Ethernet lenght and throughput

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Apr 17th, 2008
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I have a basic question.

I am having a problem with a HP switch and a Cat 3560. A 100mb uplink between them is giving very poor throughput. There are no problems in duplex/speed; STP is not running, no switching loop, no congestion, and no errors on the interfaces. The connection appears proper on both switches and stable. The only possibility I see the distance between them is large. The 3560 on 6th floor and the HP in the basement, it is like 130-150 feet. Ethernet works for 100 meter long length. A small test from a system before this lengthy cable gives 7mbps throughput in both directions, but for a system after this long length cable gives 200mbps up and 800kbps down throughput. May be the cable is of poor quality or damaged or may be some unknown compatibility issue in HP and Cisco on physical layer, signaling or impedance.

On Ethernet, is the throughput depending on length of the cable? More length less throughput, is Ethernet supposed to provide same throughput (7-10Mbps) throughout any length of a cable till 100meter?


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ciscograyaw Fri, 04/18/2008 - 10:28
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Ethernet provides the same throughput up until 100 meters, assuming the cable is made to specifications.

What sounds like has happened is this is either poor quality cable (Cat 3 maybe) or it has been terminated incorrectly (Not to 568A or 568B). I have seen a cable that was terminated with the pairs of wires on successive pins (i.e. the wire was terminated W/O, O, W/G, G, W/Bl, Bl, W/Br, Br) which would not work or not work well (although you should see errors in that case). Another bad case I saw was where it was wired for phone instead of data (so the wire was terminated something like W/Br, G, W/O, Bl, W/Bl, O, W/G, Br) and didn't work at all.

For reference, a proper termination should be W/O, O, W/Gr, Bl, W/Bl, Gr, W/Br, Br for 568B OR W/G, G, W/O, Bl, W/Bl, O, W/Br, Br for 568A - any other arrangement is not to spec and will likely cause problems.

(W/O = White with Orange, O = Orange, W/Gr = White with Green, Bl = Blue, W/Bl = White with Blue, Gr = Green, W/Br = White with Brown, Br = Brown)


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