4. Advanced services offered by SIP

The advanced services seen in the H.323 context are also provided by the SIP architecture. Call transfer, call forwarding, call waiting and call signalling are implemented differently, but with similar results.

What's more, the similarity between SIP and HTTP syntax, and in particular the use of URLs, makes it easy to integrate the Web and telephony. For example, it is possible to build an "interactive answering server" that is not just voice-controlled by telephone buttons, but which answers calls by means of a Web page, which the caller can browse in the traditional way. It is also possible to imagine a Web-based personal answering machine, which, in the event of no response from the called party, presents a page offering the recording of a message (e-mail, audio and/or video message), a priority contact in the event of an emergency, or a redirection to other...