3. OptiX BWS 1600G
Troubleshooting Tables
Tables
Table 6-1 OSNR requirements for various rates.................................................................................................6-2
Table 6-2 Common causes of bit errors ..............................................................................................................6-4
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6 Handling Bit Error
About This Chapter
The following table lists the contents of this chapter.
Title Description
6.1 Background Knowledge Describes background knowledge used in handling bit
errors.
6.2 Causes Describes causes of bit errors.
6.3 Methods and Procedures of Describes methods and procedures of locating bit error
Fault Locating faults.
6.4 Classified Fault Handling Describes methods of handling different bit error faults.
6.5 Cases of Common Fault Describes cases of handling common bit error faults.
Handling
Bit errors refer to the errors occurring in the code element during the transmission. Bit errors
are usually represented by bit. In the SDH frame structure, bytes for monitoring bit errors
include B1, B2, M1, B3, G1 and V5. But in DWDM equipment, the OTU only provides
non-intrusive monitoring on B1 and B2.
This chapter describes the methods of handling bit errors generated in the OptiX BWS 1600G
equipment.
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6.1 Background Knowledge
In the DWDM system, many factors can result in bit errors, including optical power
abnormity, insufficient dispersion tolerance, too low optical signal to noise ratio (OSNR),
non-linearity of optical fiber and performance deterioration of optical components, and so on.
6.1.1 Relationship Between Optical Power and Bit Error
There are two circumstances under which bit errors are generated due to abnormality of the
optical power:
The input optical power is below the receiver sensitivity
As a result of high attenuation of optical power, the input optical power of the OTU at the
receiving end is below the laser’s sensitivity, and thus bit errors occur to the OTU.
Two types of laser detector are adopted for OTU at the receiving end: PIN pipe and APD pipe.
For the 2.5 Gbit/s system, the receiver sensitivity of a PIN pipe is –18 dBm, or even below
–21 dBm if tested in laboratory. If an APD pipe is adopted, the receiver sensitivity is –28 dBm,
or below –31 dBm when tested in laboratory. In actual application, since optical fiber is
usually very long, if taking the optical path penalty of the system into consideration, a
redundancy of 2 dBm should be reserved for minimum receiver sensitivity. By far, the 10
Gbit/s system only adopts PIN pipe with receiver sensitivity being –17 dBm, but when the
optical power reaches –14 dBm, an alarm for too low input optical power may be generated.
The OSNR at the receiving end decreases
The decrease of optical power affects the OSNR at the receiving end. If OSNR redundancy is
not large enough, the decrease of optical power may directly lead to the deterioration of
OSNR, and thus generating bit error in OTU at the receiving end. OSNR requirements of
OTU boards of various rates are listed in Table 6-1.
Table 6-1 OSNR requirements for various rates
OTU rate OSNR requirements
2.5 Gbit/s (without FEC) ≥20 dB
2.5 Gbit/s (with FEC) ≥16 dB
10 Gbit/s (with FEC) ≥20 dB
10 Gbit/s (with AFEC) ≥17 dB
10 Gbit/s (with AFEC and Super CRZ) ≥15.5 dB
In Table 6-1, OSNR requirements are typical values.
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6.1.2 Dispersion
The dispersion of single-mode fiber includes chromatic dispersion and polarization mode
dispersion (PMD). An insufficient dispersion tolerance of the system will lead to occurrence
of bit errors at the receiving end.
Chromatic dispersion can be compensated through the dispersion compensation fiber (DCF).
Dispersion of optical fiber is usually measured with dispersion coefficient with the unit of
ps/nm⋅km. The dispersion coefficient of G.652 fiber is 17ps/nm⋅km, and that of G.655 fiber is
4.5 ps/nm⋅km usually.
The dispersion tolerance of 2.5 Gbit/s optical transmitting module is large, needing no
compensation. But the dispersion tolerance of 10 Gbit/s optical transmitting module is small
(hundreds of ps/nm), therefore, the signal needs dispersion compensation after being
transmitted for a certain distance. On G.652 fiber, the signal needs dispersion compensation
after being transmitted for a distance of 30 km, while on G.655 fiber, the signal needs
dispersion compensation after being transmitted for a distance of 100 km.
PMD is a random value, which cannot be compensated through DCF. But if the rate of a
single-channel signal is below 10 Gbit/s, the effect on the system is not great.
6.1.3 Non-Linearity of Optical Fiber
The non-linear effects of optical fiber are related to the input optical power to a large degree.
