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

                                                    Francois Le Faucheur
                                                                Liwen Wu
                                                             Bruce Davie
                                                           Cisco Systems

                                                          Shahram Davari
                                                         PMC-Sierra Inc.

                                                           Pasi Vaananen
                                                                   Nokia

                                                            Ram Krishnan
                                                        Nexabit Networks

                                                         Pierrick Cheval
                                                                 Alcatel

IETF Internet Draft
Expires: April, 2000
Document: draft-ietf-mpls-diff-ext-02.txt              October, 1999


                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
   areas, and its working groups.  Note that other groups may also
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   Internet-Drafts are draft documents valid for a maximum of six
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   at any time.  It is inappropriate to use Internet- Drafts as
   reference material or to cite them other than as "work in progress."

      The list of current Internet-Drafts can be accessed at
      http://www.ietf.org/ietf/1id-abstracts.txt

      The list of Internet-Draft Shadow Directories can be accessed at
      http://www.ietf.org/shadow.html.

Abstract

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

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

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                      MPLS Support of Diff-Serv             October 99

   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 where both the Behavior Aggregate's scheduling treatment
   and its drop precedence are conveyed to the LSR in the EXP field of
   the MPLS Shim Header.
        - LSPs where the Behavior Aggregate's scheduling treatment is
   inferred by the LSR from the packet's label value while the Behavior
   Aggregate's drop precedence is indicated 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.

   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
   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 or Traffic
   Engineered 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

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                      MPLS Support of Diff-Serv             October 99

   while some other classes of service are supported via LSPs which are
   not protected).

   Beside, 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 mandating set-up of multiple LSPs
   for a given Forwarding Equivalent Class (FEC) [MPLS_ARCH] when
   useful or required.

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

   The Diff-Serv model defines [APPENDIX A] 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 applied to the set of Behavior Aggregates forming a given OA,
   as a "PHB Scheduling Class (PSC)".

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

   Section 2 below specifies how a single LSP can be used to support up
   to eight BAs, regardless of how many OAs these BAs span. With such
   LSPs, the packet DSCP value gets entirely mapped into the EXP field
   of the MPLS Shim Header [MPLS_ENCAPS] at the Edge of the MPLS Diff-
   Serv Cloud (thus encoding both drop precedence and PSC/scheduling
   information). In other words, both PSC and Drop Precedence are
   conveyed in each labeled packet using the EXP field of the MPLS Shim
   Header [MPLS_ENCAPS].

   We refer to such LSPs as "EXP-inferred-PSC LSPs" (E-LSP). Detailed
   operations of E-LSPs are specified in section 2 below.

   E-LSPs have the following benefits:
        - label space is conserved by allowing "packing" of up to eight
   BAs per label (eg. when there are fewer than eight BAs in the
   network, this method maintains the same label space as in a non
   Diff-Serv capable MPLS network).
        - label establishment signaling is then reduced since a single
   LSP is established for up to eight BAs (eg. when there are fewer
   than eight BAs in the network, this method maintains the same level
   of signaling as in a non-Diff-Serv capable MPLS network)
        - the amount of forwarding state is also reduced, as a single
   forwarding entry can support up to 8 BAs.
        - operation of Diff-Serv MPLS over E-LSPs is analogous to
   operations of Diff-Serv in non-MPLS networks in the sense that the
   Diff-Serv PHB is triggered exclusively by a field explicitly encoded
   in every packet based on locally configured PHB mapping. This is
   expected to facilitate migration from non-MPLS Diff-Serv to MPLS
   Diff-Serv operations in some networks.
        - some early implementations of E-LSPs exist today and
   experiments have confirmed proper operations and usefulness.

   E-LSPs only allow support of eight BAs or less.

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

   Section 3 below specifies how a separate LSP can be established for
   each <FEC, OA> pair between two LSR neighbors.

   With such LSPs, the PSC is explicitly signaled at label
   establishment time so that, after label establishment, the LSR can
   infer from the label value the PSC to be applied to a labeled
   packet. When the Shim Header is used, the Drop Precedence to be
   applied by the LSR to the labeled packet is conveyed inside the
   labeled packet MPLS Shim Header using the EXP field [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 encapsulating the labeled
   packet using link layer specific drop precedence (eg. Cell Loss
   Priority).

   We refer to such LSPs as "Label-Inferred-PSC LSPs" (L-LSP). Detailed
   operations of L-LSPs are specified in section 3 below.

   L-LSPs allow support of any number of Behavior Aggregates.

   L-LSPs have the following drawbacks:
        - they require the use of a separate label for support of each
   PSC,   and
        - they require more signaling operations to set up the
   corresponding L-LSPs.

1.4 Overall Operations

   For a given FEC, and unless media specific restrictions apply as
   identified in the corresponding sections below (eg. `MPLS Support of
   Diff-Serv by ATM LSRs'), this specification allows any one of the
   following set of 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 from the
   set of allowed combinations in order to best match his/her
   environment and objectives in terms of Diff-Serv support, Traffic
   Engineering and Fast Restoration.

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

1.5 Label Forwarding Model for Diff-Serv LSRs

   In order to describe Label Forwarding by Diff-Serv LSRs, we model
   the LSR Diff-Serv label switching behavior as comprising three
   stages:
        -A- incoming PHB and FEC determination

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        -B- Optional outgoing PHB determination via Local Policy and
   Traffic Conditioning
        -C- Outgoing EXP(and possibly CLP/DE) and label determination,
   enforcement of outgoing PHB's forwarding behavior

   This model is used below for specifying LSR Label Forwarding using
   L-LSPs and E-LSPs for Diff-Serv support over MPLS.

1.6 Relationship between Label and FEC

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

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


2. Detailed Operations of E-LSPs

2.1 E-LSP Establishment

      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];

      - the Diff-Serv Code Point field (DSCP) is 6-bit long
   [DIFF_HEADER] but when 8 (or less) BAs are used, the DSCP values can
   be mapped entirely into the 3-bit long EXP field of the MPLS label
   stack entry;

      We define that:

      - one LSP established for a given Forwarding Equivalent Class
   (FEC) may be used for transport of up to eight BAs of that FEC;

      - 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
   is inferred from the EXP field of the MPLS Shim Header;

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      - the set of transported BAs can span one or multiple OAs;

      - packets belonging to this given (FEC) and from the
   corresponding set of BAs are sent down this E-LSP.

      - 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.

   MPLS specifies how LSPs can be established via multiple signaling
   protocols. Those include the Label Distribution Protocol (LDP),
   RSVP, BGP and PIM. This document specifies below, respectively in
   section 4 and section 5, how RSVP and LDP are to be used for
   establishment of E-LSPs.

2.2 Label Forwarding

2.2.1 Incoming PHB and FEC Determination On Ingress E-LSP

   When receiving a labeled packet over a E-LSP of an MPLS ingress
   interface, the LSR:
        - determines the FEC based on the incoming label
        - determines the incoming PHB by looking at the EXP field of
   the top level label entry and then by looking up the PHB<-->EXP
   mapping defined below in section 2.3.

