<pre>Network Working Group                                F. Le Faucheur, Ed.
Request for Comments: 4124                           Cisco Systems, Inc.
Category: Standards Track                                      June 2005


                  <span class="h1">Protocol Extensions for Support of</span>
                <span class="h1">Diffserv-aware MPLS Traffic Engineering</span>

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document specifies the protocol extensions for support of
   Diffserv-aware MPLS Traffic Engineering (DS-TE).  This includes
   generalization of the semantics of a number of Interior Gateway
   Protocol (IGP) extensions already defined for existing MPLS Traffic
   Engineering in <a href="./rfc3630">RFC 3630</a>, <a href="./rfc3784">RFC 3784</a>, and additional IGP extensions
   beyond those.  This also includes extensions to RSVP-TE signaling
   beyond those already specified in <a href="./rfc3209">RFC 3209</a> for existing MPLS Traffic
   Engineering.  These extensions address the requirements for DS-TE
   spelled out in <a href="./rfc3564">RFC 3564</a>.

Table of Contents

   <a href="#section-1">1</a>. Introduction ....................................................<a href="#page-3">3</a>
      <a href="#section-1.1">1.1</a>. Specification of Requirements ..............................<a href="#page-3">3</a>
   <a href="#section-2">2</a>. Contributing Authors ............................................<a href="#page-4">4</a>
   <a href="#section-3">3</a>. Definitions .....................................................<a href="#page-5">5</a>
   <a href="#section-4">4</a>. Configurable Parameters .........................................<a href="#page-5">5</a>
      <a href="#section-4.1">4.1</a>. Link Parameters ............................................<a href="#page-5">5</a>
           <a href="#section-4.1.1">4.1.1</a>. Bandwidth Constraints (BCs) .........................<a href="#page-5">5</a>
           <a href="#section-4.1.2">4.1.2</a>. Overbooking .........................................<a href="#page-6">6</a>
      <a href="#section-4.2">4.2</a>. LSR Parameters .............................................<a href="#page-7">7</a>
           <a href="#section-4.2.1">4.2.1</a>. TE-Class Mapping ....................................<a href="#page-7">7</a>
      <a href="#section-4.3">4.3</a>. LSP Parameters .............................................<a href="#page-8">8</a>
           <a href="#section-4.3.1">4.3.1</a>. Class-Type ..........................................<a href="#page-8">8</a>
           <a href="#section-4.3.2">4.3.2</a>. Setup and Holding Preemption Priorities .............<a href="#page-8">8</a>
           <a href="#section-4.3.3">4.3.3</a>. Class-Type/Preemption Relationship ..................<a href="#page-8">8</a>



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      <a href="#section-4.4">4.4</a>. Examples of Parameters Configuration .......................<a href="#page-9">9</a>
           <a href="#section-4.4.1">4.4.1</a>. Example 1 ...........................................<a href="#page-9">9</a>
           <a href="#section-4.4.2">4.4.2</a>. Example 2 ...........................................<a href="#page-9">9</a>
           <a href="#section-4.4.3">4.4.3</a>. Example 3 ..........................................<a href="#page-10">10</a>
           <a href="#section-4.4.4">4.4.4</a>. Example 4 ..........................................<a href="#page-11">11</a>
           <a href="#section-4.4.5">4.4.5</a>. Example 5 ..........................................<a href="#page-11">11</a>
   <a href="#section-5">5</a>. IGP Extensions for DS-TE .......................................<a href="#page-12">12</a>
      <a href="#section-5.1">5.1</a>. Bandwidth Constraints .....................................<a href="#page-12">12</a>
      <a href="#section-5.2">5.2</a>. Unreserved Bandwidth ......................................<a href="#page-14">14</a>
   <a href="#section-6">6</a>. RSVP-TE Extensions for DS-TE ...................................<a href="#page-15">15</a>
      <a href="#section-6.1">6.1</a>. DS-TE-Related RSVP Messages Format ........................<a href="#page-15">15</a>
           <a href="#section-6.1.1">6.1.1</a>. Path Message Format ................................<a href="#page-16">16</a>
      <a href="#section-6.2">6.2</a>. CLASSTYPE Object ..........................................<a href="#page-16">16</a>
           <a href="#section-6.2.1">6.2.1</a>. CLASSTYPE object ...................................<a href="#page-16">16</a>
      <a href="#section-6.3">6.3</a>. Handling CLASSTYPE Object .................................<a href="#page-17">17</a>
      <a href="#section-6.4">6.4</a>. Non-support of the CLASSTYPE Object .......................<a href="#page-20">20</a>
      <a href="#section-6.5">6.5</a>. Error Codes for Diffserv-aware TE .........................<a href="#page-20">20</a>
   <a href="#section-7">7</a>. DS-TE Support with MPLS Extensions .............................<a href="#page-21">21</a>
      <a href="#section-7.1">7.1</a>. DS-TE Support and References to Preemption Priority .......<a href="#page-22">22</a>
      7.2. DS-TE Support and References to Maximum Reservable
           Bandwidth .................................................<a href="#page-22">22</a>
   <a href="#section-8">8</a>. Constraint-Based Routing .......................................<a href="#page-22">22</a>
   <a href="#section-9">9</a>. Diffserv Scheduling ............................................<a href="#page-23">23</a>
   <a href="#section-10">10</a>. Existing TE as a Particular Case of DS-TE .....................<a href="#page-23">23</a>
   11. Computing "Unreserved TE-Class [i]" and Admission
       Control Rules .................................................<a href="#page-23">23</a>
       <a href="#section-11.1">11.1</a>. Computing "Unreserved TE-Class [i]" .....................<a href="#page-23">23</a>
       <a href="#section-11.2">11.2</a>. Admission Control Rules .................................<a href="#page-24">24</a>
   <a href="#section-12">12</a>. Security Considerations .......................................<a href="#page-24">24</a>
   <a href="#section-13">13</a>. IANA Considerations ...........................................<a href="#page-25">25</a>
       13.1. A New Name Space for Bandwidth Constraints Model
             Identifiers .............................................<a href="#page-25">25</a>
       13.2. A New Name Space for Error Values under the
             "Diffserv-aware TE ......................................<a href="#page-25">25</a>
       <a href="#section-13.3">13.3</a>. Assignments Made in This Document .......................<a href="#page-26">26</a>
             13.3.1. Bandwidth Constraints sub-TLV for
                     OSPF Version 2 ..................................<a href="#page-26">26</a>
             <a href="#section-13.3.2">13.3.2</a>. Bandwidth Constraints sub-TLV for ISIS ..........<a href="#page-26">26</a>
             <a href="#section-13.3.3">13.3.3</a>. CLASSTYPE Object for RSVP .......................<a href="#page-26">26</a>
             <a href="#section-13.3.4">13.3.4</a>. "Diffserv-aware TE Error" Error Code ............<a href="#page-27">27</a>
             <a href="#section-13.3.5">13.3.5</a>. Error Values for "Diffserv-aware TE Error" ......<a href="#page-27">27</a>
   <a href="#section-14">14</a>. Acknowledgements ..............................................<a href="#page-28">28</a>
   <a href="#appendix-A">Appendix A</a>: Prediction for Multiple Path Computation ..............<a href="#page-29">29</a>
   <a href="#appendix-B">Appendix B</a>: Solution Evaluation ...................................<a href="#page-29">29</a>
   <a href="#appendix-C">Appendix C</a>: Interoperability with non DS-TE capable LSRs ..........<a href="#page-31">31</a>
   Normative References ..............................................<a href="#page-34">34</a>
   Informative References ............................................<a href="#page-35">35</a>




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<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>.  Introduction</span>

   [<a id="ref-DSTE-REQ">DSTE-REQ</a>] presents the Service Provider requirements for support of
   Differentiated-Service (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.

   This document specifies the IGP and RSVP-TE signaling extensions
   (beyond those already specified for existing MPLS Traffic Engineering
   [<a href="#ref-OSPF-TE" title="&quot;Traffic Engineering (TE) Extensions to OSPF Version 2&quot;">OSPF-TE</a>][ISIS-TE][<a href="#ref-RSVP-TE" title="&quot;RSVP-TE: Extensions to RSVP for LSP Tunnels&quot;">RSVP-TE</a>]) for support of the DS-TE requirements
   spelled out in [<a href="#ref-DSTE-REQ" title="&quot;Requirements for Support of Differentiated Services-aware MPLS Traffic Engineering&quot;">DSTE-REQ</a>] including environments relying on
   distributed Constraint-Based Routing (e.g., path computation
   involving head-end Label Switching Routers).

   [<a id="ref-DSTE-REQ">DSTE-REQ</a>] provides a definition and examples of Bandwidth
   Constraints models.  The present document does not specify nor assume
   a particular Bandwidth Constraints model.  Specific Bandwidth
   Constraints models are outside the scope of this document.  Although
   the extensions for DS-TE specified in this document may not be
   sufficient to support all the conceivable Bandwidth Constraints
   models, they do support the Russian Dolls Model specified in
   [<a href="#ref-DSTE-RDM" title="&quot;Russian Dolls Bandwidth Constraints Model for Diffserv-aware MPLS Traffic Engineering&quot;">DSTE-RDM</a>], the Maximum Allocation Model specified in [<a href="#ref-DSTE-MAM" title="&quot;Maximum Allocation Bandwidth Constraints Model for Diffserv-aware Traffice Engineering&quot;">DSTE-MAM</a>], and
   the Maximum Allocation with Reservation Model specified in
   [<a href="#ref-DSTE-MAR" title="&quot;Max Allocation with Reservation Bandwidth Constraints Model for DiffServ-aware MPLS Traffic Engineering &amp; Performance Comparisons&quot;">DSTE-MAR</a>].

   There may be differences between the quality of service expressed and
   obtained with Diffserv without DS-TE and with DS-TE.  Because DS-TE
   uses Constraint-Based Routing, and because of the type of admission
   control capabilities it adds to Diffserv, DS-TE has capabilities for
   traffic that Diffserv does not:  Diffserv does not indicate
   preemption, by intent, whereas DS-TE describes multiple levels of
   preemption for its Class-Types.  Also, Diffserv does not support any
   means of explicitly controlling overbooking, while DS-TE allows this.
   When considering a complete quality of service environment, with
   Diffserv routers and DS-TE, it is important to consider these
   differences carefully.

<span class="h3"><a class="selflink" id="section-1.1" href="#section-1.1">1.1</a>.  Specification of Requirements</span>

   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 [<a href="./rfc2119" title="&quot;Key words for use in RFCs to Indicate Requirement Levels&quot;">RFC2119</a>].








