Where can I found the stack of protocols that ICQ using to develop my own client?

Question

I am going to develop ICQ client and I just wonder where can I find a reference to understand the protocols they used? Any links, books, etc.
And, by the way, if I am not mistaken - all ICQ clients - QIP, Miranda, ICQ Lite and others - uses the same version of protocol to communicate correctly with ICQ servers?

Answer 1

Wikipedia has an article on the OSCAR protocol, although it's proprietary.

Answer 2

Pidgin is open source, perhaps you can refer to its source code.

Answer 3

libpurple is a library that implements lots of IM protocols, among them the oscar protocol used by icq. It is used by many IM clients and is pretty stable, so I recommend you just use it. If you want to understand oscar though, studying libpurple might be a good idea.