They broke the lightspeed limit on communication via the simple expedient of time travel. A ChronComm network has nodes that take a message, drop back a hundred years and then start transmitting. Your message reaches a node the next star over just as you send it.
They tried having messages arrive before you sent them, but that just caused headaches.
The nodes never go anywhere–they just age really fast. What must it be like, wonders Girox as he pokes at a broken one, to have atoms older than the universe? When the Big Whimper hits, will they already be gone?