US Robotics COURIER Uživatelský manuál stáhnout pdf (Strana 262)

U.S. Robotics I-modem Command Reference

Glossary • Page G-4

asymmetrical modulation

A transmission technique that splits the communi-cations channel into one high-speed

channel and one slower channel. During a call under asymmetrical modulation, the

modem with the greatest amount of data to transmit is allo-cated the high speed channel.

The modem with less data is allocated the slow, or back channel (450 bps). The modems

dynamically reverse the channels during a call if the volume of data transfer changes.

AT&T 5ESS

A make and model of central-ofÞce switch. Before NI-1, AT&T and Northern Telecom

implemented proprietary protocols to handle ISDN calls. ThatÕs why itÕs important to

know whether an AT&T 5ESS central of

Þce switch is using ÒCustomÓ or NI-1 call-control

signaling.

asynchronous transmission

Data transmission in which the length of time between transmitted characters may vary.

Because the time lapses between transmitted characters are not uniform, the receiving

modem must be signaled as to when the data bits of a character begin and when they end.

The addition of start and stop bits to each character serves this purpose.

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US Robotics COURIER Uživatelský manuál Strana 262