V.34 High-Speed Fax

Introduction to V.34 High-Speed Fax

This white paper discusses the unique features of the V.34 facsimile standard, which delivers higher performance and reliability, and how the rapid adoption of high-speed fax results in increased economy and efficiency for businesses.

With advancement in facsimile technology, enterprises face the decision to upgrade their fax solutions to high-speed fax, namely V.34. Dubbed "V.Fast", the V.34 fax standard is a significant enhancement in fax technology with many advantages over legacy fax solutions. The adoption of the V.34 standard allows:

Data rate of up to 33.6Kbps, more than twice the speed of its predecessor, V.17 (14.4Kbps)

Support for fast handshaking, which cuts session setup and management time significantly over legacy solutions

High-speed transmission enables transport of colour fax data

In addition, fax devices supporting V.34 offer more robust and reliable fax transmissions for varied line conditions as a result of the mandatory ECM protocol and the more sophisticated modulation/demodulation scheme. These improvements result in cost savings from reduced fax phone bills especially for long-distance scenarios.

The ITU-T V.34 Fax Standard

The V.34 fax standard was derived from the V.34 data modem standard established by the International Telecommunications Union (ITU). The V.34 data modem standard is a full-duplex implementation for sending and receiving data across telephone lines with a maximum data rate of 33.6Kbps. Certain elements of the V.34 data modem standard were eliminated for V.34 fax while new features, such as a control channel and mandatory ECM, were added to enable fast and reliable fax transmission.

The V.34 Fax Connection and Session

In order to understand the benefits of the V.34 fax standard, it is first necessary to understand how a fax transmission works. V.34 session management and setup were designed with a similar mechanism to legacy handshaking procedures. The first step of a fax session is to establish a 'handshake' between the sending and the receiving devices. During handshaking, the sending and receiving devices negotiate key parameters for how the fax call should be set up such as determining what is the highest transmission speed supported by both devices. The handshaking process itself is performed at 300bps in legacy devices. In V.34 fax capable devices, handshaking is performed at a much faster data rate of 1.2Kbps. The result is a handshake time that is reduced from approximately 16 seconds of legacy systems to 9 seconds for V.34.

Data Rates Supported (Kbps)	ITU Standard
Data Rates Supported (Kbps)	V.27 V.29	V.17	V.34
2.4	X		X
4.8	X		X
7.2	X	X	X
9.6	X	X	X
12		X	X
14.4		X	X
16.8			X
19.2			X
21.6			X
24			X
26.4			X
28.8			X
31.2			X
33.6			X

Figure 1 – Comparison between Fax Modulation Speeds

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