAs in case of Shim Header and more than
       2 BAs in case of ATM/Frame Relay), the DS field can not be
       mapped entirely into the appropriate field of MPLS encapsulation
       header (i.e., EXP field in case of Shim Header and CLP/DE field
       in case of ATM/Frame Relay);

    We define that:

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                      MPLS Support of Diff-Serv               March 00

     - an LSP established for a given Forwarding Equivalent Class (FEC)
       may be used for transport of the BAs comprised in one Ordered
       Aggregate (OA) for that FEC;
     - all BAs of this OA can be transported over the LSP;
     - BAs from other OAs can not be transported over the LSP;
     - BAs from the OA transported over the LSP are given the
       appropriate scheduling treatment based on the PSC which is
       explicitly signaled at label set-up time.
     - Such an LSP is referred to as a "Label-Only-inferred-PSC" LSP or
       "L-LSP";
     - Multiple BAs from the OA transported over the LSP are granted
       different drop precedence by the MPLS LSR based on the  appropriately
       encoded relevant field of MPLS encapsulation header (EXP field
       of the top label entry for the shim header, CLP/DE bit in case
       of ATM/Frame Relay); The mapping between the relevant field of
       the MPLS encapsulation and the drop precedence is a well-known
       mapping.

   For a given FEC, there may be more than one L-LSP carrying the same
   OA, for example for purposes of load balancing of the OA. In that
   case, in order to respect ordering constraints, all packets of a
   given microflow must be transported over the same LSP.

   MPLS specifies how LSPs can be established via multiple signaling
   protocols. Those include the Label Distribution Protocol (LDP),
   RSVP, BGP and PIM. Sections 5 and 6 below specify how RSVP and LDP
   are to be used for establishment of L-LSPs.

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
   Context is populated for an incoming L-LSP for support of the
   mandatory default method for in order to allow
   Incoming PHB determination.

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                      MPLS Support of Diff-Serv              June 2000

4.2.1 `EXP-->PHB mapping'

   If the LSR terminates the MPLS Shim Layer (i.e. it is not an
   ATM-LSR or FR-LSR as defined in [MPLS ATM][MPLS FR], over this incoming L-LSP
   and it does not
   receive packets without an MPLS shim layer the L-LSP ingresses on an LC-ATM or LC-FR
   interface) interface which is not ATM nor Frame
   Relay, then the `Encaps-->PHB mapping' is populated at label setup
   in the following way:
     - it is must actually be a `EXP-->PHB mapping'
     - the this mapping is a function of the PSC which is carried on this
       LSP, and uses must use the relevant `EXP->PHB mapping' mapping entries for this PSC as from
       the Mandatory EXP/PSC-->PHB Mapping defined in Section 4.2.1.1 below.

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                      MPLS Support of Diff-Serv               March 00 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
        010        ---->    AF13

4.2.1.1 EXP/PSC -->

   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 at label setup 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

   In order to populate 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', the this
       `EXP-->PHB mapping' mapping from is a function of the L-LSP PSCs PSC which is
       carried on the L-LSP, and must use the EXP field 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 header into PHBs is
   specified as follows: layer over an ingress ATM/FR
   interface.

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
        010          AFn   <---->   ---->    AFn3

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                      MPLS Support of Diff-Serv              June 2000

        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 or it
   receives packets without a shim on an LC-ATM interface), ATM-LSR), then the
   `Encaps-->PHB mapping' of the Diff-Serv context Context for this incoming
   L-LSP is populated at label setup 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 uses should use the relevant `CLP-->PHB mapping' mapping entries for this PSC as
       from the Default CLP/PSC-->PHB Mapping defined in Section 4.2.2.1 below.
       4.2.2.1.

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

      CLP Field              PHB

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

4.2.2.1 Default CLP/PSC --> PHB mapping

   In order to populate the `Encaps-->PHB mapping', the mapping from
   the L-LSP PSCs and the CLP bit of the ATM cell header into PHBs is
   specified as follows: Mapping

      CLP Bit      PSC             PHB

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                      MPLS Support of Diff-Serv               March 00

         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. encapsulation (i.e. it is a FR-LSR or it
   receives packets without a shim on an LC-FR interface), FR-LSR), then
   the `Encaps-->PHB mapping' of the Diff-Serv context Context for this
   incoming L-LSP is populated at label setup 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 uses should use the relevant `DE-->PHB mapping' mapping entries for this PSC as
       from the Default DE/PSC-->PHB Mapping defined in Section
       4.2.3.1.

4.2.3.1 below.

