Authorized Self-Study Guide Cisco Voice over IP (CVoice)

Enabling VoIP Fax and Modem Transmission

This section describes the implementation of fax and modem traffic over a VoIP network. It explores both Cisco Systems and standard implementations of faxing, as well as various methods used to transport modem traffic over VoIP.

Cisco Fax Relay

Figure 2-43 depicts a VoIP network set up for fax relay. Initially, fax calls are digitized representations of the contents on paper. The digitized bit stream is then converted to analog for transmission over voice circuits. If Cisco equipment treated fax calls like voice calls, the analog waveform would then be converted to G.711 PCM at 64 kbps and subsequently compressed before transmission across the VoIP network. Treating fax calls like voice calls is impractical ...