| Summary: | Mobile network operators have recently started looking into ways to increase their own network scalability, in order to support a large number of customers with new bandwidth consuming multimedia services. The two most promising solutions identified are to extend the existing networks with multicast capabilities and to cooperate with network operators of different wireless access technologies. As a consequence of these trends, a next generation network environment will allow mobile users to receive multimedia service data from a variety of multicast capable access networks. Although considerable progress has been made with the standardisation of multicast mechanisms such as Multimedia Broadcast and Multicast Services (MBMS) for UMTS networks, shortcomings still exist in emerging multicast technologies and their interworking with each other. One of the critical realisations leading to this research was the observation that the establishment and release of multicast bearers, particularly in UMTS networks, requires signalling intensive procedures, as compared to the simple mechanisms of IP multicast on the Internet. Especially for services such as location based multicast services, where a user is expected to change multicast groups more frequently, a considerable signalling burden may be added to a network. This is hardly acceptable for mobile networks, where wireless resources are valuable and scarce. One contribution made in this thesis extends the currently defined mechanisms in MBMS to allow the concurrent delivery of different versions of location based content using the same multicast bearer service. It is shown by simulation study that the proposed mechanism achieves significant signalling savings, especially over the air interface, compared to the case where separate multicast bearer services are utilised for the delivery of different location specific flows. Another significant observation was that the current receiver driven service model of IP multicast is not suitable to allow efficient multicast delivery in a wireless network environment with multiple access networks. This thesis argues that efficient multicast delivery requires mechanisms for delivery coordination, in order to avoid the same multicast traffic being delivered via multiple access networks to the same location. Based on a detailed analysis of the shortcomings of current IP multicast group management mechanism, two incremental solutions to achieve multicast delivery coordination in next generation networks are developed and their advantages and disadvantages thoroughly studied. The first approach achieves delivery coordination by introducing a group management support as a session layer solution, leaving the operation of current existing IP multicast mechanisms completely unchanged. The second approach provides a solution on the network layer to achieve multicast delivery coordination, and requires the modification of the current IP multicast group management mechanisms. Proof-of-concept prototypes are built to demonstrate the feasibility of both solutions. An evaluation of their performance is achieved by analytical and simulation study and is complemented by a testbed study of the prototypes.
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