4.2.3.1 Default DE/PSC --> PHB mapping

   In order to populate the `Encaps-->PHB mapping', the mapping from
   the L-LSP PSCs and the DE bit of the Frame Relay header into PHBs is
   specified as follows: Mapping

      DE Bit      PSC             PHB

         0          DF    ---->    DF
         0          CSn   ---->    CSn
         0          AFn   ---->    AFn1

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                      MPLS Support of Diff-Serv              June 2000

         1          AFn   ---->    AFn2
         0          EF    ---->    EF

4.3 Incoming PHB Determination On Incoming L-LSP

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

   When receiving considering a labeled packet over an L-LSP of an MPLS ingress
   interface, label entry corresponding to an incoming L-LSP
   for Incoming PHB Determination, the LSR first determines the
   `Encaps-->PHB mapping' associated with the incoming top level 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
       top level
       considered label entry and by using the EXP-->PHB mapping.

   If the received EXP field value is not included in the EXP-->PHB
   mapping, this EXP value should be considered invalid. LSR behavior

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                      MPLS Support of Diff-Serv               March 00

   in such situation is a local matter and is outside the scope of this
   document.

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.

   If the received CLP field value is not included in the CLP-->PHB
   mapping, this CLP value should be considered invalid. LSR behavior
   in such situation is a local matter and is outside the scope of this
   document.

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.

   If the received DE field value is not included in the DE-->PHB
   mapping, this DE value should be considered invalid. LSR behavior in
   such situation is a local matter and is outside the scope of this
   document.

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 Context is populated for an outgoing L-LSP for support of
   the mandatory default method for in order to
   allow Encoding of Diff-Serv Information into
   Encapsulation on Outgoing L-LSP. Information.

4.4.1 `PHB-->EXP mapping'

   If the LSR uses an MPLS Shim Layer over this outgoing label (i.e. it
   is not an ATM-LSR or FR-LSR and it does not transmit packets without
   an MPLS Shim Layer on a LC-ATM or LC-FR interface), L-LSP, then
   one `PHB-->EXP mapping' is added at label setup to the `Set of
   PHB-->Encaps mapping' mappings' in the Diff-Serv context Context 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 uses must use
       the mapping entries relevant `PHB-->EXP mapping' for this PSC as from the Mandatory
       PHB-->EXP Mapping defined in section
       4.4.1.1 below. 4.4.1.1.

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                      MPLS Support of Diff-Serv              June 2000

   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

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                      MPLS Support of Diff-Serv               March 00

        AF11       ---->      000
        AF12       ---->      001
        AF13       ---->      010

4.4.1.1 PHB-->PSC/EXP mapping

   In order to populate the `Set of PHB-->Encaps mappings', the mapping
   from the PHBs into the L-LSP PSC and the EXP field of the shim
   header is specified as follows: Mandatory PHB-->EXP Mapping

        PHB                     PSC                EXP Field

        DF         ---->        DF      000
        CSn        ---->        CSn      000
        AFn1       ---->        AFn      000
        AFn2       ---->        AFn      001
        AFn3       ---->        AFn      010
        EF         ---->        EF      000

4.4.2 `PHB-->CLP mapping'

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

   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 uses should
       use the relevant `PHB-->CLP mapping' mapping entries for this PSC as from the Default
       PHB-->CLP Mapping defined below in section 4.4.2.1. 3.4.2.1.

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

        PHB                CLP Field

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

   If the L-LSP is egressing over an ATM interface which is not label
   switching controlled, the `PHB-->CLP mapping' is populated in the
   following way:
     - it is a function of the PSC supported on this LSP, and may use
       the relevant mapping entries for this PSC 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

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                      MPLS Support of Diff-Serv              June 2000

       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.

   Notice that the if the LSR is transmitting packets over a LC-ATM
   interface using the MPLS Shim Header, 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
   mapping'.

4.4.2.1 PHB-->PSC/CLP mapping

   In order to populate If the LSR is an ATM-LSR supporting an L-LSP, then the
   `Set of PHB-->Encaps mappings', the mapping
   from the PHBs into the L-LSP PSC and the CLP bit of the ATM cell
   header is specified as follows:

        PHB              PSC       CLP Bit

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                      MPLS Support of Diff-Serv               March 00

         DF       ---->   DF         0
         CSn      ---->  CSn         0
         AFn1     ---->  AFn         0
         AFn2     ---->  AFn         1
         AFn3     ---->  AFn         1
         EF       ---->   EF         0 mappings' only contains a `PHB-->CLP mapping'.

4.4.3 `PHB-->DE mapping'

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

   If the L-LSP and 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 uses should
       use the relevant mapping entries for this PSC from the Default
       PHB-->DE Mapping defined in section 3.4.3.1.

