When the router is working correctly the following lights should be;
OK [ON]
CD [ON]
RXD [FLASHING]
TXD [FLASHING]
PPP [ON]
OK – DATA [FLASHING]

Cisco 877w Router

Cisco Router

The Yellow Cable which can plug in to any of the Yellow sockets on the router.

Lilac cable goes from the Lilac socket on the router

into the ADSL filter

Plugs directly into the Eathernet socket on the till. ADSL Filter
  which plugs into the phone socket on the wall.
  Phone Socket