Design considerations for user authorization in the presence services based on SIP

SIP plays an important role in VoIP service infrastructure. Presence service is emerged to meet the needs of integrated service and presence service is a core function within integrated service. IETF SIMPLE WG generates standard SIP extensions for presence service. In this paper, we described the service scenarios of presence services based on SIMPLE. We also described the construction of presence system. Especially, we described the design considerations of presence agent supporting for multiple presence packages and those of presence agent supporting for user authorization function