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Versions: 00 01 02 03 04 05 06 07 rfc4127                               
                                            Francois Le Faucheur, Editor
                                                     Cisco Systems, Inc.



IETF Internet Draft
Expires: April, 2002
Document: draft-ietf-tewg-diff-te-russian-00.txt         October, 2002



             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.


Abstract

  This document provides a detailed description of a candidate
  Bandwidth Constraints model for Diff-Serv-aware MPLS Traffic
  Engineering, which is referred to as the Russian Dolls model.


Summary for Sub-IP related Internet Drafts

  RELATED DOCUMENTS:
  draft-ietf-tewg-diff-te-reqts-06.txt
  draft-ietf-tewg-diff-te-proto-02.txt

  WHERE DOES IT FIT IN THE PICTURE OF THE SUB-IP WORK
  This ID is a Working Group document of the TE Working Group.

  WHY IS IT TARGETED AT THIS WG(s)
  TEWG is responsible for specifying protocol extensions for support of
  Diff-Serv-aware MPLS Traffic Engineering.

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                    Russian Dolls model for DS-TE        October 2002


  JUSTIFICATION
  The TEWG charter states that "This will entail verification and
  review of the Diffserv requirements in the WG Framework document and
  initial specification of how these requirements can be met through
  use and potentially expansion of existing protocols."
  In line with this, the TEWG is in the process of selecting bandwidth
  constraints model for Diff-Serv-aware MPLS Traffic Engineering. This
  document describes one bandwidth constraints model under
  consideration.


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 Constraint Models
  for DS-TE and states that "The DS-TE technical solution must specify
  one default bandwidth constraint model which must be supported by any
  DS-TE implementation. However, additional bandwidth constraint models
  may also be specified."

  This document provides a more detailed description of one particular
  Bandwidth Constraint model introduced in [DSTE-REQ] which is called
  the Russian Dolls model. The Russian Dolls model is one of the
  candidate models under consideration by the TEWG for selection of the
  default bandwidth constraints model and/or of optional additional
  models.

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

  Considerations on the Russian Dolls model are provided in [RUSSIAN-
  CONS] and [BCMODEL].


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

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                    Russian Dolls model for DS-TE        October 2002


  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

  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.


4.      Russian Dolls Model Definition

  The "Russian Dolls" model is defined in the following manner
  (assuming for now that the optional per-CT Local Overbooking
  Multipliers defined in [DSTE-PROTO] are not used - i.e. LOM[c]=1 ,
  0<=c<=7 ):
             o Maximum Number of Bandwidth Constraints (MaxBC)= Maximum
               Number of Class-Types (MaxCT) = 8
             o All LSPs supporting Traffic Trunks from CTc (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

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                    Russian Dolls model for DS-TE        October 2002


  Purely for illustration purposes, the diagram below represents the
  Russian Doll 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------>


  While simpler or, conversely, 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
          basic Maximum Allocation model consisting of a single
          independent BC per CT (which, in typical deployment scenarios
          may result in either capacity 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] as
          illustrated in Appendix A below).
       - it remains simple and only requires limited protocol
          extensions, while more sophisticated Bandwidth Constraints
          model may require more complex extensions.

  More details on the properties of the Russian Dolls model can be
  found in [RUSSIAN-CONS] and [BCMODEL].

  As a simple example usage 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:
        - BC0 = 2.5 Gb/s (i.e. Voice + Data is limited to 2.5 Gb/s)
        - 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.


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                    Russian Dolls model for DS-TE        October 2002

  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 the Russian Dolls model, 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.
        - 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.

  For readability, formulas are first shown assuming only 4 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 <= 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,

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                    Russian Dolls model for DS-TE        October 2002

       [ 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.


6.      Support of Optional Local Overbooking Method

  We remind the reader that, as discussed in [DSTE-PROTO], the
  "LSP/link size overbooking" method (which does not use the Local
  Overbooking Multipliers - LOMs-) is expected to be sufficient in many
  DS-TE environments. It is expected that the optional Local
  Overbooking method (and LOMs) would only be used in specific
  environments, in particular where different overbooking ratios need
  to be enforced on different links of the DS-TE domain and cross-
  effect of overbooking across CTs needs to be accounted for very
  accurately.

  This section discusses the impact of the optional local overbooking
  method on the Russian Dolls model and associated rules and formula.
  This is only applicable in the cases where the optional local
  overbooking method is indeed supported by the DS-TE LSRs and actually
  deployed.

6.1.    Russian Dolls Model Definition With Local Overbooking

  Let us define "Reserved(CTc)" as the sum of the bandwidth reserved by
  all established LSPs which belong to CTc.

  Let us define "Normalised(CTc)" as "Reserved(CTc)/LOM(c)".

  As specified in [DSTE-PROTO], when the optional Local Overbooking
  method is supported, the bandwidth constraints MUST be applied to
  "Normalised(CTc)" rather than to "Reserved(CTc)". Thus, when the
  optional Local Overbooking method is supported, the "Russian Doll"
  model definition MUST be extended in the following manner:
        - Maximum Number of Bandwidth Constraints (MaxBC)= Maximum
          Number of Class-Types (MaxCT) = 8
        - SUM [ Normalised(CTc), for b<=c<=7 ] <= BCb i.e.:

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                    Russian Dolls model for DS-TE        October 2002

              o [ Normalised(CT7) ] <= BC7
              o [ Normalised(CT6) + Normalised(CT7) ] <= BC6
              o [ Normalised(CT5) + Normalised(CT6) +
                  Normalised(CT7) ] <= BC5
              o etc.
              o [ Normalised(CT0) + Normalised(CT1) +
                  ...
                  Normalised(CT6) + Normalised(CT7) ] <= BC0

  Purely for illustration purposes, the diagram below represents the
  Russian Doll Bandwidth Constraints model in a pictorial manner when 3
  Class-Types are active and the local overbooking method is used:

  I--------------------------------------------------------------I
  I-----------------------------------------I  Normalised(CT2)   I
  I--------------------I  Normalised(CT2)   I       +            I
  I  Normalised(CT2)   I        +           I  Normalised(CT1)   I
  I--------------------I  Normalised(CT1)   I       +            I
  I-----------------------------------------I  Normalised(CT0)   I
  I--------------------------------------------------------------I

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


6.2.    Example Formulas for Computing "Unreserved TE-Class [i]" With
    Local Overbooking

  Again, keeping in mind 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 the Russian Dolls
  model, 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.
        - the optional per-CT Local Overbooking Multipliers are used.

