In this paper, we look at various mobility management protocols and handover frameworks in use in BT. We also report on the results from a collaborative proof of concept mixed network prototype for a seamless handover system using Intel's early implementation of the IEEE802.21 media-independent handover standard. The paper reports the design, implementation and deployment issues/options of a handover mechanism using the Intel framework which includes a connection manager and mixed network IEEE802.21 adaptation layer together with BT's SIP-based audio/video application in a heterogeneous Wi-Fi, WiMAX and Ethernet network environment.
IntroductionFuture mobile devices or terminals will roam seamlessly across heterogeneous networks, using wired or wireless connectivity, enabled by different access technologies such as IEEE802.11, IEEE802.16, CDMA, GSM, xDSL and cable. Users, either business or residential, are looking for easy ways to access services such as voice over IP (VoIP), directory, e-mail, video, TV, etc, independent of location, terminal, network access technology, and even operators, in the future. Supporting users with a seamless mobility experience is a challenging task given that each access network uses a different set of access protocols with different coverage areas, running at different bandwidth rates with varying degrees of QoS support. Applications must be made to adapt to the underlying network changes, while abstracting these changes to the users in order to achieve ubiquitous seamless connectivity. The current single-network fixed-function devices will increasingly continue to give way to multi-network, multi-function devices based on multiple integrated radios. It is important to have an intelligent connection-monitoring layer that sits between the application and the device to monitor the network status and availability and to notify the application of any network changes. The presence of such a layer helps in selecting the next best network to connect to, minimising the delay during the handover, and most importantly, interacting with the applications in a consistent manner to ensure seamless connection handover.IEEE802.21 [1] is an effort to standardise a set of mediaindependent handover (MIH) methods and procedures that facilitate mobility, especially the handover across heterogeneous networks also referred to as mixed networks. The standard specifies three media-independent servicesevent service, command service and information service. Events may indicate changes in state and transmission behaviour of the physical, data link and logical link layers, or predict the state changes of these layers. The event service may also be used to indicate management actions or command status on parts of the network. This allows the higher layer to treat all access technologies in a generic manner. The command service defines a set of primitives or handover commands which allows clients and network to initiate and co-ordinate the switching-over process from one network to another. The information serv...
