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Versions: 00 01 02 03 04 05 06 07 08 RFC 4124

                                            Francois Le Faucheur, Editor
                                                           Thomas Nadeau
                                                     Cisco Systems, Inc.

                                                               Jim Boyle
                                                                  PDNets

                                                        Kireeti Kompella
                                                        Juniper Networks

                                                        William Townsend
                                                          Tenor Networks

                                                          Darek Skalecki
                                                         Nortel Networks



IETF Internet Draft
Expires: August, 2002
Document: draft-ietf-tewg-diff-te-proto-00.txt         February, 2002



                   Protocol extensions for support of
                Diff-Serv-aware MPLS Traffic Engineering


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 months
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  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 specifies the IGP and signaling extensions and
  procedures (beyond those already specified for existing MPLS Traffic
  Engineering) for support of Diff-Serv-aware MPLS Traffic Engineering.


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  A Bandwidth Constraints model for Diff-Serv-aware Traffic Engineering
  is also specified.


1.      Introduction

  [DSTE-REQ] presents the Service Providers requirements for support of
  Diff-Serv-aware MPLS Traffic Engineering (DS-TE). This includes the
  fundamental requirement to be able to enforce different bandwidth
  constraints for different classes of traffic.

  This document specifies:
        - the IGP and signaling extensions and procedures (beyond those
          already specified for existing MPLS Traffic Engineering
          [OSPF-TE][ISIS-TE][RSVP-TE][CR-LDP]) for support of the DS-TE
          requirements [DSTE-REQ] in environments relying on
          distributed Constraint Based Routing (i.e. path computation
          involving Head-end LSRs).
        - A Bandwidth Constraint Model for DS-TE called the Russian
          Dolls model. While Diff-Serv-aware implementations may
          support other Bandwidth Constraints model, they must all
          support the Russian Dolls model to ensure interoperability
          across all implementations.


2.      Definitions

  [DSTE-REQ] discusses how a Head-end LSR may split the set of Ordered
  Aggregates from the traffic to a given Tail-end into multiple Traffic
  Trunks. Each Traffic Trunk is transported over a separate LSP which
  is Constraint Based Routed individually.

  For readability a number of definitions from [DSTE-REQ] are repeated
  here:

  Traffic Trunk: an aggregation of traffic flows of the same class
  [i.e. which are to be treated equivalently from the DS-TE
  perspective] which are placed inside a Label Switched Path.

  Class-Type (CT): the set of Traffic Trunks crossing a link that is
  governed by  a specific set of Bandwidth constraints. CT is used for
  the purposes of link bandwidth allocation, constraint based routing
  and admission control. A given Traffic Trunk belongs to the same CT
  on all links.

  TE-Class: A pair of:
             i. a Class-Type
            ii. a preemption priority allowed for that Class-Type. This
                means that an LSP transporting a Traffic Trunk from
                that Class-Type can use that preemption priority as the
                set-up priority, as the holding priority or both.


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3.      Configurable Parameters

  This section only discusses the differences with the configurable
  parameters supported for MPLS Traffic Engineering as per [TE-REQ],
  [ISIS-TE], [OSPF-TE], [RSVP-TE] and [CR-LDP]. All other parameters
  are unchanged.

3.1.    Link Parameters

3.1.1.  Bandwidth Constraints (BCs)

  [DSTE-REQTS] states that "Regardless of the Bandwidth Constraint
  Model, the DS-TE solution must allow support for up to 8 BCs."

  For DS-TE, the existing "Maximum Reservable link bandwidth" parameter
  is retained but its semantic is generalized and interpreted as BC0.

  Additionally, on every link, a DS-TE implementation must provide for
  configuration of up to 7 additional link parameters which are the
  seven other potential Bandwidth Constraints i.e. BC1, BC2 , ... BC7.

  The LSR is responsible for interpreting these Bandwidth Constraints
  in accordance with the supported Bandwidth Constraint Model (i.e.
  what bandwidth constraint applies to what Class-Type and how). At any
  one time, all LSRs of the DS-TE domain must support the same
  Bandwidth Constraint Model.

  Where the Bandwidth Constraint Model imposes some relationship among
  the values to be configured for these Bandwidth Constraints, the LSR
  is responsible for enforcing those at configuration time. For
  example, with the "Russian Doll" Bandwidth Constraints Model defined
  below in section 9, the LSR must ensure that BCi is configured
  smaller or equal to BCj, where i is greater than j.

3.1.2.  per-CT Local Overbooking Multiplier

  DS-TE enables a network administrator to apply different overbooking
  (or underbooking) ratios for different CTs.

  The principal method to achieve this is the same as historically used
  in existing TE deployment which is to take into account the over-
  booking ratio appropriate for the OA/CT associated with the
  considered LSP at the time of establishing the bandwidth size of a
  given LSP. We refer to this as the "LSP size overbooking" method.

  Since the overbooking ratio is factored into the LSP bandwidth (which
  is invariable across all the links spanned by the LSP), using the
  "LSP size overbooking" method alone effectively has the following
  characteristics:



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        - different overbooking ratios can effectively be enforced for
          different CTs (by using a different overbooking ratios for
          LSPs of different CTs)
        - the overbooking ratio is the same on all links for a given CT
        - the overbooking ratios can even be fine-tuned on a per-LSP
          basis (i.e. different LSPs of the same CT may be sized based
          on overbooking ratios which are tweaked differently).

  The "LSP size overbooking" method is expected to be often sufficient
  in many DS-TE environments and requires no additional configurable
  parameters.

  However, in the particular DS-TE environments where, for a given CT,
  the overbooking ratio needs to be tweaked differently on different
  links, a DS-TE implementation may allow the "LSP size overbooking"
  method to be complemented by the use of the "local overbooking"
  method. The "local overbooking" method relies on optional "per-CT
  Local Overbooking Multipliers" which are configurable, on every link,
  for every CT. The per-CT Local Overbooking Multiplier effectively
  allows the network operator to increase/decrease", on some links, the
  overbooking ratio already enforced by the "LSP size overbooking"
  method. This is achieved by factoring the per-CT Local Overbooking
  Multiplier in all local bandwidth accounting for the purposes of
  admission control and IGP advertisement of unreserved bandwidths.

3.2.    LSR Parameters

3.2.1.  TE-Class Mapping

  In line with [DSTE-REQ], the preemption attributes defined in [TE-
  REQ] are retained with DS-TE and applicable across all Class Types.
  The preemption attributes of setup priority and holding priority
  retain existing semantics, and in particular these semantics are not
  affected by the Ordered Aggregate transported by the LSP or by the
  LSP's Class Type. This means that if LSP1 contends with LSP2 for
  resources, LSP1 may preempt LSP2 if LSP1 has a higher set-up
  preemption priority (i.e. lower numerical priority value) than LSP2's
  holding preemption priority regardless of LSP1's OA/CT and LSP2's
  OA/CT.

