臺灣博碩士論文加值系統

由於網際網路比公眾交換電信網路具有較高資源效益與較低通訊成本，因此近年來網路電話在網際網路上到處存在。為了提供高可靠度的公眾電話服務，網路電話必須像目前公眾交換電信網路，提供相同的可靠度與語音品質。

為了延伸網路電話服務的規模，我們設計與實作網路電話閘道器，整合公眾交換電信網路、H.323 網路電話與 SIP 網路電話，並且在差別式服務多重協定標籤交換寬頻網際網路中建置網路電話實驗環境。除此之外，我們提出內部以 SIP 為基礎之共通信令，以降低網路電話閘道器信令轉換之複雜度。

在這實驗環境中，我們發現系統軟硬體的限制，以及缺乏服務品質保證能力。因此，我們提出一套服務等級協議管理架構，包含離線評估與線上處理，以提供一個可靠、堅強、公平與有效率的網路電話服務。在這架構中，離線評估與線上處理的兩個研究議題被轉換成最佳化問題。離線評估的服務等級協議轉換結果，可以協助網路電話業者在簽訂完網路電話服務等級協議後，如何簽訂網路服務等級協議以達到最佳收益。此外，線上處理的網路電話品質等級調整結果可以協助網路電話業者達到最佳收益與制訂專屬網路電話服務策略，這些服務策略可以提供服務品質控制之依據參考，如：電話允陰惆謘B電話品質分配。

為了降低服務品質管理複雜度，我們也提出兩個服務模型，AF+_non-RA 與AF+_RA，讓一般 E-LSP 與 L-LSP 載送網路電話資料無法同時兼顧品質與成本的況狀下，提供一種選擇。AF+ 服務模型可以符合成本效益需求，並且在在差別式服務多重協定標籤交換寬頻網際網路上提供一個實用的方案。

除此之外，我們觀察到傳統分包分類機制不適合分類網路電話的封包，因為網路電話的語音封包無法事先被預測與設定。因此我們提出狀態追蹤會議分類機制，並提出兩個實作的架構，透過追蹤會議的狀態，以會議為基礎的應用程式封包都可以正確地被分類與標示。

在我們的環境中，我們也觀察到網路恢復收斂時間無法滿足網路電話對網路可靠度的要求。因此我們在網路路由區域中針對網路電話服務提出 IP Local Fast-Reroute (IPLFRR) 機制，我們的機制提供簡單且有效率的方案來保護網際網路，根據現有的連線狀態路由協定，我們的方案不需要額外的控制協定與修改路由協定。

簡單地說，本論文之服務品質控制與管理機制在在差別式服務多重協定標籤交換寬頻網際網路中可以有效地改善網路電話服務品質、服務規模、服務可存取度與可靠度，我們的貢獻對網路電話使用者、網路電話服務業者與網路服務業者都有幫助，尤其是網路電話服務業者。

Recently, VoIP applications are ubiquitous in the Internet, due to the high resource efficiency of IP-Based networks and its low cost compared to conventional voice transport service via Public Switched Telephone Network (PSTN). To provide a credible alternative to telephony service in PSTN, VoIP has to offer the same reliability and voice quality.

To extend VoIP service scalability, we design and implement a VoIP gateway to integrate the phone services of PSTN, H.323 VoIP and SIP VoIP, and then establish an experimental VoIP environment over DiffServ IP/MPLS networks. Additionally, we have proposed internal SIP-based common signaling to reduce the complexity of signaling translation.

In the environment, we observe that the limitations of system hardware and software, and the lack of VoIP QoS guarantee. To provide a credible, robust, fair, and efficient VoIP service, we propose a SLA management framework including off-line evaluation and on-line process. In this framework, two research issues in off-line evaluation and on-line process are formulated as optimization problems. The results of SLA mapping in off-line QoS evaluation can help VoIP application providers to maximize the profit and contract the N-SLA based on the contracted S-SLA. Additionally, the results of VoIP quality level adaptation in on-line process can help VoIP application providers to maximize the profit and define a proprietary VoIP service policy. Moreover, the service policy can provide a guideline to VoIP service control, such as CAC (call admission control), service quality assignment, etc.

In order to reduce the complexity of QoS management, we propose two novel service models, AF+_non-RA and AF+_RA, to enable the E-LSP and L-LSP to tradeoff between the two opposing objectives. AF+ VoIP service meets the cost-effective requirements and provides a practical solution to DiffServ-based MPLS Networks.

Additionally, we observe that the traditional classifications are inadequate for VoIP applications whose classification rules can't be configured in advance. We propose the state tracking session classification and presented two implementation alternatives. By tracking the states of the sessions, all of the packets in the session-based applications can be caught and then marked or tagged.

In our environment, we also observe that the IP restoration time cannot satisfy the reliability requirements of VoIP service. We propose an IP Local Fast-Reroute (IPLFRR) scheme for VoIP service in an intra-area IP routing domain. Our scheme provides simple and efficient solutions for IP network protection. According to the present link-state routing protocols, neither extra control protocols nor enhanced routing protocols are needed in our solutions.

Briefly, the QoS control and management schemes proposed in this thesis can improve service quality, service scalability, service availability and reliability of VoIP applications in DiffServ IP/MPLS networks efficiently. Our contributions are useful to VoIP users, VoIP application providers and network service provider, especially the VoIP application providers.

1 Introduction 1
1.1 Motivation 1
1.2 VoIP Challenges and Research Scope 2
1.3 Organization of the Thesis 8
2 VoIP System Environment 10
2.1 VoIP Applications in DiffServ IP/MPLS Networks 10
2.2 Design and Implementation of VoIP Gateway 12
2.2.1 System Design 12
2.2.2 System Performance 15
3 QoS Control and Management Schemes 17
3.1 SLA Structures and Management for VoIP Applications 17
3.1.1 Introduction 17
3.1.2 Related Works 21
3.1.3 SLA Management Framework 21
3.1.4 SLA Structures 25
3.2 SLA Mapping in Off-Line QoS Evaluation 30
3.2.1 SLAs translation 31
3.2.2 Heuristic Algorithm 35
3.3 VoIP Quality Level Adaptation in On-Line Process 36
3.3.1 Introduction 36
3.3.2 Problem Formulation 38
3.4 AF+ VoIP Service in DiffServ/MPLS Networks 42
3.4.1 Introduction 42
3.4.2 AF+ Service Models 44
3.5 Session Classification for Traffic Aggregation 52
3.5.1 Introduction 52
3.5.2 Session Classification Architectures 55
3.6 Local Fast-Reroute schemes in IP Networks 59
3.6.1 Introduction 59
3.6.2 Related Works 63
3.6.3 IP Routing and IP Local Fast-Reroute 65
3.6.4 IP Local Fast-Reroute Schemes 68
4 Analysis and Numerical Results 78
4.1 SLA Mapping in Off-Line QoS Evaluation 78
4.2 VoIP Quality Level Adaptation in On-Line Process 81
4.3 AF+ VoIP Service in DiffServ/MPLS Networks 84
4.3.1 Call Blocking Rate 84
4.3.2 Optimal Solution 85
4.4 A Session Classification Example for H.323 VoIP Applications 89
4.4.1 H.323 Overview 89
4.4.2 Design of H.323 Session Classifier 90
4.4.3 Experiment Environment 92
4.5 Local Fast-Reroute Schemes in IP Networks 96
4.5.1 Comparison with IP Local Fast Reroute and Loop Free Alternate Paths 96
4.5.2 Simulations 99
5 Conclusion 110
5.1 Our Contribution 110
5.2 Ongoing Research and Future Work 112
Bibliography 114

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