| Summary: | 碩士 === 國立彰化師範大學 === 資訊管理研究所 === 92 === Communication network become the most important activity of the people. Since the telephone was invented, peoples can communicate by telephone whenever they want in anywhere. In the 21st century, Internet Telephony is the most important application of Internet because of its high-quality voice and low cost.
SIP is also the most important VoIP protocol for call signaling using in Internet Telephony system because it is so simple and easy to implement. It is usefulness of interoperability within various devices. Thus, the 3GPP (Third Generation Partnership Project) has selected SIP as the core protocol for session establishment.
However, SIP-signaling is usually broken by NAT. Thus, how to establish a way for SIP packets passing through NATs becomes an important matter in this field.
In order to solve this problem we try to design three mechanisms: (i) Registrar-side mechanism (ii) Proxy-side mechanism and (iii) STUN-like server. Finally, we implement our mechanisms and show how it works.
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