COURIER HIGH SPEED MODEMS
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.
