This topic describes specifications and standards compliance of the GPON interfaces.
Table 1 GPON port specifications
||Rx: 2.488 Gbit/s
Tx: 1.244 Gbit/s
||ITU-T G.984.2 CLASS B+
||Tx: 1310 nm
Rx: 1490 nm
|Tx optical power
||0.5 dBm to 5.0 dBm
||> 10 dB
|Minimum receiver sensitivity
|Maximum overload optical power
The intermittent BEFFEC_EXC alarm is reported at IN/OUT optical interfaces on the LWF board housed in slot 10 of one surack NE.
Optical Transponder Unit
The intermittent BEFFEC_EXC alarms are reported at the IN/OUT optical interfaces on the LWF board housed in slot 10 of one surack NE.
- Check connection.
- Replace MR2 board in slot 8, which is connected with the IN optical interface of LWF board.
- Still alarm at NMS.
Expected operations from vendor:
- Clear the Problem
- Provide User Guide (faulty description and problem handling)
- Provide Maintenance Manual Books
The LWF board has the FEC function of correcting bit errors generated in the transmission over DWDM equipment. If the number of bit errors is beyond FEC correction ability, the number of uncorrectable bit errors and alarms is reported.
Then, initialize the current performance data and observe the NMS after a certain period. The NMS shows that the channels that report bit errors and number of bit errors are not stable.
If bit errors occur in one direction, it indicates that the fault is related to unidirectional optical fibers or boards. In this case, only the local station has bit errors. This means that the fault happens only in one direction.
- Query performance events
- After 15m performance, bit errors occur in local station for the signals that are received from the opposite station and pass through 5 OLA stations. The channels that report bit errors and number of bit errors are not stable.
- No bit error occurs on the signals sent from the opposite station to the local station.
- Conclusion: Bit errors occur in one direction.
- Check optical power.
- Check the optical power of the amplifier at each station on the NMS. The optical power is identical with the value specified during engineering commissioning.
- Check optical power of the LWF at the local station on the NMS. The optical power is identical with the value specified during engineering commissioning.
- Adjust optical power:
- Adjust the optical power. With OSNR guaranteed, increase the input optical power of the optical fiber with bit errors. Observe the variation of the number of bit errors on the NMS. It shows the number of bit errors increases with the optical power. Reduce the input optical power of the fiber. It shows that the number of bit errors decreases with the optical power.
- Check the transmit power of the LWF board in slot 10 in the local station, which the transmission direction is from the opposite station to the local station. Trace step by step each site the OAU receiving power and transmit go to the local station also power gain. Make sure the power receive and power transmit adjust equally or difference is not significant.
- The launched optical power of the upstream station is excessively high about +15 dBm and the OAU gain +28 dB.
- The bit errors are caused by the non-linearity of optical fiber. Reduce the input optical power in the local station and bit error problem is solved.
The improper setting of the interconnected FC switch results in that the bandwidth of the LOG board decreases and the service rate becomes lower.
The FC service on the LOG board slows down and no operation is performed on the LOG previously.
The service on the LOG board slows down. The engineer checks the alarms and performance events of the LOG board, and finds no exception. Therefore, the LOG may be probably normal.
The engineer checks the data on the interconnected FC switch with the customer and finds the history data is over the normal performance value, which indicates that the bandwidth on the transmit side of the switch is insufficient. This why the data slows down. Therefore, the cause lies in the setting of the switch.
- Theoretical analysis on the relation between the FC service bandwidth and packet length shows that sufficient bandwidth is available only on the following conditions if the distance from the site is 75 km:
- The BBC of the FC switch should be greater than 64.
- The frame size of the FC switch should be greater than 2000.
- In fact, the customer has changed the frame size of the switch to 1000, which leads to this problem. The frame size of the interconnected switch is changed to 2048.
- This problem is solved.
The shutdown of the RPC laser interrupts SDH-layer services in a DWDM network.
Optical Amplifier Unit
In a DWDM network, there is one MSP ring with four nodes. To perform certain operations, the customer shuts down the RPC laser between two nodes. As a result, services between these two nodes are interrupted, though the MSP is configured. When the RPC laser is enabled, the services are restored.
When the RPC laser is shutdown, signals are still received but not amplified by RPC. There is no SF event (for example, R_LOS) on related OTU or optical boards. In this case, if the SD flag is set as disabled, the MSP protection switching does not function and the services are interrupted.
- Check on the MSP parameters shows that the SD flag is not selected. Shutdown of the RPC degrades the signals but does not cause a signal failure. Therefore, the MSP protection switching is not triggered. When the SD flag is enabled, shutdown of the RPC successfully triggers the MSP switching.
