Optimizing Federated Presence with View Sharing

Presence federation refers to the exchange of presence information between systems. One of the primary challenges in presence federation is scale. With a large number of watchers in one domain obtaining presence for many presentities in another, the amount of notification traffic is large. This document describes an extension to the Session Initiation Protocol (SIP) event framework, called view sharing. View sharing can substantially reduce the amount of traffic, but requires a certain level of trust between domains. View sharing allows the amount of presence traffic between domains to achieve the theoretical lower bound on information exchange in any presence system.