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Chapter 7 - Cellular Mode Operation
7-2
good for voice, but not suitable for a modem signal. Modem signals, if too strong,
may saturate the cellular link and cause distortion. Modem signal power that is
too weak will result in lower signal-to-noise ratio at the receiving end. There is
an optimum power in cellular data communications, but it is different in each
case.
Cellular Modems and ZyCellular Technology
A truly cellular modem must handle the cellular impairments and maintain a
reliable data link with reasonable data throughput through a cellular channel.
Some modems claiming to be "cellular” lack most of these capabilities.
A link-layer-only protocol does not do anything to enhance modem data pump
performance or physical communication robustness. It does not help much to
handle cellular impairments.
ZyXEL developed special technologies for cellular data communications to
provide reliable, high throughput data links over a cellular channel. We call these
technologies ZyCellular. ZyCellular technologies specifically improve the
modem data pump's performance with respect to cellular impairments.
ZyCellular Modes
In addition to normal modem, fax, and voice operation modes, the following
cellular modes are available in the Omni 288S:
Mode Speed
Multi-Auto V.34/ZyX modes/V.32bis/V.32/V.22bis/G3 FAX/Cellular
CELL 14400 14400/12000/9600/7200/4800
CELL 12000 12000/9600/7200/4800
CELL 9600 9600/7200/4800
CELL 7200 7200/4800
CELL 4800T 4800
CELL 14400
will connect with another modem using cellular mode at a speed of
up to 14400 bps. It will also connect with another V.32bis/V.32 modem. The
actual speed depends on the line condition. The modem will automatically fall-
back or fall-forward within its speed range.
CELL 12000, CELL 9600,
and
CELL 7200
limit the maximum speed to 12000
bps, 9600 bps, and 7200 bps, respectively.
CELL 4800T
uses a trellis coded modulation at 4800 bps speed. It has a better
performance than the uncoded V.32 4800 bps mode.
The modem will automatically and dynamically select and adjust to the best speed
and mode in which to operate. Selecting one of the above cellular modes only
limits the maximum speed at which the modem will operate.