If the input optical power is very high and optical fiber transmission distance is long,
non-linearity of fibers may seriously affect the performance of the system, resulting in
performance deterioration at the receiving end and occurrence of bit errors. Therefore, in the
40-wavelength DWDM system, the input optical power should be limited within 20 dBm.
6.1.4 FEC Technology
The OTU of the OptiX BWS 1600G adopts Reed-Solomon forward error correction (FEC)
technology, which can correct up to eight bytes in any location for every 255 bytes, boasting
powerful error correction capability. The out-band FEC function can improve the OSNR
budget of the DWDM transmission system and increase the transmission distance. In addition,
the FEC function can reduce bit error rate in line transmission, and alleviate the bad effects on
the signal transmission quality caused by the aging components or deterioration of fiber
performance, thereby improving the communication quality of the DWDM transmission
network.
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6.2 Causes
The occurrence of the following alarms or performance events means that bit errors have
occurred to the equipment.
B1_EXC, B2_EXC, B1_SD, and B2_SD alarms
BEFFEC_EXC and BEFFEC_SD alarms
RSBBE, RSES, RSSES, RSUAS and RSCSES performance events
MSBBE, MSES, MSSES, MSUAS, and MSCSES performance events
Table 6-2 shows the common causes of bit errors.
Table 6-2 Common causes of bit errors
Fault type Causes Handling
External causes External interference See this chapter.
Equipment grounding problem See this chapter.
Optical power abnormity (over-high or over low) See Chapter 5.
and OSNR deterioration
Dispersion tolerance problem See this chapter.
Non-linearity of optical fiber See this chapter.
Environment problem (extra-high equipment See this chapter.
temperature)
Equipment faults OTU board failure or performance deterioration. See this chapter.
Optical amplifier board failure or performance See this chapter.
deterioration.
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6.3 Methods and Procedures of Fault Locating
6.3.1 Methods
Alarm and performance analysis
Section-by-section loopback
Replacement
Meter test
For details, refer to Chapter 2 "Basic Thoughts and Methods for Fault Locating" in this
manual.
6.3.2 Procedures
Procedures for handling bit errors are shown in Figure 6-1.
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Figure 6-1 Handling flow of bit errors
Start
T2000
1
Any external Yes Remove the
interference? interference source
No
2
Remove the
Any grounding Yes grounding
problem? fault
No
3
Is B1 at receive end Yes Remove the SDH
and transmit end the fault
same?
No
4
Is B2 at receive end Yes Remove the SDH
and transmit end the fault
same?
No
5
Is optical power Yes See handling optical
abnormal? power abnormity
No
6
Enable the FEC
Is FEC function of OTU Yes function of OTU
board disabled? board
No
7
Is optical non-linearity Yes Reduce the input
severe? optical power
No
8
Yes Replace the fan
Is fan abnormal?
No
9
Yes
Is board performance Replace the board
degraded?
No
10
Yes Replace fibre, clean
Is fibre connection
problem? connector or reroute
No
No Is bit error
Return to step N
removed?
Yes
Contact Huawei for
End
help
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6.3.3 Techniques
In removing faults such as bit error, flexible use of some analysis techniques can be helpful
for locating the fault quickly.
Determining the Channels Involved with Bit Errors
Bit error occurs either in all channels or in specific channels.
Bit Errors in All Channels
The fault exists on the line (between MPI-S and MPI-R), you should check the main path of
the system, including optical amplifier, line fiber and related fiber connection.
Bit Errors in Specific Channels
If bit errors only occur in some of the channels, maybe something is wrong with those
channels themselves or the system is working in the critical state, for example, OTU is faulty,
or the signal accessed to the client side is abnormal, or connection of fiber in a single station
is abnormal.
In this way, the fault can be located quickly.
Skillful Use of B1
OTU provides non-intrusive monitoring on B1 byte in SDH signal frame, as shown in Figure
6-2.
Figure 6-2 Monitoring B1 byte
A B
DWDM side DWDM side
O O
O O
Monitor B1 byte T T
T T Monitor B1 byte
U U
U U
Client side
The OTU at the transmitting end of station A detects the number of B1 errors and occurrence
time, and then it transmits bit errors transparently to station B. The OTU at the receiving end
of station B also detects the number of B1 errors and occurrence time. The difference of B1
errors at station A and station B is the number of bit errors generated between stations A and B,
that is, the bit errors generated in the transmission process of the DWDM equipment.
