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Modem passthrough NSE

Hi guys,

We have a site running CUCM 9.1 using a H323 GW on an E1 PRI and a MGCP VG224 with two analogue faxes on it. One is working fine, and the other doesn't seem to work at all. It seems to make the initial connection okay but never sends or receives the fax and then hangs up.

Have been looking at this document on different scenarios and I guess what we have is combination of B and C.

B. Telco – PRI – GW – MGCP – CUCM – MGCP – VG224 – Fax/Modem

     [Can do both Passthrough(NSE) and T38]

C. Telco – FXO – GW – H323/SIP – CUCM – SCCP – VG248 – Fax/Modem

     [Can do both Passthrough(NSE) and T38(NSE). Protocol based switchover is not supported with SCCP]

So, what I have on the GW connected to the PRI is:

voice service voip

allow-connections h323 to h323

allow-connections h323 to sip

allow-connections sip to h323

allow-connections sip to sip

fax protocol pass-through g711alaw


modem passthrough nse codec g711alaw


And have "modem passthrough nse codec g711alaw" and "fax protocol pass-through g711alaw" configured under the VOIP dial-peers though this probably isn't necessary:

On the CUCM VG224 config, I have modem passthrough enabled, and T38 and Cisco Pass Through disabled.

On the VG224 CLI:


mgcp call-agent 2427 service-type mgcp version 0.1

mgcp rtp unreachable timeout 1000 action notify

mgcp modem passthrough voip mode nse

mgcp package-capability rtp-package

mgcp package-capability sst-package

no mgcp package-capability res-package

no mgcp timer receive-rtcp

mgcp sdp simple

mgcp rtp payload-type g726r16 static

On the document it mentions there should be "mgcp modem passthrough codec" command, which the VG accepts, but is then deleted by CCM after a refresh. I can't find anywhere to set the codec for the modem passthrough on the VG224 config on the CUCM.

As I say, one fax machine is working fine, and the other isn't working. Anything else I should check or reconfigure?




Modem passthrough NSE

What is the problematic scenario? B or C?

Can you add the show mgcp of your VG224?

Can you add the show voice call status of VG during a call?


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