The document that originally defined IRC protocol is RFC1459 which has
a hypertext version available at http://www.irchelp.org/irchelp/rfc/rfc.html
Naturally the document can also be found on any other archive with all
the RFC documents.
As far as I remember the RFC1459 was made somewhere around 1993. There
have been many extensions to the client protocol but the basic
protocol still remains the same. You log on by giving NICK and USER
just like it is described in RFC1459. Apart from NICK and USER, the
client is required to reply to pings sent by the server. Everything
else can be considered optional, although simply logging in and
staying connected isn't fulfilling any meaningful purpose.
--
Janne Nikula, Geetee on IRCnet, http://www.zkelvin.net/jnikula/