Key Technology Research Of P2Psip System

IP multimedia communication system implements real-time multimedia information exchange such as audio, data and image between users. Based on client/server architecture, the protocols of signaling system and data transportation of traditional multimedia communication system are all designed on the assumption of existence of centric servers. With the increasing development of Peer to Peer (P2P) technology over the last decades, IP multimedia communication system also evolves accordingly from centric architecture to distributed architecture. An overlay network of distributed multimedia communication system is therefore constructed.P2P technologies are introduced into IP multimedia communication system on media session control layer, data transportation layer and content semantic layer respectively. First of all, on media session control layer, P2PSIP (Peer-to-Peer Session Initiation Protocol) takes the place of centric SIP to implement distributed session control based on a P2P SIP overlay consisted by all the user terminals or dynamic deployable servers. Second, the overlay also provides the possibility to build application layer data channels relatively independent with IP routings. Finally, the data resources produced by the multimedia communication system, such as user profile, text data and images, are stored on distributed P2PSIP nodes where a logic content semantic layer is therefore formed.The dissertation is principally concentrated on the critical technology issues of the above three layers. First, the performance of P2PSIP is mainly concerned on whether it can meet the requirements of user session control process in large scale network. To achieve deep understanding of P2PSIP performance, the models of call setup delay and traffic characteristic on server nodes of P2PSIP system are proposed. Accordingly, the optimization solution of session setup delay in terms of hierarchical architectures is further discussed, and traffic of session messages is evaluated. Second, because of the explicit search property caused by the consistent hash of traditional Distributed Hash Table (DHT), it is difficult to implement similar search on the content semantic overlay. To fulfill the semantic search requirements in distributed system, the distributed semantic resource index assignment mechanisms are studied, and algorithms of semantic search are proposed in various DHT systems. Furthermore, individual nodes in P2PSIP system could be used to compose overlay relay path shorter than the default IP path according to the phenomenon of Triangle Inequality Violation (TIV) commonly found in Internet. However, most delay prediction algorithms of network coordination adopt metric space which inherently excludes the existence of TIV. To address the issue of TIV prediction, a TIV-friendly network coordination algorithm in relaxed metric space is proposed. The main contributions of the dissertation include the following aspects:First, the evaluation model of call setup delay is proposed and utilized to analyze the latency performance of three P2PSIP architectures including pure P2PSIP, server farm P2PSIP and super-node P2PSIP. The idea of delay optimization from the aspect of architecture and message processes is discussed and a hierarchical heterogeneous P2PSIP architecture is proposed. Simulation suggests that P2PSIP is generally able to satisfy the delay requirements. The contribution is presented in chapter3.Second, a traffic model on server nodes of P2PSIP server farm is proposed through deep analysis of mechanism of DHT (Distributed Hash Table). The basic relation between traffic property of server nodes and session requests from user terminals is also described and qualified. Simulation proved that the traffic model approximately aligns with the real traffic arrived at P2PSIP server nodes. The contribution is illustrated in chapter4.Third, the issue of semantic search for data resources in DHT system is addressed. A semi-distributed and a fully distributed semantic search algorithms named B-PCA and D-PCA are proposed respectively. The algorithms focus on the assignment mechanisms of semantic index by which the data resources are directly mapped into the Euclidean space of CAN topology. Therefore, the resources can be searched according to their semantic index rather than the explicit hash mapping index. To extend the usability of distributed semantic search algorithms, S-Chord algorithm is also proposed based on location sensitive hash function which implements similar search in one dimension Chord ring. The contribution is presented in chapter5.Fourth, a TIV (Triangle Inequality Violation) friendly network coordination algorithm, embedded in relaxed metric space called KL_vivaldi, is proposed. The delay space model created by the algorithm supports the existence of unbalanced delay and TIV phenomena commonly measured in Internet. Therefore, the TIV could be directly and explicitly predicted by network coordination, which facilitates user terminals to create overlay relay paths with more desirable performance than default IP routes. The contribution is described in chapter6.