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Versions: 00 01 02 03 04 RFC 4125

  TEWG
  Internet Draft                               Francois Le Faucheur
                                               Cisco Systems, Inc.
                                                       Waisum Lai
                                                        AT&T Labs
  draft-ietf-tewg-diff-te-mam-04.txt
  Expires: June 2005                                 December 2004


         Maximum Allocation Bandwidth Constraints Model for
               Diff-Serv-aware MPLS Traffic Engineering


Status of this Memo

  This document is an Internet-Draft and is subject to all provisions
  of section 3 of RFC 3667. By submitting this Internet-Draft, each
  author represents that any applicable patent or other IPR claims of
  which he or she is aware have been or will be disclosed, and any of
  which he or she become aware will be disclosed, in accordance with
  RFC 3668.

  Internet-Drafts are working documents of the Internet Engineering
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  This Internet-Draft will expire on June 13, 2005.


Copyright Notice

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


Abstract



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


Table of Contents

  1. Introduction...................................................2
  2. Definitions....................................................3
  3. Maximum Allocation Model Definition............................4
  4. Example Formulas for Computing "Unreserved TE-Class [i]" with
  Maximum Allocation Model..........................................6
  5. Security Considerations........................................7
  6. Acknowledgments................................................7
  7. Intellectual Property Considerations...........................7
  8. IANA Considerations............................................8
  9. Normative References...........................................8
  10. Informative References........................................9
  11. Authors' Address:.............................................9
  12. Full Copyright Statement.....................................10
  Appendix A - Addressing [DSTE-REQ] Scenarios.....................10
  Disclaimer of Validity...........................................12
  Copyright Statement..............................................12
  Acknowledgment...................................................12


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 Maximum Allocation Model (MAM).



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


2.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    Formatted:
                                                                    Bullets and
              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 Maximum Allocation 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 need to also belong to CTx;
  Excess Traffic LSPs sharing bandwidth with Backup LSPs of CTx need to
  also belong to CTx).

  We also introduce the following definition:


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  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.


3.Maximum Allocation Model Definition

  MAM 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 c in the range 0 <= c <= (MaxCT - 1):
            Reserved (CTc) <= BCc <= Max-Reservable-Bandwidth,
       o SUM (Reserved(CTc)) <= Max-Reservable-Bandwidth
            where the SUM is across all values of c in the range
            0 <= c <= (MaxCT - 1)


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


  To increase the degree of bandwidth sharing among the different CTs,
  the sum of Bandwidth Constraints may exceed the Maximum Reservable
  Bandwidth, so that the following relationship may hold true:
           o SUM (BCc) > Max-Reservable-Bandwidth,
              where the SUM is across all values of c in the range
              0 <= c <= (MaxCT - 1)

  The sum of Bandwidth Constraints may also be equal to (or below) the
  Maximum Reservable Bandwidth. In that case, the Maximum Reservable
  Bandwidth does not actually constrain CT bandwidth reservations (in
  other words, the 3rd bullet item of the MAM definition above will
  never effectively come into play). This is because the 2nd bullet
  item of the MAM definition above implies that:
      SUM (reserved(CTc)) <= SUM (BCc)
  and we assume here that
      SUM (BCc) <= Maximum Reservable Bandwidth
  therefore, it will always be true that:
      SUM (Reserved(CTc)) <= Max-Reservable-Bandwidth.


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




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  Where 8 Class-Types are active, the MAM Bandwidth Constraints can
  also be expressed in the following way:
       - All LSPs from CT7 use no more than BC7
       - All LSPs from CT6 use no more than BC6
       - All LSPs from CT5 use no more than BC5
       - etc.
       -
        All LSPs from CT0 use no more than BC0
       -
        All LSPs from all CTs collectively use no more than the
         Maximum Reservable Bandwidth

  Purely for illustration purposes, the diagram below represents MAM in
  a pictorial manner when 3 Class-Types are active:



        I----------------------------I
        <---BC0--->                  I
        I---------I                  I
        I         I                  I
        I   CT0   I                  I
        I         I                  I
        I---------I                  I
        I                            I
        I                            I
        <-------BC1------->          I
        I-----------------I          I
        I                 I          I
        I       CT1       I          I
        I                 I          I
        I-----------------I          I
        I                            I
        I                            I
        <-----BC2----->              I
        I-------------I              I
        I             I              I
        I     CT2     I              I
        I             I              I
        I-------------I              I
        I                            I
        I        CT0+CT1+CT2         I
        I                            I
        I----------------------------I

        <--Max Reservable Bandwidth-->


  (Note that, in this illustration, the sum BC0 + BC1 + BC2 exceeds the
  Max Reservable Bandwidth.)



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  While more flexible/sophisticated Bandwidth Constraints Models can be
  defined (and are indeed defined - see [DSTE-RDM]), the Maximum
  Allocation Model is attractive in some DS-TE environments for the
  following reasons:
       - Network administrators generally find MAM simple and
         intuitive
       - MAM matches simple bandwidth control policies that Network
         Administrators may want to enforce such as setting individual
         Bandwidth Constraint for a given type of traffic (aka. Class-
         Type) and simultaneously limit the aggregate of reserved
         bandwidth across all types of traffic.
       - MAM can be used in a way which ensures isolation across
         Class-Types, whether preemption is used or not.
       - MAM can simultaneously achieve isolation, bandwidth
         efficiency and protection against QoS degradation of the
         premium CT.
       - MAM only requires limited protocol extensions such as the
         ones defined in [DSTE-PROTO].

