3Com U.S. Robotics 56K Voice, Command Reference Manual

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12-4 C
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If the remote device has V.FC capability, the Business Modem uses a line
probing technique to determine the highest speed possible under current
line conditions, then completes the connection. If the remote analog
device does not have V.FC capability, the Business Modem listens to the
device's answer tones to identify what standard rate the remote analog
device is operating at, and adjusts to that rate.
When a Business Modem answers a call, it sends out a series of answer
tone signals until both devices negotiate the best connection rate.
HST We recommend that Business Modems retain the default B0 and &N0
settings. This allows them to make analog connections with "V." protocol
and HST modems in both Originate and Answer modes at a variety of
speeds.
When originating an analog call, the Business Modem set to B1 sends out
a Bell answer tone, which is the prevalent standard in the U.S. and
Canada for connections at 2400 bps and lower. At higher speeds, the
Business Modem also recognizes the ITU answer tones necessary for
connecting with V. protocol modems, and adjusts to the answering
device.
However, when answering a call, a Business Modem sending out the Bell
answer tone (B1) won't be recognized by V. protocol modems. The calling
modem, instead, will wait until it detects a tone it recognizes. The V.22bis
tone used at 2400 bps.
If you want to have your Business Modem connect with V. protocol
modems at high speeds, make sure it is set to B0 for the ITU answer
tones. It will also connect with HST modems at speeds up to 16.8 Kbps.
USR V.32terbo to USR
V.32terbo
On these analog connections, Business Modems have two features that
result in outstanding performance: Quick Connect and Adaptive Speed
Leveling (ASL).
■
Quick Connect allows two Business Modems to connect in
approximately 7 seconds, a far shorter time than with most devices.
■
ASL (described below in Other V.Protocol Operations) is used by
Business Modems operating in V.32terbo and V.32bis modes.