Dial-Up Modems
V.92 Standard
The V.92 is based on V.90 technology (56k technology), and enhances it in three main features:
* Quick Connect - V.92 defines a mechanism to shorten the dial-up connection time (the time needed for the client modem to connect to the ISP's modem).
* Modem On Hold - V.92 standard enables the modem to stay "on-hold" while another phone conversation is received.
* Upstream Speed
Enhancement -
V.92 provides a faster upstream data rate.
Quick Connect
V.90 standard modems spend several seconds in order to connect to the modem at the ISP site. As a matter of
fact that was one of the main drawbacks of using internet over the PSTN. The
V.92 standard provides a much faster connection rate (up to 50% faster), and by
that makes the use of dial-up modems
much more attractive and easy to use.
Modem On-Hold (MOH)
Before V.92, one of the main problems of the dial-up
standards lay in the way it handles an incoming call while in session.
During call-waiting a signal is transmitted by the
PSTN on the line, which could be identified by the modem.
V.90 technology modems refer to this signal as a
hang-up signal, and terminate the current session. Of course this feature is
problematic as the user doesn't want to disconnect from the server for any
incoming call.
The Modem-on-Hold feature enables the user to view the caller number and decide whether to receive the call
or continue with the current session. If the user decides to receive the call,
the server negotiates the maximum hold time allowed with the client modem, so
that it will be able to return to the previous session with the server, if not
exceeded the maximum time.
Upstream Speed Enhancement
V.92 standard improves the upload transfer rates from 31.2 to 48 Kbps. In order to do so V.92 uses Pulse Code Modulation (PCM) technique. PCM is a modulation technique that enables transmission of information over long distances with hardly any interference or distortion. The noise reduction enables faster transfer rates.
Unlike quick connect and MOH, PCM Upstream does not fundamentally change the modem’s user model. It does provide some extra utility for services that require more symmetric data flow.
Dial-Up Modems
Dial-Up Modem Network Architecture
Dial-Up Modems Standard Evolution
V.92 Standard