Full and half duplex.

Aug 09, 2004 2 Replies

What exactly will happen if a port configured for full duplex only tries to talk to one capable of half duplex only?



I tried taking a HP Procurve switch, connected a full duplex uplink from the



100Mb. port to the rest of my network, configured one of the 10 Mb. ports to full duplex, and connected it to a port on a Netgear 10Mb. hub, obviously half duplex. I then connected another port on the hub to a PC, and tried to access the network through this mismatched connection. Sometimes I seemed to get a reasonable connection, sometimes a very slow transfer, sometimes the liink light would come and go, and once the whole Procurve locked up, I couldn't get a link to anything, and I had to re-boot it. That surprised me somewhat. What exactly was happening? Why did the results vary, And would the problems have got worse if I had connected more devices to the hub?



One follows the CSMA/CD rule and the other does not. As a result, the FD side constantly stomps on the transmission of the HD side *OUTSIDE* of its collision detect window. This kills throughput.

You will get lots of errors due to the duplex mismatch and a slow connection.

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