0049-1800-xxx 326X V.34, V.34-SDC and V.32bis Series Modem – USER’S GUIDE 02/23/2010
Rev. A
Page 66
of
205
Figure 4-2 shows a configuration using an external A/B switch. Network
configuration (SDC Option Set 2) and operation is the same as with an internal
switch.
SDC Option Set 3 – Sync Dial Only
In a typical dial application, a remote terminal dials the host for file transfers. This allows remote
users to dial in as needed, with a higher throughput than formerly attainable over the PSTN.
Alternatively, the DTE and host (Figure 4-3) could be nodal equipment (e.g. X.25 PADs, routers,
bridges). In this configuration, the SDC modems are used for remote dial-up branch connectivity.
This is useful for remote uploading or downloading data over the PSTN as needed.
Select SDC Option Set 3
for either of these applications.
Note the following:
•
With Option Set 3, the modem provides the network timing (
Clock
=Internal).
•
Specify the speed at which the modem communicates with the DTE using the
DTE Rate
(AT*DE) option, to use a value other than the default. See the
DTE Rate
description in
Appendix A.
•
With Option Set 3, the modem originates calls with its V.25bis ACU. DTR is set to 108.1 so that
an off-to-on DTR transition instructs the modem to connect to the telephone line. If the modem
detects an incoming call, the call is connected. If the modem does not detect an incoming call and
you have enabled
Default Dial
(AT
*
DA), the modem dials the number specified. If the
Default
Dial
(AT
*
DA) is disabled, the modem refers to the
Mode
option (AT
*
AC). If set to answer, the
modem goes off-hook and sends an answer-back tone. An on-to-off DTR transition disconnects
the modem from the telephone line. If DTR is low, the modem does not auto-answer. DTR
transitions govern how the modem answers and disconnects calls.
•
If you want the V.25bis ACU to manipulate the DTR signal, set
DTR
=108.2. Other options in the
ACU OPT’S category are set for a typical sync DTE.
•
Select SDC Option Set 3 in both the local and remote modems, and ensure that
Mode
(AT
*
SM) is
