Whether an SS bit mismatch in the AU pointer during WDM product interconnection causes an AU_LOP alarm

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Question:
According to SDH principles, in AU-4 and TU-3 frame structures, the SS bit of the AU pointer is fixed at 10. When Huawei SDH NE is interconnected with equipment of other vendors and receives the SS bit of a value rather than 10 from the peer end, the corresponding channel of a line board on the SDH NE reports the AU_LOP alarm. As a result, services fail to be provisioned or are interrupted. Do WDM devices have this issue?
Answer:
1. OTU boards (except OCU boards) on WDM NEs transparently transmit the SS bit and do not detect it. 2. OCU boards on WDM NEs process the SS bit. The normal value of the bit is 10. When the SS bit is set to 00, 01, or 11, an AU_AIS is inserted and services are impaired. The board does not report an alarm because it does not detect the AU_AIS signal on its WDM side. According to a test in which the test instrument is Agilent OmniBer 817 and is used to send STM-16 data, the H1 SS bit can be modified when the payload is set to Framed and Structed, and Column is set to All in the overhead setup settings. The test instrument reports an AU_AIS or PDH LOF alarm when the SS bit is set to 00, 01, or 11, and does not report alarms when the SS bit is set to 10. This issue is related to the chip processing mode. Because OCU boards use the same chip, they have this issue.

Other related questions:
Whether SS bit mismatch in AU pointers during WDM product interconnection causes an AU_LOP alarm
1. OTU boards on WDM equipment, except OCU, transparently transmit SS bits without detection. 2. OCU boards process SS bits. The SS bit should be set to 10. When the SS bit is set to 00, 01, or 11, AU_AIS is inserted and services are interrupted. In this scenario, no alarm is reported on the board (because the AU_AIS alarm is not detected on the WDM side of the board.) During a test, the Agilent OmniBer 817 meter is used to transmit STM-16 data. When the Payload option is Framed or Structed and the column in the overhead setup is set to ALL, you can change the H1 SS bit. When the SS bit is set to 00, 01, or 11, an AU_AIS, PDH, or LOF alarm is reported. When it is set to 10, no abnormality occurs. This issue is related to the chip processing mode. OCU boards use the same chip and therefore have the issue.

Reasons for pointer justification on an SDH line board
Reasons for pointer justification on an SDH line board: The reason why pointer justification occurs on an SDH line board is that NE clocks are not synchronized. When the rate (frame rate) of VC-4 is higher than that of AU-4, a negative pointer justification occurs. When the rate of VC-4 is lower than that of AU-4, a positive pointer justification occurs.

Whether bit errors cause MSP switching
Whether bit errors cause MSP switching: The prerequisites for bit errors to trigger MSP switching are as follows: SD switching is enabled, bit errors are excessive, and there is no switching whose priority is higher than that of SD switching. MSP switching priority: Clear switching > Locked switching > Forced switching >SF switching (triggered by signal failures) > SD switching (triggered by bit errors) > Manual switching > Exercise switching. For details, see MSP switching conditions.

Methods for testing optical path bit errors during the acceptance of WDM devices
1. During the system commissioning of devices in back-to-back mode, use pigtails to respectively connect the Rx and Tx ports of the TQX board on the front subrack to the Tx and Rx ports of the corresponding board on the rear subrack. 2. Connect the Rx and Tx ports of the TDX board in the rear subrack at the central site to form a loopback. 3. Connect test instruments to the TI and RO ports of the TDX board on another subrack at the central site to cover most of the paths after the 24-hour bit error test. 4. If another wavelength needs to be tested, connect multiple wavelengths according to the SDH connecting method.

Possible causes of a failure of an interconnection between WDM equipment and a router
The possible causes are as follows: Possible cause 1: The line between the WDM equipment and the data equipment is faulty. Possible cause 2: The client-side parameters of the interconnected boards on WDM products are incorrectly configured. Possible cause 3: An interconnected board is faulty.

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