Duplex mismatch issue

Answered Question
Jul 5th, 2007
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Here is the scenario:

There is a PC connected to a switch, both are set to 100-Full. That switch also is connected to a server. The server is set to 100-Full and the port on the switch connecting the server is set to 100-Half.


Ok obviously there is a duplex mismatch here but this is what confuses me. When uploading files to the server it is very slow. When downloading files from the server it is normal speed as if there were no mismatched duplex.


From my understanding this should not be happening, both uploading and downloading should be slow.


Can someone please enlighten me as to why this is so?

Correct Answer by sundar.palaniappan about 9 years 8 months ago

Kevin,


Good question!! But then you have the window size in TCP where the sender can send multiple packets without being acknowledged by the recipient till the window size cap is reached.


HTH


Sundar

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sundar.palaniappan Thu, 07/05/2007 - 11:32
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The behavior is consistent with half duplex setting where the switch is probably deferring transmission of frames to avoid collisions when there are frames already out there on the wire. On the other hand the server sees the connection as full duplex and doesn't defer transmission and hence, download from the server is quicker.


HTH


Sundar

kevinlowery Thu, 07/05/2007 - 11:43
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This is what I thought might be the case accept that I was under the impression that regardless of whether you are uploading or downloading there should be two-way communication when transfering because TCP is a reliable protocol. With this in mind I am lead to beleive that if downloading is interupted then uploading would as well because the server would have to wait for Ack packets.


Am I wrong in my understanding, or is the wait for ack packets so miniscule that it doesn't effect the transfer speed?


Thanks,

Kevin

Correct Answer
sundar.palaniappan Thu, 07/05/2007 - 11:50
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Kevin,


Good question!! But then you have the window size in TCP where the sender can send multiple packets without being acknowledged by the recipient till the window size cap is reached.


HTH


Sundar

srimural Thu, 07/05/2007 - 14:01
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Hi,

I would like to add something.


if autonegotiation fails in cisco the default settings for the link are


10Mbps/100Mbps = half duplex

1000Mbps = Full duplex.


Please find the following link

http://www.cisco.com/warp/public/473/46.html

I hope it helps.


Thanks and Regards,


Srinath.M

Cable&Wireless


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