how switches work - collision-free / full-duplex

Hi,

I have a question about ethernet switches on full duplex "collision- free" LANs.

What if there are multiple nodes sending to the same segment/port, how does the switch handle that? I would think it could only let through one of the frames.

I guess that's not really considered a "collision" since one does get through. Is that right?

How do the other nodes recover from that? In full-duplex mode does Ethernet just not do any resends and let higher layers worry about it?

It seems like the switch could just tell a little fib and say to the nodes that sent the ones that didn't get through that a collision occured, so Ethernet could handle the resend. Maybe that doesn't make sense, but otherwise it just seems like you would have to wait for destination node to tell you that a packet has been lost and that would take more time.

I was just wondering about how this actually works, and I would appreciate it if some one could clear this up, I would appreciate it.

-d

Reply to
Doug Davis
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The switch actually has buffers to queue up the packets for a given port. When more than 1 sender tries to send packets to the same receiver, the switch buffers the packets while the port is busy. Of course, if too many packets are sent to the same port, the buffers could be exhausted and packets will be lost.

No, that wouldn't be considered a collision.

Except at the lowest level, ethernet always lets the higher layers worry about resending lost packets.

There are some flow control mechanisms for ethernet, but I am not too familiar with their implementation.

The basic answer to your question is that switches have buffers to queue packets up until it can send them out their target port(s). Hope that helped?

Patrick ========= For LAN/WAN Protocol Analysis, check out PacketView Pro! ========= Patrick Klos Email: snipped-for-privacy@klos.com Klos Technologies, Inc. Web:

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Reply to
Patrick Klos

yes. that helps, thanks.

Reply to
Doug Davis

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