Patent ID: 6937862

Claim:
A method for maintaining association between switching units in a network, the network comprising: a first part switched according to a first protocol; a second part switched according to a second protocol; a first switching unit and a second switching unit capable of communication with the first part; a third switching unit and a fourth switching unit capable of communication with the second part; a first base station and a second base station, each base station being capable of radio communication with a mobile station located within its respective coverage area; a first routing unit capable of communication with each of the first base station, the first switching unit and the third switching unit; and a second routing unit capable of communication with each of the second base station, the second switching unit and the fourth switching unit; and a routing link interconnecting the first routing unit and the second routing unit; the first switching unit having access to the address of the third switching unit, whereby the first switching unit is capable of addressing the third switching unit for determining whether the mobile station is communicating with the second part via the third switching unit; there being a mobile station being located within the coverage area of the first base station and being capable of being connected in a call with the first part or the second part via the first routing unit; and the method comprising the steps of, when the mobile station is connected in a call routed to the first part via the first base station, the first routing unit and the first switching unit and the mobile station is within the coverage area of the second base station; determining that the call is to be transferred to be routed to the first part via the second base station, the second routing unit, the first routing unit and the first switching unit; routing the call to the first part via the second base station, the second routing unit, the routing link, the first routing unit and the first switching unit; and transmitting an association message to the first switching unit to inform it of the address of the fourth switching unit; whereby the mobile station is capable of communicating with the second part via the fourth switching unit, and the first switching unit is capable of addressing the fourth switching unit for determining whether the mobile station is communicating with the second part via the fourth switching unit.