If the loss of quality is severe, the modem will drop the connection.

Dropped V.FC Connections

V.FC connections can only switch rates down to 14,400 bps. If you connect using V.FC, and line quality drops below that allowable for a 14,400 connection, the modem will disconnect.

If this occurs frequently for a particular call, you will want to disable V.FC before calling that modem again. A different modulation protocol (V.32bis, for example) will be established and will allow the modems to switch to lower bit rates as line quality warrants.

To find out what type of protocol your modem uses, call your modem manufacturer. Some V.FC modems do not support rate switching. These connections are more likely to drop.

Bandwidth Requirements

V.FC connection rates are based on the available bandwidth over the phone line. The modem tests the phone line before establishing a connection rate, and will select the highest symbol rate allowable. In general, a higher symbol rate allows greater speeds, but requires greater bandwidth.