Format of the RSVP DCLASS Object
RFC 2996

Document Type RFC - Proposed Standard (November 2000; No errata)
Author Yoram Bernet 
Last updated 2013-03-02
Stream Internet Engineering Task Force (IETF)
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Network Working Group                                         Y. Bernet
Request for Comments: 2996                                    Microsoft
Category: Standards Track                                 November 2000

                    Format of the RSVP DCLASS Object

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 (2000).  All Rights Reserved.


   Resource Reservation Protocol (RSVP) signaling may be used to request
   Quality of Service (QoS) services and enhance the manageability of
   application traffic's QoS in a differentiated service (diff-serv or
   DS) network.  When using RSVP with DS networks it is useful to be
   able to carry carry Differentiated Services Code Points (DSCPs) in
   RSVP message objects.  One example of this is the use of RSVP to
   arrange for the marking of packets with a particular DSCP upstream
   from the DS network's ingress point, at the sender or at a previous
   network's egress router.

   The DCLASS object is used to represent and carry DSCPs within RSVP
   messages.  This document specifies the format of the DCLASS object
   and briefly discusses its use.

1. Introduction

   This section describes the mechanics of using RSVP [RSVP] signaling
   and the DCLASS object for effecting admission control and applying
   QoS policy within a Differentiated Service network [DS].  It assumes
   standard RSVP senders and receivers, and a diff-serv network
   somewhere in the path between sender and receiver.  At least one RSVP
   aware network element resides in the diff-serv network.  This network
   element may be a policy enforcement point (PEP) [RAP] or may simply
   act as an admission control agent for the network, admitting or
   denying resource requests based on the availability of resources.  In
   either case, this network element interacts with RSVP messages
   arriving from outside the DS network, accepting resource requests

Bernet                      Standards Track                     [Page 1]
RFC 2996            Format of the RSVP DCLASS Object       November 2000

   from RSVP-aware senders and receivers, and conveying the DS network's
   admission control and resource allocation decisions to the higher-
   level RSVP.  The network element is typically a router and will be
   considered to be so for the purpose of this document.  This model is
   described fully in [INTDIFF].

1.1 Use of the DCLASS Object to Carry Upstream Packet Marking

   A principal usage of the DCLASS object is to carry DSCP information
   between a DS network and upstream nodes that may wish to mark packets
   with DSCP values.  Briefly, the sender composes a standard RSVP PATH
   message and sends it towards the receiver.  At some point the PATH
   message reaches the DS network.  The PATH message traverses one or
   more network elements that are PEPs and/or admission control agents
   for the diff-serv network.  These elements install appropriate state
   and forward the PATH message towards the receiver.  If admission
   control is successful downstream of the diff-serv network, then a
   RESV message will arrive from the direction of the receiver.  As this
   message arrives at the PEPs and/or admission control agents that are
   RSVP enabled, each of these network elements must make a decision
   regarding the admissibility of the signaled flow to the diff-serv

   If the network element determines that the request represented by the
   PATH and RESV messages is admissible to the diff-serv network, the
   appropriate diff-serv service level (or behavior aggregate) for the
   traffic represented in the RSVP request is determined.  Next, a
   decision is made to mark arriving data packets for this traffic
   locally using MF classification, or to request upstream marking of
   the packets with the appropriate DSCP(s).  This upstream marking
   could occur anywhere before the DS network's ingress point.  Two
   likely candidates are the originating sender and the egress boundary
   router of some upstream (DS or non-DS) network.  The decision about
   where the RSVP request's packets should be marked can be made by
   agreement or through a negotiation protocol; the details are outside
   the scope of this document.

   If the packets for this RSVP request are to be marked upstream,
   information about the DSCP(s) to use must be conveyed from the RSVP-
   aware network element to the upstream marking point.  This
   information is conveyed with the DCLASS object.  To do this, the
   network element adds a DCLASS object containing one or more DSCPs
   corresponding to the behavior aggregate, to the RESV message.  The
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