Verify that the interesting traffic is correctly defined, using the dialer-list x command, and applied to the interface using dialer-group x command.
Refer to the document Understanding and Troubleshooting Idle Timeouts for more information.
http://www.cisco.com/en/US/tech/tk801/tk133/technologies_tech_note09186a0080094eb7.shtml
Assuming that you have properly configured interesting traffic and applied it to the interface, this issue could be caused by a misconfigured session-timeout.
If the debug isdn q931 command does not show a TERMREQ, then Point-to-Point Protocol (PPP) and dial-on-demand routing (DDR) are probably not causing the disconnect.
In such cases, the disconnect is probably coming from one of the lower layers (modem/ISDN) and the disconnect cause code would concur.
To troubleshoot this issue:
1. Verify that dialer idle timeout is configured and the threshold is not exceeded for interesting traffic. You can choose to increase the idle timeout using the command dialer idle-timeout seconds
2. Verify that interesting traffic is defined. Refer to the document Understanding and Troubleshooting Idle Timeouts for more information.
3. The cause of the disconnect may be due to the lines being misconfigured:
The following debug isdn q931 output indicates that the router receives a disconnect.
*Mar 13 02:05:22.716: ISDN BR0: RX <- DISCONNECT pd = 8 callref =0x8A
*Mar 13 02:05:22.724: Cause i = 0x8090 - Normal call clearing
To resolve this, remove session-timeout nn from the line configuration (on both ends of the circuit).
router(config)#line 100 107
router(config-line)#no session-timeout 360
Hope this helps you.
