40G Wavelengths Are Unavailable Due to a DCM Module Connection Problem

40G wavelengths are unavailable due to a DCM module connection problem.

Product

OptiX OSN 6800, OSN 8800

Fault Type

DCM Module

Symptom

10G and 40G wavelengths are transmitted in an OptiX OSN 6800 network. The network topology is shown in the following figure. 40G wavelengths in two directions between station A and station G are unavailable. In addition, the performance of 10G wavelengths is lower than the expected performance although it is stable.

Cause Analysis

The optical power and OSNR after commissioning are normal and the optical fibers are newly routed. In this case, it is impossible that the PMD is excessively high. In addition, the link in the network is long, which results in use of many DCM modules. Therefore, it is possible that the DCM modules at a station are incorrectly connected.

Procedure

1. Each station between station A and station G uses different DCM modules in two directions and the compensation distance of the two DCM modules differs by more than 40 km. In this case, incorrect connection of DCM modules at any station can make the 40G wavelengths unavailable.
2. At each station, query the optical power of the optical amplifier boards and calculate the attenuation of the DCM modules. The attenuation of a DCM module increases with the compensation distance of the DCM module.
3. Check station D. The result shows that station D is abnormal. That is, the attenuation of the DCM module connected to optical amplifier board A03 is lower than that of the DCM module connected to optical amplifier board A05.
4. Check whether the DCM modules at station D are incorrectly connected. After rectifying the connections, confirm that the 40G wavelengths are available.

Result

The problem is resolved.

Reference Information

None.

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Dispersion Topology Affects System Performance

Dispersion topology affects system performance.

Product

OptiX BWS 1600G, OptiX OSN 6800, OSN 8800, WDM

Fault Type

Dispersion Abnormity

BEFFEC_EXC

Symptom

The AB network uses the OptiX BWS 1600G 80-channel system, the system OSNR satisfies the requirement for transmitting 10G services. However, BEFFEC_EXC alarms are reported for some wavelengths, indicating that the pre-FEC BER exceeds the permitted range. In addition, the multi-channel spectrum analyzer (MCA) scanning result shows that the OSNRs for some wavelengths are low.

The OSNRs for all wavelengths transmitted from site B to site A are low, and BEFFEC_EXC alarms are reported for some wavelengths.

The following figure shows the network topology.

Figure 1 The Network Topology of AB Network

Cause Analysis

The inherent dispersion of G.655 fibers is near 0 ps/nm.km. Therefore, the signal transmission performance is likely affected by non-linear effects during long-haul transmission of wavelengths over G.655 fibers. The non-linear effects lead to a wider spectrum. A wider spectrum results in a higher noise base than the actual noise base and lower scanned OSNRs than the actual OSNRs.

Dispersion and non-linearity affect one other. The dispersion topology in the direction from site A to site B has a relatively good quality and minimizes the impact of non-linear effects on the optical spectrum. Therefore, the scanned OSNRs in this direction are close to the actual OSNRs. The dispersion topology in the direction from site B to site A has a relatively poor quality and fails to effectively suppress the impact of non-linear effects on the optical spectrum. Therefore, the scanned OSNRs in this direction are lower than the actual OSNRs.

The impact of non-linear effects on the system performance can be minimized by optimizing the dispersion topology in the direction from site B to site A. By doing this, the scanned OSNRs will be closer to the actual OSNRs.

Procedure

1. Collect data from the live network. The network conditions satisfy the requirements for commissioning line optical power.
2. Verify that the flatness of each wavelength. The flatness of each wavelength is within the permitted range using the MCA.
3. Calculate the residual network dispersion according to the design documents. The residual dispersion is within the range defined in 10G OTU board specifications.
4. Optimize the dispersion topology in the direction from site B to site A to minimize the impact of non-linear effects on the system performance. The scanned OSNRs are closer to the actual OSNRs. The problem is resolved.

Result

The problem is resolved.

Reference Information

Optical fibers (such as LEAF and G.653 fibers) with smaller dispersion coefficients cause more intensive non-linear effects than optical fibers (such as SMF fibers) with larger dispersion coefficients. To improve the receive-end system performance, you can optimize the dispersion topology.

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Service Provisioning Fails on an LHP Network, The OTU2_LOF Alarm Is Reported

The service provisioning fails on an LHP network cause by the connectors on the RPC are burnt, the OTU2_LOF alarm is reported.

Product

OptiX BWS 1600G, OptiX OSN 6800, OptiX OSN 8800

Fault Type

OTU2_LOF

Symptom

During commissioning of a long hop (LHP) network, the OTU2_LOF alarm is reported and service provisioning fails. 

Cause Analysis

To locate this type of fault, check the optical power of signals. Most exceptions are relevant to the optical power. Before locating this type of fault, make correct power budget for each section. Therefore, the fault can be avoided.

The possible causes of the fault are as follows:

• The E2000 fiber jumpers are burnt.
• Connectors on boards such as the ROP and RPC are burnt, or the laser is not enabled or fails.
• The DCM or FOA is mis-placed on the line.

