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Problem: Duplex Mismatch

Ethernet duplex mismatch can occur when two ends of an Ethernet connection attempt to negotiate a full duplex connection, this can occasionally result in a situation where one device thinks the connection is full duplex and the other thinks it is half duplex. This can result in a high rate of packet loss without the high rate of jitter that would be typical of congestion.

This problem can be prevented by ensuring that the Ethernet connections are properly configured.


This problem can result in very high rates of corrupted packets which results in a high rate of packet loss, hence severe call quality degradation.


Duplex mismatch can be traced by looking at Switch and Router Ethernet statistics as it will result in high rates of FCS errors, Receive errors and Runt packets. The problem can be resolved by reconfiguring one or both network interfaces on the offending Ethernet segment.


Ethernet Switch Statistics, Network Analyzer, VQmon

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