視訊串流於異質行動多媒體網路傳輸之無縫服務機制

Seamless Service Mechanisms for Video Streams over Heterogeneous Mobile Multimedia Networks

杜俊育(Jiun-Yu Tu)

指導教授 ： 吳中實

國立中央大學/資訊電機學院/通訊工程學系/博士(2012年)

摘要

行動通訊技術近年快速發展。高傳輸頻寬及愈見精巧的服務品質保證機制，帶引多樣化的多媒體應用之實現。現下，多媒體內容的傳輸已經成為行動通訊網路資源消耗的大宗。因此，提供適切的存取技術來讓終端使用者在行動多媒體應用的使用上感到流暢，已是重要的議題。
事實上，行動通訊網路因提供移動性給終端使用者，而在通訊市場上獲得空前的成功。藉由移動性，行動中的使用者可以讓服務持續不斷。但移動性本身卻帶來無縫換手的議題亟待更有效的解決。
以網路技術的發展趨勢而論，下個世代的多媒體通訊係架構在all-IP的核心網路上，並整合異質性的接取網路以建構“隨處”的多媒體通訊環境。下個世代的多媒體網路不但提供通訊中訊務的移動性，並將提供服務的移動性，以達到隨處運算之隨時、隨地以任意設備進行通訊服務的目標。這將使移動性的議題變得更有彈性，但卻更為棘手。
在下個世代的多媒體通訊架構的原則下，3GPP提出IMS架構來達到提供服務動性的目標。IMS係為一整合性的多媒體服務平台，以標準SIP為該架構核心層的標準信令而提供一個易於開發並佈建多元化多媒體服務的環境。IMS的核心層架構於異質性接取網路之上，因此除了提供上述的服務移動性 (Service Mobility) 外，亦可提供行動訊務的通訊移動性 (Session Mobility)。但如上所述，該環境引發較為複雜的換手流程，使得流暢的多媒體服務之提供更為棘手。細究IMS的換手，我們發現在IMS環境下換手的行動終端使用者勢必面臨多層的換手機制而導致極為可觀的換手延遲。這可觀的換手延遲確實將對行動多媒體服務的流暢性帶來嚴重的傷害，尤其對於即時性的服務。此外，IMS所整合的異質性行動接取網路，各個網路間在服務品質保證機制及定義上的差異以及具時變特性的通訊通道俱會對穩定而流暢的提供多媒體通訊服務產生不良的影響。
在這論文中，為解決上述的問題，我們在編碼技術上採用可調式視訊編碼(SVC)來提供行動終端使用者視訊串流的服務。SVC為階層編碼型的技術，用之可使異質性接取網路各個網路間在服務品質差異以及時變通訊通道對服務流暢度所帶來的負面影響得到改善。但因現行的網路架構係依OSI網路模型而建立，分層間彼此的透通性將令SVC的特性遭受戕害。是以，此論文將針對此現象對SVC提出一個橫跨MAC層、網路層以及應用層的跨多層服務品質保證機制與策略。該機制將揭露SVC視訊編碼技術的重要指標給下層的網路節點，以令網路節點進行最適切的資源規劃。除SVC外，此論文亦將在IMS的整合架構下提出一個無縫服務的促進方案。該促進方案將引進媒介獨立換手服務(MIH)並大幅度的改善IMS的行動終端在換手時所產生的換手延遲。而此論文所提出之主動是換手機制則可令SVC視訊串流服務在IMS環境下透過資料緩衝的機制填補上述促進方案所遺留的服務間隙(Service Gap)而達到真正的無縫服務的目標，亦即真正流暢之行動可調式視訊串流服務。
末後，此論文將以系統模擬的結果來驗證所提的方案的優異性。

關鍵字

無縫服務 ； 無縫換手 ； IP多媒體子系統 ； 可調式視訊編碼

並列摘要

By the rapidly evolving mobile communication technologies, broad transmission bandwidth and sophisticated Quality of Service guarantee mechanisms enable plenty of multimedia applications. Today, multimedia contents have dominated the consumption of wireless communication network resources. Providing suitable access technologies to smooth subscribers'' experiences in multimedia service consumption is much crutial.

In fact, mobile communication networks bring mobility to mobile subscribers and win significantly success in modern communication markets. The mobility provides session continuity to mobile subscribers and assists them to obtain some level of ``smooth'' to their consuming applications. However, seamless handover has still been one of the main issues to provide service smoothly to mobile subscribers.

Toward the next generation multimedia communication, all-IP core networks and heterogeneous access networks would construct ubiquitous multimedia communication environments. The Next Generation Multimedia Network (NGMN) would provide not only session mobility, but also service mobility to subscribers. The ubiqutous communication enables multimedia subscribers access their interested multimedia services using anydevice at anytime, in anyplace. The mobility becomes more flexible but knotty.

The 3rd Generation Partnership Project proposes IP multimedia subsystem to build the NGMN. The IP multimedia subsystem is an integrated platform for developing and deploying multimedia applications speedy and easily. It overlays heterogeneous access networks, including fixed and mobile ones, to support service mobility to subscribers. Thus, heterogeneous handover is unavoidable but much difficult while one considers smoothly services. When investigating the mobile services in the IP multimedia subsystem, we find that the services suffer from several handover latencies. The latencies prevent various of multimedia services which are usually real-time from serving smoothly. In addition, inconsistent Quality of Service policies and distinct mechanisms between heterogeneous access networks corrupt the smooth, besides varing channel conditions.

In this dissertation, we invoke the scalable video coding (SVC) scheme to provide streaming video services over the IP multimedia subsystem. The scalable video coding scheme utilizes layered-based technology to overcome the inconsistency between heterogeneous access networks and radio channel conditions. The scheme can support smooth services to mobile subscribers in its design spirit, however, the existing Open Systems Interconnection (OSI) model-based networks hide the efficiency. This dissertation, thus, first exposes the importance of the SVC-encoded video data to existing OSI-based network nodes. By the exposure, the network nodes can successfully perform conscientious protection to more important parts of SVC-encoded video data, and invoke the scalability of the SVC scheme to obtain smooth service from application aspect. Furthermore, this dissertation introduces Media Independent Handover (MIH) service to the IP Multimedia Subsystem, and proposes a Fast IMS Service Recovery Mechanism (FISERM) to mitigate handover latencies in heterogeneous access networks. The Media Independent Handvoer service assists mobile subscribers to handover between mobile access network smoothly. In addition, this dissertation invokes the MIH service to achieve seamless servoce. In fact, seamless service is preferred rather than seamless handover in the design of FISERM. The seamless service considers not only lower-layer handover procedures between heterogeneous access networks, but also application layer handover that the IP Multimedia Subsystem invokes for service mobility and Quality of Service guarantee.

Finally, this dissertation proposes an active seamless service scheme to the SVC streaming video services over IP multimedia subsystem. The active seamless service scheme get really seamless service to SVC streaming video services by an advanced buffer filling strategy. The strategy fills the service gap that starves the video buffer of the streaming video services and disturbes the playback. System simulations evidence that the proposed schemes provide outstanding performance to the real-time multimedia service over the IP Multimedia Subsystem, expecially for Scalable Video Coding streaming video services.

並列關鍵字

seamless service ； seamless handover ； MIH ； IMS ； SVC

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