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<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>.  Contributing Authors</span>

   This document was the collective work of several authors.  The text
   and content were contributed by the editor and the co-authors listed
   below.  (The contact information for the editor appears in the
   Editor's Address section.)

   Jim Boyle                               Kireeti Kompella
   Protocol Driven Networks, Inc.          Juniper Networks, Inc.
   1381 Kildaire Farm Road #288            1194 N. Mathilda Ave.
   Cary, NC 27511, USA                     Sunnyvale, CA 94099

   Phone: (919) 852-5160                   EMail: kireeti@juniper.net
   EMail: jboyle@pdnets.com


   William Townsend                        Thomas D. Nadeau
   Tenor Networks                          Cisco Systems, Inc.
   100 Nagog Park                          250 Apollo Drive
   Acton, MA 01720                         Chelmsford, MA 01824

   Phone: +1-978-264-4900                  Phone: +1-978-244-3051
   EMail: btownsend@tenornetworks.com      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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<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>.  Definitions</span>

   For readability, a number of definitions from [<a href="#ref-DSTE-REQ" title="&quot;Requirements for Support of Differentiated Services-aware MPLS Traffic Engineering&quot;">DSTE-REQ</a>] are repeated
   here:

   Traffic Trunk:   an aggregation of traffic flows of the same class
                    (i.e., treated equivalently from the DS-TE
                    perspective), which is placed inside a Label
                    Switched Path (LSP).

   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 setup priority, the holding
                    priority, or both.

   Definitions for a number of MPLS terms are not repeated here.  They
   can be found in [<a href="#ref-MPLS-ARCH" title="&quot;Multiprotocol Label Switching Architecture&quot;">MPLS-ARCH</a>].

<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>.  Configurable Parameters</span>

   This section only discusses the differences with the configurable
   parameters supported for MPLS Traffic Engineering as per [<a href="#ref-TE-REQ" title="&quot;Requirements for Traffic Engineering Over MPLS&quot;">TE-REQ</a>],
   [<a href="#ref-ISIS-TE" title="&quot;Intermediate System to Intermediate System (IS-IS) Extensions for Traffic Engineering (TE)&quot;">ISIS-TE</a>], [<a href="#ref-OSPF-TE" title="&quot;Traffic Engineering (TE) Extensions to OSPF Version 2&quot;">OSPF-TE</a>], and [<a href="#ref-RSVP-TE" title="&quot;RSVP-TE: Extensions to RSVP for LSP Tunnels&quot;">RSVP-TE</a>].  All other parameters are
   unchanged.

<span class="h3"><a class="selflink" id="section-4.1" href="#section-4.1">4.1</a>.  Link Parameters</span>

<span class="h4"><a class="selflink" id="section-4.1.1" href="#section-4.1.1">4.1.1</a>.  Bandwidth Constraints (BCs)</span>

   [<a id="ref-DSTE-REQ">DSTE-REQ</a>] states that "Regardless of the Bandwidth Constraints
   Model, the DS-TE solution MUST allow support for up to 8 BCs."

   For DS-TE, the existing "Maximum Reservable link bandwidth" parameter
   is retained, but its semantics is generalized and interpreted as the
   aggregate bandwidth constraint across all Class-Types, so that,
   independently of the Bandwidth Constraints Model in use:





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      SUM (Reserved (CTc)) &lt;= Max Reservable Bandwidth,

   where the SUM is across all values of "c" in the range 0 &lt;= c &lt;= 7.

   Additionally, on every link, a DS-TE implementation MUST provide for
   configuration of up to 8 additional link parameters which are the
   eight potential BCs, i.e., BC0, BC1, ... BC7.  The LSR MUST interpret
   these BCs in accordance with the supported Bandwidth Constraints
   Model (i.e., what BC applies to what Class-Type, and how).

   Where the Bandwidth Constraints Model imposes some relationship among
   the values to be configured for these BCs, the LSR MUST enforce those
   at configuration time.  For example, when the Russian Dolls Bandwidth
   Constraints Model ([<a href="#ref-DSTE-RDM" title="&quot;Russian Dolls Bandwidth Constraints Model for Diffserv-aware MPLS Traffic Engineering&quot;">DSTE-RDM</a>]) is used, the LSR MUST ensure that BCi
   is configured smaller than or equal to BCj, where i is greater than
   j, and ensure that BC0 is equal to the Maximum Reservable Bandwidth.
   As another example, when the Maximum Allocation Model ([<a href="#ref-DSTE-MAM" title="&quot;Maximum Allocation Bandwidth Constraints Model for Diffserv-aware Traffice Engineering&quot;">DSTE-MAM</a>]) is
   used, the LSR MUST ensure that all BCi are configured smaller or
   equal to the Maximum Reservable Bandwidth.

<span class="h4"><a class="selflink" id="section-4.1.2" href="#section-4.1.2">4.1.2</a>.  Overbooking</span>

   DS-TE enables a network administrator to apply different overbooking
   (or underbooking) ratios for different CTs.

   The principal methods to achieve this are the same as those
   historically used in existing TE deployment:

   (i)    To take into account the overbooking/underbooking ratio
          appropriate for the Ordered Aggregate (OA) or CT associated
          with the considered LSP at the time of establishing the
          bandwidth size of a given LSP.  We refer to this method as the
          "LSP Size Overbooking" method.  AND/OR
   (ii)   To take into account the overbooking/underbooking ratio at the
          time of configuring the Maximum Reservable Bandwidth/BCs and
          use values that are larger (overbooking) or smaller
          (underbooking) than those actually supported by the link.  We
          refer to this method as the "Link Size Overbooking" method.

   The "LSP Size Overbooking" and "Link Size Overbooking" methods are
   expected to be sufficient in many DS-TE environments and require no
   additional configurable parameters.  Other overbooking methods may
   involve such additional configurable parameters, but are beyond the
   scope of this document.







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<span class="h3"><a class="selflink" id="section-4.2" href="#section-4.2">4.2</a>.  LSR Parameters</span>

<span class="h4"><a class="selflink" id="section-4.2.1" href="#section-4.2.1">4.2.1</a>.  TE-Class Mapping</span>

   In line with [<a href="#ref-DSTE-REQ" title="&quot;Requirements for Support of Differentiated Services-aware MPLS Traffic Engineering&quot;">DSTE-REQ</a>], the preemption attributes defined in
   [<a href="#ref-TE-REQ" title="&quot;Requirements for Traffic Engineering Over MPLS&quot;">TE-REQ</a>] are retained with DS-TE and applicable within, and across,
   all CTs.  The preemption attributes of setup priority and holding
   priority retain existing semantics, and in particular these semantics
   are not affected by the LSP CT.  This means that if LSP1 contends
   with LSP2 for resources, LSP1 may preempt LSP2 if LSP1 has a higher
   setup preemption priority (i.e., lower numerical priority value) than
   LSP2 holding preemption priority, regardless of LSP1 CT and LSP2 CT.

   DS-TE LSRs MUST allow configuration of a TE-Class mapping whereby the
   Class-Type and preemption level are configured for each of (up to) 8
   TE-Classes.

   This mapping is referred to as :

      TE-Class[i]  &lt;--&gt;  &lt; CTc , preemption p &gt;

   where 0 &lt;= i &lt;= 7, 0 &lt;= c &lt;= 7, 0 &lt;= p &lt;= 7

   Two TE-Classes MUST NOT be identical (i.e., have both the same
   Class-Type and the same preemption priority).

   There are no other restrictions on how any of the 8 Class-Types can
   be paired up with any of the 8 preemption priorities to form a TE-
   Class.  In particular, one given preemption priority can be paired up
   with two (or more) different Class-Types to form two (or more) TE-
   Classes.  Similarly, one Class-Type can be paired up with two (or
   more) different preemption priorities to form two (or more) TE-
   Classes.  Also, there is no mandatory ordering relationship between
   the TE-Class index (i.e., "i" above) and the Class-Type (i.e., "c"
   above) or the preemption priority (i.e., "p" above) of the TE-Class.

   Where the network administrator uses less than 8 TE-Classes, the DS-
   TE LSR MUST allow remaining ones to be configured as "Unused".  Note
   that configuring all the 8 TE-Classes as "Unused" effectively results
   in disabling TE/DS-TE since no TE/DS-TE LSP can be established (nor
   even configured, since as described in <a href="#section-4.3.3">Section 4.3.3</a> below, the CT
   and preemption priorities configured for an LSP MUST form one of the
   configured TE-Classes).

   To ensure coherent DS-TE operation, the network administrator MUST
   configure exactly the same TE-Class mapping on all LSRs of the DS-TE
   domain.




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   When the TE-Class mapping needs to be modified in the DS-TE domain,
   care ought to be exercised during the transient period of
   reconfiguration during which some DS-TE LSRs may be configured with
   the new TE-Class mapping while others are still configured with the
   old TE-Class mapping.  It is recommended that active tunnels do not
   use any of the TE-Classes that are being modified during such a
   transient reconfiguration period.

<span class="h3"><a class="selflink" id="section-4.3" href="#section-4.3">4.3</a>.  LSP Parameters</span>

<span class="h4"><a class="selflink" id="section-4.3.1" href="#section-4.3.1">4.3.1</a>.  Class-Type</span>

   With DS-TE, LSRs MUST support, for every LSP, an additional
   configurable parameter that indicates the Class-Type of the Traffic
   Trunk transported by the LSP.

   There is one and only one Class-Type configured per LSP.

   The configured Class-Type indicates, in accordance with the supported
   Bandwidth Constraints Model, the BCs that MUST be enforced for that
   LSP.

<span class="h4"><a class="selflink" id="section-4.3.2" href="#section-4.3.2">4.3.2</a>.  Setup and Holding Preemption Priorities</span>

   As per existing TE, DS-TE LSRs MUST allow every DS-TE LSP to be
   configured with a setup and holding priority, each with a value
   between 0 and 7.

<span class="h4"><a class="selflink" id="section-4.3.3" href="#section-4.3.3">4.3.3</a>.  Class-Type/Preemption Relationship</span>

   With DS-TE, the preemption priority configured for the setup priority
   of a given LSP and the Class-Type configured for that LSP MUST be
   such that, together, they form one of the (up to) 8 TE-Classes
   configured in the TE-Class mapping specified in <a href="#section-4.2.1">Section 4.2.1</a> above.

   The preemption priority configured for the holding priority of a
   given LSP and the Class-Type configured for that LSP MUST also be
   such that, together, they form one of the (up to) 8 TE-Classes
   configured in the TE-Class mapping specified in <a href="#section-4.2.1">Section 4.2.1</a> above.

