Cisco Cisco IOS Software Release 12.0(24)S

RSVP is a network-control, soft-state protocol that enables Internet applications to obtain special 
qualities of service (QoS) for their data flows. As a soft-state protocol, RSVP requires that state be 
periodically refreshed. If refresh messages are not transmitted during a specified interval, RSVP state 
automatically times out and is deleted.

In a network using RSVP signalling, reliability and latency problems occur when an RSVP message is 
lost in transmission. A lost RSVP setup message can cause a delayed or failed reservation; a lost RSVP 
refresh message can cause a delay in the modification of a reservation, or in a reservation timeout. 
Intolerant applications can fail as a result.

Reliability problems can also occur when there is excessive RSVP refresh message traffic caused by a 
large number of reservations in the network. Using summary refresh messages can improve reliability 
by significantly reducing the amount of RSVP refresh traffic.

RSVP packets consist of headers that identify the types of messages, and object fields that contain 
attributes and properties describing how to interpret and act on the content. 

The RSVP Refresh Reduction and Reliable Messaging feature (

) includes refresh reduction, 

which improves the scalability, latency, and reliability of RSVP signalling by introducing the following 
extensions:

Reliable messages (MESSAGE_ID, MESSAGE_ID_ACK objects, and ACK messages)

Bundle messages (reception and processing only)

Summary refresh messages (MESSAGE_ID_LIST and MESSAGE_ID_NACK objects)