Abstract: With the development of IP communication, Presence plays an increasingly important role in communication system. Presence information is sensitive and private, a Presence server needs authorization from the presentity prior to handing out Presence information. The IETF proposes two solutions to deal with authorization problem: Watcher Info mechanism and XCAP mechanism. This paper describes the implementation of the two mechanisms in a Presence server based on SIMPLE, comparatively analyzes the advantages and disadvantages of the two mechanisms, and based on this, discusses their prospects.

Key words: Presence, authorization, Watcher Info, XCAP