   If the EXP field value of a packet received on an E-LSP is not
   listed in the mapping defined in section 2.3, this EXP value should
   be considered invalid. LSR behavior in such situation is a local
   matter and is outside the scope of this document.

2.2.2 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 Behavior Aggregate demotion or promotion inside
   an MPLS Diff-Serv domain. 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").

2.2.3   Outgoing EXP Field And Label Determination On Egress E-LSP

   Once the outgoing PHB has been determined by the LSR as a function
   of the incoming PHB and of the optional Local Policy and Traffic
   Conditioning, the LSR:


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        - determines via local configuration that the outgoing PHB is
   one of the PHBs supported by the E-LSP and determines the egress E-
   LSP label for the packet's FEC
        - determines the value to be written in the EXP field of the
   top level label entry (and possibly of other level label entries in
   the case of a hierarchical tunnel entry) by looking up the
   PHB<-->EXP mapping defined below in section 2.3 for the outgoing
   PHB.
        - SHALL apply the scheduling/dropping behavior corresponding to
   the Outgoing PHB in compliance with the corresponding Diff-Serv PHB
   specification.

2.2.4 Simplified Forwarding

   When Local Policy and Traffic Conditioning are not to be performed
   by the LSR and the labeled packet is received on a E-LSP and is
   forwarded onto an E-LSP, the Forwarding operation is simplified
   since:
        - the EXP field does not need to be modified
        - the outgoing label determination depends exclusively on the
   incoming label (ie does not depend on Local Policy and Traffic
   Conditioning). The outgoing label is determined from the Incoming
   Label Map (ILM) using the same procedures as with non Diff-Serv LSPs
   (ie the incoming label is used as the index into the ILM to identify
   the NHLFE independently of the Diff-Serv operations)
        - the scheduling/dropping behavior to be applied is determined
   exclusively from the unmodified EXP field value.

2.3 PHB<-->EXP field mapping

   Like the mapping between PHBs and DSCPs in a Diff-Serv network, the
   mapping between PHB and EXP field is a local matter to be defined by
   the Service Provider and configured on every LSR.

   LSRs supporting E-LSPs must allow configuration of PHB<-->EXP
   mapping. This mapping applies to all the E-LSPs established on this
   LSR (over interfaces belonging to a given MPLS Diff-Serv domain).

   The PHB<-->EXP mapping must be consistent at every LSP hop
   throughout the MPLS Diff-Serv domain spanned by the LSP. This is
   achieved via consistent configuration by the network operator within
   the MPLS Diff-Serv domain.

   Clearly, if different Behavior Aggregates transported over an E-LSP
   are to be treated differently in the MPLS Diff-Serv cloud, different
   values of the EXP field are to configured in the PHB<-->EXP mapping
   for the corresponding PHBs.

2.4 E-LSP Merging




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   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.

   Since the BAs/PHBs supported over an E-LSP is not signalled at
   establishment time, an LSR can not rely on signaling information to
   enforce the above merge condition (ie that merged LSPs do support
   the exact same set of BAs). However all E-LSPs are to use the same
   PHB<-->EXP mapping, and transport the same set of Behavior
   Aggregates, within a given MPLS Diff-Serv domain. Thus, E-LSP
   merging is allowed within a given MPLS Diff-Serv domain.

   E-LSP Merging at a boundary between two MPLS Diff-Serv domains is
   for further study.


3.  Detailed Operation of L-LSPs

3.1 L-LSP Establishment

      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 Diff-Serv Code Point (DSCP) is 6-bit long [DIFF_HEADER]. 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);

        - Some Service Providers have a requirement for fine grain
   Traffic Engineering (such as per OA Traffic Engineering)

      We propose that:

      - All packets belonging to a single OA and the same Forwarding
   Equivalent Class (FEC) be sent down a single LSP;

      - One LSP be established per <FEC, OA> pair (rather than simply
   one LSP per FEC as in an MPLS network that does not support Diff-
   Serv). Such an LSP is referred to as a "Label-inferred-PSC" LSP or
   "L-LSP";

      - Multiple BAs belonging to the same OA be granted different Drop
   Precedence (DP) values through appropriate coding of the relevant

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                      MPLS Support of Diff-Serv             October 99

   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).

   MPLS specifies how LSPs can be established via multiple signaling
   protocols. Those include the Label Distribution Protocol (LDP),
   RSVP, BGP and PIM. This document specifies, respectively in section
   4 and section 5, how RSVP and LDP are to be used for establishment
   of L-LSPs.

3.2 Label Forwarding

3.2.1 Incoming PHB and FEC Determination On Ingress L-LSP

   When receiving a labeled packet over an L-LSP of an MPLS ingress
   interface, the LSR:
        - determines the FEC based on the incoming label
        - determines the PSC from the incoming label among the set of
   LSPs established for that FEC
        - determines the incoming PHB from the PSC and the EXP/CLP/DLE
   field of the top level label entry in accordance with the
   PSC/EXP(resp PSC/CLP, PSC/DE) -->PHB mappings defined below in
   sections 6.3 (resp 7.2 and 8.2).

3.2.2 Optional Outgoing PHB Determination Via Local Policy And Traffic
Conditioning

   This stage of Diff-Serv label switching is independent of the
   ingress/egress interface media type and method used for MPLS Diff-
   Serv support. It is optional and may be used on an LSR to perform
   Behavior Aggregate demotion or promotion inside an MPLS Diff-Serv
   domain. For the purpose of specifying a Diff-Serv over MPLS method,
   we simply note that the PHB to be actually enforced by an LSR
   (referred to as "outgoing PHB") may be different to the PHB which
   had been associated with the packet at the previous LSR (referred to
   as "incoming PHB").

3.2.3   Outgoing EXP/CLP/DE Field and Label Determination on Egress L-
LSP

   Once the outgoing PHB has been determined by the LSR as a function
   of the incoming PHB and of the optional Local Policy and Traffic
   Conditioning, the LSR:
        - determines via local configuration that the outgoing PHB is
   one of the PHBs supported by a L-LSP and determines the egress
   L-LSP label for the packet's FEC
        - determines the value to be written in the EXP/CLP/DLE field
   of the top level label entry (and possibly of other level label
   entries in the case of a hierarchical tunnel entry) by performing
   the outgoing PHB-->EXP/PSC (resp CLP/PSC, DE/PSC) mapping defined in
   sections 6.4 (resp 7.3 and 8.3).



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                      MPLS Support of Diff-Serv             October 99

        - SHALL apply the scheduling/dropping behavior corresponding to
   the "Outgoing PHB" in compliance with the corresponding Diff-Serv
   PHB specification.