In this way, you can determine whether the bit errors are generated at the DWDM side or at
the client side. In addition, you can know the number of bit errors generated at the client side
and that at the DWDM side.
The OTU with FEC provides four performance events of error correction data to reflect the
number of corrected bit errors and the number of uncorrected bit errors on DWDM line.
FEC_COR_0BIT_CNT: count of corrected 0bits
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FEC_COR_1BIT_CNT: count of corrected 1bits
FEC_COR_BYTE_CNT: count of corrected bytes
FEC_UNCOR_BLOCK_CNT: count of uncorrectable frames
If the number of bit errors during 24 hours is within the error correction range, the system
works normally without bit errors, but FEC error correction performance events are reported
by the T2000. The number of corrected errors is consistent with the number of bit errors
generated in the DWDM system.
If the number of 24-hour bit errors is beyond the error correction range, the B1 error
performance events or alarms are still reported by the receiving end.
Replacement
If bit errors occur in only one direction of the system, the replacement method is
recommended. By observing whether bit errors or error correction performance varies with
replacement, you can easily locate the fault. The following can be replaced:
Optical Fiber
Replace the optical fiber in one direction with the fiber in the other direction. Exchange the
fibers connected to the "IN" port with that to the "OUT" port of FIU at both ends.
OTU
The OTUs at the receiving end (such as LWF) can be exchanged without differentiation of
wavelength. The faulty board can be replaced by an idle or standby OTU.
The OTU at the transmitting end (such as LWF) corresponds to different wavelengths. On the
site, if there is no standby board with the corresponding wavelength; replace the faulty board
with the OTU of back-to-back OTM station in the other direction.
Optical amplifier board
Replace with the optical amplifier board in the other direction. Note that the types of optical
amplifier boards should be the same.
6.4 Classified Fault Handling
6.4.1 Handling of External Faults
Checking External Interference
The following external interference may cause bit errors:
Electromagnetic interference brought about by external electronic equipment
Electromagnetic interference from the power supply of equipment
Electromagnetic interference generated by thunderstorm electricity and high-voltage line
To prevent external electromagnetic interference, preventive measures are important, such as:
The power consumption equipment in the equipment room should be well grounded.
The interference degree of radio-frequency device should comply with the requirement.
The transmission equipment is suggested to use separate power supply.
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Power supply should be configured with a large capacitor preventing surge and line
frequency interference.
Do not build an equipment room in an area where lightning is frequent or near
high-voltage power cables and be prepared for lightning protection.
Checking Equipment Groundings
Poor grounding of equipments and cables in the equipment room is another cause for bit
errors. Therefore, when analyzing causes of bit errors, check the following items:
Grounding of the cabinet of the transmission equipment
Grounding of side panels on the cabinet of the transmission equipment
Grounding of subracks
Grounding of signal cables
Grounding of DDF and ODF
Grounding of the NM equipment, and various power consumption equipments
Whether the interconnected equipments are jointly grounded
Checking Ambient Temperature
The ambient temperature of the equipment room must comply with the requirements. Either
too high or too low temperature may cause bit errors.
Checking Optical Power
In the DWDM system, transmission distance is usually very long, which requires the
equipment to provide a large number of fiber jumper, adjustable attenuators and ring flanges.
Bad contact of fiber connector, bending or over tight binding of fibers, bad ambient
environment and minute operation may increase the optical power attenuation of fibers.
Therefore, when bit error occurs, check the optical power of each point, if the bit errors are
caused by cable performance deterioration, high connector attenuation, or incorrect fiber
connection, repair cables, adjust optical attenuator or reconnect inter-board fibers correctly.
If bit errors are generated due to optical power abnormity, see the Chapter 5 "Handling
Optical Power Abnormity" in the manual.
Removing Non-Linearity of Optical Fiber
Too low optical power may result in bit errors, so it is with over-high optical power, which
may lead to non-linearity of signals. To eliminate bit errors resulting from non-linearity, you
can query the optical transmitting power on the T2000 and keep them within the specified
range.
Checking Dispersion Compensation
For the single-channel signal at the rate of 10 Gbit/s, the dispersion compensation should be
reasonable. In system design, apart from the dispersion budget, note the following points:
The types of fibers of the whole system
The type of the dispersion compensation module and compensation distance
Whether the distribution of dispersion compensation modules is reasonable
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The effect of dispersion on the system adopting SuperWDM technology is great. Both over
compensation and under compensation will affect the OSNR at the receiving end, and thus
generating bit errors.
