USRobotics V.34 - Manual (Page 86)

COURIER HIGH SPEED MODEMS
A-2 Link Negotiation and Error Control
If the remote modem has V.34 capability, the two modems use a
line probing technique to determine the highest speed possible
under current line conditions, and complete the connection. If
the remote modem does not have V.34 capability, a calling
Courier modem listens to the other modem's answer tones to
identify what standard rate the remote modem is operating at,
and adjusts to that rate. An answering Courier modem sends
out a series of answer tone signals until both modems can
negotiate the best connection rate.
V. FAST CLASS (V.FC) HANDSHAKING
The Courier defaults to V.Fast Class and tries for the highest
possible speed when it attempts to connect with another
modem, 28.8K bps. The entire V.FC range comprises 28.8K,
26.4K, 24K, 21.6K, 19.2K, 16.8K, and 14.4K bps. If the remote
modem is not V.FC capable, a connection is made using the
highest compatible modulation scheme (V.32
terbo, V.32 bis, and
so on, down to as low as Bell 103, or 300 bps).
If the remote modem has V.FC capability, the two modems use
a line probing technique to determine the highest speed possible
under current line conditions, and complete the connection. If
the remote modem does not have V.FC capability, a calling
Courier modem listens to the other modem's answer tones to
identify what standard rate the remote modem is operating at,
and adjusts to that rate. An answering Courier modem sends
out a series of answer tone signals until both modems can
negotiate the best connection rate.
U.S. ROBOTICS V.32 TERBO TO U.S. ROBOTICS V.32 TERBO
On these connections, Couriers have two features that result in
outstanding performance: Quick Connect and Adaptive Speed
Leveling (ASL).
Quick Connect allows the modems to connect in approximately
7 seconds, a far shorter time than normal with most modems.
ASL (described below in Other V.Protocol Operations) is used by
U.S. Robotics modems operating in V.32 terbo and V.32 bis
modes.