I am doing an As-simulation with 2 zyxel modems U336 and 2 cisco routers a 1600 series and a 2600 series. I want to have an leased anolog link between the 2 modems and the routers connect from the modem to the Respective lans. I have already configured the routers and the modems but my line protocol for both routers is down. Both modems are anolouge. Am still using default Hdlc. Any help will be highly appreciated.
If your line is analogue you need to use asynchronous interfaces on your router, by default the serial interfaces on 1600s and 2600s is Synchronous. Try changing it to async with the physical-layer interface sub-command.
Also below is the URL for setting up async connectivity on a 1600