Black Box MX270A, Руководство пользователя

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DATA VOICE MULTIPLEXORS
5.1.1 A
CTIVATING A
D
IAGNOSTIC
A test or loop is activated on the channel selected by the SELECT switch by
pressing the corresponding button on the front panel. As long as any test or loop is
activated, the TEST indicator lights.
To deactivate the test or loop, press the same pushbutton again. If this was the
only active test or loop, the TEST indicator will turn off.
The commands for the activation/deactivation of remote loops are transmitted
end-toend through the main link. Therefore, when a remote loop is activated, the
DVM TEST indicators light at both ends of the link.
5.1.2 BERT
The bit-error-rate test (BERT) is available only on the data channel. This test is
used to obtain a rapid qualitative evaluation of data transmission without using
external test equipment.
When the test is activated, a test signal is applied to the selected channel of
the DVM. The test signal, an internally-generated 2 9 - 1 (511) bit pseudo-random
sequence, is internally connected to the input of the tested channel’s transmit
path. The transmitted data can either be returned to the receive path of the
channel by means of a loop somewhere along the data path (for example, by
connecting the remote channel loop, or by a physical loopback connection),
or a similar sequence can be transmitted from the other end of the data channel
(either by simultaneously activating the BERT test at the remote DVM or by
connecting a test-pattern generator).
The received signal is routed to an internal test sequence evaluator. The
evaluator compares the received data, bit by bit, to the original data and detects
any difference (bit error). Each detected error is indicated by flashing the
RD/ERR indicator.
While the BERT test is activated, the CD and CTS lines in the local data channel
connector are set low (inactive).