Motorola and V.32bis - Manual (Page 70)

4-8 Configuring the Modem
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e M
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Option Set 4—Async Answering Central Site Without an ACU (Models 3260/
62/65/67)
Option Set 4 satisfies the needs of an asynchronous application where most calls are
inbound (see Table 4-1).
Because calls are received primarily at the central site, the modem is set to answer
calls automatically. With DTR=Discon, the local DTE can control the DTR signal.
This allows the local DTE to use DTR transitions to connect the modem to the
central site at the beginning of transmission and disconnect it when transmission
ends. The DTR signal from the DTE must be high for the modem to auto-answer. If
the DTR signal is low, it does not answer incoming calls.
At the beginning of each connection, the modem negotiates the highest common data
rate with the remote modem. The modem uses the adaptive rate feature in the V.34,
V.32bis, or V.32 modulation modes. This ensures maximum throughput when line
quality is poor.
Option Set 4—Sync Leased Line Applications With Dial Restoral (Models
3261/63/66/68)
Option Set 4 uses the modem’s leased line restoral feature. With this option set, the
modem operates primarily on a leased line unless that line fails. If so, the modem
automatically restores the connection over a single dial line. You must install a 326X
Series Modem at both ends of the leased line to implement restoral operation.
Option Set 4 configures the modem for a general restoral application (see Table 4-1).
The modem uses the adaptive rate feature in the V.34 or V.32bis Auto modes. This
ensures maximum throughput when line quality deteriorates. If restoral criteria are
met, the modem automatically reroutes data traffic through the public switched
telephone network (PSTN) over a single dial line. 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.
If you operate your modems in leased-line mode with Option Set 4, and one modem
has software Revision 7.8 or 7.9, set the Fast Call parameter (AT
* FC, Modulation
Opts Menu) to Off in both modems.
Option Set Descriptions—326X FAST -SDC Modems
Option Set 1—Async Calls to Central Site
Option Set 1 in the 326X-SDC product functions the same as Option Set 1 above.
Option Set 2—Sync Dial A/B Restoral
Option Set 2 satisfies the needs of a synchronous point-to-point digital link restoral
application (see Table 4-2).
With this option set, the Clock is set to External as network timing is provided by the
DSU/CSU. NOTE: With this option set, (for Motorola and non-Motorola DSU/
CSUs), the DSU’s restoral configuration should be set to Timing=Internal.