ISDN AOC-D packet causes call to clear down

Question

I have an ISDN problem with a 2500 router running 12.1(5)T9. About 10 seconds into each call, my ISDN provider sends me an AOC-D packet, and this causes my router to clear its call. (Or is it a "display" packet that causes the problem?) The result is that my ISDN connection flaps at 10 second intervals.
To demonstrate this problem, I set up the router to call itself, and the result is in attached file R1.121.txt, showing the call cleared after 10 seconds. I set up an identical configuration on a 2610 running 12.2(17a), and that did not do it - it waited the full 120 seconds before clearing the call - see file R4.122.txt.
From the Q931 debug, it looks like the software does not recognise the AOC-D signal (or the "display" packet?) in this state, and so disconnects the call. This looks especially strange to me as the 12.1 documentation actually contains a section about how to exploit the AOC-D signal to minimise call charges.
http://www.cisco.com/en/US/products/sw/iosswrel/ps1831/products_configuration_guide_chapter09186a00800d9843.html#1000936
Can anyone explain what is going on here, and how I can get the router to ignore the offending signal?
Kevin Dorrell
Luxembourg

Answer 1

http://www.cisco.com/warp/public/129/isdn_disc_code.html
If I read the disconnect code right, it would seem that, "The switch receives the ISDN number in the correct format. However, the number does not belong to destination equipment." That almost sounds like the configured number on your router is not spitting back a result the telco switch expects and is unhappy and disconnects the circuit. If it were a DSL connection, I would say throw a hub between the router and the ethernet interface and try to capture the PPPoE traffic, but it is a little harder with ISDN unless you have a WAN sniffer.
I am not sure what type of 2500 series router you have or what version of code you are running, but I have this running on my 2520:
2520>sh ver
Cisco Internetwork Operating System Software
IOS (tm) 2500 Software (C2500-JS-L), Version 12.2(5), RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2001 by cisco Systems, Inc.
Compiled Wed 12-Sep-01 09:09 by pwade
Image text-base: 0x03078B98, data-base: 0x00001000
ROM: System Bootstrap, Version 11.0(10c)XB2, PLATFORM SPECIFIC RELEASE SOFTWARE (fc1)
BOOTLDR: 3000 Bootstrap Software (IGS-BOOT-R), Version 11.0(10c)XB2, PLATFORM SPECIFIC RELEASE SOFTWARE (fc1)
2520 uptime is 8 minutes
System returned to ROM by power-on
System image file is "flash:c2500-js-l.122-5.bin"
cisco 2520 (68030) processor (revision M) with 14336K/2048K bytes of memory.
Processor board ID 07945310, with hardware revision 00000003
Bridging software.
X.25 software, Version 3.0.0.
SuperLAT software (copyright 1990 by Meridian Technology Corp).
TN3270 Emulation software.
Basic Rate ISDN software, Version 1.1.
1 Ethernet/IEEE 802.3 interface(s)
2 Serial network interface(s)
2 Low-speed serial(sync/async) network interface(s)
1 ISDN Basic Rate interface(s)
32K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read ONLY)
Configuration register is 0x2102
Keep in mind, this is running the enterprise feature set, also known as the "kitchen sink version" - it's in there. That is not to say that the usability of the IOS stopped for 2500s at 12.2(5), but my guess is that if you booost the gain on your DRAM to the max allowed, you might be able to run that version of IOS. It just takes a while to load.
pw