T.38 Faxing

Owned by Kelli Higdon
Last updated: Mar 18, 2024
2 min read

T38 is a protocol that describes how to send a fax over a computer data network. T38 is needed because fax data can not be sent over a computer data network in the same way as voice communication.  In essence, with T38 a fax is converted to an image, sent to the other T38 fax device and then converted back to an analog fax signal. The Netborder SS7 Gateway (NSG) now supports T38 reliably.

T38 is described in RFC 3362, and defines how a device should communicate the fax data. In the picture above, if T38 faxing option is enabled in NSG, the process is transparent to the analog fax machine in both the transmission or reception of a fax. The analog fax machine does not need to know T38.

 

How To Enable T38 Faxing in NSG

  1. Access the NSG Dialplan:

    1. Select Netborder SS7 from side Menu

    2. Select Configuration -> Dialplan

  2. Add the following configuration in the "from-sip" context

<action application="export" data="nolocal:tone_detect_hits=10" />
<action application="set" data="fax_enable_t38_request=true" />
<action application="set" data="fax_enable_t38=true" />
<action application="export" data="nolocal:execute_on_answer=t38_gateway peer ced_preamble" /> 

All the above must be added BEFORE:
      <action application="bridge" data="freetdm/g1/a/${destination_number}" />

  1. Add the following configuration in the "from-pstn" context

<action application="set" data="tone_detect_hits=1" />
<action application="set" data="fax_enable_t38_request=true" />
<action application="set" data="fax_enable_t38=true" />
<action application="set" data="execute_on_answer=t38_gateway peer cng" />

All the above must be added BEFORE:
      <action application="bridge" data="sofia/internal/$1@192.168.1.149:5062" /> 

 

   4. Save all changes by clickcing on Save (Disk Icon)
       Note that Dialplan can be modified in real time without the need to restart the gateway. 
       Once you Save the Dialplan, you will be prompted to Reload the gateway which will apply the changes without any service interrupt.
       All the currently established calls will not be affected. Only the newly established calls will start using the new dialplan rules.

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