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Before V.90 was determined, three different types of
PCM communication were being considered for determination. PCM modulations were
enabled by digitally terminating the central site modems and limiting the number
of analog conversions to one. This structural network change allowed modems to
break the 33.6 Kbps barrier and come closer to the absolute maximum of 64 Kbps.
The first type of PCM communication, and the one that
was eventually determined, was the method where PCM modulations were in the
downstream direction, and QAM (V.34) modulations were in the upstream direction.
The second, labeled V.90 Issue 2, was PCM upstream, where PCM modulations were
in both the upstream and downstream direction. The third, which is still
pending, though with almost no support for moving forward, is PCM end-to-end,
which allows two client modems to use a PCM modulation.
There was very little support for V.90 Issue 2 because
of its limited utility. To make it more attractive, papers were presented at the
August 1999 TIA meeting that proposed an expansion of the features of a next
generation modem standard. These papers proposed two additional features. The
first additional feature was dubbed quick connect and provides a standard method
to shorten the negotiation time by storing line parameters in the client. The
quick connect method reduces the negotiation time from over 20 seconds to about
10 seconds. The second additional feature is a Modem-on-Hold™ (MOH) feature.
This codifies a method for the central site modem to request the client modem to
go on hold, or vice versa, and is a mechanism whereby call-waiting tones can be
better survived by voice-band dial-up modems.
Quick connect; MOH and PCM Upstream are supported in
V.34 mode. Product release dates will differ by manufacturer and product type.
You can view a list of V.92 modem suppliers here. Historically, new
communication standards are made available in client modems before the network
modems, and this will be the case with V.92. Industry-leading network equipment
companies have tested V.92 and a number of ISPs have V.92 ports available. Of
course, not all ISPs will upgrade to V.92 at the same time. You can email your
ISP and ask them when they will launch the new standard.
While much of the industry interest is in broadband DSL
and Cable connection, for the next five years, the majority of connections to
the Internet will still be via standard dial-up modems. As the next-generation
modem standard, V.92 focuses not on speed, but on ease of use and better
functionality. Increases in speed are indeed provided through PCM Upstream. MOH
and quick connect can approximate the always-on and simultaneous voice and data
functions of broadband. Modems that have these features provide a better user
experience when connecting to the Internet. |
