Internet Draft

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

                                                             Angela Chiu
                                                                    AT&T

                                                        William Townsend
                                                          Tenor Networks

                                                          Darek Skalecki
                                                         Nortel Networks

IETF Internet Draft
Expires: January, 2001
Document: draft-lefaucheur-diff-te-reqts-00.txt         July, 2000


                      Requirements 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
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Abstract

   This document defines the requirements for support of Diff-Serv-
   aware MPLS Traffic Engineering on a per-Class-Type basis, as
   discussed in the Traffic Engineering Working Group Framework
   document [TEWG-FW].

   A companion document [DIFF-TE-EXT] proposes actual extensions to
   OSPF, ISIS, RSVP and CR-LDP in order to meet those requirements.




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            Requirements for Diff-Serv Traffic Engineering   July 2000


1.      Introduction

   As Diff-Serv becomes prominent in providing scalable multi-class of
   services in IP networks, performing traffic engineering at a per-
   class level instead of an aggregated level is needed to further
   enhance networks in performance and efficiency. By mapping a traffic
   trunk in a given class on a separate LSP, it allows the traffic
   trunk to utilize resources available on both shortest path(s) and
   non-shortest paths and follow paths that meet constraints which are
   specific to the given class. It also allows each class to select the
   proper protection/restoration mechanism(s) that satisfy its
   survivability requirements in a cost effective manner.

   Besides the set of parameters defined for the general aggregate TE
   [TE-REQ], a new set of per-class parameters needs to be provided at
   each LSR interface and propagated via extensions to the IGP
   (ISIS/OSPF)  [TEWG-FW]. Furthermore, the per-class parameters can be
   aggregated into per-Class-Type parameters. The main motivation for
   grouping a set of classes into a Class-Type is to improve the
   scalability of the IGP link state advertisements by propagating
   information on a per-Class-Type basis instead of on a per-class
   basis. This approach also has the benefit of allowing better
   bandwidth sharing between classes in the same Class-Type.

   A Class-Type [TEWG-FW] is defined as a set of classes that satisfy
   the following two conditions:

     1) Classes in the same Class-Type possess common aggregate maximum
       and minimum bandwidth requirements to guarantee the required
       performance level.

     2) There is no maximum or minimum bandwidth requirement to be
       enforced at the level of an individual class within the Class-
       Type. One can still implement some "priority" policies for
       classes within the same Class-Type in terms of accessing the
       Class-Type bandwidth (e.g. via the use of preemption
       priorities).

   An example of Class-Type comprising multiple Diff-Serv classes is a
   low-loss Class-Type that includes both AF1-based and AF2-based
   Ordering Aggregates.

   Note that with per Class-Type TE, Constraint-Based Routing is
   performed with bandwidth constraints on a per Class-Type basis but
   LSPs may carry a single Diff-Serv class (Ordered Aggregate) with
   Diff-Serv scheduling (i.e. PHB) performed separately for each class.
   Diff-Serv scheduling parameters for a given class within a Class-
   Type may be automatically adjusted by the LSRs based on the
   bandwidth of all LSPs currently established for each class within
   the Class-Type.


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            Requirements for Diff-Serv Traffic Engineering   July 2000

   In this document, we will only discuss "per Class-Type TE" because
   "per Class TE" can be viewed as a special case of per Class-Type TE
   (where each Class-Type is degenerated into a single Diff-Serv
   class).

   This document focuses on intra-domain operations. Inter-domain
   operations is for further study.

   The following sections detail the requirements on OSPF/ISIS, RSVP/
   CR-LDP, Constraint Based Routing and MPLS MIBs for support of MPLS
   Traffic Engineering on a per-Class-Type basis.


2.      Requirements for ISIS/OSPF Extensions

   [OSPF-TE] and [ISIS-TE] define extensions to OSPF and ISIS for
   support of (aggregate) MPLS Traffic Engineering. In this section we
   define the requirements on OSPF and ISIS for support of Diff-Serv
   Traffic Engineering on a per-Class-Type basis. These requirements
   are expected to require further extensions to OSPF and ISIS. Such
   extensions are proposed in [DIFF-TE-EXT].

   Given that there are hard limits imposed by ISIS/OSPF TLVs, the TLV
   space must be used frugally. An additional concern is that the
   amount of information advertised by the IGP directly affects the
   scalability of the solution. These considerations strongly influence
   the requirements defined in this section.

   As pointed out in [TEWG-FW], the IGP needs to advertise separate "TE
   information" for each Class-Type. We focus now on detailing what
   this "TE information" should be.

