What are the best practices and standards for SDH pointer error management and reporting?

1 Pointer error types

There are three main types of pointer errors in SDH: positive justification events (PJE), negative justification events (NJE), and new data flag (NDF) errors. PJE and NJE occur when the pointer value changes to compensate for the frequency difference between the incoming and outgoing signals. PJE means that the pointer value is increased by one, indicating that one extra byte is inserted into the payload. NJE means that the pointer value is decreased by one, indicating that one byte is skipped from the payload. NDF errors occur when the pointer value is not valid, indicating that the pointer is corrupted or misaligned.

2 Pointer error impacts

Pointer errors can affect the performance and quality of the SDH transmission in various ways. For example, PJE and NJE can cause payload slips, which are disruptions in the data flow that result in lost or duplicated bytes. Payload slips can degrade the quality of voice, video, and data services, and may cause synchronization loss, frame loss, or bit errors. NDF errors can cause pointer interpretation errors, which are failures to correctly identify the payload boundaries and content. Pointer interpretation errors can lead to payload mismatch, payload misalignment, or loss of pointer.

3 Pointer error detection

The SDH standard defines several mechanisms for detecting pointer errors and reporting them to the network management system. The most common ones are the pointer action indicator (PAI), the pointer justification indicator (PJI), and the pointer action event counter (PAEC). PAI is a bit in the overhead that indicates whether the pointer value is valid or not. PJI is a bit in the overhead that indicates whether the pointer value has changed or not. PAEC is a counter in the overhead that increments by one for each PJE or NJE occurrence.

4 Pointer error correction

The SDH standard also defines several mechanisms for correcting pointer errors and restoring the transmission quality. The most common ones are the pointer action function (PAF), the pointer justification function (PJF), and the pointer interpretation function (PIF). PAF is a function that adjusts the pointer value according to the PAI and PJI bits. PJF is a function that inserts or deletes bytes from the payload according to the PJE or NJE events. PIF is a function that identifies and aligns the payload according to the pointer value.

5 Pointer error prevention

The best way to prevent pointer errors is to ensure that the frequency and phase of the incoming and outgoing signals are matched as closely as possible. This can be achieved by using high-quality clocks, frequency converters, and phase-locked loops. Additionally, it is important to monitor and maintain the optical power, signal-to-noise ratio, and bit error rate of the transmission, as these factors can affect the integrity and stability of the pointers.

6 Pointer error troubleshooting

If pointer errors occur, it is essential to identify and isolate the source and location of the problem. This can be done by using network management tools, test equipment, and performance monitoring indicators. To troubleshoot pointer errors, you should check the PAI, PJI, and PAEC bits and counters for any anomalies or alarms. Additionally, you should examine the payload type indicator (PTI) and the trail trace identifier (TTI) for any mismatch or loss of signal. Furthermore, look at the optical power, signal-to-noise ratio, and bit error rate for any degradation or impairment. Additionally, you should check the clock source, frequency, and phase for any drift or jitter. Finally, make sure to inspect the fiber connections, splices, and connectors for any damage or contamination.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?