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Unable to make outbound calls on PRI

Level 1
Level 1

This morning, all of a sudden we were unable to make outbound calls on our PRI. We were still receiving inbound calls just fine. We are using a 2811 gateway. I captured the attached debug isdn q931 output when the problem occurred. I did a shut/no shut on the circuit and the problem cleared. This has happened several times on two different gateways. Sometimes we are not able to make outbound calls, but inbound works. Other times inbound calls are failing but outbound works. Any ideas?

7 Replies 7

Level 10
Level 10

Which IOS version you are running?

MGCP or H323 ?


Could you please upload the config?

Is the first time this problems appear or have been reocurring?

We would need more debugs to find out the problem it may be a DSP|HW problem, IOS problem or even Telco issue.

No channel available (Requested circuit/channel not available)

This cause is returned when the circuit or channel indicated by the requesting entity cannot be provided by the other side of the interface

Nov 10 14:23:36.033: ISDN Se0/0/1:23 Q931: TX -> SETUP pd = 8 callref = 0x0001

Bearer Capability i = 0x8090A2

Standard = CCITT

Transfer Capability = Speech

Transfer Mode = Circuit

Transfer Rate = 64 kbit/s

Channel ID i = 0xA98397

Exclusive, Channel 23

Calling Party Number i = 0x0081, '2128380500'

Plan:Unknown, Type:Unknown

Called Party Number i = 0x80, '17185551212'

Plan:Unknown, Type:Unknown

Nov 10 14:23:36.089: ISDN Se0/0/1:23 Q931: RX <- RELEASE_COMP pd = 8 callref =


Cause i = 0x80AC - Requested circuit/channel not available

Cause i = 0x80AC

80 ?the router

AC- Requested channel not available

The remote equipment cannot provide the channel that the user requests, due to an unknown reason. This problem is usually temporary.

We are using IOS 12.3(14)T6 in our NY location. We are using MGCP. This is a 2811 router. I have attached the config. This problem has occurred several times over the past year. We are also experiencing it at our Zurich site. We are using MGCP and a 2811 router there as well. Our IOS version in Zurich is 12.4(9)T. Thanks.

paolo bevilacqua
Hall of Fame
Hall of Fame

Very interesting trace. Seems like the router and the switch cannot come to mutual terms on a lot of things.

a) router receives RELEASE_COMP on timer recovery. that should not happen.

b) receives SERVICE for chan 22. This is not an ITU message and usually associated with NFAS, are you running NFAS ?

c) finally sends RELEASE_COMP for (a) above

d) sends STATUS ENQUIRY for two calls and immediately disconnects these without waiting for answer

e) turns out co thinks the calls in (d) where not valid.

f) a call comes in and router says invalid channel (was it busy ? we don't know)

g) at this point router feel the urge of restarting all channels and does so.

h) at this point a call goes out on chan 23. note callref is 0001, router seem to have reinitialized counters.

i) invalid channel even for (h)

Seems like something in ISDN q.931 data structure went really messed up...

After those error messages and the restarting of every channel, every outbound call attempt got the invalid channel message. Inbound calls were all working fine. This continued until I did a shut/no shut on the interface. To answer your question, we are not running NFAS. Thanks.

i was having the same problem did you find any fixes for this every time i call out it hit the pots and not the pri but incoming calls are just fine if not any suggestions

thanks gary

I opened a TAC case. They think that we may be experiencing this bug on the DSPs:

So, we are going to replace the PVDMs and see if that solves it. I don't know. The bug specifically states that ISDN PRI and BRI is not affected because it does not use DSP resources for signaling. But, I will give it a try.

ok thanks for the advise let me know what comes about the issue