   For Constraint Based Routing to be able to compute paths which
   satisfy different bandwidth constraints for each Class-Type, the IGP
   needs to advertise different "Unreserved Bandwidth" information for
   each Class-Type. Moreover, we propose that the preemption attribute
   defined in [TE-REQ] be retained for all Class-Types. Thus, the IGP
   needs to advertise "Unreserved Bandwidth" at each preemption level
   for each Class-Type.

   For the bandwidth constraints to be effectively different for each
   Class-Type, LSRs need to allow configuration for every link of a
   "Maximum Reservable Bandwidth" for each Class-Type. Clearly, the
   "Unreserved Bandwidth" advertised for each Class-Type takes into
   account the "Maximum Reservable Bandwidth" configured for the
   corresponding Class-Type. Consequently, Constraint Based Routing can
   compute paths for the different Class-Types without receiving the
   "Maximum Reservable Bandwidth" for each Class-Type from the IGP.
   Thus we feel that the IGP need not advertise the Maximum Reservable
   Bandwidth for each Class-Type. We note that the Maximum Reservable
   Bandwidth for each Class-Type could have been used by Constraint
   Based Routing to enhance route computation in some situations (e.g.

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            Requirements for Diff-Serv Traffic Engineering   July 2000

   as a tie breaker), but we feel this does not justify the extra
   overhead in IGP advertisement.

   Current IGP extensions for (aggregate) TE [OSPF-TE][ISIS-TE] specify
   advertisement of the Maximum Reservable Bandwidth for (aggregate)
   TE. Note that this document does not propose that this be changed.

   Other TE attributes already advertised by the IGP (i.e.
   resource/color) need not be advertised per Class-Type as those will
   be applicable to all Class-Types.


   It is desirable to be able to avoid under-utilizing aggregate
   resource. To achieve this, it is necessary to allow the sum of the
   configurable Maximum Reservable Bandwidth of all Class-Types be
   larger than a configurable Maximum Reservable Aggregate Bandwidth
   (i.e. aggregate across all Class-Types). At the same time, it is
   desirable to be able to avoid over-utilizing the aggregate resource.
   To achieve this, it is necessary to be able to enforce this Maximum
   Reservable Aggregate Bandwidth; in other words it is necessary to
   ensure that the sum of all LSPs across all Class-Types never exceeds
   the Maximum Reservable Aggregate Bandwidth.

   For example, a 10Gb/s link may be configured to allow:

     - Class-Type 0 (BE) to reserve up to 9 Gb/s
     - Class-Type 1 (e.g. real time including EF) to reserve up to 5
       Gb/s
     - Class-Type 2 (eg low loss including AF1 and AF2) to reserve up
       to 8 Gb/s

   and at the same may be configured to allow:

     - on an aggregate basis, the sum of all Class-Types to reserve up
       to 10 Gb/s.

   Therefore, a path computed by the Constraint Based Routing for an
   LSP of Class-Type N must ensure that this LSP fits within the
   remaining Class-Type N bandwidth AND that this LSP fits within the
   remaining Aggregate bandwidth.

   One way to achieve this, would be:
     - for each Class-Type, that IGP uses the "Unreserved Bandwidth for
       Class-Type N" to advertise the Class-Type N bandwidth currently
       unreserved (i.e. the difference between the Maximum Reservable
       Bandwidth for Class-Type N and the bandwidth reserved by
       existing Class-Type N LSPs),
     - in addition, that IGP separately advertises the "Unreserved
       Aggregate Bandwidth" (i.e. the difference between the Maximum
       Reservable Aggregate Bandwidth and the bandwidth reserved by
       existing LSPs of all Class-Types)


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            Requirements for Diff-Serv Traffic Engineering   July 2000

     - have Constraint Based Routing ensure that a new Class-Type N LSP
       fits both in the received "Unreserved Bandwidth for Class-Type
       N" and in the "Unreserved Aggregate Bandwidth".
   Such an approach has the drawbacks that it would require that N+1
   "unreserved bandwidth" information be advertised by the IGP when N
   Class-Types are supported, and that it requires the node performing
   Constraint Based Routing to meet a double bandwidth constraints.