The wavelength wander of an OTU board causes the downstream OTU boards to report the IN_PWR_LOW alarm.
Optical power abnormity
Optical Transponder Unit
The OptiX BWS 1600G is networked in the chain mode: OTM—-OTM (A)—-OTM (B) —-OTM, that is, multiple OTM stations form a ring of 7 channels (one is standby). One day, the IN interface of the 18th-channel LWC board at station B reports the IN_PWR_LOW alarm.
- The LWC board of station B is faulty or a fault in the fiber from the D40 to LWC causes excessively high attenuation.
- The launched optical power of the opposite station A is abnormal. As a result, the local received optical power is abnormal.
- Other boards are faulty, for example, the M40 at the transmit end or the D40 at the receive end is faulty. Because these two boards are passive optical components, they are less likely to be faulty.
- Other causes.
Check the optical power of the equipment level by level from the downstream to the upstream according to the signal flow for fault locating.
- Measure the input optical power of the D40 and LWC at station B. Excessively low optical power causes the OTU board to report the alarm.
- Scan the wavelengths of the D40 and OAU at station B with a multi-wavelength meter. The 18th wavelength is absent.
- The wavelength ranges of the LWC and M40 at station A are in consistent. The 18th wavelength is not input to the M40. Measure optical interface 23 of the M40 at station A. The input optical power is measured as -2 dBm (normal).
- Scan the wavelengths of the M40 board at station A. The 18th wavelength is still absent. Use the optical power meter to measure the optical power, which is found normal.
- Directly scan the wavelengths of the OUT interface of the 18th-wavelength LWC board. The root cause of the fault is finally located. The scanning result shows that the optical power of the 18th wavelength is -2 dBm (normal value) and the wavelength is 1547.468 nm. The standard wavelength, however, is 1546.92 nm. The wavelength wander is up to 0.5 nm. In the WDM system, the wavelength wander range of the OTU board should be not more than 0.15 nm.
- Temporarily solve the problem by using the standby wavelength between the two stations. Apply for a new 18th-wavelength LWC board and replace the faulty LWC board.
The bit errors occur in a DWDM 10G network due to the incorrect PMD.
After the fiber of the OTM site (node CLS1 to node CLS2) is replaced, the MSBBE bit errors and OTU_LOF alarm occur on the OTM site.
The bit errors occur in the network due to the incorrect PMD.
- The optical power is measured and adjusted to the reference value. After the adjustment, bit errors and the alarm are cleared. Half an hour later, the bit errors and alarm occur again.
- Add or remove the DCM to extend the distance from 5 km to 10 km. Then, the bit errors and alarm are cleared. One hour later, the bit errors and alarm occur again.
- Then, the customer checks the features of the new fiber (chromatic dispersion and polarization mode dispersion). The check shows that the chromatic dispersion (CD) in the fiber is normal but the polarization mode dispersion (PMD) is excessively high. The problem is solved when the customer replaces the fiber.
PMD coefficient relation is given in Table 1.
Table 1 PMD coefficient relation
|PMD Coefficient (ps.km)
||10 (with no FECb)
|a: Standards suggest a value for 10 Gbit/s only. Values at other data rates are nonetheless accepted by the industry.
b: Most long-haul instruments perform forward error correction (FEC).
The improper configuration of protocol channels results in a failure of the ALC to start.
Automatic Level Control (ALC)
The network topology is OTM1–OADM–OTM2. The ordinary ALC mode (wave detection mode) need be configured in this network. At the initial stage of configuration, only the forward ALC (OTM1->OADM->OTM2) is configured, and the MCA board is configured at the OTM2 site. The OSC units are configured as follows: SC1 for OTM1, SC2 for OADM, and SC1 for OTM2. The protocol channel is configured as follows: SC1 of OTM1 as east, SC2-1 of OADM as west, SC2-2 of OADM as east, and SC1 of OTM2 as west. After other ALC configuration is complete, the ALC function is supposed to start. In this case, the system, however, prompts that the ALC of the OADM site is querying reference. A period later, the ALC still cannot start.
Check on all ALC-related configurations on the NMS shows no exception.
Then, all NE data is re-loaded and ALC is re-configured. The ALC, however, still cannot start and the NMS prompts the same message. Therefore, the data and configurations are correct. Then, the fiber connection direction of the OSC may be inconsistent with the configured protocol channel.
Querying of the engineering document shows that the actual OSC connection of the OADM site is SC2-1 for OTM2, and SC2-2 for OTM1.
- Change the protocol channel configuration of the OAMD site for consistency with the actual configuration.
- Then start the ALC. The ALC starts normally.