RSVP Operation Overview

RSVP creates independent sessions to handle each data flow. A session is identified by a combination of the destination address, an optional destination port, and a protocol. Within a session, there can be one or more senders. Each sender is identified by a combination of its source address and source port. An out-of-band mechanism, such as a session announcement protocol or human communication, is used to communicate the session identifier to all senders and receivers.

A typical RSVP session involves the following sequence of events:

1. A potential sender starts sending RSVP path messages to the session address.
2. A receiver, wanting to join the session, registers itself if necessary. For example, a receiver in a multicast application would register itself with IGMP.
3. The receiver receives the path messages.
4. The receiver sends appropriate Resv messages toward the sender. These messages carry a flow descriptor, which is used by routers along the path to make reservations in their link-layer media.
5. The sender receives the Resv message and then starts sending application data.

This sequence of events is not necessarily strictly synchronized. For example, receivers can register themselves before receiving path messages from the sender, and application data can flow before the sender receives Resv messages. Application data that is delivered before the actual reservation contained in the Resv message typically is treated as best-effort, non-real-time traffic with no CoS guarantee.

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