Subject: Question on BW advertisements for Diffserv aware TE based on Class Type

From: "Sudhakar Ganti" <[email-masked]>
Date: Tue, 15 May 2001 16:57:55 -0400

Hello,

A couple of questions regarding the BW advertisements
on these drafts:
    draft-ietf-mpls-diff-te-ext-01.txt
    draft-ietf-ospf-diff-te-00.txt

a) The text in both the drafts refers to "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)"

However I do not see any separate sub-TLV for Max reservable
bandwidth for each class type (class type N). There is only one 
that advertises the Max Reservable Aggregate Bandwidth.

b) Different classes can be oversubscribed differently
   depending upon the link (or network) configuration.
   If so, I think it may be necessary to advertise the
   Maximum Reservable bandwidth for each Class (Class-Type N).
  
   Is there any reason why this is omitted??

-Sudhakar

---

From: "Darek Skalecki" <[email-masked]>
Date: Wed, 16 May 2001 08:53:20 -0400

Hi Sudhakar,

See inlined answers.

Thanks,

Darek

> that advertises the Max Reservable Aggregate Bandwidth.

The Maximum Reservable Bandwidth for Class-Type N is reflected in the
Unreserved Bandwidth for Class-Type N. That is, there is no need to
advertize through IGP the Maximum Reservable Bandwidth for Class-Type N
as it is implicitely advertized  in the Unreserved Bandwidth for
Class-Type N. The intention is that the Maximum Reservable Bandwidth for
Class-Type N is configured on links that support Class-Type N. However,
when it is time to advertize bandwidth availability for that link, only
the Unreserved Bandwidth for Class-Type N is computed, as you stated by
quoting the draft, and then advertized through IGP. Route selection
through the network is then performed using only the Unreserved
Bandwidths for Class-Types.

The Maximum Reservable Aggregate Bandwidth (which can be thought of as
the Maximum Reservable Bandwidth for Class-Type 0) is advertized for
historical reasons, i.e. original IGP extensions for TE included it and
we didn't want to simply remove it as our extensions are built on the
original extensions.

>    Is there any reason why this is omitted??

See my answer to a). Since Maximum Reservable Bandwidth for Class-Type
N is implicitely "included" in the Unreserved Bandwidth for Class-Type
N and it is the Unreserved Bandwidth for Class-Type N that is advertized
through IGPs and used for route computation, there is no need to
separately advertize Maximum Reservable Bandwidth for Class-Type N. To
oversubscribe a link, the sum of Maximum Reservable Bandwidths for all
Class-Types supported by the link needs to be greater than the capacity
of the link. As I already mentioned, each Maximum Reservable Bandwidth
for Class-Type N is configured on the link and used in the computation
of the Unreserved Bandwidth for Class-Type N for advertizing purposes.

--
Darek Skalecki
Nortel
(613) 765-2252

---

From: "Darek Skalecki" <[email-masked]>
Date: Wed, 16 May 2001 10:23:58 -0400

Sudhakar Ganti wrote:

> Hi Darek,Thanks for your reply. If the Maximum Reservable Bandwidth
> for Class Type-Nis implicitly inferred, then I think the text in both
> these drafts should not refer to thisas it is implementation /
> configuration specific.

Look at "Section 2. Requirements for ISIS/OSPF Extensions" of
draft-ietf-mpls-diff-te-reqts-00.txt which is in the MPLS WG.

> Second thing is that, it may be necessary to advertise this value. It
> givesan option for Traffic Engineering not to take paths that are
> overbooked for a given class if necessary. We may not be able to infer
> this from Unreserved bandwidth. If not, is there any other way to know
> about it?

Not with the current proposals.

