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How Fax is Used in Telecommunications

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How does FAX work in VoIP environments?

FAX was designed for analog networks, and does not interoperate well at all with VOIP networks. The reason for this is that FAX communication uses the signal in a different way to regular voice communication.

When VOIP technologies digitize  and compress analog voice communication it is optimized for VOICE and not for FAX. Subsequently, if you connect a FAX machine via an ATA adapter to the VOIP network it will work, but you are likely to encounter problems during fax transmissions. If you must do it this way, you should ensure that you are using the G 711 codec, which has a minimum of compression.

To deal with fax, you have the following options:

  1. The easiest way to deal with this is to connect the fax machine directly to the existing analog phone line and bypass your VOIP environment altogether.
  2. Replace the fax machine with a fax service provider. There are many available at a very low cost per month (cheaper than the phone line subscription).
  3. Implement T38, which requires a T38 compatible gateway and a T38 compatible fax machine, fax card or fax software.
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