MGCP Gateway is receiving incorrect ISDN Cause code when Receiving Fax Iis busy.

Unanswered Question
Sep 14th, 2010

Hi there,

I have bit strainge problem,  When user sends fax to PSTN trough MGCP router and if FAX on PSTN network is busy , MGCP gateway is receiving incorrect ISDN cause code '47 ' "resource unavailable "instead of  17 - Busy  on ISDN q931 debug on MGCP router.  It seems MGCP router is getting incorrect isdn cause code from telco.  I have posted Debug example when PSTN fax was busy.

Sep 14 06:35:51.629 UTC: ISDN Se0/0/0:15 Q931: TX -> SETUP pd = 8 callref = 0x644A
Sending Complete
Bearer Capability i = 0x8090A3
Standard = CCITT
Transfer Capability = Speech
Transfer Mode = Circuit
Transfer Rate = 64 kbit/s
Channel ID i = 0xA98399
Exclusive, Channel 25
Calling Party Number i = 0x0083, N/A
Plan:Unknown, Type:Unknown
Called Party Number i = 0x80, '62932782'
Plan:Unknown, Type:Unknown
Sep 14 06:36:12.725 UTC: ISDN Se0/0/0:15 Q931: TX -> DISCONNECT pd = 8 callref = 0x644A
Cause i = 0x80AF - Resource unavailable, unspecified
Sep 14 06:36:12.785 UTC: ISDN Se0/0/0:15 Q931: TX -> RELEASE_COMP pd = 8 callref = 0x644A

This issue is not happening for Internal FAX .

Any suggestions to resolve the issue ?   any commands to map ISDN Cause code to busy ??

I have this problem too.
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Felipe Garrido Thu, 09/16/2010 - 06:36

The Disconnect is being sent by the gateway, not being received from the telco. This would indicate an issue with the CUCM or gateway where the fax machine is connected. Can you collect detailed CUCM traces for a failed call and note the calling the called party numbers.



Dinesh Chovatiya Mon, 09/20/2010 - 17:52

Hi There,

Thanks for your reply.  It seems The issue is only happening for Faxes on other network ( PSTN network )   .  Faxes connected with in network  (with VG224) gives busy tone to second caller  that indiactes no issues with internal analog Faxes.

I can still run further tests and collects logs.  What specific logs do you think I should Collect ?

Thanks in advance ..

Felipe Garrido Tue, 09/21/2010 - 07:48

can you provide the current running configuration of both the VG224 and PRI gateway? Probably an issue with either allocating an MTP, if CUCM involved, or fax configuration.


Steven Holl Sun, 09/26/2010 - 08:41

Also, get a 'sh ver' and 'sh voice dsp group all' from the gateway.  Make sure you're not on code with exposure to CSCsx67255.


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