ASCOM USER GUIDE
High Speed Base Band Modems
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Injecting Errors.
The data test will be run using a PRBS pattern with an error inserted
into it once every second. These errors will be displayed on the error count display.
Pressing the SCROLL DOWN button displays one of the following messages.
This displays the duration the test has been run in seconds.
This indicates that the modem is waiting for the received data to align with transmitted
PRBS pattern.
You can stop the test by pressing SELECT. The display will show.
Pressing SELECT will start the test again.
6.6.6
In-service Test
This mode allows the error performance of the line to be monitored without interrupting data
traffic. It operates by monitoring the CRC bits that make up part of the transmission frame
structure.
Figures produced cannot accurately be extrapolated to give the data error rate, but can be
used as a general guide. Each CRC error indicates that 1 or more bit error has occurred in the
transmission frame. Results are given for both receive and transmit directions.
When In-service Test has been selected the following option becomes available.
Select Pair 1
Select pair 2
(This option is only available for two pair modems)
The test starts as soon as the pair option has been selected
Pressing the SCROLL DOWN button brings up the number of local CRC errors.
You can stop the test by pressing SELECT. The display will show.
Pressing SELECT will start the test again.
Pressing the SCROLL DOWN button brings up the number of far end CRC errors.
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38
ASCOM USER GUIDE
High Speed Base Band Modems
6.6.5
Data Test
This mode allows the user to send a PRBS (Pseudo Random Binary Sequence) pattern to the
remote modem and monitor the received data stream for errors. The number of bits received
in error is displayed on the LCD. The test time elapsed can also be displayed, allowing the user
to calculate the effective Bit Error Rate if required. This is given by:
Error Count
Bit Error Rate (BER) = User Data Rate x Time
A loop must exist somewhere in the line system for the test to be valid. This loop can be
selected by:
(1) Remote loop selected from the Test Menu.
(2) Remote loop selected from the DTE.
(3) Loopback selected by the remote modem.
Loop 1 is usually the most convenient. It must be applied before entering Data Test Mode.
If the Data Test is On, the Local Loop and Loopback items will not be visible in the Test Menu.
Once the Data Test is selected the following option becomes available:
Select Pair 1
Select pair 2
(This option is only available for two pair modems)
The modem injects a PRBS immediately the mode is entered. The Test LED should light to
verify this.
Pressing the SCROLL DOWN button displays one of the following messages:
This message indicates that the modem is waiting for the received data to align with
transmitted PRBS pattern.
This message indicates that the test is running and any errors received will be counted up on
the display. (If this message does not appear check that you have turned on a loop at the
remote end).
You can stop the test by pressing SELECT. The display will show.
Pressing SELECT will start the test again.
Pressing the SCROLL DOWN will display the following option:
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Injecting PRBS.
The data test will be run using a PRBS pattern.