Darek

> Thanks-Sudhakar
>
>      -----Original Message-----
>      From: [email-masked] [mailto:[email-masked]]On Behalf
>      Of Darek Skalecki
>      Sent: Wednesday, May 16, 2001 8:53 AM
>      To: Sudhakar Ganti
>      Cc: mpls
>      Subject: Re: Question on BW advertisements for Diffserv
>      aware TE based on Class Type
>      Hi Sudhakar,
>
>      See inlined answers.
>
>      Thanks,
>
>      Darek
>
>
>      Sudhakar Ganti wrote:
>
>     > Hello,
>     >
>      The Maximum Reservable Bandwidth for Class-Type N is
>      reflected in the Unreserved Bandwidth for Class-Type N. That
>      is, there is no need to advertize through IGP the Maximum
>      Reservable Bandwidth for Class-Type N as it is implicitely
>      advertized  in the Unreserved Bandwidth for Class-Type N.
>      The intention is that the Maximum Reservable Bandwidth for
>      Class-Type N is configured on links that support Class-Type
>      N. However, when it is time to advertize bandwidth
>      availability for that link, only the Unreserved Bandwidth
>      for Class-Type N is computed, as you stated by quoting the
>      draft, and then advertized through IGP. Route selection
>      through the network is then performed using only the
>      Unreserved Bandwidths for Class-Types.
>
>      The Maximum Reservable Aggregate Bandwidth (which can be
>      thought of as the Maximum Reservable Bandwidth for
>      Class-Type 0) is advertized for historical reasons, i.e.
>      original IGP extensions for TE included it and we didn't
>      want to simply remove it as our extensions are built on the
>      original extensions.
>
>     >
>     >
>      See my answer to a). Since Maximum Reservable Bandwidth for
>      Class-Type N is implicitely "included" in the Unreserved
>      Bandwidth for Class-Type N and it is the Unreserved
>      Bandwidth for Class-Type N that is advertized through IGPs
>      and used for route computation, there is no need to
>      separately advertize Maximum Reservable Bandwidth for
>      Class-Type N. To oversubscribe a link, the sum of Maximum
>      Reservable Bandwidths for all Class-Types supported by the
>      link needs to be greater than the capacity of the link. As I
>      already mentioned, each Maximum Reservable Bandwidth for
>      Class-Type N is configured on the link and used in the
>      computation of the Unreserved Bandwidth for Class-Type N for
>      advertizing purposes.
>
>     >
>     >
>     > -Sudhakar
>
>      --
>      Darek Skalecki
>      Nortel
>      (613) 765-2252
>
>
>
--
Darek Skalecki
Nortel
(613) 765-2252

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

                                                             Angela Chiu
                                                                    AT&T

                                                        William Townsend
                                                          Tenor Networks

                                                          Darek Skalecki
                                                         Nortel Networks

                                                           Martin Tatham
                                                                      BT

IETF Internet Draft
Expires: May, 2001
Document: draft-ietf-mpls-diff-te-reqts-00.txt         November, 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
   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 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].

Le Faucheur, et. al                                                  1

            Requirements for Diff-Serv Traffic Engineering   July 2000

   Companion documents [DIFF-TE-EXT] [DIFF-TE-OSPF] [DIFF-TE-ISIS]
   respectively propose actual extensions to RSVP and CR-LDP, to OSPF
   and to ISIS, in order to meet those requirements.

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.

 Le Faucheur et. al                                                  2

            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, MPLS MIBs, Diff-Serv Scheduling
   and Traffic Mapping 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-OSPF] and [DIFFF-TE-ISIS].

   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. We also propose that the
   preemption attributes of setup priority and holding priority retain
   existing semantics, and in particular the preemption should work
   across class-types (i.e. independently of class-types), rather than
   having preemption levels operating only within each class-type.
   Thus, the IGP needs to advertise "Unreserved Bandwidth" at each
   preemption level for each Class-Type. However, we observe that
   within a Class-Type, the "Unreserved Bandwidth" value is often
   identical for multiple preemption levels. Firstly, many practical
   MPLS Traffic Engineering deployments will use less than the maximum
   8 possible levels of preemption. In such cases, the Unreserved
   Bandwidth corresponding to a preemption level which is not used will

 Le Faucheur et. al                                                  3

            Requirements for Diff-Serv Traffic Engineering   July 2000

   always be equal to the Unreserved Bandwidth for the preemption level
   immediately above (numerically lower). For example, if only
   preemption levels 0,1 and 4 are used in a network, then the
   "Unreserved Bandwidth" for preemption levels 2 and 3 are identical
   to the "Unreserved Bandwidth" for preemption 1, and the "Unreserved
   Bandwidth" for preemption levels 5, 6 and 7 are identical to the
   "Unreserved Bandwidth" for preemption 4. Secondly, even when all 8
   preemption levels are used in the network, whenever there is no TE
   Tunnels actually setup for a given preemption level (for that Class-
   Type) on a given link, the Unreserved Bandwidth corresponding to
   that preemption level will again be equal to the Unreserved
   Bandwidth for the preemption level immediately above (numerically
   lower).

