Re: [hylafax-users] Fax across VoIP lines working for anyone?

[Steve Underwood <steveu@xxxxxxxxxxx>]

Hi,

Ah, a heavily asked question on the Asterisk mailing lists :-)

If your VoIP links uses low bit rate codecs (e.g. G.729), faxing will 
never work. No way. No how. No question.

If your VoIP links use A-law or u-law, faxing may or may not work. Some 
faxes, maybe even a lot of faxes, will get through, but it will not be 
reliable. It depends a lot on the link quality, of course. Lost packets 
are a killer for modems. However, it also depends on the algorithms in 
the terminal equipment. Some will *always* drop a percentage of packets, 
in order to keep their latency as low as possible. Some continually 
distort time to smooth out the jitteriness received packet times. Modems 
don't like this.

If your VoIP service supports a true real time FoIP protocol (basically 
there is just one - T.38) things should work well. Quite a few T.38 
implementation seem pretty quirky, though.

If your VoIP service supports a store and forward FoIP protocol (usually 
T.37) delivery should work extremely well. However, many find the lack 
of instant success or failure notification troublesome.

Regards,
Steve


Scott Bishop - Personal wrote:

> Sorry. I always forget to change the account this is sent from to the 
> one I’m registered here with…
>
> Does anyone have a scenario with faxmodems working well across VoIP 
> lines rather than POTS lines?
>
> I’m running HylaFAX 4.2.1 on a Mandrake Linux 10.0 box with a couple 
> of MultiTech MT5634ZPX-PCI cards in it.
>
> I would love to get this working across my VoIP lines so that I 
> disconnect my POTS lines.
>
> Anyone have any suggestions, experience, solutions to VoIP delays, 
> retransmits, QoS, and losses?
>
> Thanks,
>
> Scott


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