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Community Member

VG224 SCCP relay & issue with some modems

Hi all.

I have setup a vg224 using sccp and fax/modem relay. Although all of the fax machines, franking machines and most modems are working ok, we do have a problem with a few modems not working.

i believe the problem maybe to do with the following as stated on Cisco's website

Cisco modem relay works only if both modems are high-speed modems (V.34, V.90) that use V.42bis

bidirectional compression. For low-speed modems, gateways that carry traffic use modem


• Cisco modem relay works only if both modems use the V.42 error correction protocol and if the error

correction layer in both modems is enabled.

If this is the case is my only course of action to either A) replace the modem with a compatible one or most likely B) change the VG from relay to pass through?

the modems that do not work do seem to be very old. The problem they are experiencing is that when we try to initiate the connection the dialup connection reports that it cannot detect the dial tone.

However if i connect my analogue phone there is dial tone and Im able to make a call.

can you help me on this?

i can supply config if this would help.




Re: VG224 SCCP relay & issue with some modems

Try using modem passthrough. You may find it to be more reliable than modem relay. Generally, I only configure modem relay if there is a very specific requirement to do so.

voice service voip

modem passthrough nse codec g711ulaw

fax protocol none



Community Member

Re: VG224 SCCP relay & issue with some modems

thanks for the advice nick. I will try this and update.


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