Emmanuel Proulx is a SIP (Session Initiation Protocol) developer who has written an excellent tutorial on the signaling protocol that is widely used in VoIP to initiate communications sessions between callers and respondents.
If you want to learn the basics of SIP but don’t want to take a course or invest in a book full of diagrams and equations, then maybe Emmanuel’s newly posted piece,”An Introduction To SIP, Part 1: Meet SIP” would be a great place to start.
After defining SIP and then describing the protocol’s benefits, Emmanuel dissects a “typical SIP call” in which one user wishes to call another.
He begins this section with a set-up diagram. Here it is:
Emmanuel then proceeds to offer an explanation of each of the above steps. To his immense credit, his explanations are quite understandable as well as technical. He accomplishes this by means of a two-framed presentation: basics on the left, code on the right.
I don’t want to give away the whole store here, but I do think it would be useful to provide an example of why I am so enthusiastic about Emmanuel’s work here.
As an example, I cite the way he describes INVITE, which is the first stage of a SIP call:
Check out the rest here.