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Folks, I am having a tough time figuring this out: in a full-duplex LAN segment are there any collisions to be taken care of when (i) There are only two stations connected point to point (ii) When there are multiple stations connected through a hub (ofcourse all of them would be in a different collision domain had they been connected through a switch).

Now, for (i) since they are full-duplex would mean a station can send and receive at the same time -- so these two stations should be able to send and receive at the same time to each other without any collisions, correct?

For (ii) if they are connected through hubs but are full-duplex, when exactly does collision occur?

Lastly, if multiple stations are connected to different ports of a switch, in what situations can ethernet have packet loss? I am trying to understand the recent extensions to Ethernet aka and am totally lost :(

Any clarification greatly appreciated! Thanks!

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migrated from Nov 5 '10 at 16:23

This question came from our site for professional and enthusiast programmers.

The "collision" mechanisms of older ethernet are used for flow control in newer systems. It's used as a type of back-pressure to say "ease off a bit, I'm having trouble keeping up".

In a store and forward or end-to-end style connection this is when problems are likely to occur. This is described in IEEE 802.3x, some hardware explicitly calls this flow control, but lots of kit uses the same LED to indicate both collisions and back pressure.

Packet loss can be caused by hardware failure, hardware dropping frames in normal operation (clients, or switches, typically when buffers are full), or general errors the Layer 1 parts.

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For (ii) you mention multiple computers (e.g. three or more), full duplex and a hub (not a switch). Wouldn't a collision occur if two or more stations simultaneously start to communicate with a third?

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Or even communicate with different machines. A==>B and C==>D through a hub would be a collision. Also, if I remember correctly, hubs are half-duplex, due to their nature. Not entirely certain of that last bit, though. – Jesse Nov 5 '10 at 19:10
By the nature that only one connected device can transmit across a hub at any instance does reduce its functionality to half duplex. – user48838 Nov 6 '10 at 7:39

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