6.4.2 Handling of Equipment Faults
Board Performance Deterioration
OTU performance deterioration
Signals at the client side experience O/E/O conversion on the OTU, during which, faults in
any stage may lead to performance deterioration and further result in generation of bit errors.
Furthermore, the instability and drift of wavelength of the laser at the transmitting end, or
insufficient isolation for neighboring wavelengths after being multiplexed may also result in
the generation of bit errors.
If bit errors are generated as a result of the deterioration of the OTU’s performance, the faults
can be removed by replacing the faulty board.
Optical amplifier performance deterioration
The pump laser of erbium-doped optical amplifier may bring about very strong amplified
spontaneous emission noise (ASE), which may decrease the OSNR, and thus resulting in bit
errors.
If bit errors are generated as a result of the deterioration of optical amplifier performance, the
fault can be eliminated through board replacement.
Fan Abnormity
If the fan becomes abnormal, equipment temperature may increase, resulting in the emergence
of bit errors.
Abnormity of the fan may be caused by blocked air outlet, for example, the air filter is
blocked. In this case, clean the air filter immediately. Another possible cause is the fan is
faulty, in this case, replace the fan immediately.
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6.5 Cases of Common Fault Handling
6.5.1 Bit Errors Caused by Incorrect Fiber Connections
System Overview
In a project of 40x2.5 Gbit/s (channel) system, station A and station B, fully configured with
LWC1 boards, serve as OTM stations, offering 6 channels of services. The overall distance
between them is 150 km, and the attenuation on the line is 37 dB, as shown in Figure 6-3.
Figure 6-3 Networking configuration diagram
Station A Station B
150km
SDH OTM OTM SDH
Fault Symptom
In deployment commissioning, the test of 24-hour BER between station A and station B is
passed, but it is found on the T2000 that a large number of FEC-corrected errors occur to the
performance data of all LWC1s at station B that receives signals from station A. But the
number of corrected errors at station A that receives the signals from station B is 0.
Troubleshooting
Analysis:
The LWC1 adopts FEC. The occurrence of a large number of corrected errors indicates that
bit errors occur to DWDM line in transmission. But the 24-hour BER test between station A
and station B is passed, it indicates the number of bit errors is within the FEC correction range,
that is, those errors have been corrected.
Handling procedure:
Querying alarm and performance events
Step 1 A large number of FEC-corrected errors occur to the LWC1s at station B that receives the
signals from station A, and the number of corrected errors at station A that receives the
signals from station B is 0.
----End
Conclusion: Correction occurs in one direction.
Querying input optical power
Step 1 Query the type of the receiving lasers at the DWDM side of LWC1 of station B and find they
are all APD pipes.
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Step 2 Query the input optical power at the DWDM side of LWC1 of station B and obtain the value
of –15 dBm, higher than the sensitivity.
Since error correction is found in all 6 channels, it shows that the fault does not exist in the
OTU.
Step 3 Query the optical power of each point on the T2000, and find that the optical power
transmitted from station A to station B is similar to that transmitted from station B to station
A, but a large number of corrected errors are found only at station B that receives the signals
from station A.
----End
Replacing the board
Step 1 Since corrected errors occur in one direction, notify the personnel at station B to exchange the
optical amplifier boards in two directions. But FEC correction is still found.
----End
Conclusion: The fault on the OAU is excluded.
Adjusting optical power
Step 1 Error correction may be related to non-linearity of fibers, so increase and reduce the optical
power input into optical amplifier board, the number of corrected errors varies, but error
correction still exist, and the smaller the input optical power is, the greater the number of
corrected errors will be.
----End
Conclusion: Non-linearity of fiber is excluded.
Replacing fibers
Step 1 Exchange the optical fiber connected with the "IN" port and "OUT" port of the FIU at station
A and station B respectively. View the NM and find that error correction disappears. Restore
the original connection, and error correction does not appear either. The fault is cleared.
----End
Conclusion: The fault is that the optical fibers at the line side of FIU are connected
incorrectly.
Conclusion and Suggestion
Normally, if the optical power and the OSNR meet the requirements, the system should not
generate bit errors or correction performance data (small FEC corrected errors will be exist if
the OSNR below 20 dB at the receiving end). Occurrence of correction performance data
indicates that system performance becomes deteriorated. Find out the causes to avoid hidden
troubles.
