As new multimedia contents growing exponentially around the world, the demand for mobile streaming services, which allows one to watch a selected content at anytime and anywhere through the wide spread wireless mobile networks, is increasing rapidly. In addition, since users prefer accessing content on-demand rather than following a fixed schedule, most of the streaming services are provided by on-demand manner with unicast transmission to meet the anytime and on-demand characteristics. From the network control perspective, unicast is simple and efficient when there is enough capacity and service request rate is a moderately low. However, when video requests are highly increased, for example, requests of popular User Created Contents (UCC) or newly released films, a large number of the unicast streams for the same content are established and transmitted over the network. This causes both media server and transmission network to be inefficient.
WiMAX and EPON are two promising broadband access technologies for new-generation wireless and wired access. The IEEE 802.16e working group developed the mobile WiMAX, which provides a wireless solution in metropolitan area access networks. The WiMAX is capable of wide range coverage, high data rates, secured transmission, and mobility support for vehicular speeds. Moreover, installation and maintenance costs of WiMAX systems are at a fraction of the costs of wired access networks. The high data rate and QoS assurance features of WiMAX make it commercially viable to support multimedia applications, such as mobile VoD, video gaming, and video telephony services. At the same time, Ethernet PON (EPON) has attracted a great deal of interest in both industry and academia as a promising cost-effective solution for next-generation broadband access networks. It is an inexpensive, simple, and scalable technology, with the capability of delivering integrated services. Its purpose is to significantly increase the broadband service performance while minimizing maintenance costs and support the next generation back-haul which requires high bandwidth (e.g. each WiMAX BS requires up to 75Mbps). Moreover, by using optical light splitters, multicast streams are easily copied than electronic data copy and can solve the synchronization problem between BSs. When taking advantage of these features, mobile VoD services can be designed, delivered, and managed effectively without compromising video and audio quality. Therefore, their complementary features motivate interest in using EPON as a backhaul to connect multiple dispersed WiMAX BSs.
Since the bottleneck of mobile VoD services has been observed in access networks rather than multimedia servers or the core network, this thesis provides new solutions that efficiently utilize the WiMAX and EPON downlink resources. Although the IEEE 802.16e [2] standard defined Multicast Broadcast Service (MBS) to provide an efficient way to transmit diverse multimedia streams to multiple users through a shared radio resource, there is no consideration for multicast in IEEE 802.3ah standard. Therefore, this thesis firstly provides an efficient multicast management scheme in the converged WiMAX and EPON networks. Secondly, adaptive transmission scheme is proposed. This scheme combines unicast and multicast transmission and focuses more on the decision of which contents are going to be transmitted by the multicast or unicast within limited resources in the converged WiMAX and EPON network. The decision is provided by proposed resource management scheme based on MEF which is multicast efficiency indicator compared with unicast transmission. Basically, previous researches, the decision factor were only popularity, but this thesis considers required channels and service rate of each contents. As a result, it provides the lower service blocking probability and higher throughput.
현재 통신망의 서비스 추이를 살펴보면, IPTV와 같은 멀티미디어 스트리밍 서비스가 유선 환경뿐만 아니라 무선 상황에서도 킬러 어플리케이션으로 인지되고 있으며, 관련된 많은 연구가 활발히 이루어 지고 있다. 이러한 다양한 서비스 중에서도 사용자는 정해진 스케줄로 나오는 서비스 보다, 원하는 컨텐츠를 요청해서 보는 on-demand 형식의 서비스를 선호하고 있으며, 현재 on-demand 형식이 멀티미디어 스트리밍 서비스 중에서도 대부분을 차지하고 있다. 예를 들어, 현재 국내 사업자들이 제공하는 IPTV서비스도 대부분 VoD (Video On Demand) 서비스 임을 보면 그 추이를 엿볼 수 있다. 유선 망의 경우 FTTH (Fiber To The Home), EPON (Ethernet Passive Optical Network)과 같은 광대역 통신 기술을 이용해 고품질의 비디오 스트림이 가능해 졌지만, 아직까지 무선 상황에서는 자원부족과 전송 비 효율성 때문에 서비스 제공에 문제점이 있다. 따라서 무선 상황에서 효율적인 on-demand 스트리밍을 위한 메커니즘이 필요하게 된다. 현재 on-demand 서비스는 사용자의 요청 시 스트림을 보내주는 유니케스트 기법을 이용하고 있다. 유니캐스트를 이용하면 구현이 간편하지만, 인기 있는 드라마 또는 핫 이슈가 되는 UCC등에 집중적인 컨텐트 요청이 있게 되면, 동일 컨텐트에 대해 중복적으로 많은 유니캐스트 접속이 생겨나기 때문에 전송의 비효율성이 증가 하게 된다. 본 논문은 이러한 집중 접속 문제를 해결하기 위하여 광대역 무선 통신망 중의 하나인 WiMAX와 EPON의 접속망을 고려하였으며, On Demand 형식의 스트리밍을 효율적으로 제공하기 위하여 on-demand 용 멀티캐스트 전송 기법과 MEF (Multicast Efficient Factor)기반의 자원 관리 알고리즘을 제안하여 집중 요청된 컨텐트를 관리함으로써 시스템 성능을 극대화 시켰다. 수학적 및 툴을 이용한 성능검증을 통해 결과적으로 기존 유니케스트 기법 대비 낮은 blocking probability 와 throughput 향상을 얻을 수 있었으며, 최종적으로 revenue, loss 모델링을 통해 VoD 사업자가 좀더 많은 이윤을 남길 수 있음을 증명 하였다.
