Call control

#This application is the U.S. national phase of International Application No. PCT/GB2010/000434 filed Mar. 11, 2010 which designated the U.S. and claims priority to GB 0905454.5 filed Mar. 30, 2009, the entire contents of each of which are hereby incorporated by reference.

#The present invention relates to the field of telephony networks in general and to the control of calls in telephony networks in particular.

#An increasing number of telephone subscribers have more than one telephony account, benefiting from the increased flexibility and improved accessibility that multiple accounts can provide. For example, a subscriber may have a first, Wi-Fi telephony account and a second, GSM telephony account (a list of acronyms is provided at the end of the description). In such a telephony system, the Wi-Fi account can often be out of operation either because the Wi-Fi handset is switched off or is out of range of the nearest Wi-Fi access point (or “hotspot”). It is therefore convenient for the user, when their Wi-Fi telephony account is unavailable, for calls directed to the user at their Wi-Fi account to be redirected to a second telephony account, e.g. one provided via the GSM networks. A problem arises in the case of such re-directed calls when the call is not answered at the handset operating on the second network to which the call has been redirected. The default behaviour of a telephony system in this situation would be for the call to be forwarded to a messaging service, e.g.: voicemail service, associated with the handset in the second network, to which the call has been diverted. This behaviour, however, can lead to confusion for the user with messages, which should be associated with, and directly accessible from, their Wi-Fi handset, being instead associated with their GSM handset. In addition, the user may have to pay the second network operator for a second diversion from the handset in the second network. Similar problems can occur with other combinations of telephony account, such as GSM with PSTN, where calls to the user may be redirected to the PSTN, when the user's GSM handset is switched off or out of range of a GSM transmitter.

#To aid understanding of the invention, embodiments will now be described by way of example only, with reference to the accompanying drawings in which:

#FIGS. 1a and 1b show schematics of a communications system according to the invention;

#FIG. 2 shows a schematic of a server for implementing the invention.

#FIGS. 1a and 1b show a schematic of communications system 10 comprising GSM mobile network 12 (shown in detail in FIG. 1b), IMS mobile network 16 (shown in detail in FIG. 1a) and wire-line PSTN 18. Three handsets are shown, each for use with a different communications network. Conventional, wired handset 20 is attached to provide telephone service via PSTN 18. Handset 22 operates in GSM mode via GSM network 12 and handset 24 operates in Wi-Fi mode via IMS network 16.

#IP Multimedia Subsystem (IMS) Network

#FIG. 1a shows IMS network 16 in detail. As shown in FIG. 1, Wi-Fi handset 24 exchanges radio signals with Wi-Fi access point 26 to IMS network 16. Wi-Fi handset 24 needs to register with the IMS network in order to send and receive messages.