The digital diagnosis of optical modules allows the switch to see the module status in real time. However, if the readings and thresholds are inconsistently understood, normal modules will be misjudged as faults. This article explains the DDM threshold system clearly item by item.
The threshold is written in the chip and is divided into two levels: warning and alarm.
DDM monitors five items according to the SFF-8472 specification: receive optical power, transmit optical power, laser bias current, case temperature and supply voltage. Each item has four warning and alarm thresholds, high and low, in the EEPROM alarm area. The switch compares the real-time readings with them before deciding whether to log them. When writing code, the alarm area is written into the template of the target brand along with the identification area. If only the identification area is written and the alarm area is missed, the recognition will be normal but the readings will continue to be false alarms.
Interpretation experience value of each monitoring item
- Receiving and receiving light power: 10G single-mode LR light emission is usually in the range of -1 to -8dBm. Bit errors begin to occur when the reception is lower than the overload point. The threshold is subject to the module manual;
- Bias current: slowly rises as the device ages. Short-term sharp increases are related to high temperature or drive abnormalities;
- Shell temperature: Exceeding 70°C for a long time will accelerate aging. Blockage of the air inlet and outlet of the cabinet is the most common cause;
- Supply voltage: When it deviates from the nominal value by more than 5%, check the device power supply first instead of replacing the module directly.
Use baseline readings instead of absolute value judgments
It is recommended to record the initial DDM reading when the link is opened as a baseline, and compare subsequent alarms to the baseline to see the trend: a single warning can be observed first, and the same port has two consecutive alarms or the readings continue to deteriorate before handling it. The processing sequence is generally to clean the end face, check jumpers, review the threshold pattern, and finally determine the module itself. Use of short-distance links in the computer roomSFP+ 10G multi-mode dual-fiber optical moduleWhen receiving abnormal readings, first check if the end face is dirty. Most problems can be recovered after cleaning.
EB-LINK records actual DDM values one by one before shipment and provides them with the goods. If you need to compare threshold settings or interpret on-site alarm logs, please call 0755-83179002.