  For DS-TE, LSRs must allow configuration of a TE-Class mapping
  whereby the Class-Type and preemption level are configured for each
  of (up to) 8 TE-Classes.

  This mapping is referred to as :

       TE-Class[i]  <-->  < CTc , preemption p >

  Where 0 <= i <= 7, 0 <= c <= 7, 0 <= p <= 7




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  Two TE-Classes must not be identical (i.e. have both the same Class-
  Type and the same preemption priority).

  Where the network administrator uses less than 8 TE-Classes, the
  remaining ones must be configured as "Unused".

  There are no other restrictions on how any of the 8 Class-Types can
  be paired up with any of the 8 preemption priorities to form a TE-
  class. In particular, one given preemption priority can be paired up
  with two (or more) different Class-Types to form two (or more) TE-
  classes. Similarly, one Class-Type can be paired up with two (or
  more) different preemption priorities to form two (or more) TE-
  Classes. Also, there is no mandatory ordering relationship between
  the TE-Class index (i.e. "i" above) and the Class-Type (i.e. "c"
  above) or the preemption priority (i.e. "p" above) of the TE-Class.

  To ensure coherent DS-TE operation, the network administrator must
  configure exactly the same TE-Class Mapping on all LSRs of the DS-TE
  domain.

3.3.    LSP Parameters

3.3.1.  Class-Type

  With DS-TE, LSRs must support, for every LSP, an additional
  configurable parameter which indicates the Class-Type of the Traffic
  Trunk transported by the LSP.

  There is one and only one Class-Type configured per LSP.

  The configured Class-Type indicates, in accordance with the supported
  Bandwidth Constraint Model, what are the Bandwidth Constraints
  applicable to that LSP.

3.3.2.  Setup and Holding Preemption Priorities

  As per existing TE, DS-TE assumes that every DS-TE LSP is configured
  with a setup and holding priority, each with a value between 0 and 7.

3.3.3.  Class-Type/Preemption Relationship

  With DS-TE, the preemption priority configured for the setup priority
  of a given LSP and the Class-Type configured for that LSP  must be
  such that, together, they form one of the (up to) 8 TE-Classes
  configured in the TE-Class Mapping specified is section 3.2.1 above.

  The preemption priority configured for the holding priority of a
  given LSP and the Class-Type configured for that LSP must also be
  such that, together, they form one of the (up to) 8 TE-Classes
  configured in the TE-Class Mapping specified is section 3.2.1 above.

3.4.    Examples of Parameters Configuration

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  For illustrative purposes, we now present a few examples of how these
  configurable parameters may be used. All these examples assume that
  different bandwidth constraints need to be enforced for different
  sets of Traffic Trunks (e.g. for Voice and for Data) so that two, or
  more, Class-Types must be used.

3.4.1.  Example 1

  The Network Administrator of a first network using two Class Types
  (CT1 for Voice and CT0 for Data), may elect to configure the
  following TE-Class Mapping to ensure that Voice LSPs are never driven
  away from their shortest path because of Data LSPs:

       TE-Class[0]  <-->  < CT1 , preemption 0 >
       TE-Class[1]  <-->  < CT0 , preemption 1 >
       TE-Class[i]  <-->  unused,   for 2 <= i <= 7

  Voice LSPs would then be configured with:
        - CT=CT1, set-up priority =0, holding priority=0

  Data LSPs would then be configured with:
        - CT=CT0, set-up priority =1, holding priority=1

  A new Voice LSP would then be able to preempt an existing Data LSP in
  case they contend for resources. A Data LSP would never preempt a
  Voice LSP. A Voice LSP would never preempt another Voice LSP. A Data
  LSP would never preempt another Data LSP.

3.4.2.  Example 2

  The Network Administrator of another network may elect to configure
  the following TE-Class Mapping in order to optimize global network
  resource utilization by favoring placement of large LSPs closer to
  their shortest path:

       TE-Class[0]  <-->  < CT1 , preemption 0 >
       TE-Class[1]  <-->  < CT0 , preemption 1 >
       TE-Class[2]  <-->  < CT1 , preemption 2 >
       TE-Class[3]  <-->  < CT0 , preemption 3 >
       TE-Class[i]  <-->  unused,   for 4 <= i <= 7

  Large size Voice LSPs could be configured with:
        - CT=CT1, set-up priority =0, holding priority=0

  Large size Data LSPs could be configured with:
        - CT=CT0, set-up priority = 1, holding priority=1

  Small size Voice LSPs could be configured with:
        - CT=CT1, set-up priority = 2, holding priority=2

  Small size Data LSPs could be configured with:

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        - CT=CT0, set-up priority = 3, holding priority=3.

  A new large size Voice LSP would then be able to preempt a small size
  Voice LSP or any Data LSP in case they contend for resources.
  A new large size Data LSP would then be able to preempt a small size
  Data LSP or a small size Voice LSP in case they contend for
  resources, but it would not be able to preempt a large size Voice
  LSP.

3.4.3.  Example 3

  The Network Administrator of another network may elect to configure
  the following TE-Class Mapping in order to ensure that Voice LSPs are
  never driven away from their shortest path because of Data LSPs while
  also achieving some optimization of global network resource
  utilization by favoring placement of large LSPs closer to their
  shortest path:

       TE-Class[0]  <-->  < CT1 , preemption 0 >
       TE-Class[1]  <-->  < CT1 , preemption 1 >
       TE-Class[2]  <-->  < CT0 , preemption 2 >
       TE-Class[3]  <-->  < CT0 , preemption 3 >
       TE-Class[i]  <-->  unused,   for 4 <= i <= 7

  Large size Voice LSPs could be configured with:
        - CT=CT1, set-up priority = 0, holding priority=0.

  Small size Voice LSPs could be configured with:
        - CT=CT1, set-up priority = 1, holding priority=1.

  Large size Data LSPs could be configured with:
        - CT=CT0, set-up priority = 2, holding priority=2.

  Small size Data LSPs could be configured with:
        - CT=CT0, set-up priority = 3, holding priority=3.

  A Voice LSP could preempt a Data LSP if they contend for resources. A
  Data LSP would never preempt a Voice LSP. A Large size Voice LSP
  could preempt a small size Voice LSP if they contend for resources. A
  Large size Data LSP could preempt a small size Data LSP if they
  contend for resources.

3.4.4.  Example 4

  The Network Administrator of another network may elect to configure
  the following TE-Class Mapping in order to ensure that no preemption
  occurs in the DS-TE domain:

       TE-Class[0]  <-->  < CT1 , preemption 0 >
       TE-Class[1]  <-->  < CT0 , preemption 0 >
       TE-Class[i]  <-->  unused,   for 2 <= i <= 7


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  Voice LSPs would then be configured with:
        - CT=CT1, set-up priority =0, holding priority=0

  Data LSPs would then be configured with:
        - CT=CT0, set-up priority =0, holding priority=0

  No LSP would then be able to preempt any other LSP.

