Yeastar S-Series VoIP PBX supports Fax over IP. You can send or receive a fax via a physical fax machine or receive a fax over the network.

What is T.38 Fax over IP?

T.38 is a protocol for sending faxes over a voice over IP (VoIP) network or the Internet in real time.

T.38 protocol defines the transport of data (a fax) between PSTN fax terminals through a fax gateway, between two Internet-aware fax terminals, or from a PSTN fax terminal through a fax gateway to an Internet-aware fax terminal. A T.38 stream is sometimes referred to as Fax over IP (FoIP).

PSTN fax terminals traditionally use the T.30 protocol to send analog data. To exchange analog fax data with a PSTN terminal over the Internet, the T.38 protocol first converts analog data into digital data. The protocol then converts the data back to analog on the receiving end if the receiver is a PSTN fax terminal.

T.38 Fax Settings

If the Fax over IP doesn't work, you can go to Settings > PBX > General > SIP > T.38 to change the T.38 settings.

  • No Re-invite SDP Add T.38 Attribute

    If this option is enabled, no T.38 attributes will be added in re-invite SDP packet.

  • Error Correction

    Error Correction Mode (ECM) for the Fax.

  • T.38 Max BitRate

    T38 Max Bit Rate.