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signal polarity reverse between X.21 to E1 interconnection

Publication Date:  2012-07-25 Views:  165 Downloads:  0
Issue Description
customer attemptted to test  X.21 interface of  M100 NTE via PFA35   as the following topology.

  found on both  side( x.21 for  Metro 100 NTE and E1 for OSN 3500)  PFA35  reported Sync Loss.
  when they loop the PQ1 side, the  PFA35 on X.21 for Metro 100 NTE showed normal.

Alarm Information
Sync Loss.

Handling Process
reversed the signal polarity  by adjust difference wire , the service were tested OK on both sides. 

Root Cause
1.when  we loop PQ1 side,  and we sent  all 1 signal ,the PFA35 on X.21 side was ok;

2.when we cut this loop, we received all 0 signal alarm  on PFA35 for X.21 side. when loop was cut , T-ALOS would be reported ,and E1-AIS would be inserted,so the PFA 35 on X.21 side should receive AIS or ALL 1 alarm.

3.we used two PFA35 for test,  and Sync-loss was reported as the test before, but we modify the receive mode from Norm to Inverter of   the PFA35 on X.21 side, this test side became normal; then modifed the other PFA35 on PQ1 side, it also became normal.

that is to say ,the signal polarity reversed between X.21 and E1 interface

X.21 and E1 interconnection application scene was not declared by Metro 100NTE , so we suggest to solve this issue by 3-rd polarity reversed  adapter or manually  reverse the polarity  of the difference wire.