   Thus we propose that the IGP extension encoding includes a
   compression scheme which can efficiently reduce the length of the
   "Unreserved Bandwidth" advertisement (for each Class-Type) whenever
   there are duplicate values across multiple preemption levels.

   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.
   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.
   administrative group/color, IPv4 interface and neighbor addresses,
   Maximum Link Bandwidth, TE Metric) need not be advertised per Class-
   Type as those will be applicable to all Class-Types. We note that a
   separate TE Metric per Class-Type could be defined in the future if
   required, for instance to allow Constraint Based Routing to take
   account of link propagation delay for LSPs from a Class-Type with
   strict delay requirements.

   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,

 Le Faucheur et. al                                                  4

            Requirements for Diff-Serv Traffic Engineering   July 2000

   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.

   Where a Class-Type is not effectively used in a network, it is
   recommended that the corresponding sub-TLV is not included in the IS
   reachability TLV. Therefore, the Class-Types for which "Unreserved
   Bandwidth" is to be advertised in the IGP should be configurable and
   the IGP must allow advertisement of "Unreserved Bandwidth" for any
   subset of the Class-Types.

   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.

2.1.    Bandwidth Reservation Scheme

   This section discusses the algorithm for computing the "Unreserved
   Bandwidth" for each Class-Type as a function of:
        - the configurable parameters controlling how link bandwidth
   can be reserved by each Class-Type (in particular in situations
   where Class-Types compete for bandwidth reservation) such as "Max
   Reservable Bandwidth for the Class Type",  
        - the already established LSPs of all Class-Types.
   This "Unreserved Bandwidth" for each Class-Type is computed for
   advertisement in the IGP (and therefore used as the per Class-Type
   bandwidth constraint for Constraint Based Routing). The same
   algorithm for computation of "Unreserved Bandwidth" must also be
   used for admission control of Diff-Serv-aware Traffic Engineering
   LSPs at establishment time through RSVP or CR-LDP signalling;
   otherwise persistent deadlock situations could occur whereby
   Constraint Based Routing believes that a given LSP for a given
   Class-Type can be routed through a link but local admission control
   rejects it.

   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 to 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 (eg: BE) to reserve up to 9 Gb/s
     - Class-Type 1 (eg: real time including EF) to reserve up to 5
       Gb/s

 Le Faucheur et. al                                                  5

            Requirements for Diff-Serv Traffic Engineering   July 2000

     - 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)
     - 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 constraint.

 Le Faucheur et. al                                                  6

            Requirements for Diff-Serv Traffic Engineering   July 2000

   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
   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 might 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.

   [Editor's Note: We are considering a potential enhancement to the
   Bandwidth Reservation scheme presented above and therefore to the
   calculation of advertised `unreserved bandwidth' per Class-Type.

   This potential enhancement would take into account a Minimum
   Reservable Bandwidth in addition to the Maximum Reservable Bandwidth
   and the Maximum Aggregate Reservable bandwidth and could take
   account of bandwidth `borrowing' between classes. Thus traffic
   trunks of one Class-Type (say CT-2) might initially reserve all the
   bandwidth of the link, and implicitly that Class-Type would have
   borrowed unreserved capacity from other Class-Types (say CT-1, CT-
   0). However, the LSR would continue to advertise `unreserved
   bandwidth' for CT-1 and CT-0 based on the maximum bandwidth
   entitlement of each Class-Type. A reservation may then be received
   within CT-1 or CT-0, which would preempt an existing reservation in
   CT-2. This form of preemption between Class-Types would only operate
   within existing preemption priority levels, and existing rules for
   preemption across priority levels would still be followed. The
   potential goals of this enhancement would be :
        - to allow enforcement of a Minimum Reservable Bandwidth per
   Class-Type in addition to the Maximum Reservable Bandwidth while
   still advertising a single "Unreserved Bandwidth" per Class-Type
   (for each preemption levels),
        - to match the bandwidth "sharing" properties (across Class-
   Types) of common work-conserving Diff-Serv schedulers (e.g. Weighted
   Fair Queuing). This could ensure that, even in the case of
   statically configured Diff-Serv packet scheduler, there is always
   consistency between :
             * the bandwidth reserved by each Class-Type for Constraint
        Based Routing purposes, and
             * the bandwidth actually granted to the corresponding
        Class-Type by the Diff-Serv Packet Scheduler
   As discussed in section 6 below, the Bandwidth Allocation Scheme
   currently proposed requires dynamic adjustement of the Diff-Serv
   packet scheduler.]

