行動環境下基於社交網路之階層式P2P SIP 系統

Abstract

在多媒體領域中，由於P2P SIP能夠克服傳統SIP系統的缺點，所以P2P SIP系統的研究已成為一個新趨勢。大多數的P2P SIP系統是以基於分散式雜湊表(DHT)的Chord路由演算法實作，使其能夠提供系統擴充性和可靠性。然而以往的研究並未同時考慮節點異質性、節點所在位置資訊與節點移動性。也就是說，每個節點應該視其能力(計算、儲存及頻寬)賦予適當的角色。另外，兩個使用者間傳送網路信號的延遲與其距離有很大的關聯，這將會大大的影響連線建立的時間。此外，網路中的節點不斷的加入與離開，將會需要額外的訊息以維護一個穩定的DHT網路，且會增加連線建立的延遲時間。在本論文中，我們提出一個基於社交網路之階層式P2P SIP系統，其中社交網路的性質能夠增加與朋友建立通話時的路由效率，而我們採用的混合式(結構式/非結構式)網路架構更能適用於節點不斷加入與離開的情況。模擬結果顯示，相較於傳統Chord架構的P2P SIP系統，我們能夠減少百分之三十二與非朋友之連線建立延遲時間，並且減少百分之六十三的系統維護花費。除此之外，我們將資源尋找的效率由O(logN)提升至O(1)，其中N為DHT網路的節點數目。

P2P SIP (peer to peer session initiation protocol) systems have emerged as a new trend in multimedia realm due to their abilities to overcome the shortcomings of conventional SIP systems. Most of P2P SIP systems were implemented using Chord, a Distributed Hash Table (DHT) based routing algorithm which can provide scalability and reliability. Previous studies on P2P SIP systems did not consider node heterogeneity, location information and mobility issues all together. For node heterogeneity, nodes with different capabilities (processing power, storage and bandwidth) should be treated suitably. For location information, the signaling latency is correlated with the geographic distance between end users. This will influence call setup latency greatly. As to mobility, the node churn property will involve additional messages to maintain a stable DHT-based network and increases call setup latency. To conquer these problems, we propose a hierarchical social network-based P2P SIP system. The social network property can increase routing efficiency when calling friends. In addition, the proposed hybrid (structured/unstructured) overlay is more resilient to cope with node churn. Simulation results show that our approach can improve 32% call setup latency with non-buddies and reduce 63% maintenance cost in comparison with the conventional Chord-based approach. In addition, we improve lookup efficiency from O(logN) to O(1) when making calls with buddies, where N is the number of nodes in a DHT-based network.