Next Generation Wireless Applications: Creating Mobile Applications in a Web 2.0 and Mobile 2.0 World, 2nd Edition

14.5 START HERE: INTERNET TELEPHONY, OR VoIP

IMS is an IP-based communications environment standardised by 3GPP, but its technical roots are planted in the Internet. However, within the mobile telephony ecosystem, IMS is essentially an IP-based alternative to the conventional signalling architecture already used in current mobile networks to control the flow of calls. Therefore, we start our journey through the IMS network from a telephony perspective. We shall end up at more general ‘connectedness’ applications and return to explore the notion of an ‘IMS-Web’, or universal connectedness paradigm. Does such a thing exist, or could it?

Figure 14.2 SIP agents negotiate IP-based service connections.

The core of IMS is based on Session Initiation Protocol (SIP), which supports the necessary signalling between two IP-connected entities to enable them to establish a connection suitable for some kind of media-exchange. SIP is sometimes called a rendezvous technology, as it allows network entities to rendezvous for the purposes of exchanging data, but – and this is the important bit – it doesn't get involved in the actual exchange of the data itself, as shown in Figure 14.2. SIP is an IP-based signalling protocol that can facilitate IP-based connections, including voice. The use of SIP in this fashion gives rise to a form of Internet Telephony, more generically referred to as Voice over ...