Fax Overview

Yeastar P-Series PBX System allows you to connect your fax machine to PBX system. Then you can send or receive faxes on a fax machine, and receive faxes by email. This topic describes how fax works with Yeastar P-Series PBX System, and introduces fax to email, fax detection, and Fax over VoIP settings.

How does fax work with PBX

The fax machines traditionally use the T.30 protocol to transmit analog data over Public Switched Telephone Network (PSTN). However, the analog data cannot be sent over an Voice over Internet Protocol (VoIP) network. Thus the T.38 protocol is created to provide reliable real-time faxing over IP (FoIP).

Yeastar P-Series PBX System supports both T.30 and T.38 protocols. With Yeastar P-Series PBX System, you can send or receive fax over PSTN or VoIP network in real time.

Faxing over PSTN (T.30)
T.30 protocol defines the procedures for transmitting data between two fax machines over the Public Switched Telephone Network (PSTN).
With S2 module or SO module installed on the PBX, you can connect the analog fax machine directly to the FXS port, and then send and receive fax on your fax machine.
Faxing over IP (T.38)
T.38 is a protocol for sending and receiving faxes over a VoIP network. Yeastar P-Series PBX System supports T.38.

The diagram below explains how to send fax over VoIP network.

  1. A fax machine (T.30) sends a fax over PSTN to PBX (T.38).
  2. The PBX (T.38) converts or encapsulates the T.30 protocol into T.38 data stream, and then sends the T.38 data stream to terminal PBX (T.38).
  3. The terminal PBX (T.38) converts the T.38 data stream back to analog signal, and sends to terminal fax machine (T.30).

Fax to email

Faxes traditionally are sent directly to a fax machine; the recipient receives a printed copy. Yeastar P-Series PBX System provides fax to email feature that allows you to receive faxes as PDF by email.

The benefits of fax to email:
  • Keep your faxes private without paper trail.
  • Access faxes in real-time from anywhere.
  • No need to pay for expensive hardware, printer paper, ongoing maintenance or a dedicated fax line.

Fax detection

Fax detection is used to detect automatically whether an incoming call is voice or fax. It is useful when you have fax call and voice call on the same line.

  • If the PBX detects a fax signal, the PBX immediately routes the call to the designated fax destination.
  • If the PBX does not detect a fax signal, the PBX handles the call as a regular voice call.

Fax over IP (FoIP) settings

The following settings are available when you want to improve the Fax transmission over VoIP network.
  • T.38 Support: Enable or disable T.38 protocol for extension and trunk according to your needs.
  • T.38 Max BitRate: The maximum bit rate of the fax transmission.

    The default value is 14400.

  • No T.38 Attributes in re-INVITE SDP: Whether to contain T.38 attributes in SDP re-invite packet.
  • Error Correction Mode: Error Correction Mode (ECM) is an optional transmission mode. ECM automatically detects and corrects errors in the fax transmission process that are sometimes caused by telephone line noise.