Francois Le Faucheur, Editor
                                                     Cisco Systems, Inc.



IETF Internet Draft
Expires: March, 2004
Document: draft-ietf-tewg-diff-te-russian-05.txt        January, 2004



             Russian Dolls Bandwidth Constraints Model for
                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
  distribute working documents as Internet-Drafts.

  Internet-Drafts are draft documents valid for a maximum of six months
  and may be updated, replaced, or obsoleted by other documents 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.


Copyright Notice

  Copyright (C) The Internet Society (2004).  All Rights Reserved.


Abstract

  This document provides specification for one Bandwidth Constraints
  Model for Diff-Serv-aware MPLS Traffic Engineering, which is referred
  to as the Russian Dolls Model.


Specification of Requirements

  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
  "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
  document are to be interpreted as described in [RFC2119].



Le Faucheur, et. al                                                  1

                    Russian Dolls Model for DS-TE        January 2004

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.

  [DSTE-REQ] also defines the concept of Bandwidth Constraints Model
  for DS-TE and states that “The DS-TE technical solution MUST specify
  at least one Bandwidth Constraints Model and MAY specify multiple
  Bandwidth Constraints Models.”

  This document provides a detailed description of one particular
  Bandwidth Constraints Model for DS-TE which is introduced in [DSTE-
  REQ] and called the Russian Dolls Model (RDM).

  [DSTE-PROTO] specifies the IGP and RSVP-TE signaling extensions for
  support of DS-TE. These extensions support RDM.


2.      Contributing Authors

  This document was the collective work of several. The text and
  content of this document was contributed by the editor and the co-
  authors listed below. (The contact information for the editor appears
  in Section 11, and is not repeated below.)

  Jim Boyle                            Kireeti Kompella
  Protocol Driven Networks, Inc.       Juniper Networks, Inc.
  1381 Kildaire Farm Road #288         1194 N. Mathilda Ave.
  Cary, NC 27511, USA                  Sunnyvale, CA 94099
  Phone: (919) 852-5160                Email: kireeti@juniper.net
  Email: jboyle@pdnets.com

  William Townsend                     Thomas D. Nadeau
  Tenor Networks                       Cisco Systems, Inc.
  100 Nagog Park                       250 Apollo Drive
  Acton, MA 01720                      Chelmsford, MA 01824
  Phone: +1-978-264-4900               Phone: +1-978-244-3051
  Email:                               Email: tnadeau@cisco.com
  btownsend@tenornetworks.com

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



3.      Definitions

 Le Faucheur et. al                                                  2

                    Russian Dolls Model for DS-TE        January 2004


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

  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.

  A number of recovery mechanisms under investigation or specification
  in the IETF take advantage of the concept of bandwidth sharing across
  particular sets of LSPs. “Shared Mesh Restoration” in [GMPLS-RECOV]
  and “Facility-based Computation Model” in [MPLS-BACKUP] are example
  mechanisms which increase bandwidth efficiency by sharing bandwidth
  across backup LSPs protecting against independent failures. To ensure
  that the notion of “Reserved (CTc)” introduced in [DSTE-REQ] is
  compatible with such a concept of bandwidth sharing across multiple
  LSPs, the wording of the “Reserved (CTc)” definition provided in
  [DSTE-REQ] is generalized into the following:

  Reserved (CTc): For a given Class-Type CTc ( 0 <= c <= MaxCT ) ,let
  us define "Reserved(CTc)" as the total amount of the bandwidth
  reserved by all the established LSPs which belong to CTc.

  With this generalization, the Russian Dolls Model definition provided
  in this document is compatible with Shared Mesh Restoration defined
  in [GMPLS-RECOV], so that DS-TE and Shared Mesh Protection can
  operate simultaneously, under the assumption that Shared Mesh
  Restoration operates independently within each DS-TE Class-Type and
  does not operate across Class-Types (for example back up
  LSPs protecting Primary LSPs of CTx must also belong to CTx; Excess
  Traffic LSPs sharing bandwidth with Backup LSPs of CTx must also
  belong to CTx).

  We also introduce the following definition:

  Reserved(CTb,q) : let us define “Reserved(CTb,q)” as the total amount
  of the bandwidth reserved by all the 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.



