The possibilities of providing voice over IP have captured our imaginations for some time now. Once the infrastructure is in place to carry our voices over the Internet, it may be used to send any streamed media. Then there are the add-on services associated with the telephone ” call waiting, call forwarding, and so forth. Could these be replicated in the IP world?

While all the hype is directed towards the services ” the long distance and international calls for the cost of a local ISP connection ” one rather important aspect of the Public Switched Telephone Network (PSTN) can be overlooked: signalling. Although telephone users never actually see it in action, it is the Signalling Network at the heart of the PSTN which enables us to make calls, along with all the associated services as aforementioned.

Signalling occurs both at the edge of the network (for example, ISDN) and at its very heart – SS7. It is with SS7 that this paper is most concerned. If we are to use the IP network to carry our voices (or our holiday videos) then we must enable IP to carry the signalling information which sets those calls in motion.