   If the L-LSP is egressing over a FR interface which is not label
   switching controlled, the `PHB-->DE mapping' is populated in the
   following way:
     - it is a function of the PSC supported on this LSP, and may use
       the relevant mapping entries for this PSC as from the Default
       PHB-->DE Mapping defined in section 3.4.3.1. Other mappings than
       the one defined below in section 4.4.3.1. 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 if the LSR is sending packets an Edge-LSR supporting an L-LSP egressing
   over a LC-FR interfaces
   using the MPLS Shim Header, interface, then the `Set of PHB-->Encaps mappings'
   contains both a `PHB-->EXP mapping' and a `PHB-->DE mapping'.

4.4.3.1 PHB-->PSC/DE mapping

   In order to populate If the
   LSR is a FR-LSR supporting an L-LSP, then the `Set of PHB-->Encaps mappings', the mapping
   from the PHBs into the L-LSP PSC and the DE bit of the Frame Relay
   header is specified as follows:

        PHB              PSC       DE Bit

         DF       ---->   DF         0
         CSn      ---->  CSn         0
         AFn1     ---->  AFn         0
         AFn2     ---->  AFn         1
         AFn3     ---->  AFn         1
         EF       ---->   EF         0
   mappings' only contains a `PHB-->DE mapping'.

4.4.4 `PHB-->802.1 mapping'

   If the outgoing interface L-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 at label setup to the `Set of
   PHB-->Encaps mappings' in the Diff-Serv context Context for this outgoing
   L-LSP. This `PHB-->802.1 mapping' is populated in the following way:
     - it is a function of the PSC supported on this LSP, and uses the
       relevant `PHB-->802.1 mapping' mapping entries for this PSC from the Preconfigured
       `PHB-->802.1 mapping' defined above in section
       3.4.2.1. 3.4.4.1.

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                      MPLS Support of Diff-Serv              June 2000

   Notice that if the LSR is transmitting packets supporting an L-LSP egressing over a LAN
   interface supporting multiple 802.1 Traffic Classes, then the `Set
   of

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                      MPLS Support of Diff-Serv               March 00 PHB-->Encaps mappings' contains both a `PHB-->EXP mapping' and a
   `PHB-->802.1 mapping'.

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

   This section defines the mandatory default method for encoding of how to encode Diff-Serv related information into the
   MPLS encapsulation Layer to
   be used when for a packet is transmitted onto label entry corresponding
   to an outgoing L-LSP. This method requires that the `Set of PHB-->Encaps
   mappings' is populated as defined above in section 4.4.

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

4.5.1 `PHB-->EXP mapping'

   If the `Set of PHB-->Encaps mapping' mappings' of the outer transmitted label
   contains a mapping of the form `PHB-->EXP mapping', then, for all the labels
   which are swapped or pushed, then the LSR:
     - determines the PHB-->EXP mapping by looking up the
       `PHB-->Encaps mapping' of the Diff-Serv context associated with
       the corresponding label in the NHLFE.
     - 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.

4.5.2 `PHB-->CLP mapping'

   If the `Set of PHB-->Encaps mapping' mappings' of the outer transmitted label
   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
       Layer encapsulation by looking up the "outgoing PHB" in this
       PHB-->CLP mapping table.

4.5.3 `PHB-->DE mapping'

   If the `Set of PHB-->Encaps mapping' mappings' of the outer transmitted label
   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 by looking up the "outgoing PHB" in this
       PHB-->DE mapping table.

4.5.4 `PHB-->802.1 mapping'

   If the `Set of PHB-->Encaps mapping' mappings' of the outer transmitted label
   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.

4.6 L-LSP Merging

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                      MPLS Support of Diff-Serv               March 00

4.6 L-LSP Merging              June 2000

   In an MPLS domain, two or more LSPs can be merged into one LSP at
   one LSR. The proposed support of Diff-Serv in MPLS is compatible
   with LSP Merging under the following condition:

        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

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                      MPLS Support of Diff-Serv               March 00
   specification MAY support the DIFFSERV Object. A Diff-Serv capable
   LSR supporting E-LSPs using a signaled EXP<-->PHB mapping in

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                      MPLS Support of Diff-Serv              June 2000

   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.

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

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                      MPLS Support of Diff-Serv               March 00

     MAPnb : 4 bits              June 2000

       Indicates the number of MAP entries included in the DIFFSERV
       Object. This can be set to any value from 1 to 8 (decimal). 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].

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.

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                      MPLS Support of Diff-Serv               March 00
           - 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

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                      MPLS Support of Diff-Serv              June 2000

        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|
             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.3 Handling Diff-Serv 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].
   Where the sender supports Diff-Serv, 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.

   Where the sender supports Diff-Serv, 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.

   Where the sender supports Diff-Serv, 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               March 00

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

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                      MPLS Support of Diff-Serv              June 2000

   The destination node 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 reservation is accepted and a label is associated with
   the reservation, the Diff-Serv LSRs (sender, destination,
   intermediate nodes) must:
     - update the Diff-Serv context 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 RSVP router that does 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.

   A node 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
   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.

