Core Issue
When debug isdn q921 is invoked on a Cisco IOS router with ISDN connectivity, the user receives messages indicating that the T203 timer has expired and communication with the peer device has been lost. The messages are similar to these:
Router#debug isdn q921 interface Serial 1/1:23
debug isdn q921 is ON.
Router#
Mar 20 17:16:40.206 EST: ISDN Se1/1:23 Q921: S7_T203_EXPIRY: Lost communication
with remote.
Resolution
This issue is tracked by Cisco bug ID CSCsa73950.
In the vast majority of cases, this message is completely benign and may be seen on a perfectly functioning ISDN link. The wording of the message makes it appear that there is an actual problem. This defect is considered a cosmetic problem and does not interfere with ISDN functions on the Cisco IOS router.
S7_T203_EXPIRY: Lost communication with remote means that while in Q.921 state 7 -- which is MULTIPLE_FRAME_ESTABLISHED state -- the T203 timer has expired. T203 seconds have elapsed without receiving any Q.921 message from the peer ISDN device, which may mean that the remote end has failed. In most cases, the peer device is in full Q.921 communication with the Cisco IOS router, but the T203 timer window is simply short enough that it might expire between regular Q.921 updates from the peer.
You can overcome this problem by upgrading the IOS to one of these versions: 12.3(14)T04 12.4(01.08)T 012.004(001.008). For IOS versions, refer to Software Downloads.