3.2.4 Simplified Forwarding

   When Local Policy and Traffic Conditioning are not to be performed
   by the LSR, and when the labeled packet is received on a L-LSP on
   the ingress interface and is going out onto a L-LSP on an egress
   interface of the same type, the Forwarding operation is simplified
   since:
        - the EXP/CLP/DE field does not need to be modified
        - the outgoing label determination depends exclusively on the
   incoming label (ie does not depend on Local Policy and Traffic
   Conditioning). The outgoing label is determined from the Incoming
   Label Map (ILM) using the same procedures as with non Diff-Serv LSPs
   (ie the incoming label is used as the index into the ILM to identify
   the NHLFE independently of the Diff-Serv operations)
        - the scheduling behavior to be applied is  determined
   exclusively from the Diff-Serv information stored in the NHLFE for
   the incoming label
        - the dropping behavior to be applied is determined exclusively
   from the Diff-Serv information stored in the NHLFE for the incoming
   label and from the incoming EXP/CLP/DE field
   More information is provided below in the sections titled `RSVP
   extensions for Diff-Serv Support' and `LDP extensions for Diff-Serv
   Support' on what is the Diff-Serv information stored in NHLFEs.

3.3 Merging

   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 are associated with
   the same PSC.

   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).


4. 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


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                      MPLS Support of Diff-Serv             October 99

   [RSVP_MPLS_TE], to establish label switched path (LSPs) supporting
   Differentiated Services in MPLS networks.

4.1 Diff-Serv related RSVP Messages Format

   One new RSVP Object is defined in this document: the DIFFSERV_PSC
   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_PSC 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_PSC 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_PSC Object is optional for support of LSP Tunnels as
   defined in [RSVP_MPLS_TE]. A Diff-Serv capable LSR supporting E-LSPs
   in compliance with this specification MAY support the DIFFSERV_PSC
   Object. A Diff-Serv capable LSR supporting L-LSPs in compliance with
   this specification MUST support the DIFFSERV_PSC Object.

4.1.1 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_PSC> ]
                                  [ <POLICY_DATA> ... ]
                                  [ <sender descriptor> ]

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

4.2 DIFFSERV_PSC Object

   As stated earlier, the PHB Scheduling Class associated with an L-LSP
   is to be specified through a new DIFFSERV_PSC object in RSVP Path
   messages. The DIFFSERV_PSC object has the following format :


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    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Length                |   Class-Num   |    C-Type     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        Reserved     | T |PSCnb|              PSC              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


     Length

      This is set to 4.

     Class-Num

      The Class-Num for a DIFFSERV_PSC object is [TBD] and identifies
      a new object Class called the "Class Of Service" Class (COS
      Class). (The Class-Num is to be allocated by IANA with the form
      0bbbbbbb)

     C-Type

      The C-Type for a DIFFSERV_PSC object is 1.

     Reserved

      This field is set to all zeros

     T

      This indicates the `LSP Type'. The following values are
      specified:

           T Value      LSP type
           00           E-LSP
           01           L-LSP

     PSCnb

      Indicates the number of PSC values included in the PSC object.
      This is set to 001.

     PSC

      The PSC indicates the PHB Scheduling Class to be supported by the
      L-LSP. The 16-bit 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             October 99

        - Where the PSC comprises multiple PHBs defined by standards
      action, the PSC encoding is the encoding for this set of PHB. It
      is the smallest numerical value of the recommended DSCP for the
      various PHBs in the PSC, left-justified in the 16 bit field, with
      bits 6 through 13 and bit 15 set to zero and with bit 14 set to
      one.

      For instance, the encoding of the EF PSC is :
        0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
      +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
      | 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  2  3  4  5  6  7  8  9 10 11 12 13 14 15
      +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
      | 0  0  1  0  1  0| 0  0  0  0  0  0  0  0  1  0|
      +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

4.3 Handling Diff-Serv_PSC 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 using E-LSPs, to establish an
   E-LSP tunnel with RSVP, the sender creates a Path message with a
   session type of LSP_Tunnel_IPv4, with the LABEL_REQUEST object and
   without the DIFFSERV_PSC object.

   Optionally, to establish an E-LSP over which a single Ordered
   Aggregate is going to be transported, the sender MAY create a Path
   message which contains a session type of LSP_Tunnel_IPv4, contains
   the LABEL_REQUEST object and contains the DIFFSERV_PSC object with
   its LSP-Type field set to `E-LSP' and its PSC field set to the value
   of the PSC to be supported on the E-LSP.

   The destination node of an E-LSP responds to the Path message
   containing the LABEL_REQUEST object by sending a Resv message
   containing the LABEL object and no DIFFSERV_PSC object.

   When receiving a Resv message containing a LABEL object and
   associated with a Path message which contained a LABEL_REQUEST
   object and no DIFFSERV_PSC object (or which contained the
   DIFFSERV_PSC object with its LSP-Type set to E-LSP), assuming the
   reservation can be accepted and a label can be associated with the
   reservation, a Diff-Serv E-LSP capable LSR must:
        - update its Incoming Label Map (ILM) [MPLS_ARCH] to store the
   necessary Diff-Serv information. This includes the fact that the
   Next Hop Label Forwarding Entry (NHLFE) corresponds to an E-LSP.
   This is in accordance with [MPLS_ARCH] which states that the `NHLFE


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                      MPLS Support of Diff-Serv             October 99

   may also contain any other information needed in order to properly
   dispose of the packet'.
        - install the required scheduling and dropping behavior for
   this NHLFE in order to support Diff-Serv label forwarding as
   specified for E-LSPs in section 2.2.

   Where the sender supports Diff-Serv using L-LSPs, to establish an
   L-LSP tunnel with RSVP, the sender creates a Path message with a
   session type of LSP_Tunnel_IPv4, with the LABEL_REQUEST object and
   with the DIFFSERV_PSC object. The DIFFSERV_PSC object has its LSP-
   Type set to L-LSP and its the PSC value indicating the PHB
   Scheduling Class to be supported by the L-LSP.

   An RSVP router that does recognizes the DIFFSERV_PSC object and that
   receives a path message which contains the DIFFSERV_PSC 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_PSC object'. Those are defined below in the
   section titled `Diff-Serv Errors'.

   A node receiving a Path message with the DIFFSERV_PSC object, which
   recognizes the DIFFSERV_PSC 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 Value'. Those are defined below in the section
   titled `Diff-Serv Errors'.

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

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

   The destination node of an L-LSP responds to the Path message
   containing the LABEL_REQUEST object and the DIFFSERV_PSC object by
   sending a Resv message containing the LABEL object and no
   DIFFSERV_PSC object.

   When receiving a Resv message containing a LABEL object and
   associated with a Path message which contained a LABEL_REQUEST
   object and the DIFFSERV_PSC object with its LSP-Type set to L-LSP,
   assuming the reservation can be accepted and a label can be
   associated with the reservation, a Diff-Serv L-LSP capable LSR must:
        - update its ILM to store the necessary Diff-Serv information.
   This includes the fact that the NHLFE corresponds to an L-LSP and
   its PSC.
        - install the required scheduling and dropping behavior for
   this NHLFE to support Diff-Serv label forwarding as specified for L-
   LSPs in section 3.2.


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                      MPLS Support of Diff-Serv             October 99

   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).

