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Packet Drop caused by the Ethernet Port Working Mode Mismatch

Publication Date:  2012-07-25 Views:  132 Downloads:  0

Issue Description

One new hop of Hybrid Microwave link works at a specific mode of 56MHZ and 128QAM which provides a bandwidth of 313M for the Microwave link.

After the local commissioning and service configuration, the workers tested the link by Ping, and it worked normally. But on the other day the customers responded that the data service speed on this link ran very slow which was not like the available 313Mbits/s bandwidth.

Alarm Information

Check the alarms. No alarms concerned.

Handling Process

1. Both the customer side equipment and RTN equipment are new ones, the hardware fault possibility is very slight, we can firstly exclude this reason.
2. Check the Microwave link performance, such as the received power, bit errors. All the performance is within the normal range.
3. Check the Hybrid Link configuration, query the current working mode, it is match the planned value, 56MHz, 128QAM, and the available bandwidth is 313Mbits/s.
4. Check the QoS configruation, and no bandwidth limitation.
5. Use the Ethernet tester Smartbits, got the throughput is correctly corresponding to the current bandwidth, so all the reason above can be definetly excluded.
6. Made a further check from end to end, and we finally focused the problem on the Ethernet Port of EM6F. We queried the working mode of the port from the RTN side, the result is 100M-Full Duplex Mode, however, on the customers' data equipment, the interconneted ethernet port is Auto-negotiation Mode. After we modified the RTN ethernet port's working mode to be Auto-negotiation, and the problem was removed.

Root Cause

1. Hardware fault from the customer side.
2. Microwave link performance degraded.
3. Incorrect configuration.


1. According to the auto negotiation of the ethernet port, if one side works at the auto-negotiation and the other side works at a specific mode(100M, full duplex as an example) the auto-negotiation end will finally work at the Half-duplex mode, which makes the packet lost.
2. During the data service configuration, ethernet ports on the two ends must be the same.