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By WelshPaul
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Fax is an old technology but is still used by many businesses. Configuring your OBIHAI analogue telephone adapter (ATA) with the settings shown below will help ensure the best possible result when faxing over VoIP here in the UK.

For the purposes of this guide lets presume you have your VoIP provider configures against ITSP Profile A, SP1, and that your fax machine is connected to phone port 1...
  1. Navigate to Service Providers > ITSP Profile A > SIP, in the SIP section, enter the following settings:
    • X_FaxPassThroughSignal: ReINVITE
  2. Next, navigate to Voice Services > SP1 Service, in the Calling Features section, enter the following settings:
    • MaxSessions: 1
  3. Click Submit to save your settings.
  4. Now, navigate to Physical Interfaces > PHONE1 Port, in the Calling Features section, enter the following settings:
    • CallWaitingEnable: Disabled
    • ConferenceCallEnable: Disabled
    • UseForFaxOnly: Enabled
    • DetectFaxPageBreak: Enabled
  5. Click Submit to save your settings.
  6. Finally, navigate to Codecs > Codec Profile A, enter the following settings to support T.38 fax:

    G711U Codec
    • Enable: Disabled
    G711A Codec
    • Enable: Enabled
    • SilenceSuppression: Disabled
    G729 Codec
    • Enable: Disabled
    G726R32 Codec
    • Enable: Disabled
    iLBC Codec
    • Enable: Disabled
    FAX Event
    • Enable: Enabled
    Codec Settings
    • T38Enable: Enabled
    • T38ECM: Enabled
    • FaxPassThroughCodec: G711A
  7. Click Submit to save your settings.
  8. Click Reboot to reboot the system.
  9. Verify that your fax machine BAUD rate is set to a speed between 7200 and 14400. I suggest 9600.
You should now be able to successfully send (and receive) a fax over your chosen VoIP provider using your OBi200, OBi202 and OBi302 devices. :P
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By samaksh
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Thanks for this quick guide!! Faxing over VoIP is a big challenge but I think with the changes in settings and configuration, fax machine can work well on VoIP network.

T38 protocol is specially designed to allow FAX to travel on VoIP network. T37 is a another protocol that helps Fax transmission over VoIP network. But it works offline.
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By Johnhorsley5
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Your advice please. I'm looking at ceasing my phone line and using VoIP solely. However I need to use a legacy fax machine. From what I can see the Obi-100 or 220 will do the job but I don't understand who issues the phone number for the fax or the phone if I buy the Device with two phone ports. I'm in uk by the way
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By WelshPaul
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Hi John and welcome to the forum. :wave:

Firstly, As you need to make use of a fax machine I strongly recommend that you purchase either an OBi200 or OBi202 ATA as the OBi1xx series are now end of line. It's also worth noting that it is only the OBi2xx series ATA's that supports the T.38 fax protocol.

Once you have your OBi200 or OBi202 analogue telephone adapter you're going to need to choose a VoIP provider. Your VoIP provider will provide you with a phone number of your choice and it is them you will pay for any calls that you make. They provide you with a username, password and a proxy server address that you enter into your OBi device. I use (I have had a 100% success rate when sending and receiving faxes with them) however they do charge £2 per month for a local phone number.

There are VoIP providers that supply a local number for free such as sipgate however, I'm not sure how reliable they are when it comes to faxing over VoIP though.

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