British Telecommunications Public Limited Company

David R Wisely

Rory Stewart Turnbull

Peter Paul Smyth

Richard Gedge

When a mobile station MSdetermines during communication through a first network (), that a second network () is available that offers better operational parameters for the communication, the mobile station sends a handover announcement (S) to the first network to offer it an opportunity to improve the operational parameters for the communication through the first network. The first network () may in response offer updated operational parameters (S) with a view to encouraging the communication to continue through the first network. A decision (S) whether to make a handover to the second network can then be made by comparing the updated operational parameters for the first network with the operational parameters for the second network.

Handover between mobile networks

A mobile station MScan communicate through a PLMN () and also through a number of local wireless networks e.g. WLAN () and WiMAX (). When the user of MSwishes to run an application, for example an video player application, a suitable one of the networks is selected for the communication by obtaining data from the candidate networks using SIP INVITE messages that produce responses containing network parameter data for each of the candidate networks. The handset MSmay also monitor local network traffic to determine network congestion and also check past history to determine whether many handovers have been made during previous sessions. The data is collated and checked with a service provider () so that a network selection decision can be made.

Network selection

In order to keep a pathway for time critical data packets (for example for VoIP calls) a dummy flow of data packets is established between a home hub router () and a broadband remote access server () being the first gateway to the IP network. Should a call be made from the telephone (), the dummy flow is replaced for the duration of the call by the packets generated for the VoIP call. The dummy flow is adjusted by increasing or decreasing the number of data packets transmitted in order to ensure that a minimum bandwidth having a tolerable delay is available. The dummy flow works by causing non time critical (i.e. P2P data packet flows) to back off and no modification is required to routers and the like incorporated into the network.

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Ipswich, United Kingdom

David R Wisely