   The LSR MUST enforce these two rules at configuration time.










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<span class="h3"><a class="selflink" id="section-4.4" href="#section-4.4">4.4</a>.  Examples of Parameters Configuration</span>

   For illustration purposes, we now present a few examples of how these
   configurable parameters may be used.  All these examples assume that
   different BCs need to be enforced for different sets of Traffic
   Trunks (e.g., for Voice and for Data) so that two or more Class-Types
   need to be used.

<span class="h4"><a class="selflink" id="section-4.4.1" href="#section-4.4.1">4.4.1</a>.  Example 1</span>

   The network administrator of a first network using two CTs (CT1 for
   Voice and CT0 for Data) may elect to configure the following TE-Class
   mapping to ensure that Voice LSPs are never driven away from their
   shortest path because of Data LSPs:

        TE-Class[0]  &lt;--&gt;  &lt; CT1 , preemption 0 &gt;
        TE-Class[1]  &lt;--&gt;  &lt; CT0 , preemption 1 &gt;
        TE-Class[i]  &lt;--&gt;  unused, for 2 &lt;= i &lt;= 7

   Voice LSPs would then be configured with:
        CT = CT1, setup priority = 0, holding priority = 0

   Data LSPs would then be configured with:
        CT = CT0, setup priority = 1, holding priority = 1

   A new Voice LSP would then be able to preempt an existing Data LSP in
   case they contend for resources.  A Data LSP would never preempt a
   Voice LSP.  A Voice LSP would never preempt another Voice LSP.  A
   Data LSP would never preempt another Data LSP.

<span class="h4"><a class="selflink" id="section-4.4.2" href="#section-4.4.2">4.4.2</a>.  Example 2</span>

   The network administrator of another network may elect to configure
   the following TE-Class mapping in order to optimize global network
   resource utilization by favoring placement of large LSPs closer to
   their shortest path:

        TE-Class[0]  &lt;--&gt;  &lt; CT1 , preemption 0 &gt;
        TE-Class[1]  &lt;--&gt;  &lt; CT0 , preemption 1 &gt;
        TE-Class[2]  &lt;--&gt;  &lt; CT1 , preemption 2 &gt;
        TE-Class[3]  &lt;--&gt;  &lt; CT0 , preemption 3 &gt;
        TE-Class[i]  &lt;--&gt;  unused, for 4 &lt;= i &lt;= 7

   Large-size Voice LSPs could be configured with:
        CT = CT1, setup priority = 0, holding priority = 0

   Large-size Data LSPs could be configured with:
        CT = CT0, setup priority = 1, holding priority = 1



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   Small-size Voice LSPs could be configured with:
        CT = CT1, setup priority = 2, holding priority = 2

   Small-size Data LSPs could be configured with:
        CT = CT0, setup priority = 3, holding priority = 3

   A new large-size Voice LSP would then be able to preempt a small-size
   Voice LSP or any Data LSP in case they contend for resources.  A new
   large-size Data LSP would then be able to preempt a small-size Data
   LSP or a small-size Voice LSP in case they contend for resources, but
   it would not be able to preempt a large-size Voice LSP.

<span class="h4"><a class="selflink" id="section-4.4.3" href="#section-4.4.3">4.4.3</a>.  Example 3</span>

   The network administrator of another network may elect to configure
   the following TE-Class mapping in order to ensure that Voice LSPs are
   never driven away from their shortest path because of Data LSPs.
   This also achieves some optimization of global network resource
   utilization by favoring placement of large LSPs closer to their
   shortest path:

        TE-Class[0]  &lt;--&gt;  &lt; CT1 , preemption 0 &gt;
        TE-Class[1]  &lt;--&gt;  &lt; CT1 , preemption 1 &gt;
        TE-Class[2]  &lt;--&gt;  &lt; CT0 , preemption 2 &gt;
        TE-Class[3]  &lt;--&gt;  &lt; CT0 , preemption 3 &gt;
        TE-Class[i]  &lt;--&gt;  unused, for 4 &lt;= i &lt;= 7

   Large-size Voice LSPs could be configured with:
        CT = CT1, setup priority = 0, holding priority = 0.

   Small-size Voice LSPs could be configured with:
        CT = CT1, setup priority = 1, holding priority = 1.

   Large-size Data LSPs could be configured with:
        CT = CT0, setup priority = 2, holding priority = 2.

   Small-size Data LSPs could be configured with:
        CT=CT0, setup priority = 3, holding priority = 3.

   A Voice LSP could preempt a Data LSP if they contend for resources.
   A Data LSP would never preempt a Voice LSP.  A large-size Voice LSP
   could preempt a small-size Voice LSP if they contend for resources.
   A large-size Data LSP could preempt a small-size Data LSP if they
   contend for resources.







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<span class="h4"><a class="selflink" id="section-4.4.4" href="#section-4.4.4">4.4.4</a>.  Example 4</span>

   The network administrator of another network may elect to configure
   the following TE-Class mapping in order to ensure that no preemption
   occurs in the DS-TE domain:

        TE-Class[0]  &lt;--&gt;  &lt; CT1 , preemption 0 &gt;
        TE-Class[1]  &lt;--&gt;  &lt; CT0 , preemption 0 &gt;
        TE-Class[i]  &lt;--&gt;  unused,   for 2 &lt;= i &lt;= 7

   Voice LSPs would then be configured with:
        CT = CT1, setup priority =0, holding priority = 0

   Data LSPs would then be configured with:
        CT = CT0, setup priority = 0, holding priority = 0

   No LSP would then be able to preempt any other LSP.

<span class="h4"><a class="selflink" id="section-4.4.5" href="#section-4.4.5">4.4.5</a>.  Example 5</span>

   The network administrator of another network may elect to configure
   the following TE-Class mapping in view of increased network stability
   through a more limited use of preemption:

        TE-Class[0]  &lt;--&gt;  &lt; CT1 , preemption 0 &gt;
        TE-Class[1]  &lt;--&gt;  &lt; CT1 , preemption 1 &gt;
        TE-Class[2]  &lt;--&gt;  &lt; CT0 , preemption 1 &gt;
        TE-Class[3]  &lt;--&gt;  &lt; CT0 , preemption 2 &gt;
        TE-Class[i]  &lt;--&gt;  unused, for 4 &lt;= i &lt;= 7

   Large-size Voice LSPs could be configured with: CT = CT1, setup
        priority = 0, holding priority = 0.

   Small-size Voice LSPs could be configured with: CT = CT1, setup
        priority = 1, holding priority = 0.

   Large-size Data LSPs could be configured with: CT = CT0, setup
        priority = 2, holding priority = 1.

   Small-size Data LSPs could be configured with: CT = CT0, setup
        priority = 2, holding priority = 2.

   A new large-size Voice LSP would be able to preempt a Data LSP in
   case they contend for resources, but it would not be able to preempt
   any Voice LSP even a small-size Voice LSP.






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   A new small-size Voice LSP would be able to preempt a small-size Data
   LSP in case they contend for resources, but it would not be able to
   preempt a large-size Data LSP or any Voice LSP.

   A Data LSP would not be able to preempt any other LSP.

<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>.  IGP Extensions for DS-TE</span>

   This section only discusses the differences with the IGP
   advertisement supported for (aggregate) MPLS Traffic Engineering as
   per [<a href="#ref-OSPF-TE" title="&quot;Traffic Engineering (TE) Extensions to OSPF Version 2&quot;">OSPF-TE</a>] and [<a href="#ref-ISIS-TE" title="&quot;Intermediate System to Intermediate System (IS-IS) Extensions for Traffic Engineering (TE)&quot;">ISIS-TE</a>].  The rest of the IGP advertisement is
   unchanged.

<span class="h3"><a class="selflink" id="section-5.1" href="#section-5.1">5.1</a>.  Bandwidth Constraints</span>

   As detailed above in <a href="#section-4.1.1">Section 4.1.1</a>, up to 8 BCs (BCb, 0 &lt;= b &lt;= 7)
   are configurable on any given link.

   With DS-TE, the existing "Maximum Reservable Bandwidth" sub-TLV
   ([<a href="#ref-OSPF-TE" title="&quot;Traffic Engineering (TE) Extensions to OSPF Version 2&quot;">OSPF-TE</a>], [<a href="#ref-ISIS-TE" title="&quot;Intermediate System to Intermediate System (IS-IS) Extensions for Traffic Engineering (TE)&quot;">ISIS-TE</a>]) is retained with a generalized semantics so
   that it MUST now be interpreted as the aggregate bandwidth constraint
   across all Class-Types; i.e., SUM (Reserved (CTc)) &lt;= Max Reservable
   Bandwidth, independently of the Bandwidth Constraints Model.

   This document also defines the following new optional sub-TLV to
   advertise the eight potential BCs (BC0 to BC7):

   "Bandwidth Constraints" sub-TLV:

        - Bandwidth Constraints Model Id (1 octet)
        - Reserved (3 octets)
        - Bandwidth Constraints (N x 4 octets)

   Where:
        - With OSPF, the sub-TLV is a sub-TLV of the "Link TLV" and its
          sub-TLV type is 17.

        - With ISIS, the sub-TLV is a sub-TLV of the "extended IS
          reachability TLV" and its sub-TLV type is 22.

        - Bandwidth Constraints Model Id: a 1-octet identifier for the
          Bandwidth Constraints Model currently in use by the LSR
          initiating the IGP advertisement.  See the IANA Considerations
          section for assignment of values in this name space.

        - Reserved: a 3-octet field.  This field should be set to zero
          by the LSR generating the sub-TLV and should be ignored by the
          LSR receiving the sub-TLV.



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        - Bandwidth Constraints: contains BC0, BC1,... BC(N-1).  Each BC
          is encoded on 32 bits in IEEE floating point format.  The
          units are bytes (not bits!) per second.  Where the configured
          TE-Class mapping and the Bandwidth Constraints model in use
          are such that BCh+1, BCh+2, ...and BC7 are not relevant to any
          of the Class-Types associated with a configured TE-Class, it
          is RECOMMENDED that only the Bandwidth Constraints from BC0 to
          BCh be advertised, in order to minimize the impact on IGP
          scalability.

   All relevant generic TLV encoding rules (including TLV format,
   padding and alignment, as well as IEEE floating point format
   encoding) defined in [<a href="#ref-OSPF-TE" title="&quot;Traffic Engineering (TE) Extensions to OSPF Version 2&quot;">OSPF-TE</a>] and [<a href="#ref-ISIS-TE" title="&quot;Intermediate System to Intermediate System (IS-IS) Extensions for Traffic Engineering (TE)&quot;">ISIS-TE</a>] are applicable to this
   new sub-TLV.

