Hardware Reference
In-Depth Information
connection to the CS.
56Kbps Standards
To achieve a high-speed connection, both modems and your ISP (or other hosting service to which
you connect) must support the same 56Kbps technology. The first 56Kbps chipsets were introduced in
late 1996:
• U.S. Robotics' x2 used Texas Instruments (TI) chipsets.
• Rockwell's K56flex was supported by Zoom and other modem makers.
These rival methods for achieving performance up to 56Kbps were incompatible with each other and
were replaced in 1998 by the ITU's V.90 standard.
Unfortunately, the 56Kbps name is rather misleading, in regard to actual transmission speeds.
Although all 56Kbps modems theoretically are capable of this performance on top-quality telephone
lines, the power requirements for telephone lines specified in the FCC's Part 68 regulation limit the
top speed of these modems to 53.3Kbps.
V.90
V.90 was introduced on February 5, 1998, and was ratified by the ITU-T on September 15, 1998. Its
ratification ended the K56flex/x2 standards “war.” Shortly thereafter, most modem manufacturers
announced upgrade options for users of x2 and K56flex modems to enable these products to become
V.90 compliant. Most modems manufactured since 1998 support the V.90 protocol.
V.92
56Kbps protocols, such as the early proprietary x2 and K56flex and the ITU V.90 standard, increased
the download speed from its previous maximum of 33.6Kbps to 56Kbps. However, upload speeds
with any of these 56Kbps technologies are limited to a maximum of 33.6Kbps. Other shortcomings
included the amount of time it takes the user's modem to negotiate its connection with the remote
modem and the lack of uniform support for call-waiting features.
In mid-2000, the ITU unveiled a multifaceted solution to the problem of slow connections and
uploads: the V.92 and V.44 protocols (V.92 was previously referred to as V.90 Plus). Most modems
manufactured since mid-2001 to the present are V.92 compatible.
V.92, as the name implies, is a successor to the V.90 protocol, and any modem that supports V.92
also supports V.90. V.92 doesn't increase the download speed beyond the 56Kbps barrier but offers
these major features:
QuickConnect —QuickConnect cuts the amount of time needed to make a connection by storing
telephone-line characteristics and using the stored information whenever the same phone line is
used again. For users who connect to the Internet more than once from the same location, the
amount of time the modem beeps and buzzes to make the connection will drop from as much as
27 seconds to about half that time. Bear in mind, though, that this reduction in connection time
does not come about until after the initial connection at that location is made and its
characteristics are stored for future use.
Modem-on-Hold —The Modem-on-Hold feature allows the user to pick up incoming calls and
talk for a longer amount of time than the few seconds allowed by current proprietary call-
waiting modems. Modem-on-Hold enables the ISP to control how long you can take a voice call
while online without interrupting the modem connection; the minimum amount of time supported
 
 
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