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The delay test index of the TDG board in the OptiX OSN 6800 fails.

Publication Date:  2012-07-25 Views:  41 Downloads:  0
Issue Description
In the deployment of the OptiX OSN 6800, Agilent N2620A is used to test the Ethernet performance index of the TDG board. The delay result is 0.001366 s (1.366 ms). According to the specifications, the value should be smaller than 100 us (0.1 ms). The test result does not comply with the specifications. The customer asks Huawei engineers to give an explanation. 
Alarm Information
None. 
Handling Process
1. Huawei engineers should explain the reason of the relative large test result for the customer.
2. The delay index is for the delay occurred in the TDG board. The transmission delay in the line is excluded.
3. Connect the meter to the local TDG board and perform the signal loopback with passing the TDG board. The test result is smaller than 0.1 ms. The test passes. 
 
Root Cause
Test methods: Connect the meter to the data interface of the local TDG board. The service is sent to the remote station. Perform the inloop in the remote TDG board.
1. The test is performed with the local TDG connected to the meter and the remote loopback; therefore, the round-trip delay is actually tested. The test result should be divided by 2. After the test result 1.366 ms is divided by 2, the result does not meet the specifications.
2. Engineers check the working state of the equipment and query the equipment performance. The equipment is normal.
3. The delay results of 16 1000M Ethernet interfaces in 8 TDG boards are basically the same. Hence, the board is normal.
4. Delay description: The delay refers to the duration from A sending signals to B and B receiving signals. This index is use to evaluate the forwarding capability of the data equipment. The distance between A and B is not specified. The delay index should include the transmission time in the line.
5. The transmission speed of light in vacuum is 3*10^8 m/s, and the transmission speed in optical fiber is 2*10^8. Assume that the distance is 100 km, the transmission time is 0.5 ms.
6. In this case, the distance between the local station and the remote state is 125 km. The round-trip is 250 km. The transmission time in the line is 1.25 ms. Hence, most of the delay occurs in the line. 
 
Suggestions
1. For a data service, the delay generated in the transmission system is usually ignored during the calculation of the delay.
2. The delay index of a Huawei board refers to the delay of forwarding data packets of this board.
3. In the case of the delay index test of a data board, engineers should perform the signal loopback in the local board, instead of sending service to the opposite NE for the loopback. 
 

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