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Faxing

Why can't I always send or receive faxes?
Faxing, as mentioned previously, may not always be successful for various reasons:

  • We use different carriers for termination within the US and Canada. Most carriers will support T.38; however there may be carriers who either do not fully or simply do not support T.38. The carriers available for locations may change hourly, daily or monthly and as such a fixed method for faxing may not work all of the time
  • Connection quality could vary depending on the clients bandwidth usage
  • Configurations on the user end may be incomplete or could be affected by changes
  • Pass through negotiation for faxes may not always work and may require multiple tries for proper completion

In short there are various things which could affect faxing over an internet connection. Most of our carriers support T.38 and most devices which use T.38 should work reliably on those carriers. However if changes in our routing take place it should be understood that you will want to make sure that you have configured support for pass through faxing.

As there are many devices and software options available you will want to make sure you have configured the correct options on the UA of your choice. There are some common configuration options which would need to be set:

Fax machine
  1. Try using the slowest possible speed on your fax machine. Normally 9.6k or 14.4k would be the best options, as speeds faster than 14.4k may not work properly with faxing
  2. Disable error correction
T.38
  1. Enable T.38
  2. Disable echo cancellation and echo suppression
  3. If available enable re-INVITE for faxes
Pass through
  1. Try using the G711 codecs as these would offer more bandwidth
  2. Disable echo cancellation and echo suppression
  3. Disable NSE, usually on Cisco/Linksys devices

Finally you may want to begin testing on the slowest available speed first.