   [RSVP_MPLS_TE] identifies the conditions where LSPs can be merged to
   constitute a multipoint-to-point LSP. When the LSPs to be merged are
   L-LSPs, those can only be merged if an additional condition is met:
   the DIFFSERV_PSC object in their respective path messages must all
   be strictly identical.

4.4 Non-support of the Diff-Serv_PSC Object

   An RSVP router that does not recognize the COS Class's Class-Num
   sends a PathErr with the error code "Unknown object class" toward
   the sender. An RSVP router that recognizes the COS Class's Class-Num
   but does not recognize the DIFFSERV_PSC object C-Type, sends a
   PathErr with the error code "Unknown object C-Type" toward the
   sender. 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_PSC object (eg. attempt use of E-LSPs as a back-up
   strategy).

4.5 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       Unsupported PSC value
       2       Unexpected DIFFSERV_PSC object

4.6 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             October 99

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

   A Path message containing a COS SENDER_TSPEC and containing a
   DIFFSERV_PSC object with its LSP-Type set to E-LSP indicates to a
   Diff-Serv capable LSR that the LSP to be established in an E-LSP
   without any bandwidth reservation.

   A Path message containing a COS SENDER_TSPEC and containing a
   DIFFSERV_PSC object with its LSP-Type set to L-LSP indicates to a
   Diff-Serv capable LSR that the LSP to be established in an L-LSP
   without any bandwidth reservation.

   The above is summarized in the following table:

           Path Message            LSP type
     Service   DIFFSERV_PSC  LSP
                 Object      Type

     GS/CL         No               E-LSP with bandwidth reservation
     GS/CL         Yes       E-LSP  E-LSP with bandwidth reservation
     GS/CL         Yes       L-LSP  L-LSP with bandwidth reservation
     COS           No               E-LSP without bandwidth reservation
     COS           Yes       E-LSP  E-LSP without bandwidth reservation
     COS           Yes       L-LSP  L-LSP without bandwidth 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).


5. LDP Extensions for Diff-Serv Support

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

   Two new LDP TLVs are defined in this document:
        - the `DIFF-SERV_PSC' TLV
        - the `Release Status' TLV
   Detailed descriptions of these TLV are provided below.


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                      MPLS Support of Diff-Serv             October 99

   As described in [LDP], there are two modes for label distribution:
   Downstream Unsolicited and Downstream on Demand.

   When an E-LSP is established using Downstream on Demand mode, the
   Label Request message and the Label Mapping message usually do not
   include the new Diff-Serv_PSC. In the case where, a single Ordered
   Aggregate is to be transported over the E-LSP, the Label Request
   message and the Label Mapping message may optionally include the new
   Diff-Serv_PSC (with its LSP-type defined below set to `E-LSP').

   When an E-LSP is established using Downstream Unsolicited mode, the
   new Diff-Serv_PSC MUST not be carried in the Label Request message
   nor in the Label Mapping message.

   When an L-LSP is established using Downstream on Demand mode, the
   new DIFF-SERV_PSC TLV MUST be carried in the Label Request Message
   to indicate the PHB Scheduling Class (PSC) of the LSP and may
   optionaly be carried in the Label Mapping message.

   When an L-LSP is established using Downstream Unsolicited mode, the
   new DIFF-SERV_PSC TLV MUST be carried in the Label Mapping Message
   to indicate the PHB Scheduling Class (PSC) of the LSP.

   The Release Status TLV is to be used to include diagnostic
   information in Label Release messages when handling Diff-Serv
   related errors.

   The new Diff-Serv_PSC and Release Status TLVs are optional with
   respect to LDP. A Diff-Serv capable LSR supporting E-LSPs in
   compliance with this specification MAY support the Diff-Serv_PSC TLV
   and the Release Status TLV. A Diff-Serv capable LSR supporting
   L-LSPs in compliance with this specification MUST support the Diff-
   Serv_PSC TLV and the Release Status TLV.

5.1 Diff-Serv related TLVs

5.1.1 Diff-Serv_PSC TLV

   As stated earlier, the PHB Scheduling Class associated with an L-LSP
   is to be specified through a new Diff-Serv_PSC TLV in LDP messages.
   The Diff-Serv_PSC TLV 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F| Type = PSC (0x901)        |      Length                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        Reserved     | T |PSCnb|              PSC              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   U BIT =0

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                      MPLS Support of Diff-Serv             October 99


     If this new TLV is unknown to the LSR, the LSR must reject the
     whole message and return a notification

   F BIT = 0

     If this TLV is unknown to a LSR, this new TLV is NOT forwarded.

   Type

     The Type of the PSC TLV is: 0x901.

   Length

     This is set to 4.

   Reserved

     This field is set to all zeros

   T

      This indicates the `LSP Type'. The following values are
      specified:

           T Value      LSP type
           00           E-LSP
           01           L-LSP

   PSCnb

     Indicates the number of PSC values included in the TSC TLV. This
     is set to 001

   PSC Value

     Encoding of the PSC field is as specified in section 4.2.

5.1.2 Release Status TLV

   As stated earlier, error codes are to specified through a new
   Release Status TLV in LDP Label Release messages when E-LSP or L-LSP
   set-up fails. The Release Status TLV 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |U|F| Type = PSC (0x304)        |      Length                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        Status Code                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


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                      MPLS Support of Diff-Serv             October 99


   U BIT =0

     If this new TLV is unknown to the LSR, the LSR must reject the
     whole message and return a notification

   F BIT = 0

     If this TLV is unknown to a LSR, this new TLV is NOT forwarded.

   Type

     The Type of the PSC TLV is: 0x304.

   Status Code

     Indicates the reason why the label was released. This field uses
     the same encoding and values as the `Status Code' word defined for
     the Notification message. Additional values are defined below, in
     the section titled `Status Code Values', for this Status Code
     field in addition to the values currently defined in [LDP].

5.1.3 Status Code Values

   The following values are defined for the Status Code field which is
   used in Notification message and may be used in Label Release
   messages:

        Status Code             E   Status Data

        Unsupported PSC value   0   0x00000016
        Unexpected PSC value    0   0x00000017
        Unexpected PSC TLV      0   0x00000018
        Unexpected LSP-Type     0   0x00000019

5.2 Diff-Serv Related LDP Messages

5.2.1 Label Request Message

   In Downstream on Demand mode, the Diff-Serv capable LSR requesting a
   label for an L-LSP includes the new Diff-Serv_PSC TLV in the Label
   Request message to signal that the LSP is an L-LSP and to indicate
   the PSC associated with the LSP.

   The format of the Label Request message for an L-LSP in Downstream
   on Demand mode, is as follows:

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

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                      MPLS Support of Diff-Serv             October 99

   |                     Message ID                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     FEC TLV                                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     PSC TLV                                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


5.2.2 Label Mapping Message

   In Downstream Unsolicited mode, the Diff-Serv capable LSR allocating
   a label for an L-LSP includes the Diff-Serv_PSC TLV in the Label
   Mapping message to signal that the LSP is an L-LSP and to indicate
   the PSC associated with the LSP.

