Three major alternatives for VoIP

Concept	Implementation
Use signaling concepts from the traditional telephony industry	H.323
Use control concepts from the traditional telephony industry	Softswitches
Use an internet-centric protocol	Session Initiation Protocol (SIP)

SIP ⇒ a change from telephony’s “calls” between handsets controlled by the network to “sessions” which can be between processes on any platform anywhere in the Internet and with both control and media content in digital form and hence can be easily manipulated.

thus a separate voice network is not necessary
open and distributed nature enables lots of innovation
- since both control and media can be manipulated and
- “events” are no longer restricted to start and end of calls

Transcript

[slide62] Well, there are three major alternatives for voice over IP. We can take the signaling concepts from traditional telephony, and that led to H.323. We can take the control concepts from traditional telephony, setting up and tearing down calls and routing them. And we can implement that with soft switches. Or we can take an internet-centric protocol approach, and that's what SIP is. So in SIP we change from the idea of calls to the idea of sessions. And what we're going to do is, we're going to create a session between any platforms that want, anywhere in the internet, and we use the control and the media will be both in digital form. And the advantages of this is, of course, we can happily manipulate them, right? Because now that we have everything in digital form, so we don't need a separate voice network. And it makes it very open. And it also makes it very distributed. But since both the call and the media can be manipulated, and events are no longer restricted to the start and ends of calls, we have a much, much more richer architecture than we did in traditional telephony.