3 Plug the DB-28 end of the connection cable to the corresponding DB-28 interface 
in the 4-port synchronous/asynchronous serial module with X.21.
4 Connect the other end of the cable as appropriate: 
■ If the WAN is a leased line, connect the cable to the interface of the CSU/DSU. 
■ If the WAN is a dialup line, connect the cable to the serial interface of the 
analog modem.
5 Power on the router, and check the status of the LINK LED on the faceplate of the 
router. It flashes green when the module has completed the self-check and works 
normally. The LINK LED is off if the module fails to pass the self-check or if the line 
is faulty and the signal is out of step, as described in 
Tab le  11. If the LINK LED is 
off, contact your Service representative.
4-Port E1/CE1/PRI MIM The main function of the 4-port E1/CE1/PRI module is to implement the 
transceiving and processing of E1 data streams. In addition, it provides access to 
CE1, and implements the ISDN PRI function so that one board can serve multiple 
purposes. 
Figure 13 illustrates a 4-port E1/CE1/PRI module.
Figure 13   The 4-Port E1/CE1/PRI Module
Features Tabl e 18 lists features of the 4-port E1/CE1/PRI module. 
Tabl e  18   Features of the 4-Port E1/CE1/PRI Module 
Attribute  Description
Connector DB-25 
Number of connectors 1 
Interface standard G.703, G.704
Interface speed 2.048Mbps
Cables E1 75-ohm non-balanced coaxial cable
E1 120-ohm balanced twisted pair cable
120-ohm 4E1 conversion cable
75-ohm 4E1 conversion cable
Coaxial connector, network interface connector and 75-ohm to 
120-ohm adapter (with BNC connector)
Operating mode E1, CE1, ISDN PRI 
Network protocols 
supported
1) IP
2) Novell IPX
3Com Router Release Notes for V1.20