If bit errors only occur uni-directionally, replace the optical fiber, OTU, and OAU in turn to
locate the fault.
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6.5.2 Bit Error Caused by Non-linearity of Optical Fiber
System Overview
In a chain network, as shown in Figure 6-4, both station A and station B are OTM stations,
between which there are four OLA stations. Eight channels (CH1-CH8) of 2.5 Gbit/s services
have been configured between station A and station B.
Figure 6-4 Networking configuration diagram
Station A Station B Station C Station D Station E Station F
OTM 17dB OLA 22dB OLA 21dB OLA 20dB OLA 14dB OTM
Fault Symptom
During deployment commissioning, the input and output optical interfaces at the client side of
the LWC1 of station F are looped back through the optical fiber and a fixed 10 dB optical
attenuator is installed between them. At station A, test bit errors with a meter and some
channels cannot pass the 24-hour BER test.
Troubleshooting
Analysis:
Initialize the current performance data and test bit errors with a meter again. Observe for a
period of time, then view the T2000 and find that no bit error occurs to the signals sent from
station A to station F. However, after 16 hours, bit errors occur in some channels that station A
receives from station F. The channels reporting bit errors and the number of bit errors are not
stable.
Since bit errors appear uni-directionally, the fault can be located through replacement.
Handling procedure:
Querying performance events
Step 1 After 16 hours, bit errors occur in some channels that station A receives from station F. The
channels reporting bit errors and the number of bit errors are not stable.
----End
No bit error occurs to the signals sent from station A to station F.
Conclusion: Bit errors occur uni-directionally.
Checking optical power
Step 1 Check the optical power of the amplifier at each station in NM, and find it is identical with the
value in engineering commissioning.
Step 2 Check the optical power of the LWC1 at station F in the T2000, and find it is identical with
the value in engineering commissioning.
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----End
Replacing the board
Step 1 Notify the personnel at station F to replace the LWC1 corresponding to the channel with bit
errors. Bit errors still exist, and bit errors in some channels increase, while in others reduce. It
shows that bit error is not related to the LWC1.
Step 2 Since bit errors occur uni-directionally, notify the personnel of each station to exchange
westbound and eastbound optical amplifiers. But bit errors still exist.
Step 3 Restore the original board configuration.
----End
Adjusting optical power
Step 1 On the premise that OSNR is guaranteed, increase the input optical power of the optical fiber
with bit errors (at station F transmitting signals to station A). Observe the variation of the
number of bit errors on the NM, and find the higher the optical power is, the greater the
number of bit errors will be. Reduce the input optical power of the fiber, and find that the
lower the optical power is, the smaller the bit error number will be.
----End
Conclusion: It is determined that bit errors are caused by the non-linearity of optical fiber.
Reduce the input optical power and bit error problem will be solved.
Adding an attenuator
Step 1 Add a fixed 3 dB attenuator after the optical amplifier board at the transmitting end without
decreasing the optical OSNR so as to reduce the input optical power, thus alleviating the
effect of fiber non-linearity.
----End
Test again, and bit errors disappear.
Step 1 Observe for five days and find that the system works normally.
----End
Conclusion and Suggestion
The probability of bit errors caused by fiber non-linearity is little, and bit errors appear at
random for it is mainly related to the performance of line fiber. Since the OSNR at the
receiving end may be good when bit error is caused by fiber non-linearity, the fault is likely to
be hidden.
Whether bit errors are caused by fiber non-linearity or not can be determined by increasing or
reducing the input optical power.
If the input optical power is increased, bit errors increase accordingly.
If the input optical power is reduced, bit errors reduce accordingly.
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6.5.3 Bit Errors Caused by a Faulty OTU
System Overview
Figure 6-5 illustrates a project of a 40-wavelength system with a full service configuration.
All OTUs in the system are LWFs.
Figure 6-5 Networking configuration diagram
Station A Station B Station C Station D Station E Station F Station G
OTM OLA OLA OLA OLA OLA OTM
Fault Symptom
In deployment commissioning, disable the FEC function of the LWF. Attach a meter at station
A and perform loopback at station G for BER testing. One bit error is generated every one
hour in the CH29 at station A that receives the signals from station G, but the LWF
corresponding to CH29 at station G has no bit error. There is no bit error in the other
channels.
