MPLS為新一代骨幹網路的架構，其利用標籤快速交換的方式，讓封包可以更快速地送達目的地，然而，在網路斷線造成一條LSP不通時，若無另外一條備用LSP，無法像一般IP網路，封包可以藉由Routing Table找到別的路徑送到目的地，因而造成斷線。所以斷線恢復(Fault Recovery)一直是MPLS Traffic Engineering研究的重點之一，其中最有名的，莫過於Makam Approach和Haskin Approach，而IETF也在2003年2月對MPLS斷線恢復架構制訂了RFC 3469，對相關名詞與方法做嚴格的定義。
本論文主要提出處理斷線恢復的Reverse Labeling Scheme，我們建立一條Virtual Reverse LSP，斷線時，路由器便把Working Path上的封包，轉送給對應的Virtual Reverse LSP送回Ingress，使Haskin Approach在實作上變得可行。Virtual Reverse LSP取代了Pre-Established Reverse LSP，除了節省網路資源的浪費外，更解決了路由器要如何把工作路徑轉換到備用路徑的困擾。為了改善Haskin Approach造成封包Out-of-Order的問題，Hundessa等人在路由器上加有Buffer機制，將提早送出去的封包暫時儲存起來，以解決Out-of-Order問題，我們依照其方法，並針對實作時碰到的Buffering問題，做了細微的修改，然後透過我們所提出的Reverse Labeling Scheme，實作於Linux平台上，使理論與實際相結合。
最後經由實驗證明，我們實作的方法，不僅保有原本Haskin Approach低封包遺失率的優點，更有效改善了封包Out-of-Order的問題，避免TCP Congestion Window不必要的下降，進一步提升TCP Flow的傳輸效能。

MPLS, a next generation backbone architecture, can speed up packet forwarding to destination by label switching. However, if there exists no backup LSP when the primary LSP fails, MPLS frames cannot be forwarded to destination. Therefore, fault recovery has become an important research area in MPLS Traffic Engineering. Makam approach and Haskin approach are the most famous two among the previous literatures. Besides, IETF has made strict definitions for MPLS Recovery in RFC 3469 in February, 2003.
We propose a Reverse Labeling Scheme to handle fault recovery in this thesis. We establish a virtual reverse LSP along the completely reverse direction of the primary path. When there is a link failure in the primary LSP, LSR will forward packets back to Ingress by virtual reverse LSP instead of using the primary LSP. This idea of building virtual reverse LSP makes Haskin approach practical in implementation. In addition, we save network resources by designing a scheme such that LSR is easier to convert from the primary LSP to the backup LSP. In order to solve the out-of-order packets in Haskin approach, Hundessa adds buffering on every LSR. The buffer can temporarily store the packets once a link failure has been detected. By adopting the basic idea of Hundessa approach, we embed our Reverse Labeling Scheme and implement it on Linux platform. We also make some modifications to solve the buffering problems.
Finally, we demonstrate this Reverse Labeling Scheme by several experiments. We not only show the low packet loss rate, but also solve the packet out-of-order problems. The significant decrease of out-of-order packets can further improve the efficiency of TCP flow transmission.

第一章 導論………………………..…………………………………………………1
1.1 研究動機…………….………………………………………………………1
1.2 研究方向與實作…………………………………………………………….1
1.3 章節介紹…………………………………………………………………….2

第二章 MPLS斷線恢復的介紹……………………………………………………..3
2.1 MPLS斷線恢復相關名詞簡介……………………………………………3
2.2 MPLS斷線恢復機制的介紹………………………………………………...4
2.2.1 Pre-Established、Pre-Qualified、Established-on-Demand…………….4
2.2.2 Local Repair、Global Repair…………………………………………5
2.2.3 Rerouting與Protection Switching(Makam Approach)………………7
2.2.4 Haskin Approach……………………………………………………8
2.2.5 Subtypes of Protection Switching…………………………………10
2.3其他的斷線恢復機制……………………………………………………...10
2.3.1 Hundessa Approach…………………………………………………10
2.3.2 FIS往PML送的斷線恢復機制……………………………………11
2.3.3 週期更新備用路徑的方法…………………………………………12
2.3.4幾種斷線恢復機制的比較整理……………………………………13

第三章 Reverse Labeling Scheme的設計與實作…………………………14
3.1 Reverse Labeling Scheme的介紹…………………………………………14
3.2 Reverse Labeling Scheme的狀態轉換……………………………………17
3.3 Reverse Labeling Scheme的演算法………………………………………20
3.4 在Linux平台的實作………………………………………………………23
3.4.1 Sk_buff………………………………………………………………23
3.4.2 MPLS Kernel程式的流程…………………………………………25
3.4.3 LSR如何把封包送往備用路徑……………………………………27
3.4.4 LSR Buffer部分……………………………………………………28
3.4.5如何偵測斷線………………………………………………………29

第四章 實驗結果與分析……………………………………………………………32
4.1 實驗的網路拓樸…………………………………………………………32
4.2實驗數據及討論…………………………………………………………33
4.2.1三種Model Packet Loss的比較……………………………………33
4.2.2 Out-of-Order封包對TCP造成的影響……………………………35
4.2.3 Buffer Size與Out-of-Order封包的關係…………………………39
4.2.4 Queuing Length的變化……………………………………………40
4.2.5 Real-Time與Non Real-Time Traffic不同的處理…………………40
4.2.6 數學推算……………………………………………………………43

第五章 結論與未來工作方向………………………………………………………46
5.1 結論………………………………………………………………………46
5.2 未來工作方向……………………………………………………………47

參考文獻……………………………………………………………………………49
索引…………………………………………………………………………………53

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