Setting up a Poly OBi series analog telephone adapter (ATA) to support fax

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You can set up fax support for a Poly OBi series analog telephone adapter (OBi302 or OBi508) connected to a fax machine. This article also has recommended settings to optimize the fax machine transmission rate.

This article covers:


  • Account owner or admin privileges
  • Zoom Phone license
  • Poly OBi series analog telephone adapter (OBi302 or OBi508) connected to fax machine

Limitations of fax over Voice over Internet Protocol (VoIP)

Faxing has known limitations when implemented as a fax over VoIP service. These limitations are technology-based and industry-wide. Zoom and several VoIP companies use the G.711 standard for sending faxes over the Internet. Although that standard is considered reliable, it is still open to interpretation by various providers and cannot be maintained on an end-to-end basis.

Zoom offers a fax over VoIP service that connects a traditional fax machine to the Internet via an analog terminal adapter (ATA). For occasional faxing, many of our business customers find these best-effort fax services to be cost-effective and more than adequate to serve their needs. We encourage you to assess your faxing needs to select the best option for your business.

Zoom cares about providing you with quality services that meet your business needs. If your business is heavily dependent on regularly faxing large, multi-page documents, then we recommend that you maintain an analog line and a traditional fax machine for reliable and consistent performance.

Zoom web portal

  1. Sign in to Zoom web portal.
  2. In the navigation menu, click Phone System Management then Users & Rooms.
  3. Click on the phone's user name assigned with a Poly OBi ATA.
  4. Click the Policy tab and make sure Voicemail is turned off.
  5. Click the User Settings tab.
  6. Scroll down to the Membership section and make sure the Receive Call Queue Calls option is disabled.
  7. Scroll down to the Desk Phone section, click View & Edit next to Keys & Positions.
  8. Make sure there is a dedicated line is assigned for the ATA.

OBi ATA web interface

  1. Dial *** from the analog phone connected to the ATA, then press 1 to obtain the IP address.

  2. Open a web browser and enter the IP address of the ATA.

  3. Sign in as admin for the username and enter the admin password configured in Zoom web portal.
  4. Navigate to Codecs then Codec Profile A/B,
  5. In the Codec Settings section, set the following parameters:

    • T38Enable=Disabled

    • FaxPassThroughCodec=G711U (default for North America) or G711A

  6. Navigate to Voice Services then SP1 Service.
  7. in the Calling Features section, set the following parameter:
    • MaxSessions=1

  8. Next, navigate to Physical Interfaces then PHONEx Port,
  9. In the Calling Features section, set the following parameters:

    • CallWaitingEnable: Disabled

    • ConferenceCallEnable: Disabled

    • UseForFaxOnly: Enabled

    • DetectFaxPageBreak: Enabled

Fax machine settings

The following fax machine settings are recommended. These settings vary depending on the fax machine vendor and model. Please refer to your fax machine vendor documentation for more details on these settings.

  1. Set to use a lower fax transmission speed or Baud rate (lowest speed/rate is 9600bps)

  2. Disable the Error Correction Mode (ECM)
  3. Disable the Compression mode
  4. Set the Receive/Transmit Buffer to low.

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