3.4.5.  Example 5

  The Network Administrator of another network may elect to configure
  the following TE-Class Mapping in view of increased network stability
  through a more limited use of preemption:

       TE-Class[0]  <-->  < CT1 , preemption 0 >
       TE-Class[1]  <-->  < CT1 , preemption 1 >
       TE-Class[2]  <-->  < CT0 , preemption 1 >
       TE-Class[3]  <-->  < CT0 , preemption 2 >
       TE-Class[i]  <-->  unused,   for 4 <= i <= 7

  Large size Voice LSPs could be configured with:
        - CT=CT1, set-up priority = 0, holding priority=0.

  Small size Voice LSPs could be configured with:
        - CT=CT1, set-up priority = 1, holding priority=0.

  Large size Data LSPs could be configured with:
        - CT=CT0, set-up priority = 2, holding priority=1.

  Small size Data LSPs could be configured with:
       - CT=CT0, set-up priority = 2, holding priority=2.

  A new large size Voice LSP would be able to preempt a Data LSP in
  case they contend for resources, but it would not be able to preempt
  any Voice LSP even a small size Voice LSP.

  A new small size Voice LSP would be able to preempt a small size Data
  LSP in case they contend for resources, but it would not be able to
  preempt a large size Data LSP or any Voice LSP.

  A Data LSP would not be able to preempt any other LSP.


4.      IGP Advertisement

  This section only discusses the differences with the IGP
  advertisement supported for MPLS Traffic Engineering as per [OSPF-TE]
  and [ISIS-TE]. The rest of the IGP advertisement is unchanged.

4.1.    Bandwidth Constraints



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  As detailed above in section 3.1.1, up to 8 Bandwidth Constraints (
  BCb, 0 <= b <= 7) are configurable on any given link.

  With DS-TE, the existing "Maximum Reservable Bw" sub-TLV is retained
  with a generalized semantic so that it is now interpreted as
  Bandwidth Constraint 0 (BC0).

  DS-TE also defines the following optional sub-TLV to advertise the
  eight potential Bandwidth Constraints (BC0 to BC7):

  "Bandwidth Constraints" sub-TLV:
       TBD - Bandwidth Constraint Model Id (1 octet)
              Bandwidth Constraints (Nx4 octets)

  Where:

        - Bandwidth Constraint Model Id: 1 octet identifier for the
          Bandwidth Constraints Model currently in use by the LSR
          initiating the IGP advertisement.
          Values 0 to 127 are to be allocated by the TEWG to identify
          Bandwidth Constraints Models defined in the TEWG. Value 0
          identifies the Russian Doll Bandwidth Constraint Model
          defined in section 9.
          Values 128 to 255 are for experimental use.

        - Bandwidth Constraints: contains BC0, BC1,... BCN-1. It is
          recommended that only the Bandwidth Constraints corresponding
          to active CTs be advertised in order to minimize the impact
          on IGP scalability.

  When DS-TE is deployed and only a single CT is used, the existing
  "Maximum Reservable Bw" sub-TLV is used.

  When DS-TE is deployed and multiple CTs are used, the new "Bandwidth
  Constraints" sub-TLV is used. For example, where a Service Provider
  deploys DS-TE with two active CTs, only two Bandwidth Constraints per
  link would be meaningful (assuming, for instance, the Russian Doll
  Bandwidth Constraint Model defined in section 9). The "Bandwidth
  Constraints" sub-TLV would then be used and should contain BC0 and
  BC1.
  A DS-TE LSR receiving the "Bandwidth Constraints" sub-TLV with a
  Bandwidth Constraint Model Id which does not match the Bandwidth
  Constraint Model it currently uses, may generate an error indication
  to the operator reporting the inconsistency between Bandwidth
  Constraint Models used on different LSRs and may discard the
  corresponding TLV.

4.2.    Unreserved Bandwidth

  With DS-TE, the existing "Unreserved Bandwidth" sub-TLV is retained
  as the only vehicle to advertise dynamic bandwidth information
  necessary for Constraint Based Routing on Head-ends, except that it

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  is used with a generalized semantic. The Unreserved Bandwidth sub-TLV
  still carries eight bandwidth values but they now correspond to the
  unreserved bandwidth for each of the TE-Class (instead of for each
  preemption as per existing TE).

  More precisely, the Unreserved Bandwidth sub-TLV definition is
  generalized into the following:

  The Unreserved Bandwidth sub-TLV specifies the amount of bandwidth
  not yet reserved for each of the eight TE-classes, in IEEE floating
  point format arranged in increasing order of TE-Class index, with
  unreserved bandwidth for TE-Class [0] occurring at the start of the
  sub-TLV, and unreserved bandwidth for TE-Class [7] at the end of the
  sub-TLV. The unreserved bandwidth value for TE-Class [i] ( 0 <= i <=
  7) is referred to as "Unreserved TE-Class [i]". It indicates the
  bandwidth that is available, for reservation, to an LSP which :
        - transports a Traffic Trunk from the Class-Type of TE-
          Class[i], and
        - has a setup priority corresponding to the preemption priority
          of TE-Class[i].

  The units are bytes per second.

  Since the bandwidth values are now ordered by TE-class index and thus
  can relate to different CTs with different bandwidth constraints and
  can relate to any arbitrary preemption priority, no ordered
  relationship among these bandwidth values should be assumed.

  With existing TE, since all preemption priorities reflect the same
  (and only) bandwidth constraints and since bandwidth values are
  advertised in preemption priority order, the following relationship
  is always true, and is often assumed by TE implementations:

      If i < j , then "Unreserved Bw [i]" >= "Unreserved Bw [j]"

  With DS-TE, no relationship  is  to be assumed so that:
       If i < j , then
                "Unreserved TE-Class [i]" = "Unreserved TE-Class [j]"
                    OR
                "Unreserved TE-Class [i]" > "Unreserved TE-Class [j]"
                    OR
                "Unreserved TE-Class [i]" < "Unreserved TE-Class [j]".

  Since some Bandwidth Constraints Models are such that a given Class-
  Type is constrained by multiple Bandwidth Constraints (as in the case
  of the Russian Doll Bandwidth Constraint Model specified in section
  9), the value to be advertised by the IGP in "Unreserved TE-Class
  [i]" must reflect all of the Bandwidth Constraints relevant to the CT
  associated with TE-Class [i].  .

  If TE-Class[i] is unused the value to be advertised by the IGP in
  "Unreserved TE-Class [i]" is zero.

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4.3.    Local Overbooking Multiplier

  The following additional optional sub-TLV is defined for DS-TE:

  "Local Overbooking Multiplier" sub-TLV:
       TBD - per-CT Local Overbooking Multipliers (N x 1 octet)

  where N is the number of per-CT Local Overbooking Multipliers
  actually advertised. For example, where a Service Provider only
  deploys DS-TE with two CTs and makes use of the Local Overbooking
  method, the "Local Overbooking Multiplier" sub-TLV may optionally be
  used and would then contain only LOM[0] and LOM[1] in order to
  minimize the impact on IGP scalability.

