VoIP Voice and Fax Signal Processing

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BASIC FAX AND FAX OVER IP FAQS

In this chapter, several questions related to basic fax operation, fax calls on the PSTN, fax over IP (FoIP), and various modes of operation are listed. The questions are organized in the order of fax, fax over PSTN, fax over IP, and related connected points on bandwidth, messages, timing, and various modes of operation.

1. What is fax?

   Fax is an acronym for a “facsimile” (facsimile means “a copy”) or “tele-facsimile” system. A fax machine scans and sends written or graphical material to the destination fax machine for producing hard copy. A fax makes use of a standard telephone line (or VoIP operation) to transmit electrical signals to a remote fax machine.

2. What are the main functional components of a fax machine?

   A standard facsimile terminal device consists of a paper input device (scanner); a paper output device (printer); accessories like a telephone keypad, telephone line control, display, headset, controller, and fax modem; and a limited amount of processing power.

3. How does a fax machine send pages?

   The fax machine electrically scans and breaks up the document page into picture elements or pixels. These pixels are compressed, coded for error protection, passed through digital modulation, and delivered as a voice band analog signal. At the destination, an analog signal is sampled, demodulated, decoded, and given to the printer. A fax makes use of a voice band analog signal. The intermediate transmission is not known to the fax machine. It can ...