list in a dedicated Srefresh message. On receipt of a Srefresh message, the receiver can quickly match the enclosed message IDs to its installed state, performing the normal keep- alive action for each state that is matched: Matched message IDs are not acknowledged. Unmatched message IDs are returned to the sender as unacknowledged in a NACK object. As with message ID ACKs, NACKs can be piggybacked on other RSVP messages or sent in an ACK message if no suitable RSVP message is available. When the Srefresh sender receives a NACK object, it matches it to the local state that generated that message ID and sends a full refresh message out immediately. Srefresh provides a significant reduction in the overhead of running RSVP in stable networks, reducing the processing load on both sender and receiver and reducing the bandwidth required to transmit regular refresh messages. By replacing multiple Path and Resv messages with a single Sre- fresh message, the bandwidth savings can be large. Although the reduction in the use of control channel bandwidth may not be important in optical networks where the control channel is often mas- sively overprovisioned, the reduction in processing can be significant, espe- cially in large networks with many LSPs. Srefresh provides significant benefits for regular refresh messages, but cannot be applied to trigger messages, where the full message contents are required. Message bundling provides some performance enhancement in these situations by collecting the RSVP contents of several messages behind a single IP header. This saves some transmission bandwidth in IP (and possibly Layer 2) headers at the cost of some burstiness in transmis- sion and added latency as messages are collated. It can provide benefits in failover scenarios where large numbers of teardown or setup messages are passing between neighbors. 8.4.3 Efficient Fault Handling Recovery from failed network resources is an increasingly important aspect of network design. Ideally, the user should be protected from knowledge of 