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This section is the key knowledge. Learning this knowledge is very helpful for troubleshooting SDH network alarms in the future. Therefore, it needs us to master.
Part 5: SDH Trail Hierarchies and Overhead Applications
1. For SDH path hierarchy, we need to know the relationship between them, including and included.
2. TU_AIS Generation Process：
3. Higher-order bit errors cause lower-order bit errors, but lower-order bit errors do not.
4. LCK insertion takes precedence over AIS insertion. That is if LCK insertion is configured and the conditions for automatic AIS insertion are met, LCK insertion is performed.
5. During service configuration, multiple timeslot modes are available. Huawei uses the byte interleaving mode.
6. The following alarms can trigger TU-AIS: AU-LOP, R-LOS, HP-TIM, B2-EXC.
8. Alarms that trigger AU-AIS include R-LOS, MS-AIS, and B2-EXC.
9. When a bit error is detected in the B2 byte, the peer end reports MS-FEBBE.
10. The AU-LOP alarm does not trigger the AU-AIS alarm.
11. The number of error blocks on each VC-4 path is detected by the B3 at the receiving end. At the same time, the information is sent back to the transmitting end through the G1 byte (b1-b4). The HP-REI and HP-FEBBE alarms are reported at the transmit end.
13. By default, when the number of B2 bit errors exceeds the threshold of 0.001, the B2-EXC alarm is reported.
14. When the J1 byte does not match, the HP-TIM alarm is reported and services may be interrupted.
Part 5: PCM Technology
1. PCM: pulse code modulation. It is used to convert analog signals into digital signals.
2. Workflow of PCM: A new signal generated by sampling, quantizing, and encoding continuously changing analog signals is called a digital signal.
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