  When the optional local overbooking method is supported, the example
  generalized formula of section 5 becomes:

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

  where:

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                    Russian Dolls model for DS-TE        October 2002

        - TE-Class [i] <--> < CTc , preemption p>
          in the configured TE-Class mapping.
        - Normalised(CTb,q) = Reserved(CTb/q)/LOM(b)


6.3.    Example Usage of LOM

  To illustrate usage of the local overbooking method with the Russian
  Dolls model, let's consider a DS-TE deployment where two CTs (CT0 for
  data and CT1 for voice) and a single preemption priority are used.

  The TE-Class mapping is the following:

       TE-Class  <-->  CT, preemption
       ==============================
           0           CT0, 0
           1           CT1, 0
           rest         unused

  Let's assume that on a given link, BCs and LOMs are configured in the
  following way:
       BC0 = 200
       BC1 = 100
       LOM(0) = 4  (i.e. = 400%)
       LOM(1) = 2  (i.e. = 200%)

  Let's further assume that the DS-TE LSR uses the example formulas
  presented above for computing unreserved bandwidth values.

  If there is no established LSP on the considered link, the LSR will
  advertise for that link in IGP :
          Unreserved TE-Class [0] = 4 x (200 - 0/4 - 0/2 )= 800
          Unreserved TE-Class [1] = 2 x (100- 0/2) = 200
  Note again that these values advertised for Unreserved Bandwidth are
  larger than BC1 and BC0.

  If there is only a single established LSP, with CT=CT0 and BW=100,
  the LSR will advertise:
          Unreserved TE-Class [0] = 4 x (200 - 100/4 - 0/2 )=700
          Unreserved TE-Class [1] = 2 x (100- 0/2) = 200

  If there is only a single established LSP, with CT=CT1 and BW=100,
  the LSR will advertise:
          Unreserved TE-Class [0] = 4 x (200 - 0/4 - 100/2 )= 600
          Unreserved TE-Class [1] = 2 x (100- 100/2) = 100
  Note that the impact of an LSP on the unreserved bandwidth of a CT
  does not depend only on the LOM for that CT: it also depends on the
  LOM for the CT of the LSP. This can be seen in our example. A BW=100
  tunnel affects Unreserved
  CT0 twice as much if it is a CT1 tunnel, than if it is a CT0 tunnel.
  It reduces Unreserved CTO by 200 (800->600) rather than by 100
  (800->700). This is because LOM(1) is half as big as LOM(0). This

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                    Russian Dolls model for DS-TE        October 2002

  illustrates why the local overbooking method allows very fine
  accounting of cross-effect of overbooking across CTs, as compared
  with the LSP/link size overbooking method.

  If there are two established LSPs, one with CT=CT1 and BW=100 and one
  with CT=CT0 and BW=100, the LSR will advertise:
       Unreserved TE-Class [0] = 4 x (200 - 100/4 - 100/2) = 500
       Unreserved TE-Class [1] = 2 x (100 - 100/2) = 100

  If there are two LSPs established, one with CT=CT1 and BW=100, and
  one with CT=CT0 and BW=480, the LSR will advertise:
          Unreserved TE-Class [0] = 4 x (200 - 480/4 - 100/2) = 120
          Unreserved TE-Class [1] = 2 x MIN [ (200 - 480/4 - 100/2),
                                               (100 - 100/2) ]
                                  = 2 x MIN [ 30, 50 ]
                                  = 60


7.      Security Considerations

  No new security considerations are raised by this document; they are
  the same as in the DS-TE requirements document [DSTE-REQ].


8.      Acknowledgments

  We thank Martin Tatham for his earlier contribution in this work.


9.      Normative References

  [DSTE-REQ] Le Faucheur et al, Requirements for support of Diff-Serv-
  aware MPLS Traffic Engineering, draft-ietf-tewg-diff-te-reqts-06.txt,
  September 2002.

  [DSTE-PROTO] Le Faucheur et al, Protocol extensions for support of
  Diff-Serv-aware MPLS Traffic Engineering, draft-ietf-tewg-diff-te-
  proto-02.txt, October 2002.


10.     Informative References

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

  [BCMODEL] Lai, "Bandwidth Constraints Models for DS-TE",
  draft-wlai-tewg-bcmodel-00.txt, June 2002.

  [OSPF-TE] Katz, Yeung, Traffic Engineering Extensions to OSPF, draft-
  katz-yeung-ospf-traffic-08.txt, September 2002.


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                    Russian Dolls model for DS-TE        October 2002

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

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

  [DIFF-MPLS] Le Faucheur et al, "MPLS Support of Diff-Serv", RFC3270,
  May 2002.


11.     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


Appendix A - Addressing [DSTE-REQ] Scenarios

  This Appendix provides examples of how the Russian Dolls Model
  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%
        - BC1 (for CT1+CT2) = e.g. 80%
        - BC0 (for CT0+CT1+CT2) = e.g.100%


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                    Russian Dolls model for DS-TE        October 2002

  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. 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 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 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.






























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