Intermittent ISDN calls disconnected after 4 seconds

Answered Question

Hi


Weekend we migrated clients old PBX to CUCM 7.1.3-30000-1.

Setup has  2 nos of  2911 acting as MGCP gateway named as VG01 for BT and VG02 for COLT.

Gateway and the CUCM cluster are on the same LAN.


We are noticing that calls coming via VG02 (COLT) are getting disconnected intermittently after 4 seconds.

Debugs shows CUCM is not receiving Connect_ACK timer for the setup and after 4 seconds of the call, CUCM is adivsing the VG02 to drop the call.

We tried changing the T313 timer to 20K and noticed that calls disconnect after 20 seconds intermittently. ie., if 30 calls made 25 calls will be successful and 5 calls will fail.


Any thoughts regarding this issue is much apprecaited.

Thanks in advance.

Correct Answer by David Smith about 6 years 10 months ago

Can you please grab the below data from the GW?


sho run

sho version


conf t

no logging console

no logging rate-limit

logging buffered 10000000 deb

service sequence

exit


debug isdn q931

debug mgcp packet

debug ccm-manager backhaul events

debug ccm-manager backhaul packet


Please send along the debugs and note the "calling" and "called" numbers for the failed call.


Thanks.

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Correct Answer
David Smith Thu, 08/26/2010 - 10:04
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  • Cisco Employee,

Can you please grab the below data from the GW?


sho run

sho version


conf t

no logging console

no logging rate-limit

logging buffered 10000000 deb

service sequence

exit


debug isdn q931

debug mgcp packet

debug ccm-manager backhaul events

debug ccm-manager backhaul packet


Please send along the debugs and note the "calling" and "called" numbers for the failed call.


Thanks.

David Smith Tue, 08/31/2010 - 11:21
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  • Cisco Employee,

You'll want to open a TAC case for this.

A new defect was opened for this issue within the past week:


CSCti59648

Gateway delays back-hauling ISDN CONNECT_ACK to callmanager


All layer 3 isdn signaling is backhauled to call manager, so there shouldn't be any delay...but for some reason, in the case of 151-M1, you can see the message isn't being backhauled to CUCM, causing the T313 timer to fire.


-Dave

Hi Dave


thanks for the response. We opened the case last week itself. TAC engineer has opened a defect with DE

Eventually we changed the gateway from Mgcp to h323 and noticed still calls are getting dropped .

In H323 we noticed that **Error**L2_AdvanceVA:TX_queue_empty

Bug noticed this error corresponds CSCtf08864 which required special code to be released.

Like Sods law Mgcp/h323 gw issue haunted the customer.

Today evening we eventually changed the special ios for H323.


I will check with TAC Engineer to provide the fix for MGCP as per the bug mentioned.


Thanks for your help.


regards

Ahmed Elnagar Fri, 12/21/2012 - 11:03
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Just a question if you allow please, when you were facing the issue that the router wasnot backhauling the connect act message to CUCM; did you see the message on the debug isdn q931 "and not in CUCM trace" or you were not seeing it at all in either places?

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