Troubleshooting
Analysis:
Since only one channel has bit errors, there is nothing wrong with the board and fiber line
between the signal multiplexing and signal demultiplexing. Then the factors causing bit errors
include:
The OSNR of CH29 at the MPI-R point of station A is below the standard value.
The input optical power of the LWF at the receiving end of station A is abnormal.
The LWF at the receiving end of station A is faulty.
The LWF at the transmitting end of station G is faulty.
Handling procedure:
Step 1 Test the OSNR of CH29 at the MPI-R point with an optical spectrum analyzer. It is normal.
Step 2 Check the input optical power at the DWDM side of the LWF of station A. It is in the normal
receiving range.
Step 3 At station A, check the fibers and the connections between D40 and the LWF. At station G,
check the fibers and the connections between the LWF and M40. The optical fibers and the
connections are normal.
Step 4 At station A, use a normal LWF to replace the LWF corresponding to the 29th channel, but bit
errors occur in less than one hour when testing with a meter. The LWF of the station G is
suspected to be abnormal.
Step 5 Replace the faulty LWF board at station G with the standby board of station A. There is no bit
error within 24 hours.
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Step 6 The LWF of the station G is determined to be faulty.
----End
Conclusion and Suggestion
When bit errors occur to the system, first determine whether they occur to multiple channels
simultaneously. If so, check the optical path shared by all channels; if only some channels
have bit errors, check the separate optical channel.
In the OptiX BWS 1600G, important service boards like the OTU and the OAU must be
prepared with a standby board, and each type of board must has more than one standby boards.
As for other boards like the SCC, SC2/SC1 and so on, the standby board can be prepared as
required.
6.5.4 Bit Error Caused by Unmatched Dispersion Compensation
System Overview
In a project of 40×10 Gbit/s DWDM system, station A and station B are OTMs, and the
distance between them is 80 km. The engineering documentation provided in deployment
requires that an ITU-T G.655 fiber be used bi-directionally between A and B.
Fault Symptom
During engineering acceptance, it is found that all LWFs at station A that receives signals
from station B report a large number of corrected errors. In 15-minute performance data,
thousands of RSBBE are reported.
The number of corrected LWFs at station B that receives signals from station A is small and
there is no bit error.
Troubleshooting
Analysis:
The LWF has FEC function to correct the bit errors generated in the transmission over the
DWDM equipment. If the number of bit errors is beyond the capability of FEC, besides the
corrected performance data, the number of uncorrectable bit errors and alarms will be
reported. It indicates that the system works normally.
If bit errors occur uni-directionally, it indicates that the fault is related to unidirectional optical
fibers and boards.
Handling procedure:
Step 1 Check the output and input optical power of each OAU and OTU at station A that receives
signals from station B. Both boards are normal.
Step 2 Error correction and bit errors occur to all boards. The OTU fault is excluded.
Step 3 Replace the OAUs at the receiving end and transmitting end, but the fault still exist. The
optical amplifier board fault is excluded.
Step 4 Exchange the optical fibers connected with the "IN" and "OUT" port of the FIU at both
station A and station B, and find that error correction and bit errors at station A that receives
signals from station B disappear, but all OTUs at station B that receives signals from station A
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report a large number of corrected errors and bit errors. It indicates that bit errors are related
to optical fiber.
Step 5 Check the information about optical fibers, and find that the optical fibers between station A
and station B along the direction B to A are comprised of three sections. The optical fiber in
the middle is more than 20km long, with the type of G.652.
Step 6 Replace the middle optical fiber with a ITU-T G.655 fiber, and then bit errors disappear. The
fault is cleared.
----End
The dispersion coefficient of the signal in the 1550 nm window is 4.5ps/nm·km on a ITU-T
G.655 fiber. The dispersion tolerance of the LWF is 800 ps/nm.
But for a ITU-T G.652 fiber, the signal usually needs dispersion compensation when
transmitted beyond 30 km. In this case, error correction and bit errors are caused due to
inadequate dispersion compensation.
Conclusion and Suggestion
The 10 Gbit/s signal has small dispersion tolerance, so the transmission distance without
dispersion compensation is short. During system design, the dispersion budget of the system
must be considered. An optical fiber with a small dispersion coefficient (for example G..655)
can be adopted or dispersion compensation can be implemented.
In engineering deployment and daily maintenance, you should be familiar with the type of the
optical fibers adopted in the system and the distribution of dispersion compensation modules.
Issue 01 (2007-01-20) Huawei Technologies Proprietary 6-17
