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12-2
C
HAPTER
12: H
ANDSHAKING
, E
RROR
C
ONTROL
, D
ATA
C
OMPRESSION
,
AND
T
HROUGHPUT
Selective Reject is an optional part of the ITU-T V.42 (LAPM) standard.
Attaining Speeds Above 28.8 Kbps
V.34 connections at 21.6, 24, and 26.4 Kbps are common. To get
connections of 28.8, 31.2, and 33.6 Kbps, line quality must be pristine
end-to-end. In addition, 31.2 and 33.6 Kbps connection rates are
possible only when the device to which you are connecting also runs
software that supports speeds above 28.8 Kbps.
Attaining 56 K Connections
When a client x2 modem connects to a server x2 modem, the path
through the telephone network between the modems is subject to the
following conditions for an x2 connection to be made.
A digital connection at one end.
ISPs or other online services must
have a digital connection to the public switched telephone network
(PSTN). Most major online services have a digital connection to the PSTN.
Only one digital-to-analog conversion.
There can be only one
digital-to-analog conversion in the telephone network between the x2
server modem and the x2 client modem.
Controlling the V.8 Call Indicate Tone
The V.8 protocol speeds call negotiation and specifies a call indicate tone.
Providing the call indicate tone is optional. For compatibility, we ship the
Business Modem with the call indicate tone disabled.
For your modem to Command
Enable Selective Reject
ATS51.6=0
(Default)
Disable Selective Reject
ATS51.6=1
For your modem to Command
Enable the call indicate tone
ATS54.6=0