   Instead we propose that:
     - for each Class-Type, that IGP uses the "Unreserved Bandwidth for
       Class-Type N" to directly advertise the amount of bandwidth that
       is effectively useable by Class-Type N. This is computed as the
       smaller of these two values:
           o The Class-Type N bandwidth currently unreserved (i.e. the
             difference between the Maximum Reservable Bandwidth for
             Class-Type N and the bandwidth reserved by existing Class-
             Type N LSPs).
           o The aggregate bandwidth currently unreserved (i.e. the
             difference between the Maximum Reservable Aggregate
             Bandwidth and the bandwidth reserved by existing LSPs of
             all Class-Types).
     - have Constraint Based Routing ensure that a new Class-Type N LSP
       simply fits in the received "Unreserved Bandwidth for Class-Type
       N".
   Such an approach only requires that N "unreserved bandwidth"
   information be advertised by the IGP when N Class-Types are
   supported, and only requires that the node performing Constraint
   Based Routing meets a single bandwidth constraints.


   We propose to begin by allowing a total of 4 Class-Types (i.e., 3
   beyond the existing one aka. Class-Type 0). This is expected to be
   sufficient for practical deployments in the foreseeable future. As
   an example, a total of three Class-Types already allow support of
   separate bandwidth control for Real-Time, Low-Loss and Best Effort,
   while allowing multiple classes within each Class-Type (e.g. AF1 and
   AF2 flavors of "Low-Loss"). More Class-Types could be defined in the
   future if required.

   Implementations of Diff-Serv Traffic Engineering in compliance with
   this specification MUST support at least a total of 2 Class-Types
   and MAY support a total of 3 or 4 Class-Types.

   The IGP must be able to only advertise the Bandwidth Information for
   the subset of Class-Types actually used in the network (i.e. not
   always advertise the Unreserved Bandwidth information for all the
   new Class-Types).

   It may be desirable to prevent a Class-Type from being starved by
   others. In the example given above where we defined three Class-
   Types, it may be useful to be able to always ensure that some amount
   of Class-Type 0 LSPs can be routed over that link (i.e. to prevent

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            Requirements for Diff-Serv Traffic Engineering   July 2000

   Class-Type 1 LSPs and Class-Type 2 LSPs from reserving up to 100% of
   the maximum reservable aggregate bandwidth which would result in
   Class-Type 0 LSPs not having any access to the capacity of that
   link). Such capability would require the ability from the IGP to
   advertise an optional "minimum reservable bandwidth" per Class-Type.
   This is not seen as an immediate requirement but could be defined in
   the future if required.


3.      Requirements for RSVP/CR-LDP Extensions

   [RSVP-TE] and [CR-LDP] define extensions to RSVP and LDP for support
   of (aggregate) MPLS Traffic Engineering. [DIFF-MPLS] defines the
   extensions to RSVP and LDP for support of Diff-Serv over MPLS. In
   this section we define the requirements on RSVP and CR-LDP for
   support of Diff-Serv Traffic Engineering on a per-Class-Type basis.
   These requirements are expected to require further extensions to
   RSVP and CR-LDP. Such extensions are proposed in [DIFF-TE-EXT].

   In order for an LSR to perform resource availability checking for an
   LSP that belongs to a certain Class-Type, the LSR needs to be made
   aware through RSVP/CR-LDP signaling of the Class-Type associated
   with the LSP.

   To that end, we propose that RSVP/CR-LDP be extended to be able to
   signal the Class-Type.

   We identify the following backward compatibility requirements for
   the RSVP/CR-LDP extensions:
     - operations in heterogeneous environments need to be supported
       for smooth migration, where some LSRs are Diff-Serv-TE-capable
       (as defined in this specification) while some other LSRs are not
       Diff-Serv-TE-capable (i.e. support (aggregate) TE only)
     - in heterogeneous environments, the solution needs to allow
       establishment of Class-Type 0 LSPs across paths combining Diff-
       Serv-TE-capable LSRs and non-Diff-Serv-TE-capable LSRs
     - in heterogeneous environments, the solution needs to ensure that
       a non-Diff-Serv-TE-capable LSR would reject establishment of a
       Class-Type N (N=1,2,3) LSP.

   The admission control algorithm implemented for LSP establishment
   must locally maintain different variables which keep track of the
   currently unreserved bandwidth for each Class-Type. These unreserved
   bandwidth variables must be updated in accordance with the approach
   discussed in the previous section for enforcement of the Maximum
   Reservable Aggregate Bandwidth across all Class-Types, if so
   configured on an LSR. In particular, when admitting a Class-Type N
   LSP, the LSR must take into account this Class-Type N LSP to update
   the variables tracking the unreserved bandwidth for Class-Type N, as
   well as to potentially update the variables tracking the unreserved
   bandwidth for the other Class-Types (since the new LSP eats-up


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            Requirements for Diff-Serv Traffic Engineering   July 2000

   Aggregate bandwidth which in turn may reduce the amount of LSP that
   may be established in other Class-Types).


