RFC 2996 (rfc2996) - Page 2 of 9
Format of the RSVP DCLASS Object
Alternative Format: Original Text Document
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
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