  MAM may not be attractive in some DS-TE environments because:
       - MAM cannot simultaneously achieve isolation, bandwidth
         efficiency and protection against QoS degradation of CTs
         other than the Premium CT.

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


  As a very simple example usage of the MAM Model, a network
  administrator using one CT for Voice (CT1) and one CT for Data (CT0)
  might configure on a given 2.5 Gb/s link:
       -
        BC0 = 2 Gb/s (i.e. Data is limited to 2 Gb/s)
       -
        BC1 = 1 Gb/s   (i.e. Voice is limited to 1 Gb/s)
       -
        Maximum Reservable Bandwidth = 2.5 Gb/s (i.e. aggregate Data
         + Voice is limited to 2.5 Gb/s)


4.Example Formulas for Computing "Unreserved TE-Class [i]" with Maximum
  Allocation 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 MAM MUST reflect
  the MAM Bandwidth Constraints defined in section 3 above when
  computing "Unreserved TE-Class [i]".



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  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 MAM, 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.

  Then:

     "Unreserved TE-Class [i]" =

      MIN  [
     [ BCc - SUM ( Reserved(CTc,q) ) ] for q <= p  ,
     [ Max-Res-Bw - SUM (Reserved(CTb,q)) ] for q <= p and 0 <= b <= 7,
            ]

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


5.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 MAM specified in this document.


6.Acknowledgments

  A lot of the material in this document has been derived from ongoing
  discussions within the TEWG work. This involved many people including
  Jerry Ash and Dimitry Haskin.


7.   Intellectual Property Considerations

  The IETF takes no position regarding the validity or scope of any
  Intellectual Property Rights 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; nor does it represent that it has
  made any independent effort to identify any such rights. Information
  on the procedures with respect to rights in RFC documents can be
  found in BCP 78 and BCP 79.



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  Copies of IPR disclosures made to the IETF Secretariat 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 implementers or users of this
  specification can be obtained from the IETF on-line IPR repository at
  http://www.ietf.org/ipr.

  The IETF invites any interested party to bring to its attention any
  copyrights, patents or patent applications, or other proprietary
  rights that may cover technology that may be required to implement
  this standard. Please address the information to the IETF at
  ietf-ipr@ietf.org.


8.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 14.1 of [DSTE-PROTO]. In accordance with
  these guidelines, IANA was requested to assign a Bandwidth
  Constraints Model Id for MAM 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 MAM.

  <IANA-note> To be removed by the RFC editor at the time of
  publication
       We request IANA to assign value 1 for the MAM model.
    Once the value has been assigned, please replace "TBD" above
       by the assigned value.
  </IANA-note>


9.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-08.txt, work in progress.

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

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



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10.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-RDM] Le Faucheur et al., "Russian Dolls Bandwidth Constraints
  Model for Diff-Serv-aware MPLS Traffic Engineering",
  draft-ietf-tewg-diff-te-russian-07.txt, work in progress.

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

  [ISIS-TE] Smit et al., "Intermediate System to Intermediate System
  (IS-IS) extensions for Traffic Engineering (TE)", RFC 3784.

  [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,
  May 2002.

  [DSTE-MAR] Ash, G., "Max Allocation with Reservation Bandwidth
  Constraints Model for MPLS/DiffServ TE & Performance Comparisons",
  Work In Progress.

  [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.


11.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                                           Field Code



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                Maximum Allocation Model for DS-TE    December 2004


  Wai Sum Lai
  AT&T Labs
  200 Laurel Avenue
  Middletown, New Jersey 07748, USA
  Phone: (732) 420-3712
  Email: wlai@att.com


12.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
  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 Maximum Allocation
  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


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       -
        Bandwidth Constraint 0 (for CT0=Data) = link capacity (or a
         constraint specific to data traffic)
       -
        Max Reservable Bandwidth = link capacity

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

  DS-TE with the Maximum Allocation 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 (or
         up to its own specific constraint)
       -
        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% of link capacity
       -
        BC1 (for CT1) = e.g. 35% of link capacity
       -
        BC0 (for CT0) = e.g.100% of link capacity
       -
        Max Reservable Bandwidth = link capacity

  DS-TE with the Maximum Allocation 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 Maximum Allocation 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.



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3.  Scenario 3: Guaranteed Bandwidth Services

  By configuring on every link:
       -
        BC1 (for CT1) = "given" percentage of link bandwidth
         (appropriate to achieve the QoS objectives of the Guaranteed
         Bandwidth service)
       -
        BC0 (for CT0=Data) = link capacity (or a constraint specific
         to data traffic)
       -
        Max Reservable Bandwidth = link capacity

  DS-TE with the Maximum Allocation 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 (or limited to
  the specific constraint for such traffic).


Disclaimer of Validity

  This document and the information contained herein are provided on an
  "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
  OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
  ENGINEERING TASK FORCE DISCLAIM 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.


Copyright Statement

  Copyright (C) The Internet Society (2004).  This document is subject
  to the rights, licenses and restrictions contained in BCP 78, and
  except as set forth therein, the authors retain all their rights.


Acknowledgment

  Funding for the RFC Editor function is currently provided by the
  Internet Society.










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