【正文】 tunneling techniques, especially on L2F, PPTP and L2TP (monly referred to as L2TPv2). Such idea is intended to apply tunneling techniques to protocols not only to level 2 protocols as defined in newest version in IETF draft standard (L2TPv3) but also to protocols in other layers. The work presented in this dissertation covers: 1. A prehensive study of layer 2 tunneling techniques: the incentive behind and the essence of tunneling techniques, and changes in different versions and a forward view in future application. 2. A paratively plete implementation of L2TPv3 base on the idea of the extension to tunneling techniques, which the author has chiefly contributed to the design and realization of the data layer module in the kernal and relevant test. Keywords： L2TP， LAC， LNS， Data Layer Module 西南交通大學碩士研究生學位論文 第 III 頁 目 錄 第一章 緒論 ............................................................................................................. 1 二層隧道協(xié)議 ........................................................................................... 1 研究背景 ........................................................................................ 1 L2TPv2 ........................................................................................... 3 L2TPv3 的主要擴展 .................................................................... 4 作者的工作及論文結構 ......................................................................... 6 作者的工作 .................................................................................. 6 論文結構 ....................................................................................... 7 第二章 L2TPv3 協(xié)議基本概念及實現(xiàn)的思路 .................................................. 8 L2TPv3 協(xié)議基本概念 ............................................................................ 8 部分術語定義 ............................................................................... 8 隧道結構 ........................................................................................ 9 L2TPv3 over UDP/IP ............................................................................. 10 L2TP over UDP ........................................................................... 10 L2TP over IP ............................................................................... 11 L2TP 協(xié)議幀的封裝 .............................................................................. 11 協(xié)議實現(xiàn)思路 ......................................................................................... 11 TCP/IP 協(xié)議棧內部的數據流向分析 ..................................... 12 加入 L2TP 協(xié)議后內部數據 流向分析 ................................. 12 實現(xiàn)思路 ..................................................................................... 13 第三章 L2TPv3 協(xié)議分析與設計 ...................................................................... 14 L2TPv3 隧道報文 ................................................................................... 14 控制和數據報文 ........................................................................ 14 L2TP over UDP 會話報文格式 ............................................... 16 L2TP over IP 會話報文格式 .................................................... 16 AVP 定義 ...................................................................................... 17 強制 AVP .................................................................................... 18 AVP 的隱藏 ................................................................................. 18 控制報文類型 ............................................................................ 20 控制連接 ................................................................................................. 21 西南交通大學碩士研究生學位論文 第 IV 頁 控制連接管理 ............................................................................ 21 控制信道的動態(tài) ........................................................................ 22 控制連接狀態(tài)機 ........................................................................ 24 會話連接 ................................................................................................. 27 會話管理 ..................................................................................... 27 呼入呼叫狀態(tài)機 ........................................................................ 29 呼出呼叫狀態(tài)機 ........................................................................ 31 L2TP 系統(tǒng)總體框架及各功能模塊的劃分 ....................................... 34 L2TP 系統(tǒng)總體框架 .................................................................. 34 L2TP 內核 信令層 ...................................................................... 34 L2TP 內核 數據層 ...................................................................... 34 L2TP 守護進程（ L2TPD） ..................................................... 34 第四章 L2TPv3 協(xié)議系統(tǒng)實現(xiàn) .......................................................................... 36 概述 .......................................................................................................... 36 系統(tǒng)開發(fā)意義 ............................................................................ 36 系統(tǒng)實現(xiàn)的支撐環(huán)境 ............................................................... 36 統(tǒng)一建模語言（ UML） .......................................................... 37 信令層的設計 ........................................................................................ 38 信令層模塊對象 ........................................................................ 38 信令層模塊接口 ........................................................................ 40 數據層的設計 ........................................................................................ 41 數據層模塊對象 ........................................................................ 41 數據層模塊外部接口 ............................................................... 44 L2TPD 的設計 .....................................................