 Le Faucheur et. al                                                  3

                    Russian Dolls Model for DS-TE        January 2004

4.      Russian Dolls Model Definition

  RDM is defined in the following manner:
             o Maximum Number of Bandwidth Constraints (MaxBC)=
               Maximum Number of Class-Types (MaxCT) = 8
             o for each value of b in the range 0 <= b <= (MaxCT - 1):
                    SUM (Reserved (CTc)) <= BCb,
                    Where the SUM is across all values of c in the
                    range b <= c <= (MaxCT - 1)
            o BC0= Maximum Reservable Bandwidth, so that
                    SUM (Reserved(CTc)) <= Max-Reservable-Bw,
                     where the SUM is across all values of c in the
                     range  0 <= c <= (MaxCT - 1)

  A DS-TE LSR implementing RDM MUST support enforcement of Bandwidth
  Constraints in compliance with this definition.

  Both preemption within a Class-Type and across Class-Types is
  allowed.

  Where 8 Class-Types are active, the RDM Bandwidth Constraints can
  also be expressed in the following way:
        - 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 = “Maximum Reservable Bandwidth”

























 Le Faucheur et. al                                                  4

                    Russian Dolls Model for DS-TE        January 2004


  Purely for illustration purposes, the diagram below represents the
  Russian Dolls Bandwidth Constraints Model in a pictorial manner when
  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=Max Reservable Bw--->


  While simpler Bandwidth Constraints models or, conversely, more
  flexible/sophisticated Bandwidth Constraints models can be defined,
  the Russian Dolls Model is attractive in some DS-TE environments for
  the following reasons:
       -         Although a little less intuitive than the Maximum Allocation
          Model (see[DSTE-MAM]), RDM is still a simple model to
          conceptualize.
       -         RDM can be used to simultaneously ensure bandwidth efficiency
          and protection against QoS degradation of all Class-Types,
          whether preemption is used or not.
       -         RDM can be used in conjunction with preemption to
          simultaneously achieve isolation across Class-Types (so that
          each Class-Type is guaranteed its share of bandwidth no
          matter the level of contention by other classes), bandwidth
          efficiency and protection against QoS degradation of all
          Class-Types.
       -         RDM only requires limited protocol extensions such as the
          ones defined in [DSTE-PROTO].

  RDM may not be attractive in some DS-TE environments for the
  following reasons:
       -         if the usage of preemption is precluded for some
          administrative reason, while RDM can still ensure bandwidth
          efficiency and protection against QoS degradation of all CTs,
          RDM cannot guarantee isolation across Class-Types.

  Additional considerations on the properties of RDM can be found in
  [BC-CONS] and [BC-MODEL].

  As a simple example usage of the “Russian Dolls” Bandwidth
  Constraints Model, a network administrator using one CT for Voice
  (CT1) and one CT for data (CT0) might configure on a given link:
        -
          limited to 2.5 Gb/s)

 Le Faucheur et. al                                                  5

                    Russian Dolls Model for DS-TE        January 2004

        -         BC1= 1.5 Gb/s (i.e. Voice is limited to 1.5 Gb/s).


5.      Example Formulas for Computing “Unreserved TE-Class [i]” with
   Russian Dolls Model

  As specified in [DSTE-PROTO], formulas for computing “Unreserved TE-
  Class [i]” MUST reflect all of the Bandwidth Constraints relevant to
  the CT associated with TE-Class[i], and thus, depend on the Bandwidth
  Constraints Model. Thus, a DS-TE LSR implementing RDM MUST reflect
  the RDM Bandwidth Constraints defined in section 4 above when
  computing “Unreserved TE-Class [i]”.

  Keeping in mind, as explained in [DSTE-PROTO], that details of
  admission control algorithms as well as formulas for computing
  “Unreserved TE-Class [i]” are outside the scope of the IETF work, we
  provide in this section, for illustration purposes, an example of how
  values for the unreserved bandwidth for TE-Class[i] might be computed
  with RDM, assuming 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.