3.      Requirements for RSVP/CR-LDP Extensions

 Le Faucheur et. al                                                  7

            Requirements for Diff-Serv Traffic Engineering   July 2000

   [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 such 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.

   More generally 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 Diff-Serv-TE-capable LSRs (as
       defined in this specification) support N Class-Types while other
       Diff-Serv-TE-capable LSRs support M Class-Types with M>N.
     - in such heterogeneous environments, the solution needs to allow
       establishment of Class-Type 0,.., N-1 LSPs across paths
       combining both types of LSRs
     - in such heterogeneous environments, the solution needs to ensure
       that a Diff-Serv-TE-capable LSR supporting only N Class-Types
       would reject establishment of a Class-Type X LSP if N<=X<=M-1.

   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 Bandwidth
   Reservation Scheme discussed in the previous section.

4.      Requirements for Constraint Based Routing Extensions

 Le Faucheur et. al                                                  8

            Requirements for Diff-Serv Traffic Engineering   July 2000

   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.

   The Constraint Based Routing may also take into account different
   metric for different Class-Types. As an example, when computing a
   path for a non-real-time Class-Type, the Constraint Based Routing
   may use a metric similar to the one currently used by IGP SPF
   Routing for Best Effort traffic, while when computing a path for a
   real-time Class-Type, the Constraint Based Routing may use a metric
   reflecting the link propagation delay.

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.      Diff-Serv Scheduling Requirements

    Diff-Serv-aware Traffic Engineering is expected to be deployed in
   conjunction with Diff-Serv buffer management and differential packet
   scheduling. Per-class-type performance would be controlled on longer
   timescales by Diff-Serv-aware Traffic Engineering; this would be
   complemented by Diff-Serv buffer management and differential packet

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            Requirements for Diff-Serv Traffic Engineering   July 2000

   scheduling mechanisms controlling the per-class performance on
   packet scheduling timescales.

   If the Diff-Serv packet scheduling mechanisms are configured
   statically, it is possible, however, that the allocation of
   resources by Diff-Serv-aware Traffic Engineering for reservation
   purposes will not always correspond with the resources allocated in
   the packet scheduler. As an example, consider the following 10Mbps
   link:

                   Max. Res'ble     Admitted        Pkt Scheduler
                    Bandwidth        Load         Bandwidth share
   Class-Type 0      10 Mbps        1 Mbps             3 Mbps
   Class-type 1       3 Mbps        3 Mbps             3 Mbps
   Class-type 2      10 Mbps        6 Mbps             4 Mbps

   In the above example, the Maximum Reservable Bandwidth for Class-
   Type 2 (e.g. AF) has been set above the corresponding scheduler
   share of 4 Mbps to prevent under-utilisation of the link, in case
   there was little traffic in Class-Types 0 (e.g. BE) and 1 (e.g. EF).
   Under actual load, let's assume that 6 Mbps of Class-Type 2 traffic
   was admitted on the link, possibly due to Class-type 2 LSPs being
   given a high preemption priority. However, the packet scheduler had
   been configured to give the classes comprising Class-type 2 an
   overall share of 4Mbps, reflecting the expected load and taking
   account of the performance targets of Class-type 2 traffic. Even
   though, for most link schedulers, resources would be dynamically
   redirected from Class-Type 0 to Class-Type 2, this would leave
   Class-type 2 traffic at risk of seeing poor performance, under
   conditions of link congestion. Assume for instance that :
     - there is indeed 3 Mbps worth of actual traffic sent onto the
       admitted Class-Type 1 LSPs,
     - there is indeed 6 Mbps worth of actual traffic sent onto the
       admitted Class-Type 2 LSPs,
     - although only 1 Mbps worth of Class-Type 0 (eg. Best Effort
       traffic) has been admitted by Diff-Serv-aware TE, 3 Mbps of
       Class-Type 0 traffic is actually sent onto the Class-Type 0
       LSPs.
   In that case, the packet scheduler will :
     - serve the 3 Mbps of Class-Type 0 traffic
     - serve the 3 Mbps of Class-Type 1 traffic
     - will only be able to provide 4 Mbps of service rate for the 6
       Mbps of Class-Type 2 traffic.
   This example reflects the fact that the Bandwidth allocation Scheme
   described in section 2.1 above may not under all conditions align
   with the resource allocation approach taken by a statically
   configured local link packet scheduler.