   A node 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 1 to 8 decimal, or
     - a given EXP value appears in more than one MAP entry, or
     - the PHBID encoding is invalid invalid.

   A node 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.

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                      MPLS Support of Diff-Serv               March 00

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

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                      MPLS Support of Diff-Serv              June 2000

5.4 Non-support of the Diff-Serv Object

   An RSVP router 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 ie. it must send a
   PathErr with the error code `Unknown object class' toward the
   sender.

   An RSVP router that recognizes 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 ie. 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 reservation establishment without the
   DIFFSERV object (eg. attempt to use E-LSPs with Preconfigured
   EXP<-->PHB mapping as a fall-back strategy).

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 26 (TBD).

   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

5.6 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.

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                      MPLS Support of Diff-Serv               March 00

   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

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                      MPLS Support of Diff-Serv              June 2000

   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 in 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 in 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 LSP L-LSP indicates to a Diff-Serv capable LSR that
   the LSP to be established in is an L-LSP without any bandwidth
   reservation.

   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

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                      MPLS Support of Diff-Serv               March 00

   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.

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                      MPLS Support of Diff-Serv              June 2000

   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:

      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  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 : 28 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 (decimal).

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                      MPLS Support of Diff-Serv               March 00 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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                      MPLS Support of Diff-Serv              June 2000

    |            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:

      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 : 16 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

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                      MPLS Support of Diff-Serv               March 00
        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

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                      MPLS Support of Diff-Serv              June 2000

             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             |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

        Unsupported PHB                 0   0x00000016
        Invalid EXP<-->PHB mapping      0   0x00000017
        Unsupported PSC                 0   0x00000018
        Unexpected Diff-Serv TLV        0   0x00000019

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

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                      MPLS Support of Diff-Serv               March 00

   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           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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                      MPLS Support of Diff-Serv              June 2000

   |                     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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     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                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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                      MPLS Support of Diff-Serv               March 00
   |                 Diff-Serv TLV (optional)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

6.4 Handling of the Diff-Serv TLV

6.3.1

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

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                      MPLS Support of Diff-Serv              June 2000

   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:
     - update the Diff-Serv context 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 decimal, 8, or
     - a given EXP value appears in more than one MAP entry, or

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                      MPLS Support of Diff-Serv               March 00
     - 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'.

6.3.2

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                      MPLS Support of Diff-Serv              June 2000

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.

   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 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

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                      MPLS Support of Diff-Serv               March 00
   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 decimal, 8, or

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                      MPLS Support of Diff-Serv              June 2000

     - 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 and supports the requested PSC but is not
   able to satisfy the label request for other reasons (eg. no label
   available), must send a Notification message in accordance with
   existing LDP procedures [LDP] (eg. with a `No Label Resource' Status
   Code). This Notification message must include the requested
   Diff-Serv TLV.

6.4

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 ie. it must ignore the message, return a Notification message
   with `Unknown TLV' Status.

6.5

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 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 links. While
   sections 8, 9 and 10 focus on other media specific operations,
   namely ATM, Frame Relay and LAN respectively.

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                      MPLS Support of Diff-Serv               March 00

   This document allows any of the following LSP combinations per FEC
   within an MPLS PPP Diff-Serv domain:

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

7.1 LSR implementation with PPP interfaces

   A Diff-Serv capable LSR with PPP interfaces MUST support, over these
   PPP interfaces, E-LSPs which use the pre-configured EXP<-->PHB

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                      MPLS Support of Diff-Serv              June 2000

   mapping, in compliance with all the material from this specification
   pertaining to those types of LSPs.

   A Diff-Serv capable LSR with PPP interfaces MAY support, over these
   PPP interfaces, E-LSPs which use a signaled EXP<-->PHB mapping. If a
   Diff-Serv LSR does support E-LSPs which use a signaled EXP<-->PHB
   mapping over PPP interfaces, then it MUST do so in compliance with
   all the material from this specification pertaining to those types
   of LSPs.

   A Diff-Serv capable LSR with PPP interfaces MAY support L-LSPs over
   these PPP interfaces. If a Diff-Serv LSR does support L-LSPs over
   PPP interfaces, then it MUST do so in compliance with all the
   material from this specification pertaining to L-LSPs.

   An

7.2 LSR implementation with non-LC ATM interfaces

   The E-LSP/L-LSP support requirements for an LSR running MPLS over PPP over a
   traditional ATM connection (ie. where the ATM switches do not participate in MPLS and where the ATM
   connection VPI/VCI values have interface is not been established via any label
   distribution protocol) is to be considered
   switching controlled) are the same as those specified in section 7.1
   for an LSR with PPP interfaces.