  Note that the use of this sub-TLV is only optional even when the
  optional Local Overbooking method is actually used (and thus when the
  Local Overbooking Multipliers parameters actually configured locally
  on some or all links). Its use may assist in head-end prediction of
  network response to LSP establishment.


5.      LSP Signaling

  This section only describes the signaling extensions beyond those
  already specified for MPLS Traffic Engineering as per [RSVP-TE] and
  [CR-LDP] and for Diff-Serv over MPLS as per [DIFF-MPLS].

  The Class-Type of the LSP is signaled in RSVP-TE and CR-LDP for DS-TE
  in order for LSRs to enforce the appropriate bandwidth constraint(s)
  for admission control and bandwidth accounting.

  Protocol and procedure extensions for signaling of the Class-Type are
  specified in details in Appendix A and B respectively for RSVP-TE and
  CR-LDP.


6.      Constraint Based Routing

  Let us consider the case where a path needs to be computed for an LSP
  whose Class-Type is configured to CTc and whose set-up preemption
  priority is configured to p.

  Then the pair of CTc and p will map to one of the TE-Classes defined
  in the TE-Class mapping. Let us assume that this is the i-th TE-Class
  i.e. TE-Class[i].

  The Constraint Based Routing algorithm is still only required to
  perform path computation satisfying a single bandwidth constraint
  which is to fit in "Unreserved TE-Class [i]" as advertised by the IGP
  for every link. Thus, no changes are required to the existing TE
  Constraint Based Routing algorithm itself.

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  The Constraint Based Routing algorithm may also optionally take into
  account, when used, the optional information advertised in IGP which
  are the Bandwidth Constraints and the Local Overbooking Multipliers.
  As an example, the Bandwidth Constraints might be used as a tie-
  breaker criteria in situations where multiple paths, otherwise
  equally attractive, are possible.


7.      Diff-Serv scheduling

  The Class-Type signaled at LSP establishment may optionally be used
  by LSRs to dynamically adjust the resources allocated to the Class-
  Type by the Diff-Serv scheduler. In addition, the Diff-Serv
  information (i.e. the PSC) signaled by the TE-LSP signaling protocols
  as specified in [DIFF-MPLS], if used, may optionally be used by LSRs
  to dynamically adjust the resources allocated to a PSC/OA within a
  Class Type by the Diff-Serv scheduler.


8.      Existing TE as a Particular Case of DS-TE

  We observe that existing TE can be viewed as a particular case of DS-
  TE where:

        (i) a single Class-Type is used, all 8 preemption priorities
           are allowed for that Class-Type and the following TE-Class
           Mapping is used:

                TE-Class[i]  <-->  < CT0 , preemption i >
                Where 0 <= i <= 7.

        (ii) optional per-CT Local Overbooking Multipliers are not
           used.

  In that case, DS-TE behaves exactly as existing TE.

  The IGP advertises:
        - Unreserved Bandwidth for each of the 8 preemption priorities
        - BC0= Maximum Reservable Bandwidth

  Since all LSPs transport traffic from CT0, LSP Signaling is done
  without explicit signaling of the Class-Type (which is only used for
  other Class-Types than CT0 as explained in Appendix A and B).


9.      Russian Doll Bandwidth Constraints Model

9.1.    Definition




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  [DSTE-REQ] introduces the concept of Bandwidth Constraint Model to
  characterize the Bandwidth Constraints associated with CTs, but it
  does not actually specify one particular Model.

  Although multiple Bandwidth Constraints Models are conceivable and
  may be supported by a given DS-TE implementation, DS-TE operation
  requires that the same Bandwidth Constraint Model be actually used on
  all LSRs of a given DS-TE domain. Thus, for multiple DS-TE
  implementations to interoperate, they must support the same Bandwidth
  Constraints Model. Consequently, this section specifies one default
  Bandwidth Constraint Models which must be supported by all DS-TE
  implementations to ensure interoperability. This Model is referred to
  as the "Russian Dolls" Bandwidth Constraints model. DS-TE
  implementations may also optionally support other Bandwidth
  Constraints Models.

  The "Russian Doll" model of Bandwidth Constraints is defined in the
  following manner:
             o Maximum Number of Bandwidth Constraints (MaxBC)= Maximum
               Number of Class-Types (MaxCT) = 8
             o All LSPs supporting Traffic Trunks from CTb (with
               b<=c<=7) use no more than BCb i.e.:
                  - All LSPs from CT7 use no more than BC7
                  - All LSPs from CT6 and CT7 use no more than BC6
                  - All LSPs from CT5, CT6 and CT7 use no more than BC5
            - etc.
                  - All LSPs from CT0, CT1,... CT7 use no more than BC0

  Purely for illustration purposes, the diagram below represents the
  Russian Doll Bandwidth Constraints model in a pictorial manner when
  only 3 Class-Types are active:

  I------------------------------------------------------I
  I-------------------------------I                      I
  I--------------I                I                      I
  I    CT2       I    CT2+CT1     I      CT2+CT1+CT0     I
  I--------------I                I                      I
  I-------------------------------I                      I
  I------------------------------------------------------I

  I-----BC2------>
  I----------------------BC1------>
  I---------------------------------------------BC0------>


  While more flexible/sophisticated Bandwidth Constraints models can be
  defined, the Russian Dolls model is an attractive trade-off for the
  following reasons:
       - Network administrators generally find it superior to the most
          basic model of a single independent BC per CT (which, in
          typical deployment scenarios, results in either capacity


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                   Protocols for Diff-Serv-aware TE      February 2002

          wastage, low priority Traffic Trunk starvation and/or
          degradation of QoS objectives)
       - network administrators generally find it sufficient for the
          real life deployments currently anticipated (e.g. it
          addresses all the scenarios described in [DSTE-REQ])
       - it remains simple and only requires limited protocol
          extensions, while more sophisticated Bandwidth Constraints
          model may require more complex extensions.

  Another (or other) Bandwidth Constraints Model(s) may be specified
  later if additional requirements emerge from Service Providers real
  life deployment which cannot be addressed by the Russian Dolls model.

  The Russian Doll Bandwidth Constraints Model can be supported with
  the extensions defined earlier in this document for DS-TE. Note that
  a number of other Bandwidth Constraints could also be supported with
  these same extensions. Note also that not all Bandwidth Constraints
  models could be supported with these extensions and those may require
  additional or different extensions. Both of these situations are
  beyond the scope of this specification.

