UMTS差別性服務等候機制效能應用二種佇列空間配置之研究

Abstract

自美國、日本和歐洲各國提出第三代無線通訊系統協定標準，如TD-SCDMA、CDMA2000與WCDMA / UMTS以來，較廣為業界所看好的技術規格為WCDMA / UMTS，因為目前使用人口最多的GSM歐洲系統業者也加入參與制定，且GSM是世界上最大的第二代移動通信網路，UMTS勢必成為第三代行動通訊主流規格。3GPP所提出UMTS 的3G標準，可以確保GSM核心網路無縫 (Seamless) 接取到3G的核心網路，這種相容於過去GSM / GPRS系統的考量，對於系統業者不僅可投資延續價值，也兼顧商業上的經濟效益。 3G R5以後的規格及4G網路已朝向全IP化的方向發展，並以IP作為主要通訊協定，因此，UMTS的語音會話、影音串流、網頁互動及檔案傳輸的四種資料類型，都有其特定的屬性質，並賦予不同的封包傳輸順序，以達到符合各類型資料的服務等級 (Quality of Service, QoS) 的要求及目標，由於IP協定中的盡力而為服務(Best Effort Service)，對於嚴格要求低延遲、低抖動(Jitter)等服務的多媒體類或語音的資料型態，已無法滿足需求，因此，提供優化的封包轉送能力(Packet Forwarding)以達到服務等級要求，成為UMTS核心網路中一項重要的工作。 本論文提出的方法是在UMTS系統核心網路中，對不同的資料類型，提供差異性服務及優先順序的封包傳送能力，利用兩種佇列緩衝記憶體空間配置機制：動態佇列緩衝空間配置(DQB)和邏輯佇列溢流緩衝空間配置(OQB)，另外，對各類型封包允入與允出佇列時的機制，分別以優先順序為基礎方式(Priority-Based Queuing)允入佇列及連續性加權輪詢(Sequential-Weighted Round Robin)的允出佇列機制處理。透過NS2網路模擬軟體，對不同方案想定、封包大小及參數值進行模擬評估，根據模擬的結果，每一種類型服務的封包在效能(Throughput)、封包丟失率(drop probability)、延遲及抖動率與IETF所提出之差異性服務(Differentiated Service, DiffServ)比較，兩者可達到近似的效能。

As UMTS systems will evolve into an all-IP stage in the future, packet switching becomes a prerequisite for all UMTS applications. The 3GPP defines four types of UMTS traffic: conversational, streaming, interactive and background; each type of UMTS traffic has its QoS features. Differentiated Service (DiffServ) is QoS architecture for IP networks, their based on packet marking that allows packets to be prioritized according to Service Level Agreement (SLA) management. The DiffServ is a scalable architecture and is proposed to provide QoS guarantee services and scheduling packets forwarding for each class within the IP networks. According to four types of UMTS traffic, this study proposes a priority-based queuing scheme with two queuing buffer allocations, the dynamic queuing buffer (DQB) allocation and the overflow queuing buffer (OQB) allocation, to support packet forwarding of four types of UMTS traffic in a DiffServ method. In the proposed queuing scheme, two major modules, a priority-based enqueuing module and a sequential weighted round robin (SWRR) dequeuing module, base on the DQB allocation and the OQB allocation to perform differentiated packet enqueuing / dequeuing jobs among four types of UMTS traffic. In this study, we use the ns2 (Network Simulator version 2) as the simulation platform to simulate several scenarios. Discussing the simulation results and analysis, we can find the proposed queuing scheme can base on packet transmission priorities of four types of UMTS traffic to support a differentiated packet forwarding behavior among UMTS traffic in a UMTS core network and the performance of UMTS traffic with a high priority always gets a better packet forwarding performance than that of UMTS traffic with a low priority. And, the differentiated packet forwarding behaviors with the proposed queueing scheme are similar to the packet forwarding behavior with the IETF DiffServ scheme.