   The "Bandwidth Constraints" sub-TLV format is illustrated below:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | BC Model Id   |           Reserved                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       BC0 value                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //                       . . .                                 //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       BCh value                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   A DS-TE LSR MAY optionally advertise BCs.

   A DS-TE LSR, which does advertise BCs, MUST use the new "Bandwidth
   Constraints" sub-TLV (in addition to the existing Maximum Reservable
   Bandwidth sub-TLV) to do so.  For example, in the case where a
   service provider deploys DS-TE with TE-Classes associated with CT0
   and CT1 only, and where the Bandwidth Constraints Model is such that
   only BC0 and BC1 are relevant to CT0 and CT1, a DS-TE LSR which does
   advertise BCs would include in the IGP advertisement the Maximum
   Reservable Bandwidth sub-TLV, as well as the "Bandwidth Constraints"
   sub-TLV.  The former should contain the aggregate bandwidth
   constraint across all CTs, and the latter should contain BC0 and BC1.

   A DS-TE LSR receiving the "Bandwidth Constraints" sub-TLV with a
   Bandwidth Constraints Model Id that does not match the Bandwidth
   Constraints Model it currently uses SHOULD generate a warning to the
   operator/management system, reporting the inconsistency between
   Bandwidth Constraints Models used on different links.  Also, in that
   case, if the DS-TE LSR does not support the Bandwidth Constraints



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   Model designated by the Bandwidth Constraints Model Id, or if the
   DS-TE LSR does not support operations with multiple simultaneous
   Bandwidth Constraints Models, the DS-TE LSR MAY discard the
   corresponding TLV.  If the DS-TE LSR does support the Bandwidth
   Constraints Model designated by the Bandwidth Constraints Model Id,
   and if the DS-TE LSR does support operations with multiple
   simultaneous Bandwidth Constraints Models, the DS-TE LSR MAY accept
   the corresponding TLV and allow operations with different Bandwidth
   Constraints Models used in different parts of the DS-TE domain.

<span class="h3"><a class="selflink" id="section-5.2" href="#section-5.2">5.2</a>.  Unreserved Bandwidth</span>

   With DS-TE, the existing "Unreserved Bandwidth" sub-TLV is retained
   as the only vehicle to advertise dynamic bandwidth information
   necessary for Constraint-Based Routing on head-ends, except that it
   is used with a generalized semantics.  The Unreserved Bandwidth sub-
   TLV still carries eight bandwidth values, but they now correspond to
   the unreserved bandwidth for each of the TE-Classes (instead of for
   each preemption priority, as per existing TE).

   More precisely, a DS-TE LSR MUST support the Unreserved Bandwidth
   sub-TLV with a definition that is generalized into the following:

   The Unreserved Bandwidth sub-TLV specifies the amount of bandwidth
   not yet reserved for each of the eight TE-Classes, in IEEE floating
   point format arranged in increasing order of TE-Class index.
   Unreserved bandwidth for TE-Class [0] occurs at the start of the
   sub-TLV, and unreserved bandwidth for TE-Class [7] at the end of the
   sub-TLV.  The unreserved bandwidth value for TE-Class [i] ( 0 &lt;= i &lt;=
   7) is referred to as "Unreserved TE-Class [i]".  It indicates the
   bandwidth that is available, for reservation, to an LSP that:

   - transports a Traffic Trunk from the Class-Type of TE-Class[i], and

   - has a setup priority corresponding to the preemption priority of
     TE-Class[i].

   The units are bytes per second.

   Because the bandwidth values are now ordered by TE-class index and
   thus can relate to different CTs with different BCs and to any
   arbitrary preemption priority, a DS-TE LSR MUST NOT assume any
   ordered relationship among these bandwidth values.

   With existing TE, because all preemption priorities reflect the same
   (and only) BCs and bandwidth values are advertised in preemption
   priority order, the following relationship is always true, and is
   often assumed by TE implementations:



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      If i &lt; j, then "Unreserved Bw [i]" &gt;= "Unreserved Bw [j]"

   With DS-TE, no relationship is to be assumed such that:

      If i &lt; j, then any of the following relationships may be true:
                "Unreserved TE-Class [i]" = "Unreserved TE-Class [j]"
                    OR
                "Unreserved TE-Class [i]" &gt; "Unreserved TE-Class [j]"
                    OR
                "Unreserved TE-Class [i]" &lt; "Unreserved TE-Class [j]".

   Rules for computing "Unreserved TE-Class [i]" are specified in
   <a href="#section-11">Section 11</a>.

   If TE-Class[i] is unused, the value advertised by the IGP in
   "Unreserved TE-Class [i]" MUST be set to zero by the LSR generating
   the IGP advertisement, and MUST be ignored by the LSR receiving the
   IGP advertisement.

<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>.  RSVP-TE Extensions for DS-TE</span>

   In this section, we describe extensions to RSVP-TE for support of
   Diffserv-aware MPLS Traffic Engineering.  These extensions are in
   addition to the extensions to RSVP defined in [<a href="#ref-RSVP-TE" title="&quot;RSVP-TE: Extensions to RSVP for LSP Tunnels&quot;">RSVP-TE</a>] for support
   of (aggregate) MPLS Traffic Engineering and to the extensions to RSVP
   defined in [<a href="#ref-DIFF-MPLS" title="&quot;Multi-Protocol Label Switching (MPLS) Support of Differentiated Services&quot;">DIFF-MPLS</a>] for support of Diffserv over MPLS.

<span class="h3"><a class="selflink" id="section-6.1" href="#section-6.1">6.1</a>.  DS-TE-Related RSVP Messages Format</span>

   One new RSVP object is defined in this document: the CLASSTYPE
   object.  Detailed description of this object is provided below.  This
   new object is applicable to Path messages.  This specification only
   defines the use of the CLASSTYPE object in Path messages used to
   establish LSP Tunnels in accordance with [<a href="#ref-RSVP-TE" title="&quot;RSVP-TE: Extensions to RSVP for LSP Tunnels&quot;">RSVP-TE</a>] and thus
   containing a session object with a CT equal to LSP_TUNNEL_IPv4 and
   containing a LABEL_REQUEST object.

   Restrictions defined in [<a href="#ref-RSVP-TE" title="&quot;RSVP-TE: Extensions to RSVP for LSP Tunnels&quot;">RSVP-TE</a>] for support of establishment of LSP
   Tunnels via RSVP-TE are also applicable to the establishment of LSP
   Tunnels supporting DS-TE.  For instance, only unicast LSPs are
   supported, and multicast LSPs are for further study.

   This new CLASSTYPE object is optional with respect to RSVP so that
   general RSVP implementations not concerned with MPLS LSP setup do not
   have to support this object.

   An LSR supporting DS-TE MUST support the CLASSTYPE object.




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<span class="h4"><a class="selflink" id="section-6.1.1" href="#section-6.1.1">6.1.1</a>.  Path Message Format</span>

   The format of the Path message is as follows:

   &lt;Path Message&gt; ::=      &lt;Common Header&gt; [ &lt;INTEGRITY&gt; ]
                           &lt;SESSION&gt; &lt;RSVP_HOP&gt;
                           &lt;TIME_VALUES&gt;
                           [ &lt;EXPLICIT_ROUTE&gt; ]
                           &lt;LABEL_REQUEST&gt;
                           [ &lt;SESSION_ATTRIBUTE&gt; ]
                           [ &lt;DIFFSERV&gt; ]
                           [ &lt;CLASSTYPE&gt; ]
                           [ &lt;POLICY_DATA&gt; ... ]
                           [ &lt;sender descriptor&gt; ]

   &lt;sender descriptor&gt; ::=  &lt;SENDER_TEMPLATE&gt; [ &lt;SENDER_TSPEC&gt; ]
                           [ &lt;ADSPEC&gt; ]
                           [ &lt;RECORD_ROUTE&gt; ]


<span class="h3"><a class="selflink" id="section-6.2" href="#section-6.2">6.2</a>.  CLASSTYPE Object</span>

   The CLASSTYPE object Class Name is CLASSTYPE.  Its Class Number is
   66.  Currently, there is only one defined C-Type which is C-Type 1.
   The CLASSTYPE object format is shown below.

<span class="h4"><a class="selflink" id="section-6.2.1" href="#section-6.2.1">6.2.1</a>.  CLASSTYPE object</span>

   Class Number = 66
   Class-Type = 1

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Reserved                                         |  CT |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Reserved: 29 bits
       This field is reserved.  It MUST be set to zero on transmission
       and MUST be ignored on receipt.

   CT: 3 bits
       Indicates the Class-Type.  Values currently allowed are
       1, 2, ... , 7.  Value of 0 is Reserved.







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<span class="h3"><a class="selflink" id="section-6.3" href="#section-6.3">6.3</a>.  Handling CLASSTYPE Object</span>

   To establish an LSP tunnel with RSVP, the sender LSR creates a Path
   message with a session type of LSP_Tunnel_IPv4 and with a

   LABEL_REQUEST object as per [<a href="#ref-RSVP-TE" title="&quot;RSVP-TE: Extensions to RSVP for LSP Tunnels&quot;">RSVP-TE</a>].  The sender LSR may also
   include the DIFFSERV object as per [<a href="#ref-DIFF-MPLS" title="&quot;Multi-Protocol Label Switching (MPLS) Support of Differentiated Services&quot;">DIFF-MPLS</a>].

   If the LSP is associated with Class-Type 0, the sender LSR MUST NOT
   include the CLASSTYPE object in the Path message.  This allows
   backward compatibility with non-DSTE-configured or non-DSTE-capable
   LSRs as discussed below in <a href="#section-10">Section 10</a> and <a href="#appendix-C">Appendix C</a>.

   If the LSP is associated with Class-Type N (1 &lt;= N &lt;=7), the sender
   LSR MUST include the CLASSTYPE object in the Path message with the
   Class-Type (CT) field set to N.

   If a Path message contains multiple CLASSTYPE objects, only the first
   one is meaningful; subsequent CLASSTYPE object(s) MUST be ignored and
   MUST NOT be forwarded.

   Each LSR along the path MUST record the CLASSTYPE object, when it is
   present, in its path state block.

   If the CLASSTYPE object is not present in the Path message, the LSR
   MUST associate the Class-Type 0 to the LSP.

   The destination LSR responding to the Path message by sending a Resv
   message MUST NOT include a CLASSTYPE object in the Resv message
   (whether or not the Path message contained a CLASSTYPE object).