4.      Requirements for Constraint Based Routing Extensions

   In order for Constraint Based Routing to support Diff-Serv TE on a
   per-Class-Type basis, the Constraint Based Routing algorithm need to
   be capable of taking into account the "Unreserved Bandwidth for
   Class-Type N" when computing a path for a Class-Type N LSP.


5.      Requirements for MIB Extensions

   In order for an LSR to support the configuration and monitoring of
   Diff-Serv Traffic Engineering certain enhancements to some of the
   existing MPLS Management Information Bases (MIBs) will be required.
   [LSRMIB] defines the MPLS Label Switch Router MIB (LSR MIB) which
   contains objects useful for the management and configuration of MPLS
   LSPs. [TE MIB] defines the MPLS Traffic Engineering MIB (TE MIB)
   which contains objects useful for the management and configuration
   of MPLS Traffic Engineered Tunnels.

   In particular, the MIB extensions need to:
     - track for each MPLS interface, the Maximum Reservable Bandwidth
       configured for each Class-Type.
     - track for each MPLS interface, the Maximum Reservable Aggregate
       Bandwidth configured.
     - track for each LSP, the Class-Type associated with the LSP. On
       the Head-End LSRs, the Class-Type is configured as part of the
       tunnel configuration. On other LSRs, the Class-Type is
       associated with the LSP at establishment time based on signaled
       information.

   Additional details of these changes will be provided in forthcoming
   versions of this draft. It is the authors' intent to transfer these
   MIB requirements to future versions of the MPLS TE and the MPLS LSR
   MIBs. It is not the intent of this document to define the SMI
   required for the MIB enhancements; rather, it is to flesh out and
   define the details of these changes in the context of this document.


6.      Security Considerations

   The solution developed to address the requirements defined in this
   document must address security aspects.


7.      Acknowledgments

   This document has benefited from discussions with Carol Iturralde
   and Rob Goguen.

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            Requirements for Diff-Serv Traffic Engineering   July 2000



References

   [TE-REQ] Awduche et al, Requirements for Traffic Engineering over
   MPLS, RFC2702, September 1999.

   [TEWG-FW] Awduche et al, A Framework for Internet Traffic
   Engineering, draft-ietf-tewg-framework-01.txt, May 2000.

   [DIFF-TE-EXT] Le Faucheur et al, Extensions to IS-IS, OSPF, RSVP,
   CR-LDP and MPLS MIBs for support of Diff-Serv-aware MPLS Traffic
   Engineering, draft-lefaucheur-diff-te-ext-00.txt, July 2000.

   [OSPF-TE] Katz, Yeung, Traffic Engineering Extensions to OSPF,
   draft-katz-yeung-ospf-traffic-01.txt, April 2000.

   [ISIS-TE] Smit, Li, IS-IS extensions for Traffic Engineering, draft-
   ietf-isis-traffic-01.txt, May 1999.

   [RSVP-TE] Awduche et al, "Extensions to RSVP for LSP Tunnels",
   draft-ietf-mpls-rsvp-lsp-tunnel-05.txt, February 2000.

   [DIFF-MPLS] Le Faucheur et al, "MPLS Support of Diff-Serv", draft-
   ietf-mpls-diff-ext-05.txt, June 2000

   [LDP] Andersson et al., "LDP Specification", draft-ietf-mpls-ldp-
   06.txt, October 1999

   [CR-LDP] Jamoussi et al., "Constraint-Based LSP Setup using LDP",
   draft-ietf-mpls-cr-ldp-03.txt, October 1999

   [TEMIB]     Srinivansan, C., and A. Viswanathan, "MPLS Traffic
   Engineering Management Information Base Using SMIv2", draft-ietf-
   mpls-te-mib-03.txt, March 10, 2000.

   [LSRMIB]    Srinivansan, C., Viswanathan, A., and T. Nadeau "MPLS
   Label Switch Router Management Information Base Using SMIv2", draft-
   ietf-mpls-lsr-mib-04.txt, April 26, 2000.


Authors' Address:

   Francois Le Faucheur
   Cisco Systems, Inc.
   Petra B - Les Lucioles - 291, rue Albert Caquot - 06560 Valbonne -
   France
   Phone: +33 4 92 96 75 64
   Email: flefauch@cisco.com

   Angela Chiu
   AT&T Labs

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            Requirements for Diff-Serv Traffic Engineering   July 2000

   Rm 4-204,100 Schulz Dr., Red Bank, NJ 07701
   USA
   Phone: +1 (732) 345-3441
   Email: alchiu@att.com

   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
   Email: tnadeau@cisco.com

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




























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