Network and infrastructure
ATA adapter
Acronym: ATA
An ATA converts the signal of an analogue phone or fax machine into voice over IP, so it can connect to a packet network.
On one side it offers an ordinary phone socket that provides dial tone and ringing like a classic line; on the other, a network connection. In between, it digitises the sound, splits it into packets and talks to the operator, usually over SIP. Most broadband routers have an adapter of this kind behind their phone socket.
Why it matters for fax
This is the link that decides a fax's fate on a modern line. An adapter that handles fax over IP detects the fax tone and switches to a suitable transport; an adapter that only does voice compresses the modem's tones as if they were speech, with the failures that follow.