ZyXEL Communications U-1496 series User Manual page 74

A real cellular modem must be able to conquer the cellular impairments and maintain a reliable
data link with reasonable data throughput through a cellular channel. Most modems claiming
cellular compatibility today lack most of this capability.
Link layer protocol like MNP10 responds slowly to a fast changing cellular line condition. Most
importantly, it does not do anything to enhance modem data pump performance or physical
communication robustness. It does little to help conquer cellular impairments.
ZyXEL CELLULAR TECHNOLOGY
ZyXEL developed special technologies for cellular data communications to provide reliable, high
throughput data links over a cellular channel.
A summary of these technologies includes:
FRS: Fast Re-Synchronization of the modem after cell hand-off and power level
change.
CFEC: Cellular Forward Error Correction to correct fading errors.
DCSS: Dynamic Cellular Speed Selection to dynamically select the best operating
speed and mode in order to minimize error and maximize throughput.
ATPA: Automatic Transmit Power Adjustment selects the optimum transmit power so as
not to saturate the cellular channel.
RHE: Reliable Handshake Enhancements. It ensures reliable connection set-up even
in very noisy line conditions. It also ensures reliable V.42 error control set-up. Other modems
may retry many times to make a successful handshake.
Besides physical layer enhancements, ZyXEL also does V.42 link layer enhancements.
ZyXEL CELLULAR MODES
In addition to normal modem, fax, and voice operation modes, the following cellular modes are
offered in the U-1496 series modems:
Mode Speed
Multi-Auto ZyX modes/V.32bis/V.32/V.22bis/G3 FAX/Cellular Modes
CELL 14400 14400/12000/9600/7200/4800/3600/2400
CELL 12000 12000/9600/7200/4800/3600/2400
CELL 9600 9600/7200/4800/3600/2400
CELL 7200 7200/4800/3600/2400
CELL 4800T 4800/3600/2400
CELL 4800C 4800/3600/2400
CELL 3600C 3600/2400
CELL 2400C 2400
CELL 14400 will connect with the other modem with 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.