Cross printer printing protocol.
Also manages print queues.
Client server based. TODO diagram? One server per computer that talks to many printers which are also servers?
Port: 631 TCP and UDP.
You can also visit: http://localhost:631/ to see a web front-end for CUPS. TODO check: is it standard? Works on Ubuntu 14.04.
Not possible with CUPS apparently. Consider ink.
Good tutorial: http://www.eecs.utk.edu/resources/it/kb/printing/linux-command-line