Modem Standards

Modems are used on many different types of computers, function at different speeds, and travel over different quality of wire. But all the modems also need to be able to talk to each other. That is why standards exist. The ITU-T standards are used throughout the world as the model to follow in modem communications. Below is a list of some of these standards.

Standard	Meaning
V.22	Provides 1200 bits per second at 600 baud (state changes per second)
V.22bis	The first true world standard, it allows 2400 bits per second at 600 baud
V.32	Provides 4800 and 9600 bits per second at 2400 baud
V.32bis	Provides 14,400 bits per second or fallback to 12,000, 9600, 7200, and 4800 bits per second
V.32terbo	Provides 19,200 bits per second or fallback to 12,000, 9600, 7200, and 4800 bits per second; can operate at higher data rates with compression; was not a CCITT/ITU standard
V.34	Provides 28,800 bits per second or fallback to 24,000 and 19,200 bits per second and backwards compatility with V.32 and V.32bis
V.34bis	Provides up to 33,600 bits per second or fallback to 31,200 or V.34 transfer rates
V.35	The trunk interface between a network access device and a packet network at data rates greater than 19.2 Kbps. V.35 may use the bandwidths of several telephone circuits as a group. There are V.35 Gender Changers and Adapters.
V.42	Same transfer rate as V.32, V.32bis, and other standards but with better error correction and therefore more reliable
V.90	Provides up to 56,000 bits per second downstream (but in practice somewhat less). Derived from the x2 technology of 3Com (US Robotics) and Rockwell's K56flex technology.

This table extracted from TechTarget.com

The current standard is V.90, and it functions differently from all of its predecessors. This standard was the first to make bit rates of significantly higher than 33.6 kbps a possibility. The way this happened has to do with the way the data is dealt with in the different standards. Prior to V.90, data was always converted to analog to travel over the wire. This is why bit rates were limited. V.90 makes an assumption that one end of the modem connection has a pure digital connection to the phone network. Since this is true for the service providers, the digital-analog conversion is not necessary when downloading data. Data sent from the modem is still sent in analog form, but they are usually keyboard strokes or mouse movements (for web interaction).

Thanks to the phone network being increasingly digital, the physical limit on data transfer increases by a good bit. However, the Federal Communications Commission (FCC) currently restricts the maximum download speeds to 54kbps. So even as technology increases, there is still an imposed limitation.

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