RFC 2961, RSVP Refresh Overhead Reduction Extensions, defines enhancements to the RSVP-TE signaling protocol that reduce refresh overhead, which are in addition to the message pacing function.
These extensions are:
RSVP-TE message bundling — RSVP-TE message bundling reduces the total number of RSVP-TE messages by aggregating the status information of multiple LSPs into a single RSVP-TE PDU. The 7705 SAR supports the receipt and processing of bundled RSVP-TE messages but not the transmission of bundled messages as specified in RFC 2961, section 3.3.
reliable message delivery — reliable message delivery extends RSVP-TE to support MESSAGE_ACK. Each RSVP-TE PDU has a unique message-id for sequence tracking purposes. When an RSVP-TE message arrives, the recipient acknowledges the reception of the specific message-id (this is similar to TCP ACK messages). Lost PDUs can be detected and re-sent with this method, which helps reduce the refresh rate because there are two endpoints tracking the received/lost messages.
summary refresh — the summary refresh capability uses a single message-id list to replace many individual refresh messages and sends negative ACKs (NACKs) for any message-id that cannot be matched (verified). The summary refresh capability reduces the number of message exchanges and message processing between peers. It does not reduce the amount of soft state stored in the node. The term soft state refers to the control state in hosts and routers that will expire if not refreshed within a specified amount of time (see RFC 2205 for information on soft state).
These capabilities can be enabled on a per-RSVP-TE interface basis and are referred to collectively as ‟refresh overhead reduction extensions”. When refresh-reduction is enabled on a 7705 SAR RSVP-TE interface, the node indicates this to its peer by setting a refresh-reduction-capable bit in the flags field of the common RSVP-TE header. If both peers of an RSVP-TE interface set this bit, all three of the capabilities listed above can be used. The node monitors the setting of this bit in received RSVP-TE messages from the peer on the interface. If the bit is cleared, the node stops sending summary refresh messages. If a peer did not set the refresh-reduction-capable bit, a 7705 SAR node does not attempt to send summary refresh messages.
Also, reliable delivery of RSVP-TE messages over the RSVP-TE interface can be enabled using the reliable-delivery option.