Procedure

1. When the fault occurs, check whether the transmit optical power and receive optical power are normal.
2. If the receive optical power of the OA at the transmit end is abnormal, check whether the gain of the backward RPC and the gain of the ROP are normal. If the gain of the backward RPC is higher than 10 dB, it indicates that the backward RPC is normal; if the total gain of both the backward RPC and ROP is higher than 30 dB, it indicates that the backward RPC and ROP are normal. Otherwise, further check whether the E2000 fiber jumpers or connectors on the RPC are normal.
3. Use a microscope to check the connectors of the fiber jumpers on the E2000. If the connectors are dirty, clean the connectors. If the connectors are burnt, replace the fiber jumpers.
4. Check whether the gain of the laser on the RPC is abnormal. Check whether the pump laser on the RPC is enabled. If the laser is not enabled, enable it and then check the gain of it.
5. If the gain is still abnormal at this time, check whether the pump optical power equals the pre-set value. If the pump optical power is lower than the pre-set value, use a microscope to check the connectors on the RPC. If the connectors are normal, it indicates that the laser fails.
6. Based on the preceding analysis, it is determined that the root cause of the fault is that the connectors on the RPC are burnt. Due to burnt connectors, the Raman gain of the RPC is insufficient and service provisioning fails.

Result

The problem is resolved.

Reference Information

None.

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WDM-Side Pre-FEC BER Changes Drastically

Because the accumulated PMD over a 10G line exceedes the design value, the WDM-side pre-FEC BER changes drastically.

Product

OptiX Metro 6100

OptiX Metro 6040

OptiX OSN 6800

OptiX OSN 8800

Fault Type

Bit Error

PMD Abnormity

Symptom

During expansion of WDM equipment on the network L, the pre-FEC BER in three 10G channels for expansion changes drastically. Within a day, the pre-FEC BER changes from 10^–6 to 10^–11.

The newly deployed 10G services report a transient alarm indicating that the pre-FEC BER crosses the threshold. The existing 2.5G services are normal without any bit error or alarm.

Cause Analysis

Compared with low-rate services such as 2.5G services, high-rate services such as 10G or 40G services have higher requirements for specifications of cables. For example, if the accumulated PMD is higher than the tolerance value, a large non-linear cost will be introduced. As a result, system performance deteriorates.

The possible causes of the fault are as follows:

• The line optical power fluctuates, with a deviation greater than 3 dB.
• The board at the transmit end is faulty.
• The board at the receive end is faulty.
• The quality of line cables deteriorates (for example, PMD is excessively high).

Procedure

1. The collected data indicates that the line optical power does not change drastically.
2. Replace the relevant board, but the BER still changes drastically. Therefore, the fault is irrelevant to the board.
3. The data on the line collected by using the OTDR in a test indicates that reflection is lower than or equal to -27 dB.
4. Therefore, it is suspected that the line PMD exceeds the tolerance of a 10G system. The result of an on-site test indicates that the accumulated PMD over a 10G line reaches 12 ps, exceeding the design value. After the cables are replaced, the fault is rectified.

Result

The problem is resolved.

Reference Information

None.

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Splicing of a G.652 Fiber with a G.655 or G.656 Fiber

The splicing of a G.652 fiber with a G.655 or G.656 fiber.

Product

OptiX BWS 1600G,OSN6800,OSN8800

Fault Type

Fiber

Symptom

A network adopts the OptiX BWS 1600G and with an RPC board as a Raman amplifier board. The customer uses G.656 fibers and the ODF interfaces are of the LC/PC type. By default, the RPC board of the OptiX BWS 1600G matches the G.652 fiber whose interface is of the FC/UPC type. The LC/PC interface of the fiber provided by the customer does not satisfy the requirements of high power. In addition, the FC/PC interface of a fiber is not available temporarily. After negotiation with the customer, direct splicing is adopted.

Cause Analysis

The effective sections of the G.652 fiber and the G.655 or G.656 fiber, technical specifications for manufacturers, and mode field diameters of the 1500 nm wavelength (the G.652 fiber is of a bigger diameter) are different.

When two G.652 fibers are spliced, a loss is produced. The average loss is 0.02 dB.

In the case of splicing of a G.652 fiber with a G.656 fiber, the loss is 0.38 dB due to different cross-sectional areas of fibers. In this case, the splicing loss is within the permitted range for an RPC board. In the case of splicing of a G.652 fiber and a G.656 fiber, the average loss is 0.5 dB. In the case of splicing of a G.652 fiber with a G.655 or G.656 fiber whose effective section is small, a great loss is produced (as great as 2 dB). In this case, the splicing loss is out of the permitted range.

Procedure

1. None.

Result

The problem is resolved.

Reference Information

None.

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The Upgrade of Common Services to the ASON Services Fails Because a Client Service Is Available at the Network Layer

The upgrade of common services to the ASON services fails because a client service is available at the network layer.

Product

OptiX OSN 6800, OSN8800

Fault Type

ASON

Symptom

To use the ASON function on the OptiX OSN 6800 V100R003, the common services need to be upgraded to the ASON services. Select the OCh trail over which the services travel on the T2000 and then perform the upgrade. The upgrade, however, fails. This indicates that a client service is available on the OCh trail.

Cause Analysis

The OptiX OSN 6800 V100R003 supports only the optical-layer ASON solution and does not support the electrical-layer ASON solution. To ensure successful upgrade of the common services to the ASON services, all services on the OCh layer, such as client-side services, ODU1 services, and ODU2 services, must be deleted from the network layer.

Procedure

1. Choose Trail > WDM Trail Management from the Main Menu on the T2000. In the displayed window, delete the client-side services on the OCh trail. Then, perform the upgrade. The upgrade is successful.

Result

The problem is solved. That is, the upgrade is successful.

Reference Information

None.

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