Faxing Issues

I am having problems with alot of my faxes are not going through. We use to use analog now using freepbx with asterisk just wondering if anyone has any ideas?

Faxing over SIP is almost impossible and not something we would ever advise to do.

I use an analogue fax machine (actually an MFP) over SIP with Asterisk and it works fine - I use a Linksys voice gateway device to interface between the it and Asterisk, with this configuration it works just like an extension and I use an inbound route to direct faxes to the extension.

This is what I am going with a grandstream device. But about 60% of my faxes are not going through.

As stated Faxing over SIP is almost impossible. Some people get lucky and it works ok most of the time others it almost never works.

Hi cw1972, I do the same except with a Grandstream HT503 for Faxing out over a SIP Ext. Do you use a seperate trunk from you internal phones or the same trunk? What special setting do you need to use for this to work properly (Fax detect, etc)


I’m from the other end of the supply chain; I consult for companies, where Tony is a developer.

Even from my perspective, I absolutely never, ever, ever recommend faxing over SIP. Between codecs, latency, jitter, timing, you have many variables that will cause SIP faxing to fail, by its very nature. Any experienced voip consultant will tell you that.

I don’t know what your model is or what your end-goal is, but for small businesses I recommend http://www.metrofax.com/ as the reliable model. It interfaces via email or a web portal, and the price is dirt cheap.

All the best.

And from a user: Faxing over SIP is going to be unsatisfactory…period!


I can tell you that alot of our SIPStation customers have great luck with faxing with our full inbound/outbound T38 setup but its still not perfect. More like 95% success rate but we spent alot of time in the design and setup of our T38 network.