Description of the problem

Please see the attached description for the detailed network diagram, Huawei OSN3500 device ring network, -----NE1-12(slot11)-------(Slot8)NE1-23(Slot11)-----(Slot8)NE1-13-------, all fibers are not directly connected through the optical fiber, and in the middle of the network, all the fibers are connected through the Siemens wavelength division equipment. All the fibers are not directly connected by fiber, but are connected by Siemens WDM equipment in the middle, and the clock of the whole network is extended SSM protocol, and NE1-23 starts to track the clock in the direction of NE1-12. Field engineers feedback that when disconnecting the fiber between NE1-12 and NE1-23, the NE1-23 clock is first inverted to the internal clock source, and then after a period of time, it is inverted to the line board in the direction of NE1-13 network elements.

Alarm Message

LTI, S1_SYN_CHANGE

Processing

1, first suspect that there are problems with the clock configuration, after the recovery of MO, analysis, the entire ring on the network elements have been opened to expand the SSM protocol, and the center of the clock ID of the network elements have been set up, and from the phenomenon of the problem, the clock source is inverted to the internal clock after 30 seconds or can be inverted to the other direction, so initially ruled out for the problem of clock configuration;

2, suspected that the middle through the Siemens WDM equipment for optical signal processing delays, but a line in the ring of other sites for testing, the clock can be immediately inverted, initially ruled out the doubt;

3, suspect that NE1-23 site cross board above the existence of faults, but after the cross inversion, the failure phenomenon remains;

4, a line of test again, and then let a line of the clock collected part of the data, through the data analysis, finally found the cause of the problem, see the description of the cause analysis section.

Root Cause

Please refer to the attached document for a detailed description

From the returned data, it can be judged that the clock situation is normal. But there are some irrationalities in the reporting of LTI alarms: LTI alarms are reported after S1SYNCCHANGE alarms; in fact, there is a fixed delay of 7-8 seconds for s1syncchange alarms. In this case, it is more accurate to look at the clknotracemode alarm.

The other important point about the cause of this problem is that: suppose a network element has two line clock sources A&B, when clock source A has a failure to invert to clock source B, and clock source A is troubleshooting, then by default there is a 5-minute recovery time, then in these 5 minutes, if clock source B has a failure, then before the end of the inversion recovery time, the clock source will not track the clock in B but will instead be inverted to the internal clock source. I heard from R&D that this mechanism is done as suggested. The problem should be caused by RLOF being reported above both clock sources for a short period of time at both ends.

Suggestion and Summary

You need to understand the difference between clock reversal and business reversal, when business reversal, as long as the standby channel, regardless of whether the reversal recovery time has arrived, will be reversed to the standby channel; while clock reversal, you need to be in the standby channel's reversal recovery time expires, will be reversed to the standby channel above.

The related technical information in this chapter and the SDH equipment troubleshooting process are collected and organized by Shenzhen Optical Transmission Network Technology Company Limited ( www.opticaltrans.com), please retain! Our company specializes in Huawei SDH optical transmission equipment, SDH transmission equipment sales.