  As an example of the "Russian Doll" Bandwidth Constraints Model, a
  network administrator using one CT for Voice (CT1) and one CT for
  data (CT0) might configure on a given link:
        - Existing Maximum Reservable Link Bandwidth (a.k.a. BC0) = 2.5
          Gb/s (i.e. Voice + Data is limited to 2.5 Gb/s)
        - Bandwidth Constraint 1 (a.k.a. BC1)= 1.5 Gb/s (i.e. Voice is
          limited to 1.5 Gb/s).

9.2.    Computing "Unreserved TE-Class [i]"

  We first observe that, for existing TE, details on admission control
  algorithms for TE LSPs, and consequently details on formulas for
  computing the unreserved bandwidth, are outside the scope of the
  current IETF work. This is left for vendor differentiation. Note that
  this does not compromise interoperability across various
  implementations since the TE schemes rely on LSRs to advertise their
  local view of the world in terms of Unreserved Bw to other LSRs. This
  way, regardless of the actual local admission control algorithm used
  on one given LSR, Constraint Based Routing on other LSRs can rely on
  advertised information to determine whether an additional LSP will be
  accepted or rejected by the given LSR. The only requirement is that
  an LSR advertises unreserved bandwidth values which are consistent
  with its specific local admission control algorithm and take into
  account the holding preemption priority of established LSPs.

  In the context of DS-TE, again, details on admission control
  algorithms are left for vendor differentiation and formulas for
  computing the unreserved bandwidth for TE-Class[i] are outside the
  scope of this specification. However, DS-TE places the additional
  requirement on the LSR that the unreserved bandwidth values


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                   Protocols for Diff-Serv-aware TE      February 2002

  advertised must reflect all of the Bandwidth Constraints relevant to
  the CT associated with TE-Class[i], as discussed in section 4.2.

  As with existing TE, DS-TE assumes that the holding preemption
  priority is the one considered for established LSPs (as opposed to
  their set-up preemption priority) for the purpose of computing the
  unreserved bandwidth for TE-Class [i].

  Example formulas for computing "Unreserved TE-Class [i]" are provided
  in Appendix C.

9.3.    Admission Control Rules

  Regardless of how the admission control algorithm actually computes
  the unreserved bandwidth for TE-Class[i] for one of its local link,
  an LSP of bandwidth B , of set-up preemption priority p and of Class-
  Type CTc is admissible on that link iff:

       B <= unreserved bandwidth for TE-Class[i], AND
       B <= Max Link Bandwidth

        Where

        - TE-Class [i] maps to  < CTc , p > in the LSR's configured TE-
          Class mapping
        - Max Link Bandwidth is the maximum link bandwidth configured
          on the link and advertised in IGP.

  Note that this admission control rule assumes that the optional per-
  CT Local Overbooking Multipliers are not used (i.e. LOM[c]=1).


10.     Security Considerations

  The solution is not expected to add specific security requirements
  beyond those of Diff-Serv and existing TE. The security mechanisms
  currently used with Diff-Serv and existing TE can be used with this
  solution.


11.     Acknowledgments

  We thank Martin Tatham, Angela Chiu and Pete Hicks for their earlier
  contribution in this work.


References

  [DSTE-REQ] Le Faucheur et al, Requirements for support of Diff-Serv-
  aware MPLS Traffic Engineering, draft-ietf-tewg-diff-te-reqts-03.txt,
  February 2002.


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                   Protocols for Diff-Serv-aware TE      February 2002

  [OSPF-TE] Katz, Yeung, Traffic Engineering Extensions to OSPF, draft-
  katz-yeung-ospf-traffic-06.txt, October 2001.

  [ISIS-TE] Smit, Li, IS-IS extensions for Traffic Engineering, draft-
  ietf-isis-traffic-04.txt, October 2001.

  [RSVP-TE] Awduche et al, "RSVP-TE: Extensions to RSVP for LSP
  Tunnels", RFC 3209, December 2001.

  [CR-LDP] Jamoussi et al, "Constraint-Based LSP Setup using LDP", RFC
  32 12, January 2002.

  [DIFF-MPLS] Le Faucheur et al, "MPLS Support of Diff-Serv", draft-
  ietf-mpls-diff-ext-09.txt, April 2001


Authors' Address:

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

  Jim Boyle
  Protocol Driven Networks
  1381 Kildaire Farm Road #288
  Cary, NC 27511
  Phone: +1 919 852-5160
  Email: jboyle@pdnets.com

  Kireeti Kompella
  Juniper Networks, Inc.
  1194 N. Mathilda Ave.
  Sunnyvale, CA 94099
  Email: kireeti@juniper.net

  William Townsend
  Tenor Networks
  100 Nagog Park
  Acton, MA 01720
  Phone: +1-978-264-4900
  Email: btownsend@tenornetworks.com

  Thomas D. Nadeau
  Cisco Systems, Inc.
  250 Apollo Drive
  Chelmsford, MA 01824
  Phone: +1-978-244-3051

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                   Protocols for Diff-Serv-aware TE      February 2002

  Email: tnadeau@cisco.com

  Darek Skalecki
  Nortel Networks
  3500 Carling Ave,
  Nepean K2H 8E9
  Phone: +1-613-765-2252
  Email: dareks@nortelnetworks.com


Appendix A - RSVP Extensions for Diff-Serv-aware TE

  In this section we describe extensions to RSVP for support of
  Diff-Serv-aware MPLS Traffic Engineering. These extensions are in
  addition to the extensions to RSVP defined in [RSVP-TE] for support
  of (aggregate) MPLS Traffic Engineering and to the extensions to RSVP
  defined in [DIFF-MPLS] for support of Diff-Serv over MPLS.

1.      Diff-Serv-aware TE related RSVP Messages Format

  One new RSVP Object is defined in this document: the CLASSTYPE
  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 CLASSTYPE Object in Path messages used to
  establish LSP Tunnels in accordance with [RSVP-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-TE] for support of establishment of LSP
  Tunnels via RSVP are also applicable to the establishment of LSP
  Tunnels supporting Diff-Serv-aware Traffic Engineering. For instance,
  only unicast LSPs are supported and Multicast LSPs are for further
  study.

  This new CLASSTYPE 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.

  An LSR supporting Diff-Serv-aware Traffic Engineering in compliance
  with this specification MUST support the CLASSTYPE Object. It MUST
  support Class-Type value 1, and MAY support other Class-Type values.

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> ]

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                   Protocols for Diff-Serv-aware TE      February 2002

                           [ <DIFFSERV> ]
                           [ <CLASSTYPE> ]
                           [ <POLICY_DATA> ... ]
                           [ <sender descriptor> ]

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

2.      CLASSTYPE Object

  The CLASSTYPE object format is shown below.

2.1.    CLASSTYPE object

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

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


  Reserved : 29 bits
       This field is reserved. It must be set to zero on transmission
       and must be ignored on receipt.

  CT : 3 bits
       Indicates the Class-Type. Values currently allowed are 1, 2, ...
       , 7.


