Research Of Session Setup Latency Between Sub-overlays In P2P-STP

SIP (Session Initiation Protocol) is a signaling protocol widely used in multimedia communication. P2PSIP (Peer-to-Peer SIP), which combines P2P and SIP, has been proposed to overcome the drawbacks of traditional C/S SIP (client/server architecture SIP). However, the introduction of DHT increases the registration overhead and, session setup overhead/latency. These problems become unbearable when P2P-SIP overlay grows huge because of increasing of the network nodes number in all distributed P2P-SIP. Hierarchical P2P-SIP divides the overlay into some subnets to reduce the registration overhead and session setup latency. However, the session setup latency between different subnets is not reduced.By studying the O(1) lookup algorithm, we proposed a new method that DHT routing algorithm used in hierarchical P2P-SIP system. As the subnets of P2P-SIP system are divided according to geographical location information and the upper overlay is composed by super node which are selected from subnets, the average latency within a single hop in the upper network which is composed by super nodes is significantly more than the average latency in the subnet.This method is proposed by using the super-node's high stability and high capacity advantages that adapt the O(1) lookup algorithm. When the session took place between in the different subnet, using O(1) lookup algorithm's efficiency location capability can reduce the hops of SIP signal transmission in the upper network. The validity of this method by example and latency analysis illuminates the feasibility.