捷徑優先公開協定(OSPF)曾被視為inter-domain Internet Protocol (IP)網際路由的標準。它的階層式架構及邊界路由器(ABR)提供了網路擴通性問題相當有效的解決方案。無論如何，目前手動設定邊界路由器(ABR)無法有效處理動態改變的網路負載，也無法有效的解決方。
在論文研究中，提出兩個不同的可行方法。一個是動態指定之邊界路由器機制，另一個是P-median捷徑優先公開協定(OSFP)分類集結機制。
關於一個新的動態指定之邊界路由器機制，這是建立於捷徑優先公開協定(OSPF)階層式網路上的動態指定之邊界路由器機制基於觀測動態的傳輸需求、及時監控網路承載使用率來運作。進而採用運算機制決定是否在新舊邊界路由器(ABR)之間切換，用以避免因動態流量變化所造成的網路壅塞。
本研究所提出另一個法則是P-median捷徑優先公開協定(OSFP)分類集結機制，這個機制是在進行捷徑優先公開協定(OSFP)分類集結子網域來進行P個子網域切割時，可以提供最佳的邊界路由器(ABR)位置。使得子網域內部每個節點到達邊界路由器所花費的權值都達到最小。

Open Shortest Path First (OSPF) had been recognized as a de facto standard for inter-domain Internet Protocol (IP) routing. Its hierarchical architecture and the introducing of Area Border Router (ABR) had been proved to be an effective solution to the scalability problem. However, manual selection of ABR may fail to accommodate the dynamic change in the network load and therefore lead to sub-optimal solution. There are two new schemes proposed in this thesis. One scheme is Dynamic Appointment ABR for OSPF (DAA-OSPF). Other one scheme is P-median OSPF Partition Algorithm.
DAA-OSPF scheme is proposed for the dynamic appointment of ABR for OSPF. Based on observed traffic demands and knowledge on link capacities, the proposed scheme will dynamically switch to a new ABR from an old one to avoid incipient link congestion and accompanying performance degradation. In response to traffic change,the proposed approach will locate an adequate ABR for the new traffic pattern and then direct traffics to the new ABR. System performance, in terms of link utilization, throughput, and delay, is expected to benefit from the proposed scheme, as demonstrated in the simulation results.
This study also contributes to the issue of stub area partitioning. According to our study, we recognize that the stub area partitioning problem can be well modeled by the P-median problem in logistics [WR99]. In this study, we extend and refine existing approaches to the P-median problem and apply them to the stub area partitioning problem. The refined P-median algorithm is capable of finding out the optical locations of P ABRs in a network such that the total cost is minimized. With the refined P-median algorithm, the proposed OSPF partitioning scheme is expected to minimize the cost of OSPF hierarchical routing, as well as the cost in subsequent packet transmission.

Contents Page
List of figures.............................................................................................iii
List of Tables .................................................................................v
Chapter 1 Introduction ........................................................................1
1.1 Motivation ..................................................................................................6
1.2 Objective ...................................................................................................7
1.3 Contributions of the Dissertation .................................................................8
1.4 Structure of Dissertation……………………………………………….8
Chapter 2 Background and Survey of Related work ...........................................9
2.1 Fundamentals of Open Shortest Path First Network .....................................9
2.2 Link State Routing Protocol for OSPF .......................................................13
2.2.1 The Link State Database…………………………………………....14
2.2.2 The Flooding Protocol………………………………………………...16
2.2.3 Link-state advertisements……………………………………………..16
2.2.4 The Common Header…………………………………………………18
2.2.5 OSPF Metric ………………………………………………………….20
2.3 Structure definitions of OSPF…………………………………..............22
2.4 OSPF Route Types……………………………………………………...23
2.5 Related works: Other link State Routing Protocol…………………………25
2.5.1 Max-Flow Min-Cut Theorem…………………………………………25
2.5.2 Traffic engineering for the shortest path……………………………...31
2.5.3 OSPF aggregates approaches…………………………………………32
2.6 P-median Problem………………………………………………………34
2.6.1 One-median Algorithm……………………………………………..35
2.6.2 Myopic algorithm for P-median Algorithm……………………………39
Chapter 3 Dynamic Appointment ABR scheme ..............................................48
3.1 Problem Statement ...................................................................................48
3.2 Methodology: Dynamic Appointment ABR scheme ...................................51
3.3 Performance Evaluation ............................................................................55
Chapter 4 P-median OSPF Partition Algorithm ...............................................56
4.1 Problem Statement ...................................................................................56
4.2 Methodology ............................................................................................56
4.3 P-median OSPF Partition Algorithm .........................................................58
4.4 Coalition Algorithm ..................................................................................71
Chapter 5 Conclusion and future Work ............................................................76
5.1 Conclusion ...............................................................................................76
5.2 Future Work .............................................................................................77
Bibliography ..................................................................................................79

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