RFC 2996 (rfc2996) - Page 2 of 9

Format of the RSVP DCLASS Object

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
   Information

   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
   network.

   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
   RESV message is then sent upstream towards the RSVP sender.

   If the network element determines that the RSVP request is not
   admissible to the diff-serv network, it sends a RESV error message



Bernet                      Standards Track