You can find documentation of just about everything concerning network programming (and all sorts of perl inter-process communication) by looking at the perlipc man page. (or C:/Perl/html/lib/Pod/perlipc.html if you work under Windows). There you will find examples, explanations, etc.
The same documentation is also available online at: http://search.cpan.org/dist/perl/pod/perlipc.pod.
That only deals with high level network programming (sockets, etc.). For low level details of networking protocols, the book Data and Computer Communications by William Stallings, provides a great overview.