7.3 LSR implementation with non-LC FR interfaces from the point of view of compliance to this
   specification.

   Similarly,

   The E-LSP/L-LSP support requirements for an LSR running MPLS over PPP over a
   traditional Frame Relay connection (ie. where the Frame Relay switches do not
   participate in MPLS and where the Frame Relay connection DLCI values
   have (ie. where the interface is not been established via any
   label distribution protocol) is to
   be considered switching controlled) are the same as those specified in
   section 7.1 for an LSR with PPP interfaces from the point of view
   of compliance to this specification. interfaces.

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

   The general operations for MPLS support of Diff-Serv, including
   label forwarding and LSP setup operations was specified in the
   previous sections. This section describes the specific operations
   required for MPLS support of Diff-Serv over label switching
   controlled ATM links. (LC-ATM) interfaces.

   This document allows the following set any number of LSP combinations L-LSPs per FEC within an MPLS ATM
   Diff-Serv domain:

        - any number of L-LSPs. domain. E-LSPs are not supported over LC-ATM interfaces.

8.1 Merging

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                      MPLS Support of Diff-Serv               March 00

   The use of merging is optional. In case that merging of ATM LSPs is
   used, procedures described in section 3.6 of this specification
   apply. Additionally, to avoid cell interleaving problems with AAL-5
   merging, procedures specified in [MPLS ATM] [MPLS_ATM] MUST be followed.

8.2 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

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                      MPLS Support of Diff-Serv              June 2000

   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 for encoding the PHB drop precedence
   value over ATM links, only two different drop precedence levels are
   supported in ATM LSRs. The behavior for AF MUST comply to procedures
   described 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.

8.3 LSR Implementation With ATM LC-ATM Interfaces

   A Diff-Serv capable LSR with ATM LC-ATM interfaces MUST support L-LSPs
   over these ATM interfaces in compliance with all the material from
   this specification pertaining to those types of LSPs. Additionally,
   procedures specified in [MPLS ATM] [MPLS_ATM] MUST be followed by compliant
   implementation.

   Support

   This specification assumes that Edge-LSRs of E-LSPs over ATM interfaces running native ATM MPLS by an
   LSR implementation the ATM-LSR domain use
   the "shim header" encapsulation method defined in [MPLS_ATM].
   Operations without the "shim header" encapsulation is not allowed. outside the
   scope of this specification.

9. MPLS Support of Diff-Serv by Frame Relay LSRs over LC-FR Interfaces

   The general operations for MPLS support of Diff-Serv, including
   label forwarding and LSP setup operations was specified in the
   previous sections. This section describes the specific operations
   required for MPLS support of Diff-Serv over label switching
   controlled Frame Relay links. (LC-FR) interfaces.

   This document allows the following set any number of LSP combinations L-LSPs per FEC within an MPLS
   Frame Relay Diff-Serv domain:

        - any number of L-LSPs. domain. E-LSPs are not supported over LC-FR
   interfaces.

9.1 Merging

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                      MPLS Support of Diff-Serv               March 00

   The use of merging is optional. In case that merging of Frame Relay
   LSPs is used, procedures described in section 3.6 of this
   specification apply as well as procedures in [MPLS FR]. [MPLS_FR].

9.2 Use of Frame Relay Traffic parameters and Traffic Management
mechanisms

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                      MPLS Support of Diff-Serv              June 2000

   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
   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 for encoding the PHB drop precedence
   value over Frame Relay links, only two different drop precedence
   levels are supported in Frame Relay LSRs. The behavior for AF MUST
   comply to procedures described in [DIFF_AF] for the case when only
   two drop precedence levels are supported.

9.3 LSR Implementation With Frame Relay LC-FR Interfaces

   A Diff-Serv capable LSR with Frame Relay LC-FR interfaces MUST support
   L-LSPs over these Frame Relay interfaces in compliance with all the
   material from this specification pertaining to those types of LSPs.

   Support of E-LSPs over Frame Relay interfaces running native Frame
   Relay MPLS
   Additionally, procedures specified in [MPLS_FR] MUST be followed by an LSR implementation
   compliant implementation.

   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 not allowed. outside the scope
   of this specification.

10. MPLS Support of Diff-Serv over LAN Media Interfaces

   The general operations for MPLS support of Diff-Serv, including
   label forwarding and LSP setup operations was specified in the
   previous sections. This section describes the specific operations
   required for MPLS support of Diff-Serv over LAN. LAN interfaces.

   This document allows the following set of LSP setup combinations per
   FEC over an MPLS link: a LAN interface:

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

10.1 LSR Implementation With LAN Interfaces

   A Diff-Serv capable LSR with LAN interfaces MUST support, over these
   LAN interfaces, E-LSPs which use the pre-configured EXP<-->PHB
   mapping, in compliance with all the material from this specification
   pertaining to those types of LSPs.

