Cisco Routers for the Desperate, 2nd Edition

Serial Interfaces

A serial network has only two nodes, one at each end, and only transmits data between those two points. This makes managing a serial link much simpler than an Ethernet one, but the line connecting your router to the remote network has a far wider variety of options that can be set.

While you can run a serial link between two routers by attaching the right cable between their serial ports, a serial line is usually provided by a phone company and runs between two different locations much farther apart than the few hundred feet that Ethernet can tolerate. We'll concentrate on telco-provided T1 circuits like the ones you would find in an ISP connection or between two offices.

Here's the beginning of the sho int output of a typical ...