US Robotics 56K USB Modem with HT-802


Is it compatible a US Robotics 56K USB Modem with HT-802 ?
A personal Laptop need to fax using a USB modem
Any special settings ?



More analog modem advice. HT802

the SIP Protocol should not pass data, so 99% have no chance.
Actually I have seen for example Pos connected on FXS that work, I could not tell you how and what they have configured.
Apart from that, do you know that you’d be one of the last in the world to use a 56k modem? :rofl:


Since fax machines work to send/receive faxes with a HT80x, then I would see no generic reason why it wouldn’t work.

My initial thought would be to keep it down to one Codec and turn off T.38.




transmitting data send fax is not exactly the same thing, also you would have the limit of 9600 baud, but remains a lottery.
I’d be curious to try.


It may work. The issue is that you are relying upon the fax transmission method (v.17 or other) to be converted and compressed into a voice codec and then the process reversed on the other side. You will be relying on the connection between points A and B to be able to deliver packets in the correct order and with the same timing delivery across a packet switched network. As the codec you will be using (g711u or G711a) is not error correcting, but real time, the odds of a successful fax transmission decrease as the size of the fax grows. If all is perfect, the fastest speed you will be able to use for faxing is 14.4K, so you may need to experiment to see what works best. You may also need to experiment with ECM modes and echo cancellation, which is normally suggested to be disabled. What you are trying to do is commonly called g711 fax pass-through. It is oftentimes the fall-back mode for t.38.

Depending upon doing a peer to peer arrangement or via a SIP provider, then you may be able to use t.38 which is specifically designed for faxing over the Internet (FoIP), but your provider must support t.38 as must whatever carriers are in the path to the other device (ATA) that will receive the call.

It is not so much the equipment, but rather the obstacles in between.


Thank you for your help…I’m not an expert on this and have no knowledge on FAX

  1. Codec setting (g711u or G711a it is on the HT-802 device ? Any documentation to suggest?
  2. My guess the faxing speed is set on the US robotic itself as ECM modes and Echo ?

thanks again


Yes, g711 (PCMu and PCMA) is on the device.

I would just leave the modem as currently working and give it a try.

Go from there.