What is a federated protocol?

Question

I've heard this term recently to describe Google's new hangouts protocol, and Whisper System's new encrypted texting app.

The new TextSecure push transport is a federated protocol

What does that mean?

Answer 1

I think it means a common, open protocol that allows lots of small networks to talk to one another without giving up control completely so they can still use a custom internal protocol. So SMTP and XMPP are federated protocols.

I couldn't find an exact definition anywhere but I do have evidence to support my statements:

Dictionary definition of the verb "to federate":

(with reference to a number of states or organizations) form or be formed into a single centralized unit, within which each state or organization keeps some internal autonomy.

A recent blog post by Open Whisper Systems that discusses federated vs centralized networks:

Indeed, cannibalizing a federated application-layer protocol into a centralized service is almost a sure recipe for a successful consumer product today. It's what Slack did with IRC, what Facebook did with email, and what WhatsApp has done with XMPP. In each case, the federated service is stuck in time, while the centralized service is able to iterate into the modern world and beyond.

This page refers to SMTP as a "federated email protocol":

Then, SMTP (Simple Mail Transfer Protocol) came along and allowed these systems to federate into one large email system.

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(Aside: although I'm not from the US, I find it easiest to think of this term by analogy to the American "federal government": it allows all the US states to coordinate on a national level while still retaining a lot of internal control)