step 1 use the black rj-45-to-db-25 cable, or the black rj-45 rollover cable and db-25 adapter, to connect the router to a modem. (see figure 3-47 through figure 3-50.)
for information about cable pinouts, refer to the online publication cisco modular access router cable specifications available on cisco.com and on the documentation cd-rom.
step 2 make sure that your modem and the router auxiliary port are configured for the same transmission speed (up to 115200 bps is supported) and hardware flow control with data carrier detect (dcd) and data terminal ready (dtr) operations.
on the cisco 3660 router, the auxiliary port is color-coded black.