This article will provide guidance on setting up an analog adapter to connect a traditional physical fax machine to the FluentCloud platform.  For additional information on initial device provisioning, please refer to the device specific folder.


Tested Devices:

  • ObiHai 200 (T-38 \ analog only)
  • Grandstream HT-502 (T-38 \ analog only)

Other analog devices with T-38 fax support can also work, but have not been tested for reliability.  It is important to note that testing on approved devices still had a small failure rate inherent in fax over VoIP, though this is minimal when network conditions are stable.  A majority of fax machines have automatic re-try behavior to avoid the need to manually resend on any failures that may occur.

Extension Setup:
  • Recommended to not create a voicemail box for the extension, as you do not want inbound faxes answered by the voicemail system.
  • Ensure the Caller ID number is set to the phone number to be used for inbound faxing for proper fax back behavior.
  • Under the Fax tab in extension settings, set "Analog Fax Gateway" to Yes.  This is required for incompatible endpoints to communicate properly.

Device Setup:
  • Utilize the fax specific templates for your adapter ( OBi200-Fax \ HT-502-Fax)
  • Assign the extension to only one line key.  Grandstream HT-502 devices can support 2 different fax extensions as it has 2 analog ports, but assigning the same extension to both ports is not recommended.
  • Certain legacy fax machines do not perform well using T-38.  If testing with the standard template does not work, using the "T38Disabled" version will prevent T-38 from being used.  Removing T-38 support will greatly increase the negative impact of poor network conditions, and should only be used if no other option is available.
  • Testing has shown that an active SIP-ALG in the local router can interfere with fax setup even when not impacting normal voice calls.  It is always recommended to disable any SIP-ALG at the router level.

Basic Required Inbound Number Routing:
  • Assign the phone number to User routing, with the fax extension as the destination.
  • On the Electronic Fax Settings tab:
    • "Allow As outbound eFax caller ID" -- Yes
    • "Fax Detection" -- No   (Mixed use voice \ fax lines are not currently supported with physical fax machines)
    • Remaining settings will only apply for eFax, and are not applicable.

Advanced Inbound Number Routing Suggestions:
  • Multiple fax machines:
    • Assign the inbound fax number to a route.  In the route, use a call group with multiple fax machine extensions as members to allow for multiple inbound faxes at once.
    • This also provides redundancy in case on machine is offline or otherwise disabled.
  • eFax backup:
    • Can be combined with the above call group routing for high availability and reliable backup in total site failure.
    • If using a route, you can place a Fax Answer application as the last step in a route to allow the eFax system to answer if no physical fax machines are available.  Faxes will then be delivered over email or to the my.fluentcloud.com portal rather than failing while the physical machines are offline.

Extra Settings (generally not required):
  • Physical fax machines often have some settings to help fax over VoIP reliability.
    • Transmission speed - set to 9600  (Higher speeds increase the chance of failure, and are mostly irrelevant in our system that does not charge per minute of call time)
    • Transmission speed is sometimes referred to as a "compatibility" or "VoIP" mode.
    • Disable dial tone detection if it fails to dial outbound properly.
    • Verify that no remote fax codes are programmed into the machine (numbers required after answer to send \ receive)
    • Verify that 7 digit dialing is enabled on your FluentCloud account if using existing 7 digit speed dials.