3Com Courier Reference page 133

For your modem to
The Courier V.Everything modem sends receiver clock
timing signals, which are looped to the transmit clock and
sent to the DTE over the serial interface. Typical use:
systems that require synchronisation of data flowing in
both directions.
4 Set the connection rate to be used (between the Courier V.Everythin
modem and the remote communications device) when the Courier
V.Everything modem is on line.
Try a variable connection rate first, AT&N0. If that doesn't work, try a
fixed connection rate of &N10 (19.2 Kbps), &N6 (9600 bps), or &N3
(2400 bps).
Command Rate
Variable (default)
AT&N0
Reserved
AT&N1
1200 bps
AT&N2
2400 bps
AT&N3
4800 bps
AT&N4
7200 bps
AT&N5
9600 bps
AT&N6
12 Kbps
AT&N7
Auto-Dialing 16-11
Command
AT&X2
Command Rate
14.4 Kbps
AT&N8
16.8 Kbps
AT&N9
19.2 Kbps
AT&N10
21.6 Kbps
AT&N11
24 Kbps
AT&N12
26.4 Kbps
AT&N13
28.8 Kbps
AT&N14
31.2 Kbps
AT&N15
33.6 Kbps
AT&N16