   A Diff-Serv capable LSR with LAN interfaces MAY support, over these
   LAN interfaces, E-LSPs which use a signaled EXP<-->PHB mapping. If a

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                      MPLS Support of Diff-Serv               March 00
   Diff-Serv LSR does support E-LSPs which use a signaled EXP<-->PHB
   mapping over LAN interfaces, then it MUST do so in compliance with

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                      MPLS Support of Diff-Serv              June 2000

   all the material from this specification pertaining to those types
   of LSPs.

   A Diff-Serv capable LSR MAY support L-LSPs over LAN interfaces. If a
   Diff-Serv LSR does support L-LSPs over LAN interfaces, then it MUST
   do so in compliance with all the material from this specification
   pertaining to L-LSPs.

11. Explicit Congestion Notification

   Explicit Congestion Notification is described in [ECN] and is
   proposed as an Experimental extension to the IP protocol.

   [MPLS_ECN] discusses deployment of ECN in an MPLS network using the
   Shim Header as the MPLS encapsulation. It demonstrates that,
   provided a given LSP is identified as ECN-capable or as non-ECN-
   capable (and consistently recognized as such by all the involved
   LSRs), then ECN can be supported in an MPLS domain where the Shim
   Header is used as the MPLS encapsulation via a single bit of the EXP
   field.

   The details of how a given LSP is to be identified as ECN-capable or
   non-ECN-capable (whether via extensions to the LSP establishment
   signaling and procedures, via configuration or via other means) are
   outside the scope of this specification.

   However, this specification recognizes that, within an ECN-capable
   MPLS domain where LSPs are identified as ECN-capable or not-ECN-
   capable:

     - Support of ECN does not require that any bit(s) from the EXP
       field be reserved for ECN operations across all LSPs even when
       those LSPs are not ECN-capable. Consequently, LSPs identified as
       non-ECN-capable (regardless of whether this is because at least
       one LSR on the LSP does not support ECN operations or whether
       this is because the network administrator does not wish to use
       ECN on this LSP) can make use of the full 3-bit EXP field for
       Diff-Serv purposes. Thus, non-ECN-capable E-LSPs and non-ECN-
       capable L-LSPs can operate as defined earlier in this document
       without any restriction imposed by the fact that the MPLS domain
       is ECN-capable. In particular, up to 8 BAs can still be
       transported over a non-ECN-capable E-LSP within an ECN-capable
       MPLS domain. Similarly, non-ECN-capable L-LSPs within an ECN-
       capable MPLS domain can support all the drop precedence levels
       of currently defined PSCs. Should a future PSC involve more than
       4 drop precedence levels, non-ECN-capable L-LSPs within an ECN-
       capable MPLS domain could still use the full 3-bit field EXP.

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                      MPLS Support of Diff-Serv               March 00

     - Because a single bit is required to encode the ECN information
       inside the ECN-capable MPLS domain, LSPs identified as ECN-
       capable can make use of two bits of the EXP field value for

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                      MPLS Support of Diff-Serv              June 2000

       Diff-Serv purposes. In particular, up to 4 BAs can be
       transported over an ECN-capable E-LSP. Similarly, up to 4 drop
       precedence levels can be supported over an ECN-capable L-LSP;
       since all the PSCs corresponding to PHBs currently defined
       through standards action involve less than 4 drop precedence
       levels, ECN support does not currently restrict Diff-Serv
       operations over L-LSPs. Should a PSC corresponding to future
       PHBs defined by standards action or corresponding to local use
       or experimental PHBs, involve more than 4 drop precedence
       levels, then ECN support over the corresponding LSP would
       constrain the PSC to 4 drop precedence levels; relative benefits
       of additional precedence levels beyond 4, would then be weighted
       by the network administrator over the benefits of ECN, to
       determine whether it is preferable to support this PSC over an
       ECN-capable or non-ECN-capable LSP.

11.1 MPLS ECN bit with Shim Header

   Where the Shim Header is used as the MPLS encapsulation, ECN
   information is to be encoded on ECN-capable LSPs in the first bit of
   the 3-bit EXP field in the following way:

     EXP field          MPLS ECN Meaning

     0xx        -->     `ECT, not CE'
     1xx        -->     `not ECT, or ECT+CE'

   where ECT stands for `ECN Capable Transport' and `CE' stands for
   `Congestion experienced'.

   Detailed specification for usage of this MPLS ECN bit is outside the
   scope of this document.

   For ECN-capable E-LSPs using preconfigured mapping, the
   Preconfigured EXP<-->PHB mapping defined above in section 3.2.1 is
   only operating over the last 2 bits of the 3-bit EXP field. For ECN-
   capable E-LSPs using signaled mapping, the signaled EXP<-->PHB
   mapping is only operating over the last 2 bits of the 3-bit EXP
   field. Thus it has LSPs, the following format: mappings between EXP Field                 PHB

        e00     <----->         a given PHB
        e01     <----->         a given PHB
        e10     <----->         a given PHB
        e11     <----->         a given and PHB

   where `e' is (be it the MPLS ECN bit and can take
   E-LSP Preconfigured Mapping specified in section 3.2.1, the value zero or one
   depending on ECN operations.