3.      Handling CLASSTYPE Object

  To establish an LSP tunnel with RSVP, the sender LSR creates a Path
  message with a session type of LSP_Tunnel_IPv4 and with a
  LABEL_REQUEST object as per [RSVP-TE]. The sender LSR may also
  include the DIFFSERV object as per [DIFF-MPLS].

  If the LSP is associated with Class-Type 0, the sender LSR must not
  include the CLASSTYPE object in the Path message.

  If the LSP is associated with Class-Type N (1 <= N <=7), the sender
  LSR must include the CLASSTYPE object in the Path message with the
  Class-Type (CT) field set to N.

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


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                   Protocols for Diff-Serv-aware TE      February 2002

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

  If the CLASSTYPE object is not present in the Path message, the LSR
  must associate the Class-Type 0 to the LSP.

  The destination LSR responds to the Path message by sending a Resv
  message without a CLASSTYPE object (whether the Path message
  contained a CLASSTYPE object or not).

  During establishment of an LSP corresponding to the Class-Type N, the
  LSR performs admission control over the bandwidth available for that
  particular Class-Type.

  An LSR that recognizes the CLASSTYPE object and that receives a path
  message which contains the CLASSTYPE object but which does not
  contain a LABEL_REQUEST object or which does not have a session type
  of LSP_Tunnel_IPv4, must send a PathErr towards the sender with the
  error code 'Diff-Serv-aware TE Error' and an error value of
  'Unexpected CLASSTYPE object'. Those are defined below in section 5.

  An LSR receiving a Path message with the CLASSTYPE object, which
  recognizes the CLASSTYPE object but does not support the particular
  Class-Type, must send a PathErr towards the sender with the error
  code 'Diff-Serv-aware TE Error' and an error value of 'Unsupported
  Class-Type'. Those are defined below in section 5.

  An LSR receiving a Path message with the CLASSTYPE object, which
  recognizes the CLASSTYPE object but determines that the Class-Type
  value is not valid (i.e. Class-Type value 0), must send a PathErr
  towards the sender with the error code 'Diff-Serv-aware TE Error' and
  an error value of 'Invalid Class-Type value'. Those are defined below
  in section 5.

  An LSR receiving a Path message with the CLASSTYPE object, which:
        - recognizes the CLASSTYPE object,
        - supports the particular Class-Type, but
        - determines that the tuple formed by (i) this Class-Type and
          (ii) the set-up priority signaled in the same Path message,
          is not one of the eight TE-classes configured in the TE-class
          mapping,
  must send a PathErr towards the sender with the error code 'Diff-
  Serv-aware TE Error' and an error value of 'CT and setup priority do
  not form a configured TE-Class'. Those are defined below in section
  5.

  An LSR receiving a Path message with the CLASSTYPE object, which:
        - recognizes the CLASSTYPE object,
        - supports the particular Class-Type, but
        - determines that the tuple formed by (i) this Class-Type and
          (ii) the holding priority signaled in the same Path message,


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                   Protocols for Diff-Serv-aware TE      February 2002

          is not one of the eight TE-classes configured in the TE-class
          mapping,
  must send a PathErr towards the sender with the error code 'Diff-
  Serv-aware TE Error' and an error value of 'CT and holding priority
  do not form a configured TE-Class'. Those are defined below in
  section 5.

  An LSR MUST handle the situations where the LSP can not be accepted
  for other reasons than those already discussed in this section, in
  accordance with [RSVP-TE] and [DIFF-MPLS] (e.g. a reservation is
  rejected by admission control, a label can not be associated).

4.      Non-support of the CLASSTYPE Object

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

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

  In both situations, this causes the path set-up to fail. The sender
  should notify management that a LSP cannot be established and
  possibly might take action to retry reservation establishment without
  the CLASSTYPE object.

5.      Error Codes For Diff-Serv-aware TE

  In the procedures described above, certain errors must be reported as
  a 'Diff-Serv-aware TE Error'. The value of the 'Diff-Serv-aware TE
  Error' error code is (TBD).

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

     Value    Error

       1       Unexpected CLASSTYPE object
       2       Unsupported Class-Type
       3       Invalid Class-Type value
       4       CT and setup priority do not form a configured TE-Class
       5       CT and holding priority do not form a configured
               TE-Class


Appendix B - CR-LDP Extensions for Diff-Serv-aware TE



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                   Protocols for Diff-Serv-aware TE      February 2002

  CR-LDP, defined in [CR-LDP], is an extension to LDP, defined in
  [LDP], for support of (aggregate) MPLS Traffic Engineering. In this
  section we describe extensions to CR-LDP for support of Diff-Serv-
  aware MPLS Traffic Engineering. These extensions are in addition to
  the extensions to LDP defined in [DIFF-MPLS] for support of Diff-Serv
  over MPLS. They closely resemble the extensions to RSVP defined in
  the previous section.

  Note that extensions of this section for support of Diff-Serv-aware
  Traffic Engineering are not applicable to LDP due to the fact that
  LDP does not support MPLS Traffic Engineering and bandwidth
  reservation in particular.

1.      Diff-Serv-aware TE related CR-LDP Messages Encoding

  One new CR-LDP TLV is defined in this document: the Class Type TLV.
  Detailed description of this TLV is provided below. This new TLV is
  applicable to Label Request messages.

  Restrictions defined in [CR-LDP] for support of establishment of LSPs
  via CR-LDP are also applicable to the establishment of LSPs
  supporting Diff-Serv-aware Traffic Engineering: for instance, only
  unicast LSPs are supported and multicast LSPs are for further study.

  This new Class Type TLV is optional with respect to CR-LDP so that
  general CR-LDP implementations not concerned with Diff-Serv-aware
  Traffic Engineering are not required to support this TLV.

  An LSR supporting Diff-Serv-aware Traffic Engineering in compliance
  with this specification MUST support the Class Type TLV. It MUST
  support Class-Type value 1, and MAY support other Class-Type values.

1.1.    Label Request Message Encoding

  The encoding for the CR-LDP Label Request message is extended as
  follows, to optionally include the Class Type TLV:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|   Label Request (0x0401)   |      Message Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Message ID                                |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     FEC TLV                                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Diff-Serv TLV        (LDP, optional)      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Class Type TLV       (CR-LDP optional)    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Other CR-LDP TLVs                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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                   Protocols for Diff-Serv-aware TE      February 2002



  The extension is based on a related LDP extension, defined in [DIFF-
  MPLS], for support of Diff-Serv TLV but further extended for CR-LDP
  with CR-LDP TLVs.

2.      Class Type TLV

  The Class Type TLV has the following form:
     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|0|        Class Type TLV     |      Length                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        Reserved                                         |  CT |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Reserved : 29 bits
       This field is reserved. It must be set to zero on transmission
       and must be ignored on receipt.

  CT : 3 bits
       Indicates the Class-Type. Values currently allowed are 1, 2, ...
       , 7.

