SIP通訊協定於NAT網路環境之改良與實作

The Improvement and Implementation of SIP under NAT Environment

鍾耀興(Yao-Hsing Chung)

指導教授 ： 黃紹華

國立臺北科技大學/機電學院/電機工程系所/碩士(2006年)

摘要

本論文分析主流VoIP通訊協定Session Initiation Protocol（SIP），於現行網路環境下所面臨之問題，即NAT（Network Address Translator）與虛擬IP對SIP所造成之影響。此外，本論文對NAT機制作一分析與探討，並提出互動式NAT穿越法，INT（Interactive NAT Traversal），解決NAT防火牆無法直接P2P傳輸之問題。
本論文之主軸在於將上述之互動式NAT穿越法套用於SIP上，並提出SIP with INT（SWINT）方法，以改善SIP之語音封包無法於NAT防火牆下直接對傳之困擾，並將本方法與目前被提出之NAT解決辦法作一比較。
本論文所提出之SWINT具有：1)令SIP可於NAT下直接對傳語音封包，不需透過代理伺服器交換封包；2)適用於各種型態與架構之NAT環境；3)用戶端不需更改網路環境設定；4)VoIP業者不需更換SIP伺服器即可搭配本方法；5) 封包小，幾乎不佔用頻寬…等優點。

關鍵字

網路電話 ； 會議初始協定 ； 網路位址轉換器穿越 ； 互動式NAT穿越法

並列摘要

This thesis analyzed the problems which the main VoIP protocol - Session Initiation Protocol (SIP) - is facing under networking environment nowadays. These problems are the influences brought by NAT and virtual IP to SIP. Besides, this thesis did some analysis and discussions on the mechanism of NAT (Network Address Translator), and then proposed Interactive NAT Traversal method to solve the issue of directly P2P transmission under NAT.
The main shaft of this thesis is combining the INT method with SIP, and proposed SIP with INT (SWINT) method to improve the impossibility of directly transmitting RTP packets of SIP to each other under NAT. Then, there were some comparisons between SWINT and other NAT solutions.
The SWINT method proposed by this thesis has some virtues, for examples, 1). Enable SIP transmitting RTP packets to each other directly under NAT without proxy server to exchange packets. 2). No limitation with NAT type or structure. 3). No any requirement of changing network settings to end users. 4). VoIP operators could introduce this method without replacement of SIP servers. 5). Mini packet size and almost no bandwidth occupancy…etc.

並列關鍵字

VoIP ； SIP ； NAT Traversal ； INT ； SWINT

參考文獻

[1] S.P. Shieh, F.S. Ho, Y.L. Hung, and J.N. Luo, “Network Address Translators: Effects on Security Protocols and Applications in the TCP/IP Stack”, IEEE Internet Computing, pp.42~49, Nov.~Dec. 2000

[7] J. Alan, ”SIP:Understanding The Session Initiation Protocol”, 2 Ed, Artech House, Boston, London, 2004.

[8] J. Rosenberg and H. Schulzrinne, “An Extension to the Session Initiation Protocol (SIP) for Symmetric Response Routing”, RFC 3581, IETF, Aug. 2003.

[9] P. Srisuresh and M. Holdrege, “IP Network Address Translator (NAT) Terminology and Considerations”, RFC 2663, IETF, Aug. 1999.

[2] B. Sterman, and D. Schwartz, “NAT Traversal in SIP”, Technique Report, Delta-Three Corp., The IP Communication Network.