Specifications

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CSU/DSU MS DBU
9.3 DBU Options
The DBU Options are used to select the modes of operation for the Dial Backup
features. There are ten standard options available with additional options for
specific backup services. Table 9-2 lists the DBU options and their AT commands
for all models.
9.3.1 S TANDARD DBU O PTIONS
Automatic DBU
The Automatic DBU option specifies whether the unit automatically enters dial-
backup mode or waits for manual setup. The factory-default setting is Disabled.
Number to Dial
The Number to Dial option offers a selection of stored numbers for the unit to
automatically dial. If the leased line fails, and the CSU/DSU MS DBU is set to
originate, it dials the numbers (first #1, then #2) specified under this option
to set up the dial-backup line. The factory-default setting is Dial With #1.
Originate/Answer
This option specifies whether the CSU/DSU MS DBU originates or waits to answer
if the dedicated circuit fails. One end must be set to Originate and the other to
Answer. The factory-default setting is Answer.
DBU Criteria
These options specify the conditions that will cause the CSU/DSU MS DBU
to enter the backup mode.
When Out of Service (OOS): When enabled, the CSU/DSU MS DBU enters
backup mode if an out-of-service condition is detected. The factory-default
setting is Enable.
No Receive (RX) Signal: When enabled, the CSU/DSU MS DBU enters backup
mode when a loss of signal is detected. The factory-default setting is Enable.
No Sealing Current: When enabled, the CSU/DSU MS DBU enters backup mode
when a loss of sealing current is detected. The factory-default setting is Enable.
When all 1s/0s: When this option is enabled, the CSU/DSU MS DBU monitors
the receive data for strings of 1s or 0s that are longer than the Fail Timer. If this
condition is detected, the local CSU/DSU MS DBU initiates a handshake routine
with the remote unit to determine if the DTE is generating the constant data
pattern or if the network has failed.