ADTRAN DSU IV ESP, Руководство пользователя

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Chapter 4. Applications
61204011L1-1 DSU IV ESP User Manual 4-5
Entering Dial Backup Mode
When a condition for entering dial backup mode is detected, the
A
LARM
LED turns on and the buzzer sounds. The buzzer alternates
between 30 seconds on and 30 seconds off unless the DDS line is
restored or it is disabled by using the
Quick
key and selecting T
URN
O
FF
B
EEP
. See the section Front Panel on page 3-5 for more
information on the
Quick
key.
Operation During Critical Times
The DSU IV ESP allows the user to select the conditions that initiate
the dial backup mode. The factory default enables DBU mode upon
detection of these conditions. The following four conditions can
cause a DSU IV ESP to enter dial backup mode:
Loss of Sealing Current
Sealing current is a low voltage DC current provided by the central
office (CO) to prevent corrosion over the copper wires used in the
local loop. Sealing current may also be used for local loop testing
purposes. An absence of sealing current generally is an indication
that the loop is open.
Out of Service (OOS) Signal
An OOS signal, generated by the network, indicates a device (or
devices) in the network is out of service.
No Receive Signal
This is an indication that the local loop copper pairs may be either
open or shorted or the OCU in the CO is inoperative. In a private
network this may indicate that the transmitter of the remote DSU is
inoperative.
All 1s or all 0s Condition
This condition is usually generated by the network to indicate some
device (or devices) in the network is inoperative. Upon detecting an
all 1s or all 0s condition, the DSU IV ESP initiates a handshake
routine to determine whether the remote unit's DTE is the source of
the all 1s or 0s condition or if an actual network failure exists.