Where can I learn how to program ip-telephony?

Question

Telephony

Hello!
I want to learn ip-telephony, but I don't know where to start. Tell me where to get the basics (best) books / articles on the basics.
And as far as I understand, you have to train on something, but I don’t have the appropriate equipment. Are there emulators online or something like that?

Answer 1

asterisk + old sistemnik with 2 setevushki + a lot of desire.

Answer 2

What Vladimir Makarov said and must-read asterisk.ru/store/files/Asterisk_RU_OReilly_DRAFT.pdf

Answer 3

At one time, I began to study IP-telephony immediately in practice in a real project.
The book and documentation will give you only theoretical knowledge - this is not bad for a start, but it will not advance in the study of the subject at all!
Without the practical application of knowledge, you will not understand anything.
The easiest way to learn the basics of SIP telephony is to deploy your Asterisk and experiment on it, while studying the documentation (fortunately, there is a sufficient amount of it) and related forums.
A more complex, but the most productive method of studying all the subtleties of the SIP protocol (on which all this disgrace is actually based) is to deploy OpenSIPS and blast through this document (you can find a "free" version).
It is also worth paying attention to FreeSwitch (off documentation may well be enough at the initial level).