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



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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