Author Topic: HT802 and SIP FAX via T.38 - is it possible to get it to work reliably?  (Read 268 times)


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I have a hosted voip provider that states that their service is compatible with T.38.

I have a Grandstream HT802. (Actually 3, but I am trying to get one working before deciding whether to attempt the same on the other two.) The ATA is registered to the hosted provider, and set up to use T.38. The ATA has a fax machine connected to it. On some occasions the fax even completes a transmission without reporting communication errors - however that is by no means a majority outcome.

What am I doing wrong? If the answer is "not using a Cisco SPA112", I've heard it. I am considering that as a solution. However, I'd like to get some use out of the Grandstream hardware we purchased. IF anyone has managed to get this working in the UK and has some notes or config settings that might help, please reply.


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Hi ITTJamie,

I suggest to open a ticket on our helpdesk in order to share with us a packet capture from the SIP side of the HT as well as a Syslog capture, it may guide us to solve your issue.

Link to helpdesk:

Best regards,

Luke Escude

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We use a LOT of HT802s and they work flawlessly.

Even our legal & medical customers, who send 20+ page faxes at a time, typically don't complain.
PrimeVOX Communications
Affordable and Reliable Cloud PBX Solutions


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Alot of the fax problems are related to signaling. If the fax machine supports overseas mode try that, also you need a wireshark capture to see if it is a signal or timing issue. Doesn't take many errors to fail a fax. Also try going to g.711 instead of T.38. You may also want to try and open the jitter buffer just a little and switch from dynamic to static.