   The format of the Label Mapping message for an L-LSP in Downstream
   Unsolicited mode, is as follows:

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


   In Downstream on Demand mode, the Diff-Serv capable LSR allocating a
   label for an L-LSP in response to a Label Request message containing
   the Diff-Serv_PSC TLV, may optionally include the same Diff-Serv_PSC
   TLV in the Label Mapping message to confirm the PSC associated with
   the LSP.

   The format of the Label Mapping message for an L-LSP in Downstream
   Unsolicited mode, is as follows:

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

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                      MPLS Support of Diff-Serv             October 99

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     PSC TLV (optional)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


5.2.3 Label Release Message

   [LDP] specifies that `an LSR sends a Label Release message to an LDP
   peer to signal the peer that the LSR no longer needs specific FEC-
   label mappings previously requested of and/or advertised by the
   peer.'

   This specification extends the use of the Label Release message so
   that, when an LSR cannot accept a label mapping for an E-LSP or an
   L-LSP, the LSR should send a Label Release message to the LDP Peer
   to signal the peer that the LSR cannot accept the label mapping.

   This specification also extends the encoding of the Label Release
   message so that the new Release Status TLV can optionally be
   included in the message. Thus the encoding of the Label Release
   message is:

       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)                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Release Status TLV (optional)                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


5.2.4 Notification Message

   This specification allows inclusion of the Diff-Serv_PSC TLV in the
   Notification. Thus the encoding of the Notification message is:

    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             October 99

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Diff-Serv_PSC TLV (optional)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


5.3 Handling of the Diff-Serv_PSC TLV

5.3.1 Handling of the Diff-Serv_PSC TLV in Downstream Unsolicited Mode

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

   When allocating a label for an E-LSP, a Diff-Serv capable LSR issues
   a Label Mapping message without the Diff-Serv_PSC TLV.

   A Diff-Serv capable LSR receiving a Label Mapping message without
   the Diff-Serv_PSC TLV, must:
        - update its Incoming Label Map (ILM) [MPLS_ARCH] to store the
   necessary Diff-Serv information. This includes the fact that the
   Next Hop Label Forwarding Entry (NHLFE) corresponds to an E-LSP.
        - install the required scheduling and dropping behavior for
   this NHLFE to support Diff-Serv forwarding as specified for E-LSPs
   in section 2.2.

   When allocating a label for an L-LSP, a Diff-Serv capable LSR issues
   a Label Mapping message which contains the Diff-Serv_PSC TLV with
   its PSC field indicating the PSC of the L-LSP.

   A Diff-Serv capable LSR receiving a Label Mapping message containing
   the Diff-Serv_PSC TLV, must:
        - update its ILM to store the necessary Diff-Serv information.
   This includes the fact that the NHLFE corresponds to an L-LSP and
   its PSC.
        - install the required scheduling and dropping behavior for
   this LSP to support Diff-Serv forwarding as specified for L-LSPs in
   section 3.2.

   A Diff-Serv capable LSR receiving a Label Mapping message with the
   Diff-Serv_PSC TLV 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 Release Status TLV with a Status Code
   of `Unsupported PSC Value'.

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

5.3.2 Handling of the Diff-Serv_PSC TLV in Downstream on Demand Mode

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

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                      MPLS Support of Diff-Serv             October 99


   When requesting a label for an E-LSP, a Diff-Serv capable LSR sends
   a Label Request message without the Diff-Serv_PSC TLV.

   Optionally, when requesting a lebel for an E-LSP over which a single
   Ordered Aggregate is to going to be transported, the Diff-Serv
   capable LSR may send a Label Request message containing the Diff-
   Serv_PSC TLV with its LSP type set to E-LSP and its PSC field set to
   the value of the PSC to be supported on the E-LSP.

   A Diff-Serv capable LSR sending a Label Mapping message in response
   to a Label Request message which did not contain the Diff-Serv_PSC
   TLV, must not include Diff-Serv_PSC TLV in this Label Mapping
   message.

   A Diff-Serv capable LSR sending a Label Mapping message in response
   to a Label Request message which contained the Diff-Serv_PSC TLV
   with its E-LSP type set to E-LSP, may send this Label Mapping
   message without the Diff-Serv_PSC TLV. Optionally, the LSR may send
   this Label Mapping message with the Diff-Serv_PSC TLV with its LSP-
   Type set to E-LSP and its PSC field set to the same value as the one
   received in the Label Request message.

   A Diff-Serv capable LSR receiving a Label Mapping message without
   the Diff-Serv_PSC TLV in response to its Label Request message for
   an E-LSP, must:
        - update its ILM to store the necessary Diff-Serv information.
   This includes the fact that the NHLFE corresponds to an E-LSP.
        - install the required scheduling and dropping behavior for
   this NHLFE to support Diff-Serv forwarding as specified for E-LSPs
   in section 2.2.

   A Diff-Serv capable LSR receiving a Label Mapping message containing
   the Diff-Serv_PSC TLV in response to its Label Request message for
   an E-LSP which did not contain the Diff-Serv_PSC TLV, must reject
   the label mapping by sending a Label Release message which includes
   the Label TLV and the Release Status TLV with a Status Code of
   `Unexpected PSC TLV'.

   A Diff-Serv capable LSR receiving a Label Mapping message containing
   the Diff-Serv_PSC TLV in response to its Label Request message for
   an E-LSP which contained the Diff-Serv_PSC TLV, must compare the
   received and sent Diff-Serv_PSC TLVs.

   If those are equal, the LSR must:
        - update its ILM to store the necessary Diff-Serv information.
   This includes the fact that the NHLFE corresponds to an E-LSP.
        - install the required scheduling and dropping behavior for
   this NHLFE to support Diff-Serv forwarding as specified for E-LSPs
   in section 2.2.



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                      MPLS Support of Diff-Serv             October 99

   If those are not equal because they have a different LSP-Type, the
   LSR must reject the Label Mapping by sending a Label Release message
   which includes the Label TLV and the Release Status TLV with a
   Status Code of `Unexpected LSP-Type'.

   If those are not equal because they have a different PSC value, the
   LSR must reject the Label Mapping by sending a Label Release message
   which includes the Label TLV and the Release Status TLV with a
   Status Code of `Unexpected PSC Value'.

   When requesting a label for an L-LSP, a Diff-Serv capable LSR sends
   a Label Request message with the Diff-Serv_PSC TLV which indicates
   the PSC of the L-LSP.

   A Diff-Serv capable LSR receiving a Label Request message with the
   Diff-Serv_PSC TLV containing a PSC value which is not supported or
   for which no EXP/PSC<-->PHB mapping is configured, must send a
   Notification message with a Status Code of `Unsupported PSC Value'.

   A Diff-Serv capable LSR that recognizes the Diff-Serv_PSC 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_PSC TLV.

