Can I connect an analogue modem to the FXS port?


No, we do not support analogue modems connected to the T640/T440 FXS port.

Analogue modems are designed to use analogue lines and are not reliable to work via SIP(VoIP) lines. As the backbone of the T640/T440 uses VoIP and the incoming lines are always routed via the Backbone, the modem traffic will also be routed via VoIP.

Modem network requirements.

To be able to use modem via VoIP networks, the following requirements must be fulfilled.

  • No Packet loss in the network
  • No/Low delay
  • No compression, G.711 codec only
  • TDM-like synchronisation between the 2 modems

When using SIP trunks, the above can never be guaranteed.

The T640/T440 has T.38 (FAX) enabled and modem connections will be seen as FAX transmissions and the system will switch to T.38 that can't be used for modem connections. T.38 is enabled also when using ISDN or analogue lines.

We suggest to connect analogue modems direct to the ISDN/analogue lines and not using the T640/T440 fxs ports.



  • No labels