V.92 Definition

V.92 is the most recent International Telecommunications Union (ITU-T) standard for analog modem connections. First released in August 1999, it focuses on improved performance rather than increased speed.

The major improvements are the additions of quick connect, modem-on-hold (MOH), PCM upstream and V.44 data compression. Quick connect cuts the modem negotiation (i.e., handshake) time approximately in half, from more than 20 seconds to about ten. It works by storing the analog and digital characteristics from the first call and then retrieving them for future connections.

MOH allows connections to be temporarily severed and then automatically reestablished, thereby reducing the possibility of dropped connections. This feature is particularly useful for lines that have call waiting.

PCM (pulse code modulation) upstream replaces the the analog transmission used by V.90 with digital transmission, thereby boosting the maximum modem transmission speed to about 48 kilobits per second. In V.90 this speed was attained only on the downstream (i.e., reception) side. Both V.90 and V.92 have a maximum downstream speed of approximately 56 kbps.

The V.44 algorithm provides substantially more efficient data compression than that obtainable with V.42bis, formerly the most widely used modem compression algorithm. Even though V.92 does not increase the downstream bit rate, its use of V.44 results in a greater throughput (i.e., the amount of data that can be transferred per unit of time).

Although the computer industry has become increasingly focused on broadband (i.e., high bandwidth) connections to the Internet in recent years, dial-up connections are still in widespread use around the world and are expected to remain so for a number of years. V.92 represents an important advance in dial-up modems and helps bring the user experience closer to that attained with DSL (digital subscriber line) and other forms of broadband.

The ITU-T, still sometimes referred to by its former name, CCITT (Comité Consultatif International Téléphonique et Télégraphique), is a Geneva-based organization that sets international telecommunications standards.

Created November 28, 2005.
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