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Community Member

T.38 fax relay not working inbound through 1760 Router

I have been trying to get T.38 fax relay to work with calls going from a 1760 router PRI PSTN connection to callmanager and then to a GFI fax maker fax server. I can fax outbound from GFI faxmaker to an outside analog fax machine and it works fine, however if I try an inbound fax call to the fax server coming from the PSTN the fax server sees the call but it is immediately disconnected, I'm assuming because of a lack of T.38 recognition. Even a debug fax relay t30 all only gives me output on outbound fax calls and nothing on inbound ones. Does anyone have any ideas? The connection from the router to the callmanagers is MGCP and the connection from callmangager to the fax server is SIP. We are running version of callmanager and have 12.4(17) code on the 1760 router. A short set of my mgcp configuration is below. Any advice would be appreciated. Cisco TAC is telling me I might need to use a hardware MTP, but I'm not sure about that and they have so far been unable to help me get that setup right either.

ccm-manager redundant-host

ccm-manager mgcp

ccm-manager music-on-hold

ccm-manager config server

ccm-manager config



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

mgcp package-capability sst-package

mgcp default-package fxr-package

no mgcp package-capability res-package

no mgcp timer receive-rtcp

mgcp sdp simple

mgcp rtp payload-type g726r16 static


mgcp profile default

Community Member

Re: T.38 fax relay not working inbound through 1760 Router


The only way I ever got this to work is to setup the gateway as h323 instead of mgcp and then use the command :

voice service voip

fax protocol t38 ls-redundancy 0 hs-redundancy 0 fallback cisco

Hope this helps,


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