anyone know how a 10/100 ethernet switch works?

Forums › LAN (ethernet/Wifi/routers/Bluetooth) › anyone know how a 10/100 ethernet switch works?

jim.cox

224 posts

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#16627 19-Oct-2007 13:51

Kia ora

We've just moved to a new office, and we upgraded our network to Cat5 TP

I've set ALL the machines to 100Mbits full duplex - and they seem happy at that

But I'm not getting anything like the network throughput I expected.

Doing some big file copies afterhours (so minimal network contention) the best throughput I can get is about 9.3Mbits, and mostly its down around 3 or 4

Watching the server it appears to be spending most of its time in the system idle process. And the network loading is low.

Watching the timing of the packets I see them come in short bursts with long pauses of nothing in between.

I'm wondering if the (cheap) ethernet switch might be the cause.

It looks to me like the switch might be squirting the data at 100 and then waiting long enough to have sent the data at 10, effectively slowng the whole shooting match down to 10

How do 10/100 switches handle the different data rates ?

=mjc=
.

BartManGeek

187 posts

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#92054 23-Oct-2007 12:30

Have you tried a crossover cable connected directly between PC and server? This will eliminate the switch as a problem.

Let us know how you go,
Bart.

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pando

235 posts

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#92058 23-Oct-2007 13:26

Was my understanding that switches prefer autonegotiation.

Forcibly setting the nic's in each machine to use the top setting can have a detrimental effect on overall performance, you should leave them on the autonegotiate.

Next you should then get a TCP optimizer program, if you're using windows 2000/XP or earlier the OS is preconfigured for a 10Mbps network not a 100Mbps one.

cyril7

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#92062 23-Oct-2007 14:11

Agreed definitely let the NICs autonegotiate, however that said if they are not doing 100 duplex then there is either a cable problem or the NICs or switch are substandard.

Even the cheapest of switches use commonly available switch chip sets that are also used in better priced products. Realtek chipsets are the most common Ive found at the low end of the market, and these work very well, you should readily be able to achieve 70-80Mb/s through put of TCP traffic. I use wsttcp.exe as a simple throughput check. Remember that TCP will only achieve around 80% full throughput due to TCP overheads.

As others have suggested, get a crossover cable (although a straight through will work most autoconfiging NICs) and check the throughput with local cables and no switch, then add cable and switch back into the mix to see whats causeing the issue.

Cyril

Fraktul

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#92097 23-Oct-2007 18:14

Autonegoiate does not always work best, sometime it flaps or otherwise results in corruped frames.

If you have a decent switch and NICs they will report any CRC errors allowing you to rule out any speedmismatch, cabling issues or other problems at layer 1.

jim.cox

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#92183 24-Oct-2007 09:04

Fraktul: Autonegoiate does not always work best, sometime it flaps or otherwise results in corruped frames.

If you have a decent switch and NICs they will report any CRC errors allowing you to rule out any speedmismatch, cabling issues or other problems at layer 1.

As I say, I'm not seeing any error messages

Just the system sitting mostly idle, the network utilisation well under 25% and the throughput around 3% :(

But thankx for the hints guys. I'm planning on some afterhours testing with a a spare machine directly connected. That should confirm whether it is the switch

Cheers

Jim

=mjc=
.

=mjc=
.

kdn

203 posts

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#92201 24-Oct-2007 12:15

generally when one device is set to auto and the other is strapped to 100/full the link will run at 100mb half duplex.. if its not a managed switch that you can set the ports to run at 100 full on then change the pc back to auto auto.

Unfortunately there is no easy way to check what duplex its running at from the pc side, you can foudn out the manufacturer of the network card you are using andf see if they have a downloadable tool to tell you.

But in my experience (which is quite a lot with switches) setting oen side as static and one as auto neg usually results in half duplex which is why you ar egettign such poor performance, one way is also a cross over between the two pc's and see what sort of speed you get then.

Flamer.

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mcraenz

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#95336 15-Nov-2007 12:44

Tha's my understanding as well, when one side is set to auto and the other is satic then the autonegotation will fail and it will default to 100/half

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