   A Diff-Serv capable LSR sending a Label Mapping message in response
   to a Label Request message which contained the Diff-Serv_PSC TLV,
   may optionally include the exact same Diff-Serv_PSC TLV in this
   Label Mapping message.

   A Diff-Serv capable LSR receiving a Label Mapping message without
   the Diff-Serv_PSC TLV in response to its Label Request message for
   an L-LSP, must:
        - update its ILM to store the necessary Diff-Serv information.
   This includes the fact that the NHLFE corresponds to an L-LSP and
   its PSC.
        - install the required scheduling and dropping behavior for
   this NHLFE to support Diff-Serv forwarding as specified for L-LSPs
   in section 3.2.

   A Diff-Serv capable LSR receiving a Label Mapping message with the
   Diff-Serv_PSC TLV in response to its Label Request message for an L-
   LSP, must verify that the Diff-Serv_PSC TLV received in the Label
   Mapping message is equal to the Diff-Serv_PSC TLV sent in the Label
   Request message.

   If those are equal, the LSR must:
        - update its ILM to store the necessary Diff-Serv information.
   This includes the fact that the NHLFE corresponds to an L-LSP and
   its PSC

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                      MPLS Support of Diff-Serv             October 99

        - install the required scheduling and dropping behavior for
   this NHLFE to support Diff-Serv forwarding as specified for L-LSPs
   in section 3.2.

   If those are not equal because they have a different LSP-Type, the
   LSR must reject the Label Mapping by sending a Label Release message
   which includes the Label TLV and the Release Status TLV with a
   Status Code of `Unexpected LSP-Type'.

   If those are not equal because they have a different PSC value, the
   LSR must reject the Label Mapping by sending a Label Release message
   which includes the Label TLV and the Release Status TLV with a
   Status Code of `Unexpected PSC Value'.

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

5.4 Non-Handling of the Diff-Serv_PSC TLV

   An LSR that does not recognize the Diff-Serv_PSC TLV Type, on
   receipt of a Label Request message or a Label Mapping message
   containing the Diff-Serv_PSC TLV, must ignore the message and return
   a Notification message with _Unknown TLV_ Status.

5.5 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].


6. MPLS Support of Diff-Serv over PPP

   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 PPP links. While
   sections 7, 8 and 9 focus on other media specific operations, namely
   ATM, Frame Relay and LAN respectively.

   This document allows the following set of LSP setup 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.

6.1. E-LSP Operations over PPP



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                      MPLS Support of Diff-Serv             October 99

   Since MPLS uses the Shim Header for encapuslation over PPP, E-LSPs
   are supported over PPP. The E-LSP setup, label forwarding and
   merging operations over PPP follows exactly the procedures defined
   in section 2. No additional PPP specific procedures are defined for
   E-LSPs.

6.2  L-LSP Operations over PPP

   L-LSPs are also supported over PPP. The L-LSP operations over PPP
   follows the general procedures of section 3. However, the following
   PPP specific procedures are also defined for L-LSP operations over
   PPP :

        - An MPLS PPP ingress interface determines the incoming PHB
   from the PSC and the EXP field of the top level label entry in
   accordance with the PSC/EXP -->PHB mappings defined below in section
   6.3.

        - If the EXP field value of a packet received on an L-LSP is
   such that the PSC/EXP combination is not listed in the mapping of
   section 6.3, this PSC/EXP combination should be considered invalid.
   LSR behavior in such situation is a local matter and is outside the
   scope of this document.

        - An MPLS PPP egress interface determines the value to be
   written in the EXP field of the top level label entry (and possibly
   of other level label entries in the case of a hierarchical tunnel
   entry) by performing the outgoing PHB-->EXP/PSC mapping defined
   below in section 6.4.

6.3 PSC/EXP --> PHB mapping

   The mapping from the L-LSP PSC and the EXP field of the shim header
   into PHBs is as follows:

      EXP Field      PSC             PHB

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

6.4 PHB --> PSC/EXP mapping

   The mapping from PHBs into the L-LSP PSC and the EXP field of the
   shim header is as follows:

      PHB              EXP Field     PSC

      DF     ----->     000          DF

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                      MPLS Support of Diff-Serv             October 99

      CSn    ----->     000          CSn
      AFn1   ----->     000          AFCn
      AFn2   ----->     001          AFCn
      AFn3   ----->     010          AFCn
      EF     ----->     000          EF

6.5 LSR implementation with PPP interfaces

   For an LSR implementation with PPP interfaces, support of E-LSPs
   over the PPP interfaces is mandatory with respect to this
   specification. A Diff-Serv capable LSR with PPP interfaces MUST
   support E-LSPs over these PPP interfaces in compliance with this
   specification.

   Support of L-LSPs over PPP interfaces by an LSR implementation is
   optional. A Diff-Serv capable LSR MAY support L-LSPs over PPP
   interfaces. However, 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 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 not been established via any label
   distribution protocol) is to be considered as an LSR with PPP
   interfaces from the point of view of compliance to this
   specification.

   Similarly, an LSR running MPLS over PPP over a traditional Frame
   Relay connection (ie where the Frame Realy switches do not
   participate in MPLS and where the Frame Relay connection DLCI values
   have not been established via any label distribution protocol) is to
   be considered as an LSR with PPP interfaces from the point of view
   of compliance to this specification.


7. MPLS Support of Diff-Serv by ATM LSRs

   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 ATM links.

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

        - any number of L-LSPs.

7.1 L-LSP Operations over ATM

   The L-LSP operations over ATM follows the general procedures of
   section 3. However, the following ATM specific procedures are also
   defined for L-LSP operations over ATM links :

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        - An MPLS ATM ingress interface determines the incoming PHB
        from the PSC and the ATM Cell Loss Probability (CLP) bit in
        accordance with the incoming PSC/CLP-->PHB mapping defined
        below in section 7.2;

       - If the CLP value of a packet received on an L-LSP is such that
       the PSC/CLP combination is not listed in the mapping of section
       7.2, this PSC/CLP combination should be considered invalid. LSR
       behavior in such situation is a local matter and is outside the
       scope of this document.

        - An MPLS ATM egress interface determines the value to be
        written in the ATM Cell Loss Probability (CLP) bit by
        performing the outgoing PHB-->PSC/CLP mapping defined below in
        section 7.3. This is performed by an LSR on the Edge of the ATM
        Diff-Serv MPLS Cloud and is performed by an ATM LSR in the
        middle of the ATM Diff-Serv MPLS cloud when doing optional
        Local Policy and Traffic Conditioning. When not doing optional
        Local Policy and Traffic Conditioning, an LSR in the middle of
        the ATM Diff-Serv MPLS cloud may simply leave the CLP bit
        untouched;

        - when packet is segmented to cells on edge LSR, all cells of
        the packet SHOULD be encoded with the same CLP bit value.

7.2 PSC/CLP --> PHB mapping

   The mapping from L-LSP PSC and CLP bit of the ATM cell header into
   PHBs is as follows:

      CLP Bit      PSC             PHB

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

   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 behaviour for AF MUST comply to
   procedures described in [DIFF_AF] for the case when only two drop
   precedence levels are supported.

