4A0-265 Nokia Optical Diagnostics and Troubleshooting Exam Questions and Answers

When troubleshooting possible generic fiber cuts, the recommended first step is to review alarms at nodes where power loss occurs. This can help identify the location and extent of the fiber cut and the affected services. The next recommended step is to perform network power traces to attempt to determine the point of power loss. Network power traces are graphical representations of the optical power levels along a span or a path. They can be used to compare the measured power levels with the expected power levels and to pinpoint any significant deviations or drops that indicate a fiber cut. The other options are incorrect because they either do not help locate the fiber cut or are not as effective as network power traces. References: Nokia Optical Diagnostics and Troubleshooting Course, OAM and Diagnostics Guide

The recommended order for the troubleshooting steps is B, as follows:

• Retrieve the channel power trace. This step is useful to identify the affected channel and its power level, as well as to check if there are any fluctuations or anomalies in the power trace that could indicate a channel absent issue1.
• Retrieve the cross-connection (XC) details and see what Wave Keys should be present. This step is necessary to verify which Wave Keys are expected to be present on the node, card, and port based on the XC configuration2. Wave Keys are unique identifiers for wavelength tracking that are encoded by Optical Transponders (OTs) into each service wavelength direction3.
• Go to the suspected troubled node / card / port and look at Wave Keys (in / out). This step is helpful to compare the observed Wave Keys with the expected Wave Keys, and to locate the source of the problem. If a Wave Key is missing or mismatched, it means that there is a channel absent issue on that node, card, or port4.
• Check observed Wave Keys against expected Wave Keys. This step is the final solution to resolve the issue and restore the normal operation of the node. The observed Wave Keys should match the expected Wave Keys based on the XC configuration. If not, the XC configuration should be corrected or the faulty node, card, or port should be replaced5. References : Nokia Optical Diagnostics and Troubleshooting Course | Nokia, Optical User Guide - Nokia, Alcatel-Lucent 1830 PSS-8 and PSS-16 Photonic Service Switch

On a bidirectional optical amplifier configuration, the Wavelength Tracker detection points are the LINE and SIG interfaces. The Wavelength Tracker is a feature that monitors the wavelength of each channel on the optical amplifier and provides feedback to the control system. The Wavelength Tracker can detect wavelength drifts, channel failures, or channel additions or removals on both directions of the optical amplifier. The LINE interface is the input/output port for the optical line signal, while the SIG interface is the input/output port for the optical signal from/to the transponder. The other options are incorrect because the LINEOUT and SIGOUT interfaces are not Wavelength Tracker detection points, and an optical amplifier has Wavelength Tracker detection points. References: Nokia Optical Diagnostics and Troubleshooting Course, OAM and Diagnostics Guide

The command show wavekey wtsource power displays a list of the expected and measured output power for the channels whose admin state is up. This command is useful to monitor the power levels of the channels that are encoded with Wave Keys, which are unique identifiers for wavelength tracking. The command output shows the channel number, wavelength, Wave Key ID, Wave Key Code, expected output power, measured output power, and power difference for each channel1. The command can be used on both OTs and amplifiers that support WT capability2. References : Nokia Optical Diagnostics and Troubleshooting Course | Nokia, Optical User Guide - Nokia

Performance Measurement (PM) is a feature that collects and reports various statistics related to the performance of an optical network element. PM data can be retrieved at different levels, such as Optical Channel (OCh), Optical Channel Data Unit (ODU), Optical Channel Transport Unit (OTU), and Ethernet. An Optical Transponder (OT) is a device that converts an electrical signal into an optical signal and vice versa. An OT has two interfaces: a client interface and a line interface. The client interface connects to the service provider network, while the line interface connects to the optical transport network. At the OT line interface, PM data can be retrieved for the OCh, ODU, OTU, and Digital Wrapper (DW) levels. The DW is a layer that encapsulates the client signal and provides overhead information for monitoring and management purposes. Ethernet collision counters are not typically retrieved at the OT line interface, as they are related to the Ethernet level, which is usually monitored at the client interface. References: Nokia Optical Diagnostics and Troubleshooting Course, Nokia 1830 PSS-32 and PSS-16 Photonic Service Switch Release 8.0 Performance Monitoring Reference Guide

The statement that is false is that no OSC-related alarms will raise on the local node. OSC stands for Optical Supervisory Channel, which is a dedicated wavelength used for out-of-band signaling and management of optical network elements. If a node is experiencing a little unexpected attenuation over the OSC transmit direction, it means that the OSC signal is weaker than expected when it reaches the adjacent node. This can cause a “Data Link Down” alarm to raise on the adjacent node, indicating that the OSC communication link is broken or degraded. However, this can also cause an “OSC Power Low” alarm to raise on the local node, indicating that the OSC transmit power is below the threshold. Therefore, there will be OSC-related alarms on both nodes. The other statements are true because a power adjustment action will fail on the local node due to insufficient OSC power, and traffic will pass between the nodes as long as there is no other issue affecting the data channels. References: Nokia Optical Diagnostics and Troubleshooting Course, Optical Supervisory Channel Module product data sheet

A “Loss too low” message can be displayed after a power adjustment has been provided if there is an issue with unstable optical power levels. Unstable optical power levels can be caused by various factors, such as environmental conditions, fiber aging, equipment malfunction, or configuration errors. Unstable optical power levels can affect the accuracy and reliability of the power adjustment process, which relies on measuring the optical loss between two points in the network. A “Loss too low” message means that the measured optical loss is lower than the expected value, which can indicate a problem with the optical signal quality or integrity. The other issues are incorrect because they either cause a different type of message or do not affect the power adjustment process. References: Nokia Optical Diagnostics and Troubleshooting Course, OAM and Diagnostics Guide

The exhibit shows a diagram of a network of nodes and edges, where a single directional fiber cut is occurring between two amplifiers in bidirectional configuration. The node that will report a “LD Input LOS” alarm is node B only. A “LD Input LOS” alarm indicates that the input signal to the laser diode (LD) of an amplifier is lost or below the threshold3. In this case, node B will not receive any signal from node A due to the fiber cut, and will generate this alarm. Node A will not report this alarm, because it can still receive a signal from node C through the other fiber. Node C will not report this alarm either, because it is not directly affected by the fiber cut between node A and node B. References : Nokia Optical Diagnostics and Troubleshooting Course | Nokia, Troubleshooting Guide for Synchronous Digital Hierarchy - Cisco

The command show wavekey wtmonitor 1/6/LINE summary displays a list of all channels detected against the selected interface (in and out); it shows if a Wave Keys pair is expected, if a Wave Keys pair is received, and if the received Wave Keys pair is unexpected. A Wave Keys pair is a pair of unique identifiers that are transmitted along with an optical channel to provide channel identification and monitoring functions. The command can be used to verify the presence and correctness of the Wave Keys pairs on an interface and to detect any mismatch or misconfiguration. The other options are incorrect because they either describe a different command or provide incorrect information. References: Nokia Optical Diagnostics and Troubleshooting Course, OAM and Diagnostics Guide