   During establishment of an LSP corresponding to the Class-Type N, the
   LSR MUST perform admission control over the bandwidth available for
   that particular Class-Type.

   An LSR that recognizes the CLASSTYPE object and that receives a Path
   message that:

         - contains the CLASSTYPE object, but

         - does not contain a LABEL_REQUEST object or does not have a
           session type of LSP_Tunnel_IPv4,

   MUST send a PathErr towards the sender with the error code
   "Diffserv-aware TE Error" and an error value of "Unexpected CLASSTYPE
   object".  These codes are defined in <a href="#section-6.5">Section 6.5</a>.





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   An LSR receiving a Path message with the CLASSTYPE object that:

         - recognizes the CLASSTYPE object, but

         - does not support the particular Class-Type,

   MUST send a PathErr towards the sender with the error code
   "Diffserv-aware TE Error" and an error value of "Unsupported Class-
   Type".  These codes are defined in <a href="#section-6.5">Section 6.5</a>.

   An LSR receiving a Path message with the CLASSTYPE object that:

         - recognizes the CLASSTYPE object, but

         - determines that the Class-Type value is not valid (i.e.,
           Class-Type value 0),

   MUST send a PathErr towards the sender with the error code
   "Diffserv-aware TE Error" and an error value of "Invalid Class-Type
   value".  These codes are defined in <a href="#section-6.5">Section 6.5</a>.

   An LSR receiving a Path message with the CLASSTYPE object, which:

         - recognizes the CLASSTYPE object and

         - supports the particular Class-Type, but

         - determines that the tuple formed by (i) this Class-Type and
           (ii) the setup priority signaled in the same Path message, is
           not one of the eight TE-Classes configured in the TE-class
           mapping,

   MUST send a PathErr towards the sender with the error code
   "Diffserv-aware TE Error" and an error value of "CT and setup
   priority do not form a configured TE-Class".  These codes are defined
   in <a href="#section-6.5">Section 6.5</a>.

   An LSR receiving a Path message with the CLASSTYPE object that:

         - recognizes the CLASSTYPE object and

         - supports the particular Class-Type, but

         - determines that the tuple formed by (i) this Class-Type and
           (ii) the holding priority signaled in the same Path message,
           is not one of the eight TE-Classes configured in the TE-class
           mapping,




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   MUST send a PathErr towards the sender with the error code
   "Diffserv-aware TE Error" and an error value of "CT and holding
   priority do not form a configured TE-Class".  These codes are defined
   in <a href="#section-6.5">Section 6.5</a>.

   An LSR receiving a Path message with the CLASSTYPE object that:

         - recognizes the CLASSTYPE object and

         - supports the particular Class-Type, but

         - determines that the tuple formed by (i) this Class-Type and
           (ii) the setup priority signaled in the same Path message, is
           not one of the eight TE-Classes configured in the TE-class
           mapping, AND

         - determines that the tuple formed by (i) this Class-Type and
           (ii) the holding priority signaled in the same Path message,
           is not one of the eight TE-Classes configured in the TE-class
           mapping

   MUST send a PathErr towards the sender with the error code
   "Diffserv-aware TE Error" and an error value of "CT and setup
   priority do not form a configured TE-Class AND CT and holding
   priority do not form a configured TE-Class".  These codes are defined
   in <a href="#section-6.5">Section 6.5</a>.

   An LSR receiving a Path message with the CLASSTYPE object and with
   the DIFFSERV object for an L-LSP that:

         - recognizes the CLASSTYPE object,

         - has local knowledge of the relationship between Class-Types
           and Per Hop Behavior (PHB) Scheduling Class, e.g., via
           configuration, and

         - determines, based on this local knowledge, that the PHB
           Scheduling Class (PSC) signaled in the DIFFSERV object is
           inconsistent with the Class-Type signaled in the CLASSTYPE
           object,

   MUST send a PathErr towards the sender with the error code
   "Diffserv-aware TE Error" and an error value of "Inconsistency
   between signaled PSC and signaled CT".  These codes are defined below
   in <a href="#section-6.5">Section 6.5</a>.






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   An LSR receiving a Path message with the CLASSTYPE object and with
   the DIFFSERV object for an E-LSP that:

         - recognizes the CLASSTYPE object,

         - has local knowledge of the relationship between Class-Types
           and PHBs (e.g., via configuration)

         - determines, based on this local knowledge, that the PHBs
           signaled in the MAP entries of the DIFFSERV object are
           inconsistent with the Class-Type signaled in the CLASSTYPE
           object,

   MUST send a PathErr towards the sender with the error code
   "Diffserv-aware TE Error" and an error value of "Inconsistency
   between signaled PHBs and signaled CT".  These codes are defined in
   <a href="#section-6.5">Section 6.5</a>.

   An LSR MUST handle situations in which the LSP cannot be accepted for
   reasons other than those already discussed in this section, in
   accordance with [<a href="#ref-RSVP-TE" title="&quot;RSVP-TE: Extensions to RSVP for LSP Tunnels&quot;">RSVP-TE</a>] and [<a href="#ref-DIFF-MPLS" title="&quot;Multi-Protocol Label Switching (MPLS) Support of Differentiated Services&quot;">DIFF-MPLS</a>] (e.g., a reservation is
   rejected by admission control, and a label cannot be associated).

<span class="h3"><a class="selflink" id="section-6.4" href="#section-6.4">6.4</a>.  Non-support of the CLASSTYPE Object</span>

   An LSR that does not recognize the CLASSTYPE object Class-Num MUST
   behave in accordance with the procedures specified in [<a href="#ref-RSVP" title="&quot;Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification&quot;">RSVP</a>] for an
   unknown Class-Num whose format is 0bbbbbbb (i.e., it MUST send a
   PathErr with the error code "Unknown object class" toward the
   sender).

   An LSR that recognizes the CLASSTYPE object Class-Num but that does
   not recognize the CLASSTYPE object C-Type, MUST behave in accordance
   with the procedures specified in [<a href="#ref-RSVP" title="&quot;Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification&quot;">RSVP</a>] for an unknown C-type (i.e.,
   it MUST send a PathErr with the error code "Unknown object C-Type"
   toward the sender).

   Both of the above situations cause the path setup to fail.  The
   sender SHOULD notify the operator/management system that an LSP
   cannot be established and might take action to retry reservation
   establishment without the CLASSTYPE object.

<span class="h3"><a class="selflink" id="section-6.5" href="#section-6.5">6.5</a>.  Error Codes for Diffserv-aware TE</span>

   In the procedures described above, certain errors are reported as a
   "Diffserv-aware TE Error".  The value of the "Diffserv-aware TE
   Error" error code is 28.




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   The following table defines error values for the Diffserv-aware TE
   Error:

      Value     Error

      1      Unexpected CLASSTYPE object
      2      Unsupported Class-Type
      3      Invalid Class-Type value
      4      Class-Type and setup priority do not form a configured
                TE-Class
      5      Class-Type and holding priority do not form a
                configured TE-Class
      6      Class-Type and setup priority do not form a configured
                TE-Class AND Class-Type and holding priority do not form
             a configured TE-Class
      7      Inconsistency between signaled PSC and signaled
                Class-Type
      8      Inconsistency between signaled PHBs and signaled
                Class-Type

   See the IANA Considerations section for allocation of additional
   values.

<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>.  DS-TE Support with MPLS Extensions</span>

   There are a number of extensions to the initial base specification
   for signaling [<a href="#ref-RSVP-TE" title="&quot;RSVP-TE: Extensions to RSVP for LSP Tunnels&quot;">RSVP-TE</a>] and IGP support for TE [<a href="#ref-OSPF-TE" title="&quot;Traffic Engineering (TE) Extensions to OSPF Version 2&quot;">OSPF-TE</a>][ISIS-TE].
   Those include enhancements for generalization ([<a href="#ref-GMPLS-SIG" title="&quot;Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description&quot;">GMPLS-SIG</a>] and
   [<a href="#ref-GMPLS-ROUTE" title="&quot;Routing Extensions in Support of Generalized MPLS&quot;">GMPLS-ROUTE</a>]), as well as for additional functionality, such as LSP
   hierarchy [<a href="#ref-HIERARCHY" title="&quot;LSP Hierarchy with Generalized MPLS TE&quot;">HIERARCHY</a>], link bundling [<a href="#ref-BUNDLE" title="&quot;Link Bundling in MPLS Traffic Engineering&quot;">BUNDLE</a>], and fast restoration
   [<a href="#ref-REROUTE" title="&quot;Fast Reroute Extensions to RSVP-TE for LSP Tunnels&quot;">REROUTE</a>].  These specifications may reference how to encode
   information associated with certain preemption priorities, how to
   treat LSPs at different preemption priorities, or they may otherwise
   specify encodings or behavior that have a different meaning for a
   DS-TE router.

   In order for an implementation to support both this specification for
   Diffserv-aware TE and a given MPLS enhancement, such as those listed
   above (but not limited to those), it MUST treat references to
   "preemption priority" and to "Maximum Reservable Bandwidth" in a
   generalized manner, i.e., the manner in which this specification uses
   those terms.

   Additionally, current and future MPLS enhancements may include more
   precise specification for how they interact with Diffserv-aware TE.






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<span class="h3"><a class="selflink" id="section-7.1" href="#section-7.1">7.1</a>.  DS-TE Support and References to Preemption Priority</span>

   When a router supports both Diffserv-aware TE and one of the MPLS
   protocol extensions such as those mentioned above, encoding of values
   of preemption priority in signaling or encoding of information
   associated with preemption priorities in IGP defined for the MPLS
   extension, MUST be considered an encoding of the same information for
   the corresponding TE-Class.  For instance, if an MPLS enhancement
   specifies advertisement in IGP of a parameter for routing information
   at preemption priority N, in a DS-TE environment it MUST actually be
   interpreted as specifying advertisement of the same routing
   information but for TE-Class [N].  On receipt, DS-TE routers MUST
   also interpret it as such.

   When there is discussion on how to comparatively treat LSPs of
   different preemption priority, a DS-TE LSR MUST treat the preemption
   priorities in this context as those associated with the TE-Classes of
   the LSPs in question.

<span class="h3"><a class="selflink" id="section-7.2" href="#section-7.2">7.2</a>.  DS-TE Support and References to Maximum Reservable Bandwidth</span>

   When a router supports both Diffserv-aware TE and MPLS protocol
   extensions such as those mentioned above, advertisements of Maximum
   Reservable Bandwidth MUST be done with the generalized interpretation
   defined in <a href="#section-4.1.1">Section 4.1.1</a> as the aggregate bandwidth constraint across
   all Class-Types.  It MAY also allow the optional advertisement of all
   BCs.

