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Measurements at Multiplex Systems Siemens TT2510EU01AL_01 1 Contents 1 In-Service Measurement 3 2 Out-of-Service Measurement 7 3 Exercise 17 4 Solution 21 Measurements at Multiplex Systems
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Measurements at Multiplex Systems Siemens
TT2510EU01AL_011
Contents
1 In-Service Measurement 3
2 Out-of-Service Measurement 7
3 Exercise 17
4 Solution 21
Measurements at Multiplex Systems
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Siemens Measurements at Multiplex Systems
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1 In-Service Measurement
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Siemens Measurements at Multiplex Systems
TT2510EU01AL_014
At the front panel of multiplexer devices manufactured by Siemens test jacks for alloutgoing data signals are provided. The measurement outputs are decoupled of themain signal path, the levels do not correspond to the interface levels. It is compulsory
that during measurement the main outputs are always terminated with the correctimpedance.
The error pulses generated in case bit errors occur during the supervision of the FASare also available at a measurement output, which thus allows the in-servicemeasurement of the bit error rate of the receiving signal to be effected.
After removal of the front panel, test points for different clocks are normallyaccessible. These clocks can be for example:
Clock oscillator of the MUX-side, frame clock of transmitting end, frame clock of receiving end.
These signals can be measured with high impedance.
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Measurements at Multiplex Systems Siemens
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Designation Function Impedance
MF 1 Output F1 75 9 coax
MF 2-1 Output F2 Syst.1 75 9 coax
MF 2-2 Output F2 Syst.2 75 9 coax
MF 2-3 Output F2 Syst.3 75 9 coax
MF 2-4 Output F2 Syst.4759
coax
FH Error pulses F1 75 9 coax
Fig. 1
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Measurements at Multiplex Systems Siemens
TT2510EU01AL_017
2 Out-of-Service Measurement
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Siemens Measurements at Multiplex Systems
TT2510EU01AL_018
Out-of-service measurement are mainly effected during commissioning, or if failuresoccur.
Typical out-of-service measurement are
a) Biterror test at subsystem in F1 loop configuration
l The measurement is effected at the subsystems and must not yield any bit errorsduring the observed period (approx. 1 min.)
l The bitrate of the BER measuring set’s output signal is varied by a certain amount. Also for this deviation from the nominal clock bit errors must not occur.
l The test signal is a pseudo-random bit pattern in both cases.
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Measurements at Multiplex Systems Siemens
TT2510EU01AL_019
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bit error
mesasurementset
F1
F2/1
F2/2
F2/3
F2/4
Fig. 2 Measurement setup of BER loop measurement
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Siemens Measurements at Multiplex Systems
TT2510EU01AL_0110
b) Measurement of the subsystem’s jitter tolerance.
This measurement is not necessary during commissioning. The measurementstructure is the same as for bit error measurement.
l The pseudo-random test signal is jittered with a modulator
l The measurement is effected for various jitter frequencies.
l For each jitter frequency the jitter amplitude is increased until bit error occur.
l This limit value of the jitter amplitude has to be above the curve specified byCCITT (see fig. 4).
l The jitter compatibility indicates which maximum jitter amplitude can be taken bythe system for a specified jitter frequency so that no bit errors occur.
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Measurements at Multiplex Systems Siemens
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bit error
mesasurementset
bit error
mesasurementset F2/1
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F2/4
F1
Fig. 3
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Siemens Measurements at Multiplex Systems
TT2510EU01AL_0112
CCITT Jitter Tolerances
A1
A2
f 1
f 2
f 3
f 4
jitter amplitude
peak-to-peak
jitter frequency
bitrate
(kbit/s)
min. jitter amp.
A1(Ulpp)
A2
(Ulpp)
f1
(Hz)
f2
(Hz)
f3
(Hz)
f4
(Hz)
test
signal
2048
8448
34368
139268
1,5
1,5
1,5
1,5
0,2
0,2
0,15
0,075
20
20
100
200
2400
400
1000
500
18
3
10
10
100
400
800
3500
215-1
215-1
223-1
223-1
Fig. 4 Limit values of jitter tolerances for various interfaces
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Measurements at Multiplex Systems Siemens
TT2510EU01AL_0113
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c) Testing of the alarm functions
l Alarms for the F2IN interface
if there is no incoming signal the alarm display of the corresponding channel mustlight up.
if an all-one-signal is fed from a BER measurement set the display has to flash.
l Alarms for the F1IN interface
interruption of the signal to F1IN-interface has to initiate SYN alarm.
an all-one signal is fed from the BER measurement set. This has to release aflashing SYN alarm.
a 16 bit word is fed from the BER measurement set, the contents of the wordcorresponds to the FAW. As for all hierarchies the number of bits per frame can be
divided by 16 bit it is ensured that this combination always occurs at the beginningof the frame.
The following alarms can now be simulated:
BER > 10-3 (SYN alarm), BER > 10-6 (FH alarm), by adjusting the correspondingerror rate at the measurement set.
D-bit (D-Ext) or N-Bit (FH-Ext) received, by setting the corresponding bit position inthe 16 bit word.
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Measurements at Multiplex Systems Siemens
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BER measurement
set
- all alone
- prog. 16 bit word
F1
F2/1
F2/2
F2/3
F2/4
Fig. 5 Configuration for testing of the alarm functions
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Siemens Measurements at Multiplex Systems
TT2510EU01AL_0116
Example:
l testing of the alarms of a 2/8 MUX device
the 8-Mbit/s-FAS has the following content
11010000DN
at the BER-measurement set programmation to
111101000001xxxx is effected.
The positions designated with (x) can be selected freely, as they are notevaluated.
l testing of the error pulse output
feed AIS signal at FIN and measure the pulse frequency at the FH-output with acounter. This frequency corresponds exactly to the frame repetition frequency (1error pulse per frame).
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TT2510EU01AL_0117
3 Exercise
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TT2510EU01AL_0118
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Measurements at Multiplex Systems Siemens
TT2510EU01AL_0119
Exercise
1. Which bit combination would you adjust at the BER measurement set in order totest the alarm display for the D-bit at a 140 Mbit/s multiplexer?
2. Is it possible to effect a bit error rate measurement at the F1-interface if allF2-interfaces are looped back?
BER measurement
set
F1
F2/1
F2/2
F2/3
F2/4
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Siemens Measurements at Multiplex Systems
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Measurements at Multiplex Systems Siemens
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4 Solution
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Siemens Measurements at Multiplex Systems
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Siemens Measurements at Multiplex Systems
2. It is not possible.
a measurement with a pseudo-random signal cannot be effected, as the framesynchronization has to be ensured.
with a bit combination similar to that of exercise 1 the receiver of the BERmeasurement set would indicate a SYN-alarm.
Explanation: The transmitting signal is demultiplexed, and, via a loop, fed withthe internal clock of the multiplexer to the receiver of the BERmeasurement set, but this clock is not synchronous with the
transmitting clock of the BER measurement set.
Reaction: SYN-alarm at the test set.
even if it were possible to synchronize the transmitting clock at the measurementset and the external clock of the multiplexer, the measurement would lead to
wrong results.
Explanation: Certain bits of the transmitting signal of the test set areinterpreted as justification service bits respectively as
justification bits. These bits are removed at the F2-output fromthe corresponding separate signal. However, justification for themultiplex direction is performed independently of the signal of the demux direction. This means that bits which have beeninterpreted as justification service bits in demux direction willprobably be occupied differently in mux direction.
Reaction: Indication of bit errors, even though there are none.