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                      MPLS Support of Diff-Serv               March 00

   For ECN-capable L-LSPs, E-LSP
   Signaled Mapping, the `EXP/PSC-->PHB mapping' L-LSP Mappings defined above in section 4.2.1.1 is and
   4.4.1.1) are adjusted accordingly to only operating over take into account the last
   2 bits of the 3-bit EXP field and is field.

   Note that when the following:

      EXP Field      PSC             PHB

        e00          DF    ----->    DF
        e00          CSn   ----->    CSn
        e00          AFn   ----->    AFn1
        e01          AFn   ----->    AFn2
        e10          AFn   ----->    AFn3
        e00          EF    ----->    EF

   where `e' E-LSP signaled mapping is the MPLS ECN bit and can take the value zero or one
   depending used on ECN operations.

   For an ECN-capable L-LSPs, the `PHB--> PSC/EXP mapping' defined above
   in
   E-LSP, the section 4.4.1.1 is signaled mapping only operating over the last 2 bits of the
   3-bit EXP field and is the following:

        PHB              EXP Field     PSC

        DF     ----->     e00          DF
        CSn    ----->     e00          CSn
        AFn1   ----->     e00          AFn
        AFn2   ----->     e01          AFn
        AFn3   ----->     e10          AFn
        EF     ----->     e00          EF

   where `e' is the MPLS ECN bit and can take the needs to contain a single MAP entry
   for a given PHBID, which includes an EXP value zero or one
   depending on ECN operations. with its first bit
   set to zero.

   For non-ECN-capable LSPs, the first bit of the 3-bit EXP field is
   NOT reserved for ECN and can be used to encode any Diff-Serv
   information. In particular, for non-ECN-capable E-LSPs, the
   EXP<-->PHB mapping defined in the section titled `EXP<-->PHB Field
   Mapping' and configured on the LSR is operating over the 3 bits of
   the EXP field.

12. Security Considerations

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                      MPLS Support of Diff-Serv              June 2000

   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.

13. Acknowledgments

   This document has benefited from discussions with K. K.
   Ramakrishnan, Eric Rosen, Angela Chiu and Carol Iturralde.

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                      MPLS Support of It has
   also borrowed from the work done by D. Black regarding Diff-Serv               March 00 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 less) fewer) BAs, no Traffic Engineering, no Fast
Reroute

   A Service Provider running 8 (or less) fewer) BAs over MPLS, not
   performing Traffic engineering, not performing protection via Fast
   Reroute 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
       (eg. 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 (eg.
       drop profile for AF11, AF12, AF13)
     - LSRs signal establishment of a single E-LSP per FEC using LDP in
       accordance with the specification above (ie 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 Fast
Reroute

   A Service Provider running more than 8 BAs over MPLS, not performing
   Traffic Engineering and not performing protection via Fast Reroute

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                      MPLS Support of Diff-Serv              June 2000

   and using MPLS Shim 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:

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                      MPLS Support of Diff-Serv               March 00
     - 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 (ie 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 (ie 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 Fast Reroute

   A Service Provider running 8 (or less) fewer) BAs over MPLS, performing
   aggregate Traffic Engineering (ie performing a single common path
   selection for all BAs), performing aggregate protection via Fast
   Reroute (ie performing Fast Reroute for 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
       (eg. 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 (ie no DIFFSERV
       RSVP Object in the PATH message containing the LABEL_REQUEST
       Object), OR

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                      MPLS Support of Diff-Serv              June 2000

           * using the CR-LDP protocol as specified above (ie no Diff-
       Serv TLV in LDP Label Request/Label Mapping messages).

A.4 Scenario 4: per-OA Traffic Engineering/Fast Reroute

   A Service Provider running any number of BAs over MPLS, performing
   per-OA Traffic Engineering (ie performing a separate path selection
   for each OA) and performing per-OA protection via Fast Reroute (ie

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                      MPLS Support of Diff-Serv               March 00
   performing protection with different Fast Reroute policies 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 (ie 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 (ie Diff-Serv TLV in LDP Label
       Request/Label Mapping messages).

A.5 Scenario 5: 8 (or less) fewer) BAs, per-OA Traffic Engineering/Fast
Reroute

   A Service Provider running 8 (or less) fewer) 8 BAs over MPLS, performing
   per-OA Traffic Engineering (ie performing a separate path selection
   for each OA) and performing per-OA protection via Fast Reroute (ie
   performing protection with different Fast Reroute policies 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
       (eg. 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 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
       (ie no DIFFSERV RSVP Object in the PATH message containing the
       LABEL_REQUEST), OR

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                      MPLS Support of Diff-Serv              June 2000

                * using the CR-LDP protocol as specified above to
       signal that the LSP is an E-LSP  which uses the preconfigured
       mapping (ie 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.