   In general, therefore, the requirements on Diff-Serv packet
   scheduling are that:
     1) An LSR should be capable of dynamically adjusting resource
       allocation to Classes based on per-class LSP resource requests.

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            Requirements for Diff-Serv Traffic Engineering   July 2000

     2) The dynamic adjustment should take account of the performance
       requirements of the classes. This may be achieved using, for
       example, per-Class maximum allocation multipliers or overbooking
       factors to adjust scheduling weights.

7.      Traffic Mapping Requirements

   This section describes the requirement for an LSR which is the Head-
   end of Diff-Serv-aware Traffic Engineering LSPs to map incoming
   traffic onto these LSPs.
   Each Diff-Serv-aware Traffic Engineering LSP has the following
   attributes:
       - it can transport one (or a set of) Diff-Serv class(es)
       (Ordered Aggregate) in accordance with [DIFF-MPLS]
       - it has been constraint based routed based on the Class-Type
       which comprises this (or these) class(es), in accordance with
       the previous sections of this document.

   Mapping of incoming traffic onto Diff-Serv-aware Traffic Engineering
   LSPs is to be performed in accordance with [DIFF-MPLS] so that only
   packets that belong to the (set of) Behavior Aggregate(s)
   transported over a given Diff-Serv-aware TE LSP should be mapped to
   that LSP. In particular, where the Head-end LSR is also the MPLS
   Edge LSR, determination of the Behavior Aggregate (and thus
   determination of the egress Diff-Serv-aware TE LSP) is based on the
   Diffserv Codepoint (DSCP) in the packet header.

8.      Security Considerations

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

9.      Acknowledgments

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

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-02.txt, July 2000.

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            Requirements for Diff-Serv Traffic Engineering   July 2000

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

   [DIFF-TE-OSPF] Le Faucheur et al,  Extension to OSPF for support of
   Diff-Serv-aware MPLS Traffic Engineering, draft-lefaucheur-diff-te-
   ospf-01.txt, November 2000.

   [DIFF-TE-ISIS] Le Faucheur et al,  Extension to ISIS for support of
   Diff-Serv-aware MPLS Traffic Engineering, draft-lefaucheur-diff-te-
   isis-01.txt, November 2000.

   [OSPF-TE] Katz, Yeung, Traffic Engineering Extensions to OSPF,
   draft-katz-yeung-ospf-traffic-03.txt, September 2000.

   [ISIS-TE] Smit, Li, IS-IS extensions for Traffic Engineering, draft-
   ietf-isis-traffic-02.txt, September 2000.

   [RSVP-TE] Awduche et al, "RSVP-TE: Extensions to RSVP for LSP
   Tunnels", draft-ietf-mpls-rsvp-lsp-tunnel-07.txt, August 2000.

   [DIFF-MPLS] Le Faucheur et al, "MPLS Support of Diff-Serv", draft-
   ietf-mpls-diff-ext-07.txt, August 2000

   [LDP] Andersson et al., "LDP Specification", draft-ietf-mpls-ldp-
   11.txt, August 2000

   [CR-LDP] Jamoussi et al., "Constraint-Based LSP Setup using LDP",
   draft-ietf-mpls-cr-ldp-04.txt, July 2000

   [TEMIB]     Srinivansan, C., and A. Viswanathan, "MPLS Traffic
   Engineering Management Information Base Using SMIv2", draft-ietf-
   mpls-te-mib-04.txt, July 2000.

