3com Switch  giving problem

Posted on 2003-12-01
Last Modified: 2012-06-27
Hi all..

I got a 3COM 16 Port 10/100 Mbps swith 3 days before. In my network I have machines installed with 100Mbps and 10Mbps cards. I tried to access my netware server from a client which is installed with 100Mbps RTL8139 card. In windows/Dos both operating system I am unable to access the server. I suspect the cable first. but with the same card and cable I accessed the server via a 8 port 10 Mbps hub. That time the card was worked in half duplex/10Mbps mode.

What's the problem with my switch..? I connected two machines installed with windows 98 ,100 Mbps card in the swith as a peer to peer network. In that network also when I try to copy files from one machine to another, It 's copied the files very slowly...

Is there any problem in the UTP cable crimping..? Is it necessary to crimp all the cables in side the RJ45 Jack..?
Question by:shanraj
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Expert Comment

ID: 9852495
Try configuring the switch for the specfic speed and duplex you want rather than letting the autosense do the job.  Often that can cause you grief.

All other things being equal, if the switch is behaving badly, and you've tested/replaced all the other cables and cards, it's probably a fault in the switch.
LVL 35

Expert Comment

ID: 9856644
You also might want to set it to specify half-duplex rather than full-duplex.

Not that it's a BAD thing, but I have experienced that different vendors' 100Mbit Ethernet equipment won't necessarily work well in full-duplex.  I  agree with Robing66066 that autosense can cause lots of grief too.

Try going into the NIC properties and specifying bitrate and half-duplex.  I don't think it would be the switch.

Your question about crimping cable ends concerns me though.   Are you making your own patch cables?  Do you have non-standard, non-certified patch cables?

In order to get a "clean" 100-base-T connection, you need to make sure the pinouts are correct for Cat5, including color codes.  A straight-through patch cable MIGHT "work" but is likely to be a problem in a fast Ethernet connection.

You need to observe the specification for UTP Cat5/5e/6 compliance to be confident that crosstalk isn't part of the problem.  There are reasons for the specified pinouts, not the least of which is crosstalk.  It MUST be observed explicitly, because the number of twists per inch in each cable pair, the way the cable pairs are twisted amongst each other, and how close the twists go before the RJ45 termination all factor in to Cat5/5e/6 compliance, to maximize bandwidth and minimize crosstalk.

If you make your own patch cables, please be careful to observe the Cat5 spec.

If you do NOT make your own patch cables, and you have some non-standard ones, then that could well be your problem here.  Replace whatever you have in the circuit that cannot be verified as meeting the Cat5 spec, and see if that clears up the problem.
LVL 35

Expert Comment

ID: 9856664
Just because a cable will work with 10-base-T does NOT mean it will work with 100-base-T and DEFINITELY does not mean it will work with 100-base-4 or 1000-base-T.  Patch cables and UTP cable runs are not simple electrical connections where you have to make sure termination A connects to termination A on the other end, B-to-B, C-to-C, etc. This is not simple 20-ga. DC wiring - this is communications cable and must meet the spec or it will NOT be likely to work well, if at all, depending on your devices, length of run, other flaws like running too close to an EM source like a fluorescent ballast or an electric motor, or having a long, close parallel run to an AC power cable.

10-base-T was much more forgiving of these factors.  Anything past 10-base-T is SO reliant on meeting the spec that your problem could be entirely with the copper between the NIC and the switch.
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Author Comment

ID: 9861489
Hi guys....

Robing66066 asking me to configure the switch.. but how to do it..? it's a 3Com Office connect dual speed 16 port switch.

Today I got some improvement by shineon's comments... I changed my NIC's speed to 10Mbps half duplex and now I can access my server. 10 Mbps full duplex also working. 100 Mbps half/full both are not working. I formed a peer to peer network by connecting only three machines in the switch. Now I can ping between machines. but file sharing is very slow. Even a 10K file takes 15Mins.... Often the machine gets hang.
LVL 35

Expert Comment

ID: 9862166
As far as I know, the Office Connect line of products doesn't have managed switches, so there shouldn't be any configuration.

Have you checked your cables to make sure they are wired correctly?  Is your cabling Cat5 or better?  Cat3 is a crapshoot in getting 100mbit Ethernet.

If you are using certified Cat5 patch cables or better, and your wiring infrastructure (patch panels, wall jacks, etc) has been certified for cat5 or better, you should have no problems with half-duplex 100-base-T.
LVL 35

Expert Comment

ID: 9862202
You did mention crimping all the cables in the RJ45 jack.

For a good Cat5 connection you need to have all 8 wires connected, in a straight-through fashion (both ends wired the same way,) with the following color-to-pin scheme, looking left-to-right from the contact side of the connector, NOT the clip side:


LVL 35

Accepted Solution

ShineOn earned 125 total points
ID: 9862272
This diagram shows what I mean by left-to-right:

     1 2 3 4 5 6 7 8
   | | | | | | | | | |
   | | | | | | | | | |
   |                     |
   |                     |
   |                     |
   |   _________  |
   |  |________|  |
   |                     |
          |       |
          |       |

Author Comment

ID: 9876183
The machine which is not working in 100Mbps full or half duplex mode is a slow pentium 100 Mhz. Is there any link between the processor speed and NIC's speed..? This particular machine is only working in 10Mbps speed only. The patch cables are ok as I confirmed with shineon's diagram....

LVL 35

Expert Comment

ID: 9878099
It could be.  What is the NIC model?  Is it PCI?  Is it in a slot that is sharing an interrupt with, say, your video controller or disk controller? (older Pentiums that have PCI, often had PCI "bus master" slots and "shared-interrupt" PCI slots)

It could just be that the bus speed won't handle the bandwidth, depending on what that bus is.  The link capacity is affected more by the bus speed than the processor speed, and you should avoid "shared interrupt" slots.

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