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

  For readability, formulas are first shown assuming only 3 CTs are
  active. The formulas are then extended 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 <= 2


  If CTc = CT1, then “Unreserved TE-Class [i]” =
       MIN  [
       [ BC1 - SUM ( Reserved(CTb,q) ) ] for q <= p and 1 <= b <= 2,
       [ BC0 – SUM ( Reserved(CTb,q) ) ] for q <= p and 0 <= b <= 2
            ]


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


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


 Le Faucheur et. al                                                  6

                    Russian Dolls Model for DS-TE        January 2004

    “Unreserved TE-Class [i]” =
     MIN  [
   [ BCc - SUM ( Reserved(CTb,q) ) ] for q <= p and c <= b <= 7,
   [ BC(c-1) - SUM ( Reserved(CTb,q) ) ] for q <= p and (c-1)<= 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.


6.      Receiving both Maximum Reservable Bandwidth and Bandwidth
   Constraints sub-TLVs

  [DSTE-PROTO] states that
  " A DS-TE LSR which does advertise Bandwidth Constraints MUST use the
  new “Bandwidth Constraints” sub-TLV (in addition to the existing
  Maximum Reservable Bandwidth sub-TLV) to do so."

  With RDM, BC0 is equal to the Maximum Reservable Bandwidth since they
  both represent the aggregate constraint across all Class-Types. Thus,
  a DS-TE LSR receiving both the "Maximum Reservable Bw" sub-TLV and
  the new "Bandwidth Constraints" sub-TLV (which contains BC0) for a
  given link where the RDM model is used, MAY ignore the "Maximum
  Reservable Bw" sub-TLV.


7.      Security Considerations

  Security considerations related to the use of DS-TE are discussed in
  [DSTE-PROTO]. Those apply independently of the Bandwidth Constraints
  Model, including RDM specified in this document.


8.      Acknowledgments

  We thank Martin Tatham for his key contribution in this work. Tatiana
  Renko is also warmly thanked for her instantiation of the Russian
  Doll.


9.      IANA Considerations

  [DSTE-PROTO] defines a new name space for "Bandwidth Constraints
  Model Id". The guidelines for allocation of values in that name space
  are detailed in section 14 of [DSTE-PROTO]. In accordance with these
  guidelines, IANA was requested to assign a Bandwidth Constraints
  Model Id for RDM from the range 0-127 (which is to be managed as per
  the "Specification Required" policy defined in [IANA-CONS]).

  Bandwidth Constraints Model Id = TBD was allocated by IANA to RDM.

 Le Faucheur et. al                                                  7

                    Russian Dolls Model for DS-TE        January 2004


  <IANA-note> To be removed by the RFC editor at the time of
  publication
       We request IANA to assign value 0 for the RDM model.
       Once the value has been assigned, please replace “TBD” above
        by the assigned value.
  </IANA-note>


10.     Normative References

  [DSTE-REQ] Le Faucheur et al, Requirements for support of Diff-Serv-
  aware MPLS Traffic Engineering, RFC3564.

  [DSTE-PROTO] Le Faucheur et al, Protocol extensions for support of
  Diff-Serv-aware MPLS Traffic Engineering, draft-ietf-tewg-diff-te-
  proto-06.txt, work in progress.

  [RFC2119] S. Bradner, Key words for use in RFCs to Indicate
  Requirement Levels, RFC2119, March 1997.

  [IANA-CONS], T. Narten et al, “Guidelines for Writing an IANA
  Considerations Section in RFCs”, RFC2434.


11.     Informative References

  [BC-CONS] Le Faucheur, “Considerations on Bandwidth Constraints Model
  for DS-TE”, draft-lefaucheur-tewg-russian-dolls-00.txt, June 2002.

  [BC-MODEL] Lai, “Bandwidth Constraints Models for DS-TE”,
  draft-wlai-tewg-bcmodel-03.txt,  work in progress.

  [DSTE-MAM] Le Faucheur, Lai, “Maximum Allocation Bandwidth
  Constraints Model for Diff-Serv-aware MPLS Traffic Engineering”,
  draft-ietf-tewg-diff-tet-mam-02.txt, work in progress.

  [DSTE-MAR] Ash, “Max Allocation with Reservation Bandwidth
  Constraints Model for MPLS/DiffServ TE & Performance Comparisons”,
  work in progress.

  [OSPF-TE] Katz et al., “Traffic Engineering (TE) Extensions to OSPF
  Version 2”, RFC3630.

