Re: [hylafax-users] Reducing FAX data rate

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

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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