7.3 PHB --> PSC/CLP mapping

   The mapping from PHBs into the L-LSP PSC and the CLP bit of the ATM
   cell header is as follows:

      PHB             CLP Bit     PSC


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                      MPLS Support of Diff-Serv             October 99

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

7.4 Merging

   The use of merging is optional. In case that merging of ATM LSPs is
   used, procedures described in section 3.5. of this specification
   apply. Additionally, to avoid cell interleaving problems with AAL-5
   merging, procedures specified in [MPLS ATM] MUST be followed.

7.5 Use of ATM Traffic Classes and Traffic Management mechanisms

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

   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.

7.6 LSR Implementation With ATM Interfaces

   For an LSR implementation with ATM interfaces running native ATM
   MPLS, support of L-LSPs over the ATM interfaces is mandatory with
   respect to this specification. A Diff-Serv capable LSR with ATM
   interfaces MUST support L-LSPs over these ATM interfaces in
   compliance with this specification. Additionally, procedures
   specified in [MPLS ATM] MUST be followed by compliant
   implementation.

   Support of E-LSPs over ATM interfaces running native ATM MPLS by an
   LSR implementation is not allowed.


8. MPLS Support of Diff-Serv by Frame Relay LSRs

   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 Frame Relay links.

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

        - any number of L-LSPs.

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8.1 L-LSP Operations over Frame Relay

   The L-LSP operations over Frame Relay follows the general procedures
   of section 3. However, the following Frame Relay specific procedures
   are also defined for L-LSP operations over Frame Relay links :

        - An MPLS Frame Relay ingress interface determines the incoming
        PHB from the PSC and the Frame Relay Discard Eligible(DE) bit
        in accordance with the incoming PSC/CLP-->PHB mapping defined
        below in section 8.2;

       - If the DE value of a packet received on an L-LSP is such that
       the PSC/DE combination is not listed in the mapping of section
       8.2, this PSC/DE combination should be considered invalid. LSR
       behavior in such situation is a local matter and is outside the
       scope of this document.

        - An MPLS Frame Relay egress interface determines the value to
        be written in the Frame Relay Discard Eligible (DE) bit by
        performing the outgoing PHB-->PSC/DE mapping defined below in
        section 8.3. This is performed by an LSR on the Edge of the
        Frame Relay Diff-Serv MPLS Cloud and is performed by an Frame
        Relay LSR in the middle of the Frame Relay Diff-Serv MPLS cloud
        when doing optional Local Policy and Traffic Conditioning. When
        not doing optional Local Policy and Traffic Conditioning, an
        LSR in the middle of the Frame Relay Diff-Serv MPLS cloud may
        simply leave the DE bit untouched;

8.2 PSC/DE --> PHB mapping

   The mapping from L-LSP PSC and DE bit of the Frame Relay header into
   PHBs is as follows:

      DE Bit       PSC             PHB

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

   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 behaviour for AF MUST
   comply to procedures described in [DIFF_AF] for the case when only
   two drop precedence levels are supported.

8.3 PHB --> PSC/DE mapping

   The mapping from PHBs into the L-LSP PSC and the DE bit of the Frame
   Relay header is as follows:

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                      MPLS Support of Diff-Serv             October 99


      PHB               DE Bit     PSC

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

8.4 Merging

   The use of merging is optional. In case that merging of Frame Relay
   LSPs is used, procedures described in section 3.5. of this
   specification apply as well as procedures in [MPLS FR].

8.5 Use of Frame Relay Traffic parameters and Traffic Management
mechanisms

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

8.6 LSR Implementation With Frame Relay Interfaces

   For an LSR implementation with Frame Relay interfaces running native
   Frame Relay MPLS, support of L-LSPs over the Frame Relay interfaces
   is mandatory with respect to this specification. A Diff-Serv capable
   LSR with Frame Relay interfaces MUST support L-LSPs over these Frame
   Relay interfaces in compliance with this specification.

   Support of E-LSPs over Frame Relay interfaces running native Frame
   Relay MPLS by an LSR implementation is not allowed.


9. MPLS Support of Diff-Serv over LAN Media

   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.

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

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


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9.1. E-LSP Operations over PPP

   Text to be written (in particular regarding use of 802.1 COS field).

9.2  L-LSP Operations over PPP

   Text to be written (in particular regarding use of 802.1 COS field).

9.3 LSR Implementation With LAN Interfaces

   For an LSR implementation with LAN interfaces, support of E-LSPs
   over the LAN interfaces is mandatory with respect to this
   specification. A Diff-Serv capable LSR with LAN interfaces MUST
   support E-LSPs over these LAN interfaces in compliance with this
   specification.

   Support of L-LSPs over LAN interfaces by an LSR implementation is
   optional. A Diff-Serv capable LSR MAY support L-LSPs over LAN
   interfaces. However, 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.


10. Operations at MPLS Diff-Serv Boundaries

10.1 Operations at E-LSP/L-LSP Boundary Within Single MPLS Diff-Serv
Domain

   Text to be added

10.2 Operations At Boundary across Diff-Serv domains

   Text to be added


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.

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   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.

        - 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. 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'.

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

   For ECN-capable E-LSPs, the PHB<-->EXP mapping defined above in the
   section titled `PHB<-->EXP Field Mapping' and configured on the LSR
   is only operating over the last 2 bits of the 3-bit EXP field. Thus
   it has the following format:

      EXP Field                 PHB

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

   where `e' is the MPLS ECN bit and can take the value zero or one
   depending on ECN operations.

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

      EXP Field      PSC             PHB

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

   where `e' is the MPLS ECN bit and can take the value zero or one
   depending on ECN operations.

   For ECN-capable L-LSPs, the PHB--> PSC/EXP mapping defined above in
   the section titled `PHB--> PSC/EXP Mapping' is 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          AFCn
        AFn2   ----->     e01          AFCn
        AFn3   ----->     e10          AFCn
        EF     ----->     e00          EF

   where `e' is the MPLS ECN bit and can take the value zero or one
   depending on ECN operations.



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                      MPLS Support of Diff-Serv             October 99

   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
   PHB<-->EXP mapping defined in the section titled `PHB<-->EXP Field
   Mapping' and configured on the LSR is operating over the 3 bits of
   the EXP field.


12. Security Considerations

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


13. Acknowledgments

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




APPENDIX A. Ordered Aggregate (OA) and PHB Scheduling Class (PSC)

   This Appendix contains the definition of two Diff-Serv concepts:
        - the Ordered Aggregate (OA)
        - the PHB Scheduling Class (PSC)
   In the future, it is expected that these definitions will be
   incorporated in new versions of the Diff-Serv specifications.

A.1 Ordered Aggregate (OA)

   [DIFF_AF] states that "a DS node does not reorder IP packets of the
   same microflow if they belong to the same AF class" (even if
   different packets of the microflow contain different AF codepoints
   of the same AF class).