   [LSRMIB]    Srinivansan, C., Viswanathan, A., and T. Nadeau "MPLS
   Label Switch Router Management Information Base Using SMIv2", draft-
   ietf-mpls-lsr-mib-06.txt, July 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: [email-masked]

   Angela Chiu
   AT&T Labs
   200 Laurel Ave. Rm A5-1F06
   Middletown, NJ 07748, USA

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            Requirements for Diff-Serv Traffic Engineering   July 2000

   Tel: 1-(732) 420-9057
   Email: [email-masked]

   William Townsend
   Tenor Networks
   100 Nagog Park
   Acton, MA 01720
   Phone: +1-978-264-4900
   Email: [email-masked]

   Thomas D. Nadeau
   Cisco Systems, Inc.
   250 Apollo Drive
   Chelmsford, MA 01824
   Phone: +1-978-244-3051
   Email: [email-masked]

   Darek Skalecki
   Nortel Networks
   3500 Carling Ave,
   Nepean K2H 8E9
   Phone: +1-613-765-2252
   Email: [email-masked]

   Martin Tatham
   BT
   Adastral Park,
   Martlesham Heath,
   Ipswich IP5 3RE
   UK
   Phone: +44-1473-606349
   Email: [email-masked]

 Le Faucheur et. al                                                 13

---

From: "Sudhakar Ganti" <[email-masked]>
Date: Wed, 16 May 2001 10:01:26 -0400

Hi Darek,

Thanks for your reply. If the Maximum Reservable Bandwidth for Class Type-N
is implicitly inferred, then I think the text in both these drafts should not refer to this
as it is implementation / configuration specific.

Second thing is that, it may be necessary to advertise this value. It gives
an option for Traffic Engineering not to take paths that are overbooked for a 
given class if necessary. We may not be able to infer this from Unreserved 
bandwidth. If not, is there any other way to know about it? Thanks

-Sudhakar
  -----Original Message-----
  From: [email-masked] [mailto:[email-masked]]On Behalf Of Darek Skalecki
  Sent: Wednesday, May 16, 2001 8:53 AM
  To: Sudhakar Ganti
  Cc: mpls
  Subject: Re: Question on BW advertisements for Diffserv aware TE based on Class Type

  Hi Sudhakar, 
  See inlined answers. 

  Thanks, 

  Darek 

  Sudhakar Ganti wrote: 

    Hello, 

  The Maximum Reservable Bandwidth for Class-Type N is reflected in the Unreserved Bandwidth for Class-Type N. That is, there is no need to advertize through IGP the Maximum Reservable Bandwidth for Class-Type N as it is implicitely advertized  in the Unreserved Bandwidth for Class-Type N. The intention is that the Maximum Reservable Bandwidth for Class-Type N is configured on links that support Class-Type N. However, when it is time to advertize bandwidth availability for that link, only the Unreserved Bandwidth for Class-Type N is computed, as you stated by quoting the draft, and then advertized through IGP. Route selection through the network is then performed using only the Unreserved Bandwidths for Class-Types. 

  The Maximum Reservable Aggregate Bandwidth (which can be thought of as the Maximum Reservable Bandwidth for Class-Type 0) is advertized for historical reasons, i.e. original IGP extensions for TE included it and we didn't want to simply remove it as our extensions are built on the original extensions. 

  See my answer to a). Since Maximum Reservable Bandwidth for Class-Type N is implicitely "included" in the Unreserved Bandwidth for Class-Type N and it is the Unreserved Bandwidth for Class-Type N that is advertized through IGPs and used for route computation, there is no need to separately advertize Maximum Reservable Bandwidth for Class-Type N. To oversubscribe a link, the sum of Maximum Reservable Bandwidths for all Class-Types supported by the link needs to be greater than the capacity of the link. As I already mentioned, each Maximum Reservable Bandwidth for Class-Type N is configured on the link and used in the computation of the Unreserved Bandwidth for Class-Type N for advertizing purposes. 
      
    -Sudhakar

-- 
Darek Skalecki
Nortel 
(613) 765-2252