臺灣博碩士論文加值系統

多重協定標籤交換(multi-protocol label switching，MPLS) 是近年來在網際網路上的一個新技術，其基本概念是將路由資訊對映到一個較短且固定長度的標籤上，使用連線導向之資料連結層，以標籤交換為基礎，快速的交換資料至下一個路由器位置。對於MPLS網路中標籤(label)不敷使用的問題， 並為了減小標籤表格(label table)，一般的作法是將不同入口但有相同出口的資料流合併以解決此問題，這種方式我們稱為匯集(aggregation)，此方法主要是針對不具服務品質需求的竭力 (best-effort) 資料流。對於具服務品質(quality of service, QoS)的資源預留協定 (Resource reSerVation Protocol, RSVP) 資料流，為了維持其的服務品質，目前並無法使用匯集來減少標籤的使用。
本論文在MPLS網路上對匯集RSVP資料流的研究，如何決定資源預留資料流所要使用的標籤。在MPLS網路中，使用非同步交換為硬體的標籤交換路由器(ATM-label switching router，ATM-LSR)時，可用虛擬路徑辨識碼(virtual path identifier, VPI)欄位，虛擬通道辨識碼(virtual channel identifier, VCI)欄位，或虛擬路徑辨識碼加虛擬通道辨識碼(VPI/VCI)欄位做為標籤。
現有網際網路對RSVP資料流的匯集乃依據一般的服務層級(VC-merge with service class) 來分類，將具有相同服務等級和相同出口標籤交換路由器(egress label switching router, egress LSR)的資源用同一標籤匯集預留資料流。其缺點是有要求過多額外緩衝器(additional buffer)。因此我們提出具有服務品質等級的虛擬通道合併(VC merge with QoS level) 來匯集RVSP資料流，並以VPI為標籤，透過其中的細胞遺失率(cell loss rate, CLR)以區分RVSP資料流，再透過具有VC-merge 功能的ATM-LSR，解決VCI碰撞的問題。
在模擬的結果中發現，對於所需的額外緩衝器方面:相較於無匯集的情況，VC-merge with service class的機制會要求高達83%的額外緩衝器，而具有VC-merge with QoS level的機制僅要求23.5%的額外緩衝器。在標籤表格的大小方面：以VC-merge with service class的機制匯集RSVP資料流，其標籤表格的大小會從O(N2)降為O(N)；而VC-merge with QoS level的機制，其標籤表格的大小亦為O(N)， N為邊緣標籤交換路由器(edge LSR)的數目。
其次，我們考慮透過LSR來執行RSVP處理元(RSVP process)所送收的訊號(signaling message)。為提供服務品質給匯集後的資源預留資料流並減少網路負荷，我們提出兩種資源預留的訊號匯集的機制：代理的標籤交換路由器(Proxy LSR) 和匯集後的路徑訊號(PATH)及預留訊號(RESV)以減少網路上的訊務和中間的LSR處理資源預留的次數。當RSVP訊號會修改資源預留狀態(RSVP State) 的機率p越低，在網路上RSVP訊號的數量和中間的LSR處理執行RSVP process的次數(MN2 p) 越少。本論文假設RSVP資料流數量多，因此匯集相同標籤的RVSP訊號來預留虛擬路徑的資源以減少網路中匯集RSVP訊息的數量，並利用統計頻寬小於總和頻寬的特性，將多餘頻寬給匯集的best-effort資料流使用。然而在RSVP資料流數量少的時候，我們僅需藉由匯集相同VPI/VCI 的RSVP訊號預留VC的資源即可。

Flow aggregation in ATM networks can basically be categorized into two branches. The first one is VC-merge which requires more latency time and up to 53% more additional buffer than non-VC-merge. Especially, VC-merge with service class requires up to 83% more additional buffer than non-VC-merge for RSVP data flows. The second branch is VP-merge which has scalability problem resulted from the size of VPI field and VCI collision problem resulted from the size of VCI field.
This thesis studies issues of aggregating RSVP flows and aggregating RSVP signaling messages in MPLS networks. Two aggregation mechanisms are proposed. The first mechanism is the VC-merge with QoS level which aggregates data flows with QoS request by combining the advantage of VC-merge and VP-merge. This mechanism requires 23% more additional buffer than non-VC-merge for RSVP data flows. The second one is RSVP signaling message aggregation which aggregates several RSVP control messages to a new one so as to reduce the number of RSVP control messages to be processed in label switching routers (LSRs) and to conserve the bandwidth in transferring these messages.
The results indicate that VC-merge with QoS level mechanism reduces the label consumption from O(M’N2) to O(K’N), requires less buffer than the VC-merge does, provides reasonable QoS for each flow in the same merged link, and solves the VCI collision problem, where M is the number of RSVP flows in each ingress LSR, N is the number of ingress LSRs and K is the QoS levels. The RSVP signaling message aggregation mechanism reduces the number of RSVP signaling messages from O(M’N) to O(N) while most flows are RSVP flows.
1.1 RSVP 1
1.2 IP over ATM 4
1.3 Multi-Protocol Label Switching 5
1.4 RSVP over MPLS 6
1.5 Stream Aggregation 9
1.6 Others issues 13
1.7 Plans of This Thesis 15
Chapter 2 Stream Aggregation Problem 17
2.1 VC-Merge Mechanisms 18
2.2 VP Merging Mechanisms 22
Chapter 3 VC Merging with QoS Level Mechanism 25
3.1 Format of Cell Header 25
3.2 VCI Assignment Mechanism 26
3.3 Architecture of LSR 28
3.4 Extending RSVP protocol 30
Chapter 4 Simulation Results and Comparison 38
4.1 Simulation Model 38
4.2 Simulation Results 40
4.3 Numerical Analysis 45
Chapter 5 RSVP Signaling Message 47
5.1 Related Works 47
5.2 RSVP Signaling Message Aggregation Mechanism 53
5.3 Simulation Results 55
Chapter 6 Conclusion 58
References 61

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