VOIP關(guān)于NAT穿越問(wèn)題的解決方法

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摘 要
VoIP(Voice over Internet Protocol)是一種以IP電話為主，并推出相應(yīng)的增值業(yè)務(wù)的技術(shù)。VoIP最大的優(yōu)勢(shì)是能廣泛地采用Internet和全球IP互連的環(huán)境，提供比傳統(tǒng)業(yè)務(wù)更多、更好的服務(wù)。它也是目前Internet應(yīng)用領(lǐng)域的一個(gè)熱門(mén)話題。
VoIP的大規(guī)模應(yīng)用將極大地增加對(duì)IP地址的需求。當(dāng)前VoIP主要使用NAT技術(shù)來(lái)解決地址匱乏的問(wèn)題。隨之而來(lái)卻是NAT穿越的問(wèn)題?；贖.323、SIP等協(xié)議的VoIP應(yīng)用需通過(guò)信令消息中的IP地址和端口參數(shù)來(lái)實(shí)現(xiàn)目的地尋址，因此NAT穿越時(shí)不僅需要對(duì)TCP/UDP層的端口信息以及IP層的源地址和目的地址進(jìn)行變換，還需對(duì)IP包載荷中的相關(guān)地址信息進(jìn)行變換。NAT穿越是目前開(kāi)展VoIP業(yè)務(wù)最大的障礙，迫切需要解決。
本文深入分析了VoIP中NAT穿越問(wèn)題的現(xiàn)有解決方案，然而，當(dāng)這些解決方案應(yīng)用于不同的網(wǎng)絡(luò)拓?fù)鋾r(shí)都有著顯著的利弊，以至于我們只能根據(jù)不同的接入方式來(lái)應(yīng)用不同的方案。所以我們目前需要一種綜合的足夠靈活的方法，使之盡可能的解決大部分情況下的NAT穿越。
本文的創(chuàng)新點(diǎn)在于通過(guò)采用端口預(yù)測(cè)的機(jī)制來(lái)推斷出對(duì)稱(chēng)NAT的下一個(gè)分配地址，使得STUN協(xié)議可以穿越大部分對(duì)稱(chēng)NAT和所有別的NAT。該方案無(wú)需現(xiàn)有NAT設(shè)備作任何改動(dòng)，并支持多個(gè)NAT串聯(lián)的網(wǎng)絡(luò)環(huán)境，同時(shí)對(duì)STUN協(xié)議自身不能穿越對(duì)稱(chēng)NAT的問(wèn)題做出了有益的探索和實(shí)踐。研究和實(shí)踐表明，本文所提出的STUN改進(jìn)方案能夠有效的解決典型的SIP穿越NAT問(wèn)題，為VoIP的大規(guī)模應(yīng)用提供了幫助。

關(guān)鍵詞: IP網(wǎng)上的語(yǔ)音通信 會(huì)話初始化協(xié)議 UDP對(duì)NAT的簡(jiǎn)單穿越 網(wǎng)絡(luò)地址轉(zhuǎn)換

Abstract
This thesis deeply analyzes current solutions of NAT traversal on the VoIP. However, these solutions present obvious advantages VoIP is a technology that mostly utilized in IP phone, and relevant value-added services. The most advantage of VoIP is that can make use of the global IP internetworking environment, to provide the more and more the better and better services than traditional PSTN network. It is also the hot research field of Internet.
The widely application of VoIP increases the requirement of a large number of IP addresses. VoIP mainly uses NAT to solve this. Accompanied by the matter of NAT traversal .The VoIP application based on H.323 and SIP uses the IP address and port in the message body of signaling to route. So besides transforming the TCP/UDP layer port and IP layer address, VoIP NAT traversal needs to transform parts of the payload of IP packages. NAT traversal is the biggest drawback of VoIP application and it should be solved soon.
This thesis deeply analyzes current solutions of NAT traversal on the VoIP. However, these solutions present obvious advantages and disadvantages depending on the topological conditions of the network. So we need a complete solution that is flexible enough to through most of NAT in different network topology.