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SRST fallback fails for in/outbound calls on PRI

Hi Guys,

I have multiple site experiencing similar problems. I have 37xx routers with PRI working OK when running on CCM. When I fail the WAN SRST does not allow me to do in/outbound calls via the PRI line - I ge ta busy tone).

I am running IOS c3745-ipvoice-mz.123-8.T8.bin

The PRI works OK when running on CCM.

I have 6 digits DNs. I only use the last 2 digits from the DDI to route to DNs.

Please see config extract.

pri-group timeslots 1-31 service mgcp


interface Serial1/0:15

no ip address

isdn switch-type primary-net5

isdn incoming-voice voice

isdn bind-l3 ccm-manager

isdn bchan-number-order ascending

no cdp enable



call application alternate DEFAULT



voice-port 1/0:15

cptone GB



mgcp call-agent 2427 service-type mgcp version 0.1

mgcp dtmf-relay voip codec all mode out-of-band

mgcp rtp unreachable timeout 1000 action notify

mgcp modem passthrough voip mode nse

mgcp package-capability rtp-package

no mgcp package-capability res-package

mgcp package-capability sst-package

no mgcp package-capability fxr-package

no mgcp timer receive-rtcp

mgcp sdp simple

mgcp fax t38 inhibit

mgcp rtp payload-type g726r16 static


mgcp profile default




dial-peer cor custom




dial-peer voice 100 pots

preference 1

application mgcpapp

destination-pattern 9T

incoming called-number .


port 1/0:15


num-exp 67.. 1122..



secondary-dialtone 9

max-conferences 8

limit-dn 7910 2

limit-dn 7940 2

limit-dn 7960 2

timeouts interdigit 5

ip source-address port 2000

max-ephones 24

max-dn 15 dual-line

dialplan-pattern 1 1234567.. extension-length 6 extension-pattern 1122..

access-code pri 9T direct-inward-dial

call-forward busy 112260

call-forward noan 112260 timeout 30

Many thanks



Re: SRST fallback fails for in/outbound calls on PRI

Please add:

ccm-manager fallback-mgcp

and after that when testing SRST check the status of the PRI circuit.

show isdn status

debug isdn q931 and debug voice ccapi inout are always helpful.

T otroubleshoot dial plan issues: debug voice dial peer.

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