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Configuring the Modem 4-27
Configuring
the Modem
SDC Option Set 4—Sync Leased Line with Dial Restoral; N oACU
(Models 3261/63/66/68)
Point-to-Point Leased Line Application with Dial Restoral
Figure 4-5 shows a typical point-to-point leased line application, with SDC modems
providing leased line and dial back-up for a bridge/router network. A Telenetics
Network Management System (NMS) is shown. This application could apply to any
nodal equipment connections (e.g., bridges, routers, or X.25 PADs).
With the modem’s integral restoral capabilities, if leased circuit operation is
disrupted, the modems restore the connection over a single dial line through the
PSTN.
The modem uses the adaptive rate feature in the V.34 Auto modulation mode. This
ensures maximum throughput when line quality deteriorates. If restoral criteria are
met, the modem automatically reroutes data traffic through the PSTN. At that time,
the modem attempts to run at its maximum rate over the dial line, and falls back to
lower speeds if required. After an hour, the modem returns to the leased line.
Select SDC Option Set 4 for this application.
Note the following:
• The line configuration default of Option Set 4 is Two-Wire Leased Line.
• With Option Set 4, the modem provides the network timing (Clock=Internal).
• To specify a non-default rate at which the modem communicates with the DTE,
use the DTE Rate (AT
*
DE). See the DTE Rate description in Appendix A.
• Select SDC Option Set 4 in both the local and remote modems, and ensure that
Mode (AT
*
SM) is set the same in both modems.
• If operating with the Telenetics or Motorola 6500
PLUS
that has the Link Back-
Up option, set DTR=108.2 (the default is 108.1 for 6500s without the Link
Back-Up option).
Figure 4-5. Point-to-Point Leased Line Application with Dial Restoral—Option Set 4
33.6 kbps
PSTN
Bridge/
Router
To 56/64 kbps
NMS
Network Management Channel
Bridge/
Router
326X
FA S T
SDC
326X
FAS T
SDC