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                      MPLS Support of Diff-Serv               March 00

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

   A Service Provider not performing Traffic Engineering/Fast Reroute
   on 8 (or less) fewer) BAs, performing per-OA Traffic Engineering/Fast
   Reroute on the other BAs (ie performing a separate path selection
   for each OA corresponding to the other BAs and performing protection
   with a 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 less) fewer) non-traffic-engineered/non-fast-
       rerouted 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 (ie no Diff-
       Serv TLV in LDP Label Request/Label Mapping messages)
     - 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 (ie 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 (ie Diff-Serv TLV in LDP Label
       Request/Label Mapping messages).

A.7 Scenario 7: More than 8 BAs, no Traffic Engineering, no Fast
Reroute

   A Service Provider running more than 8 BAs over MPLS, not performing
   Traffic engineering, not performing protection via Fast Reroute and

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                      MPLS Support of Diff-Serv              June 2000

   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)

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                      MPLS Support of Diff-Serv               March 00
     - LSRs signal establishment of two E-LSPs per FEC using LDP in
       accordance with the specification above (ie 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:
     - 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

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                      MPLS Support of Diff-Serv              June 2000

     - 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

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                      MPLS Support of Diff-Serv               March 00
   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", work in progress, (draft-ietf-mpls-arch-06.txt),
   August 1999.

   [MPLS ATM]

   [MPLS_ATM] Davie et al., _MPLS "MPLS using LDP and ATM VC Switching_, Switching", work
   in progress, (draft-ietf-mpls-atm-02.txt), April 1999

   [MPLS FR] (draft-ietf-mpls-atm-03.txt), May 2000

   [MPLS_FR] Conta et al., _Use "Use of Label Switching on Frame Relay
   Networks Specification_, (draft-ietf-mpls-fr-03.txt), November 1998 Specification", (draft-ietf-mpls-fr-04.txt), May 2000

   [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.

   [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.

   [MPLS_ECN] Ramakrishnan et al., "A Proposal to Incorporate ECN in
   MPLS", draft-ietf-mpls-ecn-00.txt, June 1999.

   [LDP] Andersson et al., "LDP Specification", draft-ietf-mpls-ldp-
   05.txt, June
   06.txt, October 99

   [RSVP_MPLS_TE] Awduche et al, "Extensions to RSVP for LSP Tunnels",
   draft-ietf-mpls-rsvp-lsp-tunnel-03.txt, September 1999
   draft-ietf-mpls-rsvp-lsp-tunnel-05.txt, February 2000

   [CR-LDP_MPLS_TE] Jamoussi et al., "Constraint-Based LSP Setup using
   LDP", draft-ietf-mpls-cr-ldp-03.txt, October 1999

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                      MPLS Support of Diff-Serv              June 2000

   [PHBID] Brim et al., "Per Hop Behavior Identification Codes
   draft-ietf-diffserv-phbid-00.txt, October 99 Codes"
   RFC 2836, May 2000

   [DIFF_NEW] Grossman, _New "New Terminology for Diffserv_, Diffserv", draft-ietf-
   diffserv-new-terms-02.txt, November 99

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                      MPLS Support of Diff-Serv               March 00

   [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", draft-
   ietf-diffserv-tunnels-00-txt, February 2000.

   [MPLS_VPN] Rosen et al., "BGP/MPLS VPNs", draft-rosen-rfc2547bis-
   00.txt, March 2000.

Author's Addresses:

   Francois Le Faucheur
   Cisco Systems
   Petra B - Les Lucioles - 291, rue Albert Caquot - 06560 Valbonne -
   France
   Phone: +33 4 92 96 75 64
   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.
   105-8555 Baxter Place
   Burnaby, BC V5A 4V7
   555 Legget drive,
   Suit 834, Tower B,
   Ottawa, ON K2K 2X3
   Canada
   E-mail: Shahram_Davari@pmc-sierra.com
   Phone: +1 (613) 271-4018
   Email: shahram_davari@pmc-sierra.com

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                      MPLS Support of Diff-Serv              June 2000

   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
   Nexabit Networks
   200 Nickerson Road,
   Marlboro, MA 01752
   USA
   E-mail: ram@nexabit.com

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                      MPLS Support of Diff-Serv               March 00

   Pierrick Cheval
   Alcatel
   5 rue Noel-Pons
   92734 Nanterre Cedex
   France
   E-mail:

           pierrick.cheval@alcatel.fr
   E-mail:pierrick.cheval@alcatel.fr

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

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