Patent ID: 8666039

Claim:
A voice traffic gateway comprising: a voice traffic input arranged to receive voice traffic from a first traffic domain of a communications network, the voice traffic including voice messages and signalling messages; a voice traffic output arranged to deliver output voice messages and output signalling messages to a second, different traffic domain of the communications network; a first domain router coupled to the voice traffic input and configured to route voice messages received from the first traffic domain to a non-secure warning tone application apparatus and to route signalling messages received from the first traffic domain to a signalling filter; wherein the non-secure warning tone application apparatus is configured to apply a non-secure warning tone to each voice message that it receives to form a respective output voice message; and the signalling filter is configured to compare a feature of each signalling message that it receives with a reference feature, to pass said signalling message as an output signalling message if said feature is the same as the reference feature, and to block said signalling message if said feature is not the same as the reference feature.