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It seems there are routers and modem/routers.
It was my mistake to be honest. Instead of buying a modem/router of high spec to replace a rubbishy TTT modem/router, I bought a high spec router.
The rear of the router does not have a socket to connect the phone line. It has a row of ethernet type sockets only. My broadband is ADSL. When I realised that the router had no phone connection, I plugged the phone lead into the back of the old TT modem/router and used the ethernet cable supplied with the router to connect the TT modem/router to the router ( the cable was supplied with the new router) The set-up works but I've had intermittent problems with the TT modem/router which means I'd like to buy a new modem to replace the TT modem/router. I don't need a new modem/router as the AC3200 is a router itself, if you see what I mean.
Sorry if this sounds confusing!