   For the sake of generality, we define a set of Behavior Aggregates
   which share such an ordering constraint to constitute a "Ordered
   Aggregate" (OA).

A.2 PHB Scheduling Class (PSC)

   We refer to the set of one or more PHBs applied to the set of
   Behavior Aggregates forming a given OA, as a "PHB Scheduling Class"
   (PSC).

   The PHBs currently specified are Default PHB (DF), Class Selector
   PHB group (CSx), Assured Forwarding PHB group (AFxy), Expedited
   Forwarding PHB (EF).


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                      MPLS Support of Diff-Serv             October 99

A.2.1 DF PSC

   The Default PHB is a single PHB specified in [DIFF_Header]. Thus,
   the corresponding PSC comprises a single PHB and thus coincides with
   the DF PHB.

A.2.2 CSn PSC

   [DIFF_HEADER] defines up to 8 CS Codepoints referred to as CSn,
   where 1 <= i <= 8. [DIFF_HEADER] states that "... PHBs selected by
   distinct Class Selector Codepoints SHOULD be independently
   forwarded; that is, packets marked with different Class Selector
   Codepoints MAY be re-ordered". Thus, there is one PSC corresponding
   to each CSn PHB. Each CSn PSC comprises a single PHB and thus
   coincides with this CSn PHB.

A.2.3 AFn PSC

   As described in [DIFF_AF], the Assured Forwarding (AF) PHB group
   provides forwarding of IP packets in N independent AF classes.
   Within each AF class, an IP packet is assigned one of M different
   levels of drop precedence. An IP packet that belongs to an AF class
   i and has drop precedence j is marked with the AF codepoint AFij,
   where 1 <= i <= N and 1 <= j <= M. Currently, four classes (N=4)
   with three levels of drop precedence in each class (M=3) are
   defined for general use.

   [DIFF_AF] states that "a DS node does not reorder IP packets of the
   same microflow if they belong to the same AF class" (even if
   different packets of the microflow contain different AF codepoints
   of the same AF class). As noted above, each AF class in the AF PHB
   group is the primary example of a PSC. Each PSC comprises 3 PHBs and
   coincides with the AF Class. Those PSCs are thus referred to as AFn,
   where 1 <= n <= 4.

A.2.4 EF PSC

   [DIFF_EF] defines the Expedited Forwarding (EF) PHB for traffic
   requiring forwarding with low loss, low latency, low jitter.
   [DIFF_EF] defines a single PHB. Thus, the corresponding PSC
   comprises a single PHB and thus coincides with the DF PHB.

A.2.5 Summary list of PSC

   The following PSCs have thus been identified:
        - DF
        - CSn , 1 <= i <= 8
        - AFn, 1 <= i <= 4
        - EF


APPENDIX B. Example Deployment Scenarios

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                      MPLS Support of Diff-Serv             October 99


   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.

B.1 Scenario 1: 8 BAs, no Traffic Engineering, no Fast Reroute

   A Service Provider running 8 (or less) 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.

   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 bandwdith
   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 using LDP
   in accordance with the specification above (ie no Diff-Serv_PSC TLV
   in LDP Label Request/Label Mapping messages to implicitly indicate
   that the LSP is an E-LSP)

B.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
   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 to support a set of 8 (or less)
   BAs,
        AND
        - one L-LSP per <FEC,OA> established via LDP for support of the
   other BAs.

   Operations can be summarized as follows:
        - the Service Provider configures at every LSR the bi-
   directional mapping between each PHB and a value of the EXP field
   for the BAs transported over the E-LSP
        - the Service Provider configures at every LSR, and for every
   interface, the scheduling behavior for each PSC supported over the
   E-LSP and the dropping behavior for each corresponding PHB
        - the Service Provider configures at every LSR, and for every
   interface, the scheduling behavior for each PSC supported over the
   L-LSPs and the dropping behavior for each corresponding PHB


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                      MPLS Support of Diff-Serv             October 99

        - 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_PSC TLV in LDP Label Request/Label Mapping messages to
   implicitly indicate that the LSP is an E-LSP)
   - LSRs signal establishment of one L-LSP per <FEC,OA> for the other
   BAs using LDP as specified above (ie Diff-Serv_PSC TLV in LDP Label
   Request/Label Mapping messages to indicate the L-LSP's PSC).

B.3 Scenario 3: 8 BAs, Aggregate Traffic Engineering, Aggregate Fast
Reroute

   A Service Provider running 8 (or less) 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].

   Operations can be summarized as follows:
        - the Service Provider configures at every LSR the
   bidirectional 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:
            * using the RSVP protocol as specified above (ie no
   DIFFSERV_PSC RSVP Object in the PATH message containing the
   LABEL_REQUEST Object), OR
            * using the CR-LDP protocol as specified above (ie no Diff-
   Serv_PSC TLV in LDP Label Request/Label Mapping messages).

B.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
   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>:



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                      MPLS Support of Diff-Serv             October 99

                * using the RSVP as specified above to signal the
   L-LSP's PSC (ie DIFFSERV_PSC 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_PSC TLV in LDP Label
   Request/Label Mapping messages).

B.5 Scenario 5: less than 8 BAs, per-OA Traffic Engineering/Fast
Reroute

   A Service Provider running less than 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.

   Operations can be summarized as follows:
        - the Service Provider configures at every LSR the
   bidirectional 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 L-LSP per <FEC,OA>:
                * using the RSVP protocol as specified above to signal
   that the LSP is an E-LSP (ie no DIFFSERV_PSC RSVP Object in the PATH
   message containing the LABEL_REQUEST), OR
                * using the CR-LDP protocol as specified above to
   signal that the LSP is an E-LSP (ie no Diff-Serv_PSC 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 packets
   belonging to a given OA are forwarded on the E-LSP established for
   the corresponding FEC and corresponding OA.

B.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) 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 established via LDP to support the set of 8 (or
   less) non-traffic-engineered/non-fast-rerouted BAs,
        AND


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                      MPLS Support of Diff-Serv             October 99

        - 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_PSC 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_PSC 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_PSC TLV in LDP Label
   Request/Label Mapping messages).



References

   [MPLS_ARCH] Rosen et al., "Multiprotocol label switching
   Architecture", work in progress, (draft-ietf-mpls-arch-06.txt),
   August 1999.

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

   [MPLS FR] Conta et al., _Use of Label Switching on Frame Relay
   Networks Specification_, (draft-ietf-mpls-fr-03.txt), November 1998

   [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.


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                      MPLS Support of Diff-Serv             October 99

   [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 99

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

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

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


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: (978)-244-3087
   Email:


          liwwu@cisco.com

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




   Shahram Davari
   PMC-Sierra Inc.
   105-8555 Baxter Place
   Burnaby, BC V5A 4V7
   Canada
   E-mail: Shahram_Davari@pmc-sierra.com

   Pasi Vaananen
   Nokia
   3 Burlington Woods Drive, Suit 250
   Burlington, MA 01803

 Le Faucheur et. al                                                 41


                      MPLS Support of Diff-Serv             October 99

   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

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




































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