Cellular Communications
D-3
Issue 2 May 1995
Understanding ETC
To ensure successful data transfer over a cellular channel, your
modem supports the ETC (Enhanced Throughput Cellular)
protocol, which increases modem performance and reliability
when transferring data over cellular telephone channels. The
ETC protocol provides a number of enhancements to both the
V.42 error control protocol and the V.32bis modem protocol.
For maximum performance, the modem on the other end of the
connection should also use ETC. The AT&T COMSPHERE
r
3800 and 3800
Plus modems are good choices; they both
support ETC. (If you connect to a 3800, make sure it has
firmware Release 4.21 or higher. To upgrade either of these
COMSPHERE modems, dial 1-813-530-7026 with the modem.
The new firmware is automatically downloaded when this
number is called.)
If you must connect to a modem that does not support ETC,
refer to the sections
Using Cellular Modem Pools and
Connecting with Non-ETC Modems in this appendix.
Understanding Automatic
Cellular Setup
There are several modem settings (configuration options) that
are changed when you connect your modem to a cellular
telephone. These settings turn on the ETC protocol. Your
modem
automatically changes to these cellular settings each
time it detects a direct cellular connection. When the cellular
direct connection is broken and replaced by a normal telephone
line connection, the modem switches back to its land-line
settings. This feature, called Automatic Cellular Setup, allows
you to easily switch between cellular and land-line telephones
without manually changing individual modem settings.
The modem settings changed by Automatic Cellular Setup when
using a direct cellular connection are listed in Table D-1.
