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2M cable disconnection during OptiX 155662H’s 2M service interconnection with PDH of NOKIA because the 2M cable is too short

Publication Date:  2012-07-24 Views:  47 Downloads:  0
Issue Description
An exchange uses Huawei switch to interconnect with another switch with 2M (NO1 signaling) trunk. The access network at the 2M cable of Huawei switch has a built-in transmission (OptiX 155622H, Version 4. 2. 5.2), which interconnects with PDH of NOKIA after dropped from 2M halfway, and then reaches the oppisite switch through PDH transmission, that is, (CC08-OptiX155622H)--optical fiber--(OptiX155622H--2M cable--PDH)--optical fiber--(PDH--opposite switch).
After the successful interconnection, the trunk LOS indicator of Huawei switch flashes and the opposite switch also has 2M disconnection indication every half hour, but the transmission shows no alarm!
Alarm Information
There is PCM alarm at the switch side, recover the alarm, the transmission still has no alarm?
Handling Process
1. Grounding wire handling: directly short-circuit PDH and SDH and the fault stands still.
2. Clock and interface measuring: the 2M waveform, inherent frequency and output/input jitter of PDH and SDH are measured to be up to standard.
3. To self loop segment by segment repeatedly for two days to find that, at the interconnection point, the fault remains where PDH self loops to SDH side, but disappears where SDH self loops to CC08 switch. So we are now certain the fault is from the connection point where PDH and SDH interconnect.
4. Both 2M cable and 2M jumper at the interconnection point are measured to be normal. Finally, replace 2M line for a try, the fault disappears and 2M interconnects stably.
5. After some analysis, the impedance of the replaced 2M line turns out to be of 14?, while that of the 2M line before replacement is 6?, thus we can conclude that the signal interference is caused by the too-short 2M line.
Root Cause
The following factors are responsible for the unsuccessful interconnection between transmission and PDH.
1. The grounding wire: the screen layer of 2M line does not ground or the two devices do not co-ground.
2. The clock: the clock does not synchronize or PDH cannot accept the pointer adjustment of SDH.
3. The non-standard interface: 2M interface isn’t up to G703 standard: the inherent frequency of 2MBITS signal waveform has deviations.