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Re: [hylafax-users] Reducing FAX data rate



John Matthews wrote:

We are using hylafax with a VOIP PBX which results in poor quality phone lines and lots of hdlc fcs errors. We would like to try reducing the fax datarate to see if this helps reduce errors.


It probably won't... but it's possible.


Our modem supports V.17, V.29, V.27ter and V.21 channel 2. I notice that Hylafax always issues a +FRH=3 command to my modem. Apparently the +FRH command sets the protocol and rate. Maybe this could be used, but hylafax doesn’t seem to support changing the value provided in the +FRH command.


That's because there's really no reason to use +FRH with anything other than 3. Some people would like to use +FRH with V.17 and V.29 for Class 1 ECM (using the modem for HDLC framing instead of doing it in software), but in practice it doesn't work very well at all due to timing reasons.


Does the receiving FAX machine have any way to negotiate say V.29 9600bps instead?


You can disable V.17 by putting this in you modem config file:

Class1RMQueryCmd: "!24,48,72,96"

Lee.


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