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OSN3500When the clocksignal is passed through multiple network elements, it may generate certain frequency deviation and drift, resulting in thedeterioration ofthe clocksignalpassed to the downstream network elements.To avoidclocksignal degradation, a 2M phase-locked source should be set to optimizethe clocksignal. For OptiX OSN devices, the 2M phase-locked source external source attribute can also be set.In complex clock networks, there may be some unknown clock sources. Uniformly defining such clock sources as unavailable clocks prevents network elements from tracking the wrong clock sources. Meanwhile, for the clock sources assigned to the network element, the network element will automatically extract its quality information, so the quality level of the clock only needs to be defined for testing and maintenance.
Setting a 120-ohm 2MHz external clock as the clock source causes the gateway network element to report a SYN_BAD alarm for the entire network for the OptiX OSN 7500 device, and the clock jitter is exceeded for the entire network.
Product Name: OptiX OSN 3500
OptiX OSN 3500
Fault category
Pointer adjustment
Phenomenon Description
The OptiX OSN 7500 is used as a gateway network element, and after configuring a 120-ohm 2MHz external clock on it, a large number of SYN_BAD alarms are reported in the whole network, and the clock jitter of the whole network exceeds the standard.
Cause Analysis
On the OptiX OSN 7500 device, because the 120-ohm 2MHz interface has a very high reception sensitivity, environmental noise and poor grounding of the device may cause its recovery circuit to amplify the noise and generate an irregular reference clock. And when the device tracks this irregular reference clock, it generates very large clock frequency jitter. Since all other network elements on the ring are tracking the clock of the gateway network element, the SYN_BAD alarm occurs throughout the network and the clock jitter is exceeded.
Procedure
- There are two ways to resolve this issue:
- Change the external clock source from 2MHz to 2MBit.
- Using a 120-ohm to 75-ohm clock conversion cable and connector, convert the 120-ohm clock signal to a 75-ohm clock signal, and then plug it into the OptiX OSN 7500 device 75-ohm interface.
Reference Information
The effect of this high sensitivity only relates to the 120 Ohm 2MHz interface circuitry, it has no effect on the 75 Ohm interface and the 2Mbit/s clock input.
When the input is configured in 2MHz mode, do not set the external clock as the clock source if no external clock signal is connected. Otherwise, it will result in tracking the external clock source even without any source input, which will trigger the device clock jitter overrun.
The technical information in this chapter and the related SDH equipment troubleshooting procedures are provided by Shenzhen Optical Transmission Network Technology Co. Huawei SDH optical transmission equipment, SDH transmission equipment sales phone: 13430988088 Welcome to call!