  [ISIS-TE] Smit et al., “IS-IS extensions for Traffic Engineering”,
  draft-ietf-isis-traffic-05.txt, work in progress.

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

  [DIFF-MPLS] Le Faucheur et al, "MPLS Support of Diff-Serv", RFC3270.


 Le Faucheur et. al                                                  8

                    Russian Dolls Model for DS-TE        January 2004

  [GMPLS-RECOV] Lang et al, “Generalized MPLS Recovery Functional
  Specification”, draft-ietf-ccamp-gmpls-recovery-functional-02.txt,
  work in progress.

  [MPLS-BACKUP] Vasseur et al, “MPLS Traffic Engineering Fast reroute:
  bypass tunnel path computation for bandwidth protection”, draft-
  vasseur-mpls-backup-computation-02.txt, work in progress.


12.        Intellectual Property Considerations


  The IETF takes no position regarding the validity or scope of any
  intellectual property or other rights that might be claimed to
  pertain to the implementation or use of the technology described in
  this document or the extent to which any license under such rights
  might or might not be available; neither does it represent that it
  has made any effort to identify any such rights.  Information on the
  IETF's procedures with respect to rights in standards-track and
  standards-related documentation can be found in RFC 2028.  Copies of
  claims of rights made available for publication and any assurances of
  licenses to be made available, or the result of an attempt made to
  obtain a general license or permission for the use of such
  proprietary rights by implementors or users of this specification can
  be obtained from the IETF Secretariat.

  The IETF invites any interested party to bring to its attention any
  copyrights, patents or patent applications, or other proprietary
  rights which may cover technology that may be required to practice
  this standard.  Please address the information to the IETF Executive
  Director.


13.     Editor's 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


14.     Full Copyright Statement

  Copyright (C) The Internet Society (2004).  All Rights Reserved.

  This document and translations of it may be copied and furnished to
  others, and derivative works that comment on or otherwise explain it
  or assist in its implementation may be prepared, copied, published
  and distributed, in whole or in part, without restriction of any


 Le Faucheur et. al                                                  9
                    Russian Dolls Model for DS-TE        January 2004

  kind, provided that the above copyright notice and this paragraph are
  included on all such copies and derivative works.  However, this
  document itself may not be modified in any way, such as by removing
  the copyright notice or references to the Internet Society or other
  Internet organizations, except as needed for the purpose of
  developing Internet standards in which case the procedures for
  copyrights defined in the Internet Standards process must be
  followed, or as required to translate it into languages other than
  English.

  The limited permissions granted above are perpetual and will not be
  revoked by the Internet Society or its successors or assigns.

  This document and the information contained herein is provided on an
  "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
  TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
  BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
  HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
  MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Appendix A – Addressing [DSTE-REQ] Scenarios

  This Appendix provides examples of how the Russian Dolls Bandwidth
  Constraints Model can be used to support each of the scenarios
  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 (for CT1=Voice + CT0= Data) =  link capacity

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

  DS-TE with the Russian Dolls Model will address all the requirements:
        -         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%
        -         BC0 (for CT0+CT1+CT2) = e.g.100%



 Le Faucheur et. al                                                 10

                    Russian Dolls Model for DS-TE        January 2004

  DS-TE with the Russian Dolls Model 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.

  By also configuring:
        -         every CT2/Voice TE-LSP with preemption =0
        -         every CT1/Premium Data TE-LSP with preemption =1
        -         every CT0/Best-Effort TE-LSP with preemption =2

  DS-TE with the Russian Dolls Model will also ensure that:
        -         CT2 Voice LSPs always have first preemption priority in order
          to use the CT2 capacity
        -         CT1 Premium Data LSPs always have second preemption priority
          in order to use the CT1 capacity
        -         Best-Effort can use up to link capacity whatever is left by
          CT2 and CT1.

  Optional automatic adjustment of Diff-Serv 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 link bandwidth
          (appropriate to achieve the Guaranteed Bandwidth service’s
          QoS objectives)
        -         BC0 (for CT0+CT1) = 100% of link bandwidth

  DS-TE with the Russian Dolls Model will ensure that the amount of
  Guaranteed Bandwidth Traffic 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.










 Le Faucheur et. al                                                 11