Tech-invite3GPPspaceIETF RFCsSIP
9190898887868584838281807978777675747372717069686766656463626160595857565554535251504948474645444342414039383736353433323130292827262524232221201918171615141312111009080706050403020100
in Index   Prev   Next

RFC 4125

Maximum Allocation Bandwidth Constraints Model for Diffserv-aware MPLS Traffic Engineering

Pages: 12
Experimental

Top   ToC   RFC4125 - Page 1
Network Working Group                                     F. Le Faucheur
Request for Comments: 4125                           Cisco Systems, Inc.
Category: Experimental                                            W. Lai
                                                               AT&T Labs
                                                               June 2005

         Maximum Allocation Bandwidth Constraints Model for
                Diffserv-aware MPLS Traffic Engineering

Status of This Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

This document provides specifications for one Bandwidth Constraints Model for Diffserv-aware MPLS Traffic Engineering, which is referred to as the Maximum Allocation Model.

Table of Contents

1. Introduction ....................................................2 1.1. Specification of Requirements ..............................2 2. Definitions .....................................................2 3. Maximum Allocation Model Definition .............................3 4. Example Formulas for Computing "Unreserved TE-Class [i]" with Maximum Allocation Model.........................................6 5. Security Considerations .........................................7 6. IANA Considerations .............................................7 7. Acknowledgements ................................................7 Appendix A: Addressing [DSTE-REQ] Scenarios.........................8 Normative References...............................................10 Informative References.............................................10
Top   ToC   RFC4125 - Page 2

1. Introduction

[DSTE-REQ] presents the Service Providers requirements for support of Diffserv-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). [DSTE-PROTO] specifies the IGP and RSVP-TE signaling extensions for support of DS-TE. These extensions support MAM.

1.1. 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].

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 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.
Top   ToC   RFC4125 - Page 3
   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 that 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.  This assumes that Shared Mesh
   Restoration operates independently within each DS-TE Class-Type and
   does not operate across Class-Types (for example, backup LSPs
   protecting Primary LSPs of CTx also need to belong to CTx; Excess
   Traffic LSPs sharing bandwidth with Backup LSPs of CTx also need to
   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 that 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 cannot
                    be any established LSPs that belongs to CTb and has
                    a holding priority of q; therefore, in this 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,
Top   ToC   RFC4125 - Page 4
        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 CT and across CTs is allowed.

   Where 8 CTs 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
Top   ToC   RFC4125 - Page 5
      - 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 CTs 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.)

   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
Top   ToC   RFC4125 - Page 6
      - MAM matches simple bandwidth control policies that Network
        Administrators may want to enforce, such as setting an
        individual Bandwidth Constraint for a given type of traffic
        (a.k.a. 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 of usage of MAM, 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 when computing "Unreserved TE-Class [i]". As explained in [DSTE-PROTO], the details of admission control algorithms, as well as formulas for computing "Unreserved TE-Class [i]", are outside the scope of the IETF work. Keeping that in mind,
Top   ToC   RFC4125 - Page 7
   we provide in this section an example, for illustration purposes, of
   how values for the unreserved bandwidth for TE-Class[i] might be
   computed with MAM.  In the example, we assume the use of 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. 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 13.1 of [DSTE-PROTO]. In accordance with these guidelines, IANA has assigned a Bandwidth Constraints Model Id for MAM from the range 0-239 (which is to be managed as per the "Specification Required" policy defined in [IANA-CONS]). Bandwidth Constraints Model Id 1 was allocated by IANA to MAM.

7. Acknowledgements

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.
Top   ToC   RFC4125 - Page 8

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].

A.1. Scenario 1: Limiting Amount of Voice

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

A.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
Top   ToC   RFC4125 - Page 9
   DS-TE with the Maximum Allocation Model will ensure that the amount
   of traffic of each CT established on a link is within acceptable
   levels as compared to the resources allocated to the corresponding
   Diffserv Per Hop Behaviors (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 of what is left by CT2
        and CT1.

   Optional automatic adjustment of Diffserv scheduling configuration
   could be used for maintaining very strict relationships between the
   amounts of established traffic of each CT and corresponding Diffserv
   resources.

A.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
Top   ToC   RFC4125 - Page 10
   the rest of the traffic such that links can be filled up (or limited
   to the specific constraint for such traffic).

Normative References

[DSTE-REQ] Le Faucheur, F. and W. Lai, "Requirements for Support of Differentiated Services-aware MPLS Traffic Engineering", RFC 3564, July 2003. [DSTE-PROTO] Le Faucheur, F., Ed., "Protocol Extensions for Support of Diffserv-aware MPLS Traffic Engineering", RFC 4124, June 2005. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [IANA-CONS] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.

Informative References

[BC-CONS] Le Faucheur, F., "Considerations on Bandwidth Constraints Model for DS-TE", Work in Progress, June 2002. [BC-MODEL] Lai, W., "Bandwidth Constraints Models for Differentiated Services (Diffserv)-aware MPLS Traffic Engineering: Performance Evaluation", RFC 4128, June 2005. [DSTE-RDM] Le Faucheur, F., Ed., "Russian Dolls Bandwidth Constraints Model for Diffserv-aware MPLS Traffic Engineering", RFC 4127, June 2005. [GMPLS-RECOV] Lang, et al., "Generalized MPLS Recovery Functional Specification", Work in Progress. [MPLS-BACKUP] Vasseur, et al., "MPLS Traffic Engineering Fast reroute: Bypass Tunnel Path Computation for Bandwidth Protection", Work in Progress.
Top   ToC   RFC4125 - Page 11

Authors' Addresses

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 Wai Sum Lai AT&T Labs 200 Laurel Avenue Middletown, New Jersey 07748, USA Phone: (732) 420-3712 EMail: wlai@att.com
Top   ToC   RFC4125 - Page 12
Full Copyright Statement

   Copyright (C) The Internet Society (2005).

   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.

   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.

Intellectual Property

   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.

   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.

Acknowledgement

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