<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>.  Constraint-Based Routing</span>

   Let us consider the case where a path needs to be computed for an LSP
   whose Class-Type is configured to CTc and whose setup preemption
   priority is configured to p.

   Then the pair of CTc and p will map to one of the TE-Classes defined
   in the TE-Class mapping.  Let us refer to this TE-Class as TE-
   Class[i].

   The Constraint-Based Routing algorithm of a DS-TE LSR is still only
   required to perform path computation satisfying a single BC which is
   to fit in "Unreserved TE-Class [i]" as advertised by the IGP for
   every link.  Thus, no changes to the existing TE Constraint-Based
   Routing algorithm itself are required.

   The Constraint-Based Routing algorithm MAY also take into account,
   when used, the optional additional information advertised in IGP such
   as the BCs and the Maximum Reservable Bandwidth.  For example, the




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   BCs MIGHT be used as tie-breaker criteria in situations where
   multiple paths, otherwise equally attractive, are possible.

<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>.  Diffserv Scheduling</span>

   The Class-Type signaled at LSP establishment MAY optionally be used
   by DS-TE LSRs to dynamically adjust the resources allocated to the
   Class-Type by the Diffserv scheduler.  In addition, the Diffserv
   information (i.e., the PSC) signaled by the TE-LSP signaling
   protocols as specified in [<a href="#ref-DIFF-MPLS" title="&quot;Multi-Protocol Label Switching (MPLS) Support of Differentiated Services&quot;">DIFF-MPLS</a>], if used, MAY optionally be
   used by DS-TE LSRs to dynamically adjust the resources allocated by
   the Diffserv scheduler to a PSC/OA within a CT.

<span class="h2"><a class="selflink" id="section-10" href="#section-10">10</a>.  Existing TE as a Particular Case of DS-TE</span>

   We observe that existing TE can be viewed as a particular case of
   DS-TE where:

      (i)   a single Class-Type is used,
      (ii)  all 8 preemption priorities are allowed for that Class-Type,
            and
      (iii) the following TE-Class mapping is used:
                  TE-Class[i]  &lt;--&gt;  &lt; CT0 , preemption i &gt;
                  Where 0 &lt;= i &lt;= 7.

   In that case, DS-TE behaves as existing TE.

   As with existing TE, the IGP advertises:
        - Unreserved Bandwidth for each of the 8 preemption priorities.

   As with existing TE, the IGP may advertise:
        - Maximum Reservable Bandwidth containing a BC applying across
          all LSPs .

   Because all LSPs transport traffic from CT0, RSVP-TE signaling is
   done without explicit signaling of the Class-Type (which is only used
   for Class-Types other than CT0, as explained in <a href="#section-6">Section 6</a>) as with
   existing TE.

<span class="h2"><a class="selflink" id="section-11" href="#section-11">11</a>.  Computing "Unreserved TE-Class [i]" and Admission Control Rules</span>

<span class="h3"><a class="selflink" id="section-11.1" href="#section-11.1">11.1</a>.  Computing "Unreserved TE-Class [i]"</span>

   We first observe that, for existing TE, details on admission control
   algorithms for TE LSPs, and consequently details on formulas for
   computing the unreserved bandwidth, are outside the scope of the
   current IETF work.  This is left for vendor differentiation.  Note
   that this does not compromise interoperability across various



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   implementations because the TE schemes rely on LSRs to advertise
   their local view of the world in terms of Unreserved Bw to other
   LSRs.  This way, regardless of the actual local admission control
   algorithm used on one given LSR, Constraint-Based Routing on other
   LSRs can rely on advertised information to determine whether an
   additional LSP will be accepted or rejected by the given LSR.  The
   only requirement is that an LSR advertises unreserved bandwidth
   values that are consistent with its specific local admission control
   algorithm and take into account the holding preemption priority of
   established LSPs.

   In the context of DS-TE, again, details on admission control
   algorithms are left for vendor differentiation, and formulas for
   computing the unreserved bandwidth for TE-Class[i] are outside the
   scope of this specification.  However, DS-TE places the additional
   requirement on the LSR that the unreserved bandwidth values
   advertised MUST reflect all the BCs relevant to the CT associated
   with TE-Class[i] in accordance with the Bandwidth Constraints Model.
   Thus, formulas for computing "Unreserved TE-Class [i]" depend on the
   Bandwidth Constraints Model in use and MUST reflect how BCs apply to
   CTs.  Example formulas for computing "Unreserved TE-Class [i]" Model
   are provided for the Russian Dolls Model and Maximum Allocation Model
   respectively in [<a href="#ref-DSTE-RDM" title="&quot;Russian Dolls Bandwidth Constraints Model for Diffserv-aware MPLS Traffic Engineering&quot;">DSTE-RDM</a>] and [<a href="#ref-DSTE-MAM" title="&quot;Maximum Allocation Bandwidth Constraints Model for Diffserv-aware Traffice Engineering&quot;">DSTE-MAM</a>].

   As with existing TE, DS-TE LSRs MUST consider the holding preemption
   priority of established LSPs (as opposed to their setup preemption
   priority) for the purpose of computing the unreserved bandwidth for
   TE-Class [i].

<span class="h3"><a class="selflink" id="section-11.2" href="#section-11.2">11.2</a>.  Admission Control Rules</span>

   A DS-TE LSR MUST support the following admission control rule:

   Regardless of how the admission control algorithm actually computes
   the unreserved bandwidth for TE-Class[i] for one of its local links,
   an LSP of bandwidth B, of setup preemption priority p and of Class-
   Type CTc is admissible on that link if, and only if,:

        B &lt;= Unreserved Bandwidth for TE-Class[i]

   where TE-Class [i] maps to  &lt; CTc , p &gt; in the TE-Class mapping
   configured on the LSR.

<span class="h2"><a class="selflink" id="section-12" href="#section-12">12</a>.  Security Considerations</span>

   This document does not introduce additional security threats beyond
   those described for Diffserv ([<a href="#ref-DIFF-ARCH" title="&quot;An Architecture for Differentiated Service&quot;">DIFF-ARCH</a>]) and MPLS Traffic
   Engineering ([<a href="#ref-TE-REQ" title="&quot;Requirements for Traffic Engineering Over MPLS&quot;">TE-REQ</a>], [<a href="#ref-RSVP-TE" title="&quot;RSVP-TE: Extensions to RSVP for LSP Tunnels&quot;">RSVP-TE</a>], [<a href="#ref-OSPF-TE" title="&quot;Traffic Engineering (TE) Extensions to OSPF Version 2&quot;">OSPF-TE</a>], [<a href="#ref-ISIS-TE" title="&quot;Intermediate System to Intermediate System (IS-IS) Extensions for Traffic Engineering (TE)&quot;">ISIS-TE</a>]) and the same



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   security measures and procedures described in these documents apply
   here.  For example, the approach for defense against theft- and
   denial-of-service attacks discussed in [<a href="#ref-DIFF-ARCH" title="&quot;An Architecture for Differentiated Service&quot;">DIFF-ARCH</a>], which consists of
   the combination of traffic conditioning at DS boundary nodes along
   with security and integrity of the network infrastructure within a
   Diffserv domain, may be followed when DS-TE is in use.  Also, as
   stated in [<a href="#ref-TE-REQ" title="&quot;Requirements for Traffic Engineering Over MPLS&quot;">TE-REQ</a>], it is specifically important that manipulation of
   administratively configurable parameters (such as those related to
   DS-TE LSPs) be executed in a secure manner by authorized entities.

<span class="h2"><a class="selflink" id="section-13" href="#section-13">13</a>.  IANA Considerations</span>

   This document creates two new name spaces that are to be managed by
   IANA.  Also, a number of assignments from existing name spaces have
   been made by IANA in this document.  They are discussed below.

<span class="h3"><a class="selflink" id="section-13.1" href="#section-13.1">13.1</a>.  A New Name Space for Bandwidth Constraints Model Identifiers</span>

   This document defines in <a href="#section-5.1">Section 5.1</a> a "Bandwidth Constraints Model
   Id" field (name space) within the "Bandwidth Constraints" sub-TLV,
   both for OSPF and ISIS.  The new name space has been created by the
   IANA and they will maintain this new name space.  The field for this
   namespace is 1 octet, and IANA guidelines for assignments for this
   field are as follows:

         o values in the range 0-239 are to be assigned according to the
           "Specification Required" policy defined in [<a href="#ref-IANA-CONS" title="">IANA-CONS</a>].

         o values in the range 240-255 are reserved for "Private Use" as
           defined in [<a href="#ref-IANA-CONS" title="">IANA-CONS</a>].

<span class="h3"><a class="selflink" id="section-13.2" href="#section-13.2">13.2</a>.  A New Name Space for Error Values under the "Diffserv-aware TE</span>
<span class="h3">       Error"</span>

   An Error Code is an 8-bit quantity defined in [<a href="#ref-RSVP" title="&quot;Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification&quot;">RSVP</a>] that appears in
   an ERROR_SPEC object to define an error condition broadly.  With each
   Error Code there may be a 16-bit Error Value (which depends on the
   Error Code) that further specifies the cause of the error.

   This document defines in <a href="#section-6.5">Section 6.5</a> a new RSVP error code, the
   "Diffserv-aware TE Error" (see <a href="#section-13.3.4">Section 13.3.4</a>).  The Error Values for
   the "Diffserv-aware TE Error" constitute a new name space to be
   managed by IANA.

   This document defines, in <a href="#section-6.5">Section 6.5</a>, values 1 through 7 in that
   name space (see <a href="#section-13.3.5">Section 13.3.5</a>).





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   Future allocations of values in this name space are to be assigned by
   IANA using the "Specification Required" policy defined in
   [<a href="#ref-IANA-CONS" title="">IANA-CONS</a>].

<span class="h3"><a class="selflink" id="section-13.3" href="#section-13.3">13.3</a>.  Assignments Made in This Document</span>

<span class="h4"><a class="selflink" id="section-13.3.1" href="#section-13.3.1">13.3.1</a>.  Bandwidth Constraints sub-TLV for OSPF Version 2</span>

   [<a id="ref-OSPF-TE">OSPF-TE</a>] creates a name space for the sub-TLV types within the "Link
   TLV" of the Traffic Engineering Link State Advertisement (LSA) and
   rules for management of this name space by IANA.

