Cisco MC3810 Multiservice Access Concentrators

Field Notice: MC3810 System Requirements for Simultaneous ISDN and SERIAL 1 Operation

November 4, 1998

Products Affected




MC3810 Multi-Service Access Concentrator

Problem Description

The MC3810 requires a minimum revision of the System Control Board (SCB) in order to use ISDN and the SERIAL 1 interface simultaneously. ISDN includes ISDN Q Signaling (QSIG) on a digital voice module, and the ISDN BRI port of a Multi-Flex Trunk (MFT) Module.


The SCB revision 6.07 supports the use of ISDN and SERIAL 1. You can see the revision of the SCB with the Cisco IOS show version command. See example show version command output below:

Cisco MC3810 (MPC860) processor (revision 06.07) with 27648K/5120K bytes of memory.

Problem Symptoms

Without this fix, the SERIAL 1 port will be inoperative when ISDN is active.


When using a newer SCB-06.07 board with the QSIG features enabled and/or the BRI backup feature active, the following constraints are imposed:

  • Serial port 1 is limited to speeds of 3xDS0 (less than or equal to 192kbps or 168 kbps).

  • The serial ports will not support async, bisync, and half-duplex.

  • Serial 0 cannot be setup to run the time-division multiplexing (TDM) cross-connect function if serial port 1 is in use due to FIFO limitations.

  • If slot 3 is empty (that is, no MFT installed), and the QSIG features are enabled, serial 1 cannot be used. This is because hardware on the MFT is used to enable the TDM sharing of serial port 1.

For More Information

If you require further assistance, or if you have any further questions regarding this field notice, please contact the Cisco Systems Technical Assistance Center (TAC) by one of the following methods: