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How an Ethernet switch creates a collision domain on each port?

 

 

Hi , 

How an  Ethernet switch creates a collision domain on each port?

 

Thanks 

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Super Bronze

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Posting

A switch port running in half duplex is basically the same as any other two hosts running half duplex between them.  When either host transmits, each has a chance to collide with a transmission from the other host.

 

As frames between switch ports are buffered, hosts on two different ports, even if they transmit at the same time, won't directly collide.  Again, though, if port is running half duplex, host can collide with switch port retransmitting the other host's traffic.  I.e. two hosts, on two different ports, behave (practically) as if they were directly connected.  The advantage of a switch, however, is another two hosts transmitting to each other won't collide between the two pairs, as they would on a hub.  I.e. on a hub A<>B frames may collide with C<>D frames, but they shouldn't on a switch.

 

If host ports are running in full duplex, there should be no collisions at all (which would also be true with a pair of hosts on a full duplex wire between them).

 

NB: above is just for unicast when switch "knows" destination MAC's port.

Community Member

Hi Joseph Thanks for reply

Hi Joseph 

Thanks for reply 

can you brief  if port is running half duplex, how  host can collide with switch port re transmitting the other host's traffic "

Thanks 

 

Super Bronze

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Posting

Sorry, I don't think I can briefly explain half duplex Ethernet collisions. However, you should find much material on the Internet that does explain (but perhaps also not briefly).

Community Member

 Hi  Thanks again , if i

 

Hi 

 

Thanks again , if i rephrase the question  

 Why are collisions possible between a switch port set to half duplex ?

Thanks :)

 

Super Bronze

DisclaimerThe Author of this

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The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

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In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Because if both the switch port and connected host are running half duplex, if both start transmitting at about the same time, you get a collision.

Community Member

ThanksIf  there is only

Thanks

If  there is only switch port set to half duplex and  the station is set to full duplex , the switch port will always see lot of collision . so the station has to re transmit all the frames ?

 

Super Bronze

DisclaimerThe Author of this

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

That would be an incorrect configuration.  You want both to be full duplex or half duplex, not one of each.

 

If they are incorrectly mixed like that, interface will pass traffic, but besides collisions, you get other errors and very, very slow throughput.

Community Member

Hi Supportsib,Switch has port

Hi Supportsib,

Switch has port phy which are connected via classic bus or switch fabric.

You may like reading this blog

http://etherealmind.com/what-is-the-definition-of-switch-fabric/

 

 

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