Chapter 1. Commissioning
Vol. V-1-4 Alcatel-Lucent
Trib BER Measurement
Trib BER measurements can be made using an external BER tester, or the
built-in 9500 MXC capability.
Unlike a background measurement, which is single-link based, a trib test is used
to check a tributary circuit from end-to-end, meaning multiple links can be
involved.
E1/DS1, E3/DS3, and STM1/OC3 DACs include a PRBS generator and a G.821
receiver to support looped, and both-way tests on tribs:
•For a looped test the originating DAC provides the PBBS generator and G.821
receiver. Requires a loopback on the trib/circuit, which can be applied using CT
or a physical loop.
•For a both-way test, a PRBS generator on one DAC is G.821 received on its
remote DAC, and vice-versa. No loopback is required.
Within 9500 MXC, loopbacks can be set within DACs, RACs, and on the TDM
bus. For information on these options refer to System/Controls on page 15-43,
Volume IV, and to Circuit Loopbacks for 9500 MXC Node on page 15-67.
Where an external BER tester is to be used, refer to manufacturer’s instructions.
Fade Margin
This test is designed to check that the expected (calculated) fade margin for a link
matches actual performance.
The expected fade margin should be included in the link installation datapack
together with Tx power, system losses, antenna gains, the effective radiated
power, free space path loss, expected receive signal level and the calculation for
link availability.
The fade margin test measures the difference in receive signal level between the
normal, operational level, and the threshold level, the level at which bit errors
appear. The threshold level can be specified for a bit error rate (BER) of 10
-6
or
10
-3
. For 9500 MXC, the difference between 10
-3
and 10
-6
thresholds is not more
than 2dB
External testers provide superior measurement accuracy and access to a wider
range of test and measurement functions.
Fade margin measurement should only be conducted after it has been verified
that expected RSLs, as indicated in CT performance screens, are correct at both
ends of the link. If an RSL is low, the reason for this must first be investigated and
resolved.
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