3.3 Batched SUBSCRIBE and NOTIFY Extension Details

Session Initiation Protocol Extensions uses the SUBSCRIBE and NOTIFY mechanism, as specified in [RFC3265], to accept subscriptions for and send presence updates on members of the user's contact list.

Session Initiation Protocol Extensions defines additional optimizations of that basic SUBSCRIBE and NOTIFY mechanism to reduce message overhead associated with presence. The first such extension is the batched SUBSCRIBE mechanism. This mechanism allows the client to subscribe to a list of contacts at once rather than send an individual SUBSCRIBE for each contact.

This extension is optional. An implementation may support it.