US Robotics COURIER Manual do Utilizador descarregar pdf (Página 115)

U.S. Robotics I-modem Command Reference

Handshaking, Error Control, Data Compression, and Throughput • Page 11-6

the highest compatible modulation scheme (V.FC, V.32terbo, V.32bis, and so on, down to

as low as Bell 103, or 300 bps).

If the remote analog device has V.34 capability, the I-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.34 capability, the I-modem listens

to the deviceÕs answer tones to identify the standard rate at which the remote analog device

is operating, and then adjusts to that rate.

When the I-modem answers a call from an analog device, the I-modem sends out a series

of answer tone signals until both devices negotiate the best connection rate.

Fast Class (V.FC) Handshaking

After trying V.34, the I-modem tries for the fastest possible V.Fast Class (28.8 Kbps) con-

nection. The V.FC range spans 28.8, 26.4, 24, 21.6, 19.2, 16.8, and 14.4 Kbps. If the

remote device is not V.FC- capable, a connection is made using the highest compatible

modulation scheme (V.32terbo, V.32bis, and so on, down to as low as Bell 103, or 300

bps).

If the remote device has V.FC capability, the I-modem uses a line-probing technique to

determine the highest speed possible under current line conditions, then completes the

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US Robotics COURIER Manual do Utilizador Página 115