Fax Over IP (Part II)

FoIP Software Architecture
The facsimile interface unit (FIU) is the software module that resides within a
FoIP IWF. It demodulates voiceband signals from an analog interface and
converts them to a digital format suitable for transport over a packet network. It
also remodulates data received from the packet network and transmits it to the
analog interface. In doing so, the FIU performs protocol conversion between
Group-3 facsimile protocols and the digital facsimile protocol employed over the
packet network.
The FIU, shown in Figure 10, consists of the following three units:
fax-modem unit (FM)—This processes PCM samples based on the current
modulation mode and supports the following functions:
• V.21 Channel 2 (300 bps) binary signaling modulation and
demodulation
• high-level data link control (HDLC) framing (0 bit insertion/removal,
cyclic redundancy check (CRC) generation/checking)
• V.27 ter (2400/4800 bps) high-speed data modulation and
demodulation
• V.29 (7200/9600 bps) high-speed data modulation and demodulation
• V.17 (7200/9600/12000/14400 bps) high-speed data modulation and
demodulation
• V.33 (12000/14400 bps) high-speed modulation and demodulation
• CED detection and generation
• CNG detection and generation
• V.21 Channel-2 detection