Importance

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Abstract

A technique for mobility signaling between a Base Transceiver System (BTS) and Mobile Switching Center (MSC) in a mobile telecommunications system. The MSC is interconnected to a number of BTSs using one or more primary rate links using a protocol such as Integrated Digital Services Network (ISDN), including a number of bearer (B) channels for voice transmission and at least one data (D) channel for control function transmission. Standard call processing messages are utilized on the ISDN D channel to support basic telephone functions such as call origination, call termination, and call release as much as possible. However, an additional logical communication link is established over each ISDN D channel to accommodate mobility related messaging which may include messages such as hand-off and registration messaging needed to support mobile communications. The logical communication links are implemented in an unbalanced mode such as provided by the unnumbered information (UI) feature of ISDN and utilizing a Service Access Point Indicator (SAPI) address different from that address used for the standard call processing functions. As a result, the link used for the UI frames having mobility messaging does not need to use call reference values and may be routed over any available virtual communication link. Mobility messaging may thus be transmitted with minimal overhead and is not restricted to either the physical ISDN link which is handling the standard call processing for a call or even the ISDN link which handled previous mobility messages for the same call.

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First Claim