Call set-up process

The arrangement disclosed allows a user of a mobile telephone 11 to use intelligent network (IN) services specific to his home network, regardless of whether the network 12, 13, 14 to which he is currently connected can support the service. When the user makes an outgoing call attempt (step 1) the associated signalling is transmitted over a signalling channel. The mobile switching centre (MSC) 13 recognises a customer identity (encoded electronically in the call set-up signals ) and accesses the data relating to the user which is stored in a register 14. The data in the register 14 relating to the user 11 includes a marking identifying him as an IN served customer, causing the MSC 13 to halt the call process and send a signal (2), protocol, to the service control point (SCP) 15 in the user's home network. The SCP 15 then activates the user's service profile and as part of that profile recognises the need to retrieve additional information from the user 11, e.g. a PIN (personal identity number) or some other information. Having identified the information needed, the SCP initiates a message 3 to the mobile station, for example requesting an authorisation code, which is passed back to the MS 11 by way of the switching centre MSC 13 and base station BSS 12, using a signalling protocol. The user, having received the message 3, responds such that the mobile station 11 sends a second signal 4 by way of the host network back to the SCP 15. The SCP 15 acts on the message received and returns a response 5 to the MSC 13, whereby the MSC 13 will then act on that information for example to set up a call, including a full speech channel if required (6). This system allows data to be transmitted directly between the SCP 15 and the user 11, the host network not requiring to be compatible with the signalling protocols except for the initial and final states 1, 5. Moreover, since signalling channels are used, traffic (speech) channels, which have a larger bandwidth, are not used unless and until the call set-up process is completed.