   This document defines in <a href="#section-5.1">Section 5.1</a> a new sub-TLV, the "Bandwidth
   Constraints" sub-TLV, for the OSPF "Link" TLV.  In accordance with
   the IANA considerations provided in [<a href="#ref-OSPF-TE" title="&quot;Traffic Engineering (TE) Extensions to OSPF Version 2&quot;">OSPF-TE</a>], a sub-TLV type in the
   range 10 to 32767 was requested, and the value 17 has been assigned
   by IANA for the "Bandwidth Constraints" sub-TLV.

<span class="h4"><a class="selflink" id="section-13.3.2" href="#section-13.3.2">13.3.2</a>.  Bandwidth Constraints sub-TLV for ISIS</span>

   [<a id="ref-ISIS-TE">ISIS-TE</a>] creates a name space for the sub-TLV types within the ISIS
   "Extended IS Reachability" TLV and rules for management of this name
   space by IANA.

   This document defines in <a href="#section-5.1">Section 5.1</a> a new sub-TLV, the "Bandwidth
   Constraints" sub-TLV, for the ISIS "Extended IS Reachability" TLV.
   In accordance with the IANA considerations provided in [<a href="#ref-ISIS-TE" title="&quot;Intermediate System to Intermediate System (IS-IS) Extensions for Traffic Engineering (TE)&quot;">ISIS-TE</a>], a
   sub-TLV type was requested, and the value 22 has been assigned by
   IANA for the "Bandwidth Constraints" sub-TLV.

<span class="h4"><a class="selflink" id="section-13.3.3" href="#section-13.3.3">13.3.3</a>.  CLASSTYPE Object for RSVP</span>

   [<a id="ref-RSVP">RSVP</a>] defines the Class Number name space for RSVP object, which is
   managed by IANA.  Currently allocated Class Numbers are listed at
   <a href="http://www.iana.org/assignments/rsvp-parameters">http://www.iana.org/assignments/rsvp-parameters</a>.

   This document defines in <a href="#section-6.2.1">Section 6.2.1</a> a new RSVP object, the
   CLASSTYPE object.  IANA has assigned a Class Number for this RSVP
   object from the range defined in Section 3.10 of [<a href="#ref-RSVP" title="&quot;Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification&quot;">RSVP</a>] for objects
   that, if not understood, cause the entire RSVP message to be rejected
   with an error code of "Unknown Object Class".  Such objects are
   identified by a zero in the most significant bit of the class number
   (i.e., Class-Num = 0bbbbbbb).

   IANA assigned Class-Number 66 to the CLASSTYPE object.  C_Type 1 is
   defined in this document for the CLASSTYPE object.





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<span class="h4"><a class="selflink" id="section-13.3.4" href="#section-13.3.4">13.3.4</a>.  "Diffserv-aware TE Error" Error Code</span>

   [<a id="ref-RSVP">RSVP</a>] defines the Error Code name space and rules for management of
   this name space by IANA.  Currently allocated Error Codes are listed
   at <a href="http://www.iana.org/assignments/rsvp-parameters">http://www.iana.org/assignments/rsvp-parameters</a>.

   This document defines in <a href="#section-6.5">Section 6.5</a> a new RSVP Error Code, the
   "Diffserv-aware TE Error".  In accordance with the IANA
   considerations provided in [<a href="#ref-RSVP" title="&quot;Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification&quot;">RSVP</a>], Error Code 28 was assigned by IANA
   to the "Diffserv-aware TE Error".

<span class="h4"><a class="selflink" id="section-13.3.5" href="#section-13.3.5">13.3.5</a>.  Error Values for "Diffserv-aware TE Error"</span>

   An Error Code is an 8-bit quantity defined in [<a href="#ref-RSVP" title="&quot;Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification&quot;">RSVP</a>] that appears in
   an ERROR_SPEC object to define an error condition broadly.  With each
   Error Code there may be a 16-bit Error Value (which depends on the
   Error Code) that further specifies the cause of the error.

   This document defines in <a href="#section-6.5">Section 6.5</a> a new RSVP error code, the
   "Diffserv-aware TE Error" (see <a href="#section-13.3.4">Section 13.3.4</a>).  The Error Values for
   the "Diffserv-aware TE Error" constitute a new name space to be
   managed by IANA.

   This document defines, in <a href="#section-6.5">Section 6.5</a>, the following Error Values for
   the "Diffserv-aware TE Error":

      Value     Error

      1      Unexpected CLASSTYPE object
      2      Unsupported Class-Type
      3      Invalid Class-Type value
      4      Class-Type and setup priority do not form a configured
                TE-Class
      5      Class-Type and holding priority do not form a configured
                TE-Class
      6      Class-Type and setup priority do not form a configured
                TE-Class AND Class-Type and holding priority do not
                form a configured TE-Class
      7      Inconsistency between signaled PSC and signaled
                Class-Type
      8      Inconsistency between signaled PHBs and signaled
                Class-Type

   See <a href="#section-13.2">Section 13.2</a> for allocation of other values in that name space.







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<span class="h2"><a class="selflink" id="section-14" href="#section-14">14</a>.  Acknowledgements</span>

   We thank Martin Tatham, Angela Chiu, and Pete Hicks for their earlier
   contribution in this work.  We also thank Sanjaya Choudhury for his
   thorough review and suggestions.














































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Appendix A: Prediction for Multiple Path Computation

   There are situations where a head-end needs to compute paths for
   multiple LSPs over a short period of time.  There are potential
   advantages for the head-end in trying to predict the impact of the
   n-th LSP on the unreserved bandwidth when computing the path for the
   (n+1)-th LSP, before receiving updated IGP information.  For example,
   better load-distribution of the multiple LSPs would be performed
   across multiple paths.  Also, when the (n+1)-th LSP would no longer
   fit on a link after establishment of the n-th LSP, the head-end would
   avoid Connection Admission Control (CAC) rejection.  Although there
   are a number of conceivable scenarios where worse situations might
   result, doing such predictions is more likely to improve situations.
   As a matter of fact, a number of network administrators have elected
   to use such predictions when deploying existing TE.

   Such predictions are local matters, are optional, and are outside the
   scope of this specification.

   Where such predictions are not used, the optional BC sub-TLV and the
   optional Maximum Reservable Bandwidth sub-TLV need not be advertised
   in IGP for the purpose of path computation, since the information
   contained in the Unreserved Bw sub-TLV is all that is required by
   Head-Ends to perform Constraint-Based Routing.

   Where such predictions are used on head-ends, the optional BCs sub-
   TLV and the optional Maximum Reservable Bandwidth sub-TLV MAY be
   advertised in IGP.  This is in order for the head-ends to predict as
   accurately as possible how an LSP affects unreserved bandwidth values
   for subsequent LSPs.

   Remembering that actual admission control algorithms are left for
   vendor differentiation, we observe that predictions can only be
   performed effectively when the head-end LSR predictions are based on
   the same (or a very close) admission control algorithm as that used
   by other LSRs.

Appendix B: Solution Evaluation

<span class="h3"><a class="selflink" id="appendix-B.1" href="#appendix-B.1">B.1</a>.  Satisfying Detailed Requirements</span>

   This DS-TE Solution addresses all the scenarios presented in
   [<a href="#ref-DSTE-REQ" title="&quot;Requirements for Support of Differentiated Services-aware MPLS Traffic Engineering&quot;">DSTE-REQ</a>].

   It also satisfies all the detailed requirements presented in
   [<a href="#ref-DSTE-REQ" title="&quot;Requirements for Support of Differentiated Services-aware MPLS Traffic Engineering&quot;">DSTE-REQ</a>].





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   The objective set out in the last paragraph of Section 4.7 of
   [<a href="#ref-DSTE-REQ" title="&quot;Requirements for Support of Differentiated Services-aware MPLS Traffic Engineering&quot;">DSTE-REQ</a>], "Overbooking", is only partially addressed by this DS-TE
   solution.  Through support of the "LSP size Overbooking" and "Link
   Size Overbooking" methods, this DS-TE solution effectively allows CTs
   to have different overbooking ratios and simultaneously allows
   overbooking to be tweaked differently (collectively across all CTs)
   on different links.  But, in a general sense, it does not allow the
   effective overbooking ratio of every CT to be tweaked differently in
   different parts of the network independently of other CTs, while
   maintaining accurate bandwidth accounting of how different CTs
   mutually affect each other through shared BCs (such as the Maximum
   Reservable Bandwidth).

<span class="h3"><a class="selflink" id="appendix-B.2" href="#appendix-B.2">B.2</a>.  Flexibility</span>

   This DS-TE solution supports 8 CTs.  It is entirely flexible as to
   how Traffic Trunks are grouped together into a CT.

<span class="h3"><a class="selflink" id="appendix-B.3" href="#appendix-B.3">B.3</a>.  Extendibility</span>

   A maximum of 8 CTs is considered more than comfortable by the authors
   of this document.  A maximum of 8 TE-Classes is considered sufficient
   by the authors of this document.  However, this solution could be
   extended to support more CTs or more TE-Classes if deemed necessary
   in the future; this would necessitate additional IGP extensions
   beyond those specified in this document.

   Although the prime objective of this solution is support of
   Diffserv-aware Traffic Engineering, its mechanisms are not tightly
   coupled with Diffserv.  This makes the solution amenable, or more
   easily extendable, for support of potential other future Traffic
   Engineering applications.

<span class="h3"><a class="selflink" id="appendix-B.4" href="#appendix-B.4">B.4</a>.  Scalability</span>

   This DS-TE solution is expected to have a very small scalability
   impact compared to that of existing TE.

   From an IGP viewpoint, the amount of mandatory information to be
   advertised is identical to that of existing TE.  One additional sub-
   TLV has been specified, but its use is optional, and it only contains
   a limited amount of static information (at most 8 BCs).

   We expect no noticeable impact on LSP Path computation because, as
   with existing TE, this solution only requires Constrained Shortest
   Path First (CSPF) to consider a single unreserved bandwidth value for
   any given LSP.




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   From a signaling viewpoint, we expect no significant impact due to
   this solution because it only requires processing of one additional
   item of information (the Class-Type) and does not significantly
   increase the likelihood of CAC rejection.  Note that DS-TE has some
   inherent impact on LSP signaling in that it assumes that different
   classes of traffic are split over different LSPs so that more LSPs
   need to be signaled.  However, this is due to the DS-TE concept
   itself and not to the actual DS-TE solution discussed here.

<span class="h3"><a class="selflink" id="appendix-B.5" href="#appendix-B.5">B.5</a>.  Backward Compatibility/Migration</span>

   This solution is expected to allow smooth migration from existing TE
   to DS-TE.  This is because existing TE can be supported as a
   particular configuration of DS-TE.  This means that an "upgraded" LSR
   with a DS-TE implementation can directly interwork with an "old" LSR
   supporting existing TE only.

