Cat 5 cable problem

[Martyuk39]

I had a broadband problem and had to move my master socket to the front of the house. So that's where I plug in my router. The person who identified and fixed the problem was a telephone engineer. I got him to lay 3 network cables under the floorboards to my workstation area for a small fee. I say small fee - it was 90 of our English Pounds. That's currently about 5 dollars I think. He laid the cable then crimped the ends.

Anyway, I tested them all on my desktop, and connectivity and particularly download speeds were great. That's got an Nvidia nForce networking controller. Tried one in my Dell XPS laptop, I think with an Intel chipset, and that was fine too.

I've just been playing about with my little mini-itx boxes with a Via chipset (Via Rhine II Ethernet controller) and they can't connect to the router.

I've tried a conventional off the shelf cable and that's fine. So it's definitely these cables. I'm just surprised that they work with some systems and not others.

As I look at the network port on the back of a mini-itx box (I've tried several motherboards by the way), the bottom (or the right, depending on your perspective) of the 2 lights flashes constantly. When a good cable is plugged in, it's on constantly. Which I think is what I would expect.

I'd appreciate some opinions as to what is most likely wrong. Obviously it's a cable issue, but why work on some systems and not others?

Thanks
Martin

 

[ScottMac]

Verify that the Ethernet port is set for 100Meg, full duplex at both ends. If the speeds are auto selected, then check the status ... maybe try hard setting them. Duplex mismatch (one side half, the other full) is fairly common and what you describe fits the bill.

It doesn't *have* to be 100/full; it can be anything, as long as it agrees at both ends.

 

[Martyuk39]

The nail can consider itself hit on the head.

Changed the connection type to 10BaseT Full Duplex and it connects. Also 10BaseT Half Duplex works. No flavour of 100BaseT, nor auto-negotiation works.

So my next question - is this down to the network cable being not quite right? Given the fact that a commercially bought cable works on auto...

Thanks for your help

Martin

 

[kevnich2]

Originally posted by: Martyuk39
The nail can consider itself hit on the head.

Changed the connection type to 10BaseT Full Duplex and it connects. Also 10BaseT Half Duplex works. No flavour of 100BaseT, nor auto-negotiation works.

So my next question - is this down to the network cable being not quite right? Given the fact that a commercially bought cable works on auto...

Thanks for your help

Martin

Well this is why you never run cable and then crimp on ends, always punch them down to a jack and then plug in standard bought patch cables. Problem solved

 

[ScottMac]

Marty:

It sounds like the ends were crimped with a pair ordering of {1pair2}{3pair4}{5pair6}{7pair8} ... it doesn't matter what colors are where for this representation, it's ALWAYS wrong. Ethernet and fast ethernet use pins 1&2, 3&6 .. if you look at the {pair} layout above, you'll see that when you use that pair ordering, pin 3 goes in one color, and pin 6 goes in another (i.e., it's not a pair that's twisted to itself). That is significant, because that how Unshielded twisted pair reduces common mode noise and crosstalk.

The correct pair ordering, according to EIA/TIA 568 spec is {1orange-white|Orange2}{3green-white|blue4}{5blue-white|green6}{7brown-white|brown8}
Above is per 568b spec, the 568a spec exchanges the orange and green pair in an exact position swap. Either is fine and acceptable, but they should match at both ends. A crssover cable pins out like 568a at one end, and 568b at the other.

You'll notice in the above, that the green pair conductors (pins 3&6) are now a pair and fight crosstalk and common-mode noise like they are supposed to.

The symptom you described in the second post (works slow, or at half duplex) is a classic symptom of a split pair on pins 3&6, and probably the most common misconfiguration by folks that figure "wire is wire." Also note that up to Cat5, colors are significant in addition to position. At cat5e and above, colors are less significant, but you should still adhere to the spec (so you don't have to remember how you pinned out each connector, you can just Google for the spec)

There are other specifications as well, like having no more than 1/2" of conductors external to the sheath, no more than 1/2" untwisted, minimum bend radius, pulling tension ....

BTW: GigE uses all four pair to transmit and receive, in both directions concurrently ... some interesting magic there.

Good Luck

 

[Martyuk39]

Thanks for all your help. I've passed on the comments to the engineer who's coming back next week.

Martin

 

[torsec7g]

You should also look into getting a cheap $10 cable tester from eBay. Whenever I install any kind of cabling, (i.e Cat5e, RG6, etc.), I always use a tester to verify it.