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AM64/128A User Manual Test Menu
25
5.4.6 In Service Test
5.4.6.1 Overview
This mode allows the error performance of the line to be monitored, without interrupting data traffic. This
works by monitoring the accuracy of some of the overhead bits that make up the transmission frame
structure. As the data channel itself is not monitored, the figures produced cannot accurately be
extrapolated to give the data error rate, but can be used as a general guide. In order to understand this
feature better, an understanding of the transmission frame structure is required. This is included as
Appendix C. A brief discussion on the operation is as follows.
5.4.6.2 Operation
The display to select in the test menu is T > In Svc Test
The mode can be exited and re-entered with no effect on any other tests or data.
There are four different displays within this mode:
(1) Comms framing error display
(2) Received envelope errors
(3) Transmitted envelope errors (master only)
(4) Time of test
The SELECT and SCROLL keys operate in the same manner as in Data Test.
This mode may be left running over a long period, so an abort indication has been added to the displays.
The character ‘a’ is displayed prior to the count if the test has been aborted. The monitoring is aborted
when the system error rates get so high that the envelope alignment pattern / comms framing word can
not be locked on to, or when the system loses line sync. (The error count would be meaningless if the line
had been broken in the middle of a test). Note that the different displays may abort at different times, but
the clock will stop when the first abort occurs.
The error count displays appear as follows: (refer to Appendix C for greater detail)
Comms 000000 Comms word error count.
Evp Rx 000000 Received envelope errors.
Evp Tx 000000 Transmitted envelope errors (Master mode only).
The time display simply shows the time since the test has started in seconds.
For example Time 000010 If the count is stopped the display is T Stop 000010
If the count has been aborted the display is T Abort 000010