This M.Sc. thesis, part of the EU FP6 IST project MUSIC, presents a P2PSIP event notification architecture where a traditional SIP event server is replaced by a distributed P2P overlay network. Our objective is a scalable, fault resilient, and redundant SIP architecture that meets the state of the art in handling event state subscriptions, notifications, and publications. The users of the architecture - non overlay SIP user agents - continue to transparently access the overlay according to the IETF specifications for event state publications (RFC3903 [1]), and notifications (RFC3265 [2]). The proposed architecture leverages a structured P2P overlay network, an application level multicast protocol, and a modified SIP stack that invokes the P2P functionality. The overlay installs a routing and transport infrastructure that distributes the total processing load among the peers. The application level multicast protocol builds dissemination trees each of which serves a particular subscriber group. It also provisions for the failure and recovery features of the overlay in coordination with the P2P subsystem. Finally the SIP stack receives out of overlay SIP calls and invokes the internal P2P functionality. However, not all the overlay peers need to have a SIP stack; only the ones acting as gateways to out of overlay SIP requests. This design allows for lightweight peers, completely unaware of SIP operations and semantics. Moreover, we are evaluating the performance of the notification mechanism in a mobile environment where the peers disconnect and join the overlay at random intervals. The evaluation is performed with a packet level simulator that introduces a variable churn rate to the P2P overlay network. The simulation
results show that the architecture experiences service discontinuities when the overlay connections break faster than the overlay repairs these connections. However it is also seen that, when appropriately configured, the notification architecture can partially mitigate the effect of churn and achieve a stable operation.