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T.38 FAX Call Issues


I am having trouble with a FAX Machine not able to send FAX's to certain numbers when using T.38 Fax Relay.

The FAX Machine is attached to a FXS port on a VG224 which is setup as H323. The PSTN gateway is a H323 3845 with PRI at the same location, so same network. The calls are being made to a FAX machine over the PSTN which is an outside company so not sure about their setup. The FAX machine is able to receive FAX's just fine and can place FAX's almost anywhere without problem except a few places. The places they are having trouble with get a blank sheet of paper.

The network-clock configuration is there, and there are no errors or slip seconds on the PRI or on the network interfaces between the gateway and FAX machine.

We are using 12.4(15)T3 on the 3845 and 12.4(15)T1 on the VG224.

The configs are the same on both routers/gateways for the voip dial peers and incoming voip dial peer. t38 is configured globally under voice services voip. On the dial peers, we have it set to do fax rate 14400, make sg3 faxes g3.

Another problem FAX call, is when this FAX machine calls another FAX machine within the network attached to a VG248 port configured for T.38. Does the same thing (blank page of paper) and that is internal to network between the VG224 and VG248. The same thing happens when we try the external number for this FAX machine, but the call comes in a CMM gateway at another location then to the VG248 this way.

Any ideas on how to correct this? We had been using modem passthrough instead of T38 and had some issues with some FAXs, so changed to T38 which fixed up the other issues we had but now we have some other problems.

Community Member

Re: T.38 FAX Call Issues


We are also having the same issues, however it seems the problem is on the digtal gateway side (not detecting the tones). What's the hardware of the digital gateways?


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