3.      Handling Class Type TLV

  To establish an LSP using CR-LDP, an ingress LSR generates a Label
  Request message as per [CR-LDP]. This Label Request may optionally
  include the Diff-Serv TLV as defined in [DIFF-MPLS] for LDP but
  extended to CR-LDP.

  If the LSP is associated with Class-Type 0, the ingress LSR must not
  include the Class Type TLV in the Label Request message.

  If the LSP is associated with Class-Type N (1 <= N <= 7), the ingress
  LSR must include the Class Type TLV in the Label Request message with
  the Class-Type (CT) field set to N.

  If a Label Request message contains multiple Class Type TLVs, only
  the first one is meaningful; subsequent Class Type TLV(s) must be
  ignored and not forwarded.

  If the Class Type TLV is not present in the Label Request message, an
  LSR must associate the Class-Type 0 to the LSP.

  A downstream LSR sending a Label Mapping message in response to a
  Label Request message must not include the Class-Type TLV (whether
  the Class-Type TLV was included in the Label Request message or not).




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                   Protocols for Diff-Serv-aware TE      February 2002

  During establishment of an LSP corresponding to the Class-Type N, an
  LSR performs admission control over the bandwidth available for that
  particular Class-Type.

  An LSR that recognizes the Class Type TLV and receives a Label
  Request message which contains the Class Type TLV but which does not
  contain any of the CR-LDP TLVs, must reject the label request by
  sending upstream a Notification message which includes the Status TLV
  with a Status Code of 'Unexpected Class-Type TLV'. This is defined
  below in section 4. This error can only occur when an LDP LSP as
  opposed to CR-LDP LSP is being established. As was already mentioned,
  Class Type TLV extension for Diff-Serv-aware Traffic Engineering is
  not applicable to LDP.

  An LSR receiving a Label Request message with the Class Type TLV,
  which recognizes the Class Type TLV but does not support the
  particular Class-Type, must reject the label request by sending
  upstream a Notification message which includes the Status TLV with a
  Status Code of 'Unsupported Class-Type'. This is defined below in
  section 4.

  An LSR receiving a Label Request message with the Class Type TLV,
  which recognizes the Class Type TLV but determines that the Class-
  Type value is not valid (i.e. Class-Type value 0), must reject the
  label request by sending upstream a Notification message which
  includes the Status TLV with a Status Code of 'Invalid Class-Type
  value'. This is defined below in section 4.

  An LSR receiving a Label Request message with the Class Type TLV,
  which:
        - recognizes the Class Type TLV,
        - supports the particular Class-Type, but
        - determines that the tuple formed by (i) this Class-Type and
          (ii) the set-up priority signaled in the same Label Request
          message,  is not one of the eight TE-classes configured in
          the TE-class mapping,
  must reject the label request by sending upstream a Notification
  message which includes the Status TLV with a Status Code of 'CT and
  setup priority do not form a configured TE-Class'. This is defined
  below in section 4.

  An LSR receiving a Label Request message with the Class Type TLV,
  which:
        - recognizes the Class Type TLV,
        - supports the particular Class-Type, but
        - determines that the tuple formed by (i) this Class-Type and
          (ii) the holding priority signaled in the same Label Request
          message,  is not one of the eight TE-classes configured in
          the TE-class mapping,
  must reject the label request by sending upstream a Notification
  message which includes the Status TLV with a Status Code of 'CT and


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                   Protocols for Diff-Serv-aware TE      February 2002

  holding priority do not form a configured TE-Class'. This is defined
  below in section 4.

  An LSR MUST handle the situations where the LSP can not be accepted
  for other reasons than those already discussed in this section, in
  accordance with [CR-LDP], [LDP] and [DIFF-MPLS] (e.g. reservation
  rejected by admission control, a label can not be associated).

4.      Status Code Values for Diff-Serv-aware TE

  In the procedures described above, certain errors must be reported.
  The following values are defined for the Status Code field of the
  Status TLV:

     Status Code                       E       Status Data

     Unexpected Class Type TLV         0       TBD
     Unsupported Class-Type            0       TBD
     Invalid Class-Type value          0       TBD
     CT and setup priority do not      0       TBD
       form a configured TE-Class
     CT and holding priority do not    0       TBD
       form a configured TE-Class'



Appendix C - Example Formulas for Computing "Unreserved TE-Class [i]"

  Keeping in mind that details of admission control algorithms as well
  as formulas for computing "Unreserved TE-Class [i]" are outside the
  scope of this specification, we provide below, for illustration
  purposes, an example of how values for the unreserved bandwidth for
  TE-Class[i] might be computed, assuming:
        - the Russian Doll Bandwidth Constraints Model is used
        - the basic admission control algorithm which simply deducts
          the exact bandwidth of any established LSP from all of the
          Bandwidth Constraints relevant to the CT associated with that
          LSP.
        - the optional per-CT Local Overbooking Multipliers are not
          used (.i.e. LOM[c]=1, 0<= c <=7).

  We assume that:
       TE-Class [i] <--> < CTc , preemption p>
  in the configured TE-Class mapping.

  Let us define "Reserved(CTb,q)" as the sum of the bandwidth reserved
  by all established LSPs which belong to CTb and have a holding
  priority of q. Note that if q and CTb do not form one of the 8
  possible configured TE-Classes, then there can not be any established
  LSP which belong to CTb and have a holding priority of q, so in that
  case Reserved(CTb,q)=0.


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                   Protocols for Diff-Serv-aware TE      February 2002

  For readability, formulas are first shown assuming only 4 CTs are
  active. The formulas below can be extended trivially to cover the
  cases where more CTs are used.

  If CTc = CT0, then "Unreserved TE-Class [i]" =
       [ BC0 - SUM ( Reserved(CTb,q) ) ] for q <= p and 0 <= b <= 3


  If CTc = CT1, then "Unreserved TE-Class [i]" =
       MIN  [
       [ BC1 - SUM ( Reserved(CTb,q) ) ] for q <= p and 1 <= b <= 3,
       [ BC0 - SUM ( Reserved(CTb,q) ) ] for q <= p and 0 <= b <= 3
            ]


  If CTc = CT2, then "Unreserved TE-Class [i]" =
       MIN  [
       [ BC2 - SUM ( Reserved(CTb,q) ) ] for q <= p and 2 <= b <= 3,
       [ BC1 - SUM ( Reserved(CTb,q) ) ] for q <= p and 1 <= b <= 3,
       [ BC0 - SUM ( Reserved(CTb,q) ) ] for q <= p and 0 <= b <= 3
            ]


  If CTc = CT3, then "Unreserved TE-Class [i]" =
       MIN  [
       [ BC3 - SUM ( Reserved(CTb,q) ) ] for q <= p and 3 <= b <= 3,
       [ BC2 - SUM ( Reserved(CTb,q) ) ] for q <= p and 2 <= b <= 3,
       [ BC1 - SUM ( Reserved(CTb,q) ) ] for q <= p and 1 <= b <= 3,
       [ BC0 - SUM ( Reserved(CTb,q) ) ] for q <= p and 0 <= b <= 3
            ]


  The formula can be generalized to 8 active CTs and expressed in a
  more compact way in the following:

        "Unreserved TE-Class [i]" =
       MIN  [
       [ BCc - SUM ( Reserved(CTb,q) ) ] for q <= p and c <= b <= 7,
       . . .
       [ BC0 - SUM ( Reserved(CTb,q) ) ] for q <= p and 0 <= b <= 7,
            ]

  where:
       TE-Class [i] <--> < CTc , preemption p>
  in the configured TE-Class mapping.



