PRI is not down when the MGCP VG fails to talk with CCM

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Mar 29th, 2008
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I got a MGCP voice gateway with PRI line registered to CCM. When I disconnected the voice gateway from the network, I found that the layer 3 (q.931) of PRI is still up.

Just wonder if there's any command to bring the PRI down when the MGCP VG is out sync with the CCM?

If there's no such configuration, then it seems that all incoming call will continue to send to the failure PRI line from PSTN.

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Jaime Valencia Sat, 03/29/2008 - 15:05
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OK, if you issue a show isdn status on the GW when you pull the cable do you still see the ISDN layer 2 and layer 3 active?

you should see not only layer 2 and 3 as if the configuration for framing or linecode was wrong but also layer 1 down since there is nothing in there

what IOS u running?



if this helps, please rate

b-cho Mon, 04/07/2008 - 22:51
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The IOS version 12.4(13r). There's nothing happened after all CCM servers are disconnected from the network.

Below please find the capture -

CCM#show ccm-manager

MGCP Domain Name: CCM

Priority Status Host


Primary Down

First Backup Down

Second Backup None


CCM#show isdn status

Global ISDN Switchtype = primary-4ess

ISDN Serial0/1/0:23 interface

dsl 0, interface ISDN Switchtype = primary-4ess

Layer 1 Status:


Layer 2 Status:


Layer 3 Status:

0 Active Layer 3 Call(s)

Active dsl 0 CCBs = 0

The Free Channel Mask: 0x807FFFFF

Number of L2 Discards = 0, L2 Session ID = 9

Total Allocated ISDN CCBs = 0


marshall.d.higg... Fri, 07/04/2008 - 18:42
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I have this same problem. I have a CUCM 4.2.3 SR3a with router IOS is C3845-spservicesk9-mz.124-7h.bin & c3845-spservicesk9-mz.124-11.T1.bin. Has this problem been resolved? and how?

Ayodeji Okanlawon Sat, 07/05/2008 - 05:09
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With MGCP,

Layer 2 (q.921) terminates on the local router,

layer 3 (q.931) is backhauled to the CCM, so if the link to CCM is down, then Layer 3 shoiuld be down.

However layer 1 and layer 2 should be up since they terminate on the local gateway and the trunk from the gateway to the Tekco swicth is up....Am I worng?

marshall.d.higg... Sun, 07/06/2008 - 07:24
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If you have a switch or router on the network, that fails, you expect the frames/packets to route around the failed device. If I have T1s or PRI that can not accept a call I expect calls to be able to route around it. To do this the PRIs must indicate to the connected network it is down. I expect the loss of Layer 3 for X seconds(CCM/CUCM) to result in both layer 2 and Layer 1 going down. The CO or PBX will then route calls around the failed T1 or PRI. PBXs and COs work this way. [So I think you are wrong ;-)]

marshall.d.higg... Sun, 01/18/2009 - 09:38
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Fixed - Mostly by this IOS command ccm-manager shut-backhaul-interfaces However, there is a significant delay with a Siemens HiPath 4XXX PABX.

b-cho Tue, 03/10/2009 - 03:02
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Thanks Marshall! I will try this shortly

Yorick Petey Tue, 02/02/2010 - 05:41
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Thank you very much!

I cannot believe this command was not enabled by default...


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