12
H
ANDSHAKING
, E
RROR
C
ONTROL
,
D
ATA
C
OMPRESSION
,
AND
T
HROUGHPUT
This chapter contains information about:
■
Handshaking
■
Selective Reject
■
V.90 Capabilities
■
Error Control
■
Data compression
■
Getting maximum throughput
Handshaking
With each call, Business Modems go through a link negotiation process
with the remote device. Another name for the negotiation process is
"handshaking."
Business Modems default to V.90 modulation and try for the highest
possible speed when they attempt to connect with another modem: 56
Kbps. If the remote device is not V.34-capable, a connection is made
using the highest compatible modulation scheme (x2, V.34, V.FC, V.32
terbo, V.32 bis, and so on, down to as low as Bell 103, or 300 bps).
Selective Reject
The Business Modem supports Selective Reject for analog calls. Selective
Reject improves performance on noisy lines by reducing the amount of
overhead incurred when the protocol must resend data due to errors.
When Selective Reject is active, only the frame that contained the error is
resent, instead of the frame plus all of the following unacknowledged
frames.