Appendix D - Prediction for Multiple Path Computation

  There are situations where a Head-End needs to compute paths for
  multiple LSPs. There are potential advantages for the Head-end in

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                   Protocols for Diff-Serv-aware TE      February 2002

  trying to predict the impact of the n-th LSP on the unreserved
  bandwidth when computing the path for the (n+1)-th LSP, before
  receiving updated IGP information. One example would be to perform
  better load-distribution of the multiple LSPs across multiple paths.
  Another example would be to avoid CAC rejection when the (n+1)-th LSP
  would no longer fit on a link after establishment of the n-th LSP.
  While there are also a number of conceivable scenarios where doing
  such predictions might result in a worse situation, it is more likely
  to improve the situation. As a matter of fact, a number of network
  administrators have elected to use such predictions when deploying
  existing TE.

  Such predictions are local matters, are optional and are outside the
  scope of this specification.

  Where such predictions are not used, the optional Bandwidth
  Constraint sub-TLV and the optional Local Overbooking Multiplier sub-
  TLV need not be advertised in IGP since the information contained in
  the Unreserved Bw sub-TLV is all that is required by Head-Ends to
  perform Constraint Based Routing.

  Where such predictions are used on Head-Ends, the optional Bandwidth
  Constraint sub-TLV (and the optional Local Overbooking Multiplier
  sub-TLV if different overbooking ratios need to be supported on
  different links) may be advertised in IGP. This is in order for the
  Head-ends to predict as accurately as possible how an LSP affects
  unreserved bandwidth values for subsequent LSPs.

  Remembering that actual admission control algorithms are left for
  vendor differentiation, we observe that predictions may only be used
  effectively when the Head-end LSR predictions are based on the same
  (or a very close) admission control algorithm as used by other LSRs.


Appendix E - Addressing [DSTE-REQ] Scenarios

  This Appendix provides examples of how the DS-TE solution can be used
  to support each of the scenario described in [DSTE-REQ].

1.      Scenario 1: Limiting Amount of Voice

  By configuring on every link:
        - Bandwidth Constraint 1 (for CT1=Voice) = "certain percentage"
          of link capacity
        - BC0= Max Reservable Link Bandwidth =  link capacity

  By configuring:
        - every CT1/Voice TE-LSP with preemption =0
        - every CT0/Data TE-LSP with preemption =1

  The proposed solution will address all the requirements:


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                   Protocols for Diff-Serv-aware TE      February 2002

        - amount of Voice traffic limited to desired percentage on
          every link
        - data traffic capable of using all remaining link capacity
        - voice traffic capable of preempting other traffic

2.      Scenario 2: Maintain Relative Proportion of Traffic Classes

  By configuring on every link:
        - BC2 for CT2 = e.g. 45%
        - BC1 for CT1+CT2 = e.g. 80%
        - BC0 for CT0+CT1+CT2= e.g.100%

  The proposed DS-TE solution will ensure that the amount of traffic of
  each Class Type established on a link is within acceptable levels as
  compared to the resources allocated to the corresponding Diff-Serv
  PHBs regardless of which order the LSPs are routed in, regardless of
  which preemption priorities are used by which LSPs and regardless of
  failure situations. Optional automatic adjustment of Diff-Sev
  scheduling configuration could be used for maintaining very strict
  relationship between amount of established traffic of each Class Type
  and corresponding Diff-Serv resources.

3.      Scenario 3: Guaranteed Bandwidth Services

  By configuring on every link:
        - BC1 for CT1 = "given" percentage of bandwidth (appropriate to
          achieve the Guaranteed Bandwidth service's QoS objectives)
        - BC0 for CT0+CT1 = 100%

  The proposed DS-TE solution will ensure that the amount of Guaranteed
  Bandwidth Trafic established on every link remains below the given
  percentage so that it will always meet its QoS objectives. AT the
  same time it will allow traffic engineering of the rest of the
  traffic such that links can be filled up.


Appendix F - Solution Evaluation

1.      Satisfying Detailed Requirements

  This DS-TE Solution address all the scenarios presented in [DSTE-REQ]
  as explained in Appendix E. It also satisfy all the detailed
  requirements presented in [DSTE-REQ].

2.      Flexibility

  This DS-TE solution supports 8 CTs. It is entirely flexible as to how
  Traffic Trunks are grouped together into a CT.

3.      Extendibility



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                   Protocols for Diff-Serv-aware TE      February 2002

  A maximum of 8 CTs is considered by the authors of this document as
  more than comfortable. However, this solution could be extended to
  support more CTs if deemed necessary in the future. However, this
  would necessitate additional IGP extensions beyond those specified in
  this document.

4.      Scalability

  This DS-TE solution is expected to have a very small scalability
  impact compared to existing TE.

  From an IGP viewpoint, the amount of mandatory information to be
  advertised is identical to existing TE. Two additional sub-TLVs have
  been specified, but their use is optional and those contained a
  limited amount of static information (at most 8 Bandwidth Constraints
  and 8 LOMs).

  We expect no noticeable impact on LSP Path computation since, as with
  existing TE, this solution only require CSPF to consider a single
  unreserved bandwidth value for any given LSP.

  From a signaling viewpoint we expect no significant impact due to
  this solution since it only requires processing of one additional
  information (the Class-Type) and does not significantly increase the
  likelihood of CAC rejection. Note that DS-TE has some inherent impact
  on LSP signaling in the sense that it assumes that different classes
  of traffic are split over different LSPs so that more LSPs need to be
  signaled; but this is due to the DS-TE concept itself and not to the
  actual DS-TE solution discussed here.

5.      Backward Compatibility/Migration

  This solution is expected to allow smooth migration from existing TE
  to DS-TE. This is because existing TE can be supported exactly as
  today as a particular configuration of DS-TE. This means that an
  "upgraded" LSR with a DS-TE implementation can directly interwork
  with an "old" LSR supporting existing TE only.

  This solution is expected to allow smooth migration when increasing
  the number of CTs actually deployed since it only requires
  configuration changes. however, these changes must be performed in a
  coordinated manner across the DS-TE domain.











 Le Faucheur et. al                                                 28


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