Federation enables direct and efficient communication between any two autonomous organizations connected to the public Internet. Email is already distributed thanks to SMTP federation. The same paradigm has taken hold in the world of voice and video communications. Any two users or organisations can connect to each other dynamically without requiring cumbersome, outdated and expensive solutions from traditional phone companies.

A number of technologies help make federation work optimally. ENUM helps map traditional phone numbers to Internet domains, it is described in Chapter 15, Adding ENUM to DNS. DNS NAPTR and SRV records make it possible to locate servers willing to accept calls any given domain, they are described in Chapter 5, DNS setup. The SIP and XMPP protocols allow users to do much more than they can do with traditional phones, including cost-effective chat messaging, desktop sharing and videoconferencing.