There are router+modem combination units but your title and question is about router replacement, not router+modem combination units.
I'm looking to upgrade my router and have been looking at 802.11ac routers which seem to offer great performance. But am I right in believing they don't REPLACE my old router, they just connect to it as an add-on?
For example, in the review of the D-Link DIR-868L, it says:
'There’s no ADSL modem, only a Gigabit Ethernet WAN port, but external modems can be picked up fairly cheaply these days.' Although I have some tech knowledge, I know zip about routers - so I'm baffled by this which seems to suggest it wont replace my existing router but is an add-on. Is that right? and why wouldn't they make a complete replacement???