A mobile telephone system providing general packet radio service (GPRS) includes
a radio network controller (RNC) (2A) and/or a base station controller (BSC)
and an associated serving GPRS support node (10A) for each domain. The RNCs
(2A) and the SGSNs (10A) are interconnected by an Internet protocol
(IP) network. When a mobile telephone (6A) moves from one domain to another,
the RNC, in the new domain, takes over handling the mobile telephone. The current
SGSN (10A) has a detector (20) which detects whether the existing
transmission is a real-time transmission and, if it is, a diverter (22)
comes into operation to couple the RNC in the new domain to the current SGSN (10A)
rather than its associated SGSN (10A). When the call ends, the current SGSN
(10A) hands-over the call to the SGSN (10A) in the new domain. This
procedure ensures minimal interruption to real-time services by keeping the call
anchored to the current SGSN (10A).
