Cisco 2611 - Router - EN User Manual page 33

Serial Connections
X.21 Connections
The X.21 interface uses a 15-pin connection for balanced circuits and is commonly used in
the United Kingdom to connect public data networks. X.21 relocates some of the logic
functions to the DTE and DCE interfaces and, as a result, requires fewer circuits and a
smaller connector than EIA/TIA-232.
The network end of the X.21 adapter cable is a standard DB-15 connector. (See
Figure 2-11.) X.21 cables are available as either DTE (DB-15 plug) or DCE (DB-15
receptacle).
Figure 2-11 X.21 Adapter Cable Connectors, Network End
DTE
8 1
DCE
15 9
Preparing to Install the Router 2-19