MPLS Guide MPLS and RSVP-TE
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A bundle RSVP-TE message is intended to reduce the overall message handling load. A
bundle message consists of a bundle header followed by one or more bundle sub-messages.
A sub-message can be any regular RSVP-TE message except another bundle message. A
7705 SAR node will only process received bundle RSVP-TE messages but will not generate
them.
When reliable RSVP-TE message delivery is supported by both the node and its peer over
the RSVP-TE interface, an RSVP-TE message is sent with a message_id object. A
message_id object can be added to any RSVP-TE message when sent individually or as a
sub-message of a bundle message.
If the sender sets the ack_desired flag in the message_id object, the receiver acknowledges
the receipt of the RSVP-TE message by piggy-backing a message_ack object to the next
RSVP-TE message it sends to its peer. Alternatively, an ACK message can also be used to
send the message_ack object. In both cases, one or many message_ack objects could be
included in the same message.
The 7705 SAR supports the sending of separate ACK messages only, but is capable of
processing received message_ack objects piggy-backed to hop-by-hop RSVP-TE
messages, such as PATH and RESV.
The 7705 SAR sets the ack_desired flag only in non-refresh RSVP-TE messages and in
refresh messages that contain new state information.
A retransmission mechanism based on an exponential backoff timer is supported in order to
handle unacknowledged message_id objects. The RSVP-TE message with the same
message_id is retransmitted every 2 × rapid-retransmit-time interval. The rapid-retransmit-
time is referred to as the rapid retransmission interval because it must be smaller than the
regular refresh interval configured in the config>router>rsvp>refresh-time context.
There is also a maximum number of retransmissions of an unacknowledged RSVP-TE
message rapid-retry-limit. The node will stop retransmission of unacknowledged RSVP-TE
messages whenever the updated backoff interval exceeds the value of the regular
refresh-time interval or the number of retransmissions reaches the value of the
rapid-retry-limit parameter, whichever comes first. These two parameters are configurable
globally on a system in the config>router>
rsvp context.
Summary refresh consists of sending a summary refresh message containing a message_id
list object. The fields of this object are populated each with the value of the
message_identifier field in the message_id object of a previously sent individual PATH or
RESV message. The summary refresh message is sent every refresh regular interval as
configured by the user using the refresh-time command in the config>router>rsvp context.
The receiver checks each message_id object against the saved PATH and RESV states. If a
match is found, the state is updated as if a regular PATH or RESV refresh message was
received from the peer. If a specific message_identifier field does not match, then the node
sends a message_id_nack object to the originator of the message.
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