Fax Services
The ATA 191 provides two modes of fax services that provide internetworking with Cisco IOS gateways over IP networks. These modes are called fax pass-through mode and T.38 fax relay mode.
With fax pass-through mode, the ATA 191 encodes fax traffic within the G.711 voice codec. The fax traffic is then passed through the Voice Over IP (VoIP) network as though the fax were a voice call.
With T.38 fax relay mode, the ATA 191 supports the transmission of faxes, in real time, between two standard fax terminals communicating over SIP networks. T.38 fax relay mode provides a more reliable and error-free method of sending faxes over an IP network.