   This solution is expected to allow smooth migration when the number
   of CTs actually deployed is increased, as it only requires
   configuration changes.  However, these changes need to be performed
   in a coordinated manner across the DS-TE domain.

Appendix C: Interoperability with Non-DS-TE Capable LSRs

   This DSTE solution allows operations in a hybrid network where some
   LSRs are DS-TE capable and some are not, as may occur during
   migration phases.  This appendix discusses the constraints and
   operations in such hybrid networks.

   We refer to the set of DS-TE-capable LSRs as the DS-TE domain.  We
   refer to the set of non-DS-TE-capable (but TE-capable) LSRs as the
   TE-domain.

   Hybrid operations require that the TE-Class mapping in the DS-TE
   domain be configured so that:

         - a TE-Class exists for CT0 for every preemption priority
           actually used in the TE domain, and

         - the index in the TE-class mapping for each of these TE-
           Classes is equal to the preemption priority.










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   For example, imagine the TE domain uses preemption 2 and 3.  Then,
   DS-TE can be deployed in the same network by including the following
   TE-Classes in the TE-Class mapping:

           i   &lt;---&gt;       CT      preemption
         ====================================
           2               CT0     2
           3               CT0     3

   Another way to look at this is to say that although the whole TE-
   class mapping does not have to be consistent with the TE domain, the
   subset of this TE-Class mapping applicable to CT0 effectively has to
   be consistent with the TE domain.

   Hybrid operations also require that:

         - non-DS-TE-capable LSRs be configured to advertise the Maximum
           Reservable Bandwidth, and

         - DS-TE-capable LSRs be configured to advertise BCs (using the
           Max Reservable Bandwidth sub-TLV as well as the BCs sub-TLV,
           as specified in <a href="#section-5.1">Section 5.1</a>).

   This allows DS-TE-capable LSRs to identify non-DS-TE-capable LSRs
   unambiguously.

   Finally, hybrid operations require that non-DS-TE-capable LSRs be
   able to accept Unreserved Bw sub-TLVs containing non decreasing
   bandwidth values (i.e., with Unreserved [p] &lt; Unreserved [q] with p &lt;
   q).

   In such hybrid networks, the following apply:

         - CT0 LSPs can be established by both DS-TE-capable LSRs and
           non-DS-TE-capable LSRs.

         - CT0 LSPs can transit via (or terminate at) both DS-TE-capable
           LSRs and non-DS-TE-capable LSRs.

         - LSPs from other CTs can only be established by DS-TE-capable
           LSRs.

         - LSPs from other CTs can only transit via (or terminate at)
           DS-TE-capable LSRs.







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   Let us consider the following example to illustrate operations:

      LSR0--------LSR1----------LSR2
           Link01       Link12

      where:
         LSR0 is a non-DS-TE-capable LSR
         LSR1 and LSR2 are DS-TE-capable LSRs

   Let's assume again that preemptions 2 and 3 are used in the TE-domain
   and that the following TE-Class mapping is configured on LSR1 and
   LSR2:
           i   &lt;---&gt;       CT      preemption
         ====================================
           0               CT1     0
           1               CT1     1
           2               CT0     2
           3               CT0     3
           rest            unused

   LSR0 is configured with a Max Reservable Bandwidth = m01 for Link01.
   LSR1 is configured with a BC0 = x0, a BC1 = x1 (possibly = 0), and a
   Max Reservable Bandwidth = m10 (possibly = m01) for Link01.

   In IGP for Link01, LSR0 will advertise:

         - Max Reservable Bw sub-TLV = &lt;m01&gt;

         - Unreserved Bw sub-TLV = &lt;CT0/0, CT0/1, CT0/2, CT0/3, CT0/4,
           CT0/5, CT0/6, CT0/7&gt;

   On receipt of such advertisement, LSR1 will:

         - understand that LSR0 is not DS-TE-capable because it
           advertised a Max Reservable Bw sub-TLV and no Bandwidth
           Constraints sub-TLV, and

         - conclude that only CT0 LSPs can transit via LSR0 and that
           only the values CT0/2 and CT0/3 are meaningful in the
           Unreserved Bw sub-TLV.  LSR1 may effectively behave as if the
           six other values contained in the Unreserved Bw sub-TLV were
           set to zero.









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   In IGP for Link01, LSR1 will advertise:

         - Max Reservable Bw sub-TLV = &lt;m10&gt;

         - Bandwidth Constraints sub-TLV = &lt;BC Model ID, x0, x1&gt;

         - Unreserved Bw sub-TLV =
           &lt;CT1/0, CT1/1, CT0/2, CT0/3, 0, 0, 0, 0&gt;

   On receipt of such advertisement, LSR0 will:

         - ignore the Bandwidth Constraints sub-TLV (unrecognized)

         - correctly process CT0/2 and CT0/3 in the Unreserved Bw sub-
           TLV and use these values for CTO LSP establishment

         - incorrectly believe that the other values contained in the
           Unreserved Bw sub-TLV relate to other preemption priorities
           for CT0; but it will actually never use those since we assume
           that only preemptions 2 and 3 are used in the TE domain.

Normative References

   [<a id="ref-DSTE-REQ">DSTE-REQ</a>]    Le Faucheur, F. and W. Lai, "Requirements for Support
                 of Differentiated Services-aware MPLS Traffic
                 Engineering", <a href="./rfc3564">RFC 3564</a>, July 2003.

   [<a id="ref-MPLS-ARCH">MPLS-ARCH</a>]   Rosen, E., Viswanathan, A. and R. Callon,
                 "Multiprotocol Label Switching Architecture", <a href="./rfc3031">RFC 3031</a>,
                 January 2001.

   [<a id="ref-TE-REQ">TE-REQ</a>]      Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M. and
                 J. McManus, "Requirements for Traffic Engineering Over
                 MPLS", <a href="./rfc2702">RFC 2702</a>, September 1999.

   [<a id="ref-OSPF-TE">OSPF-TE</a>]     Katz, D., Kompella, K. and D. Yeung, "Traffic
                 Engineering (TE) Extensions to OSPF Version 2", <a href="./rfc3630">RFC</a>
                 <a href="./rfc3630">3630</a>, September 2003.

   [<a id="ref-ISIS-TE">ISIS-TE</a>]     Smit, H. and T. Li, "Intermediate System to
                 Intermediate System (IS-IS) Extensions for Traffic
                 Engineering (TE)", <a href="./rfc3784">RFC 3784</a>, June 2004.

   [<a id="ref-RSVP-TE">RSVP-TE</a>]     Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan,
                 V. and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
                 Tunnels", <a href="./rfc3209">RFC 3209</a>, December 2001.





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   [<a id="ref-RSVP">RSVP</a>]        Braden, R., Zhang, L., Berson, S., Herzog, S. and S.
                 Jamin, "Resource ReSerVation Protocol (RSVP) -- Version
                 1 Functional Specification", <a href="./rfc2205">RFC 2205</a>, September 1997.

   [<a id="ref-DIFF-MPLS">DIFF-MPLS</a>]   Le Faucheur, F., Wu, L., Davie, B., Davari, S.,
                 Vaananen, P., Krishnan, R., Cheval, P. and J. Heinanen,
                 "Multi-Protocol Label Switching (MPLS) Support of
                 Differentiated Services", <a href="./rfc3270">RFC 3270</a>, May 2002.

   [<a id="ref-RFC2119">RFC2119</a>]     Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>, March 1997.

   [<a id="ref-IANA-CONS">IANA-CONS</a>]   Narten, T. and H. Alvestrand, "Guidelines for Writing
                 an IANA Considerations Section in RFCs", <a href="https://www.rfc-editor.org/bcp/bcp26">BCP 26</a>, <a href="./rfc2434">RFC</a>
                 <a href="./rfc2434">2434</a>, October 1998.

Informative References

   [<a id="ref-DIFF-ARCH">DIFF-ARCH</a>]   Blake, S., Black, D., Carlson, M., Davies, E., Wang,
                 Z., and W. Weiss, "An Architecture for Differentiated
                 Service", <a href="./rfc2475">RFC 2475</a>, December 1998.

   [<a id="ref-DSTE-RDM">DSTE-RDM</a>]    Le Faucheur,F., Ed., "Russian Dolls Bandwidth
                 Constraints Model for Diffserv-aware MPLS Traffic
                 Engineering", <a href="./rfc4127">RFC 4127</a>, June 2005.

   [<a id="ref-DSTE-MAM">DSTE-MAM</a>]    Le Faucheur, F. and W. Lai, "Maximum Allocation
                 Bandwidth Constraints Model for Diffserv-aware Traffice
                 Engineering", <a href="./rfc4125">RFC 4125</a>, June 2005.

   [<a id="ref-DSTE-MAR">DSTE-MAR</a>]    Ash, J., "Max Allocation with Reservation Bandwidth
                 Constraints Model for DiffServ-aware MPLS Traffic
                 Engineering &amp; Performance Comparisons", <a href="./rfc4126">RFC 4126</a>, June
                 2005.

   [<a id="ref-GMPLS-SIG">GMPLS-SIG</a>]   Berger, L., "Generalized Multi-Protocol Label Switching
                 (GMPLS) Signaling Functional Description", <a href="./rfc3471">RFC 3471</a>,
                 January 2003.

   [<a id="ref-GMPLS-ROUTE">GMPLS-ROUTE</a>] Kompella, et al., "Routing Extensions in Support of
                 Generalized MPLS", Work in Progress.

   [<a id="ref-BUNDLE">BUNDLE</a>]      Kompella, Rekhter, Berger, "Link Bundling in MPLS
                 Traffic Engineering", Work in Progress.

   [<a id="ref-HIERARCHY">HIERARCHY</a>]   Kompella, Rekhter, "LSP Hierarchy with Generalized MPLS
                 TE", Work in Progress.




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   [<a id="ref-REROUTE">REROUTE</a>]     Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
                 Extensions to RSVP-TE for LSP Tunnels", <a href="./rfc4090">RFC 4090</a>, May
                 2005.

Editor's Address

   Francois Le Faucheur
   Cisco Systems, Inc.
   Village d'Entreprise Green Side - Batiment T3
   400, Avenue de Roumanille
   06410 Biot-Sophia Antipolis
   France

   Phone: +33 4 97 23 26 19
   EMail: flefauch@cisco.com




































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Full Copyright Statement

   Copyright (C) The Internet Society (2005).

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Acknowledgement

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







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