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'[OT:] Serious network problem'
2004\03\28@201211 by john chung

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Hi there,

   I have the strangest problem with my network that I have been
fiddling with currently.
Here goes.

   I have a cable that is 10 meters long that would not work for some
computers at all.
The test machine is a P133 with an Intel Pro 10/100B/100+ Ethernet. Even
a newer machine
from IBM with a realtek card could not detect the network at all. The
status light on the nic
was blinking when the LONG cable was connected but there wasn't any
communication with the
local network. Couldn't even ping my local network machines. The LONG
cable was attached to
the floor's switch located in the server room. *The cable tested okay
for connectivity when using a
multimeter *

  The problem was solved when I used a shorter cable???? Can some one
explain this strange behaviour?

*I have used another cable around the same length and it worked!!!! Both
are Cat 5E cables.....*

Thanks,
John

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2004\03\28@202704 by Jake Anderson

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network environment is much more demanding than simply conducting
did you also check the cable for shorts? (ie make sure that each wire in one
end is only connected to one at the other end)

the cable might have some worn insulation or something giving it too much
capacatance or anything of a hundred things
a bad connection
not enough fish sacrificed during the creation of the cable
cable made during the Cat-3 phase of the moon not Cat-5
{Original Message removed}

2004\03\28@215404 by SM Ling

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1. Check standard short and open.
2. Check is cross and through cable and equipment matching.
3. If connection is right, likely the twist pair is wrong.  You need to have
the twisting right, else the noise-effect of long cable would become a
problem.  This caught me, once or twice.

Good luck,

Ling SM

{Quote hidden}

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2004\03\28@221310 by john chung

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SM Ling wrote:

> 1. Check standard short and open.
>
>
   Not sure what you mean here. Can you explain further? Thanks.

>2. Check is cross and through cable and equipment matching.
>
>
   Yeap the cable is matching the equipment.

>3. If connection is right, likely the twist pair is wrong.  You need to have
>the twisting right, else the noise-effect of long cable would become a
>problem.  This caught me, once or twice.
>
>
>
   The problem is that the cable is straight from the machine to the
switch.........
I am not sure whether the twist in the cable is okay or not..... How to
check for this problem?
Perhaps it is the noise but still not sure..... Maybe all cables are not
equally made even with the cat 5E stamp!

John

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2004\03\28@225252 by Anthony Toft

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>     Yeap the cable is matching the equipment.

Matching the equipment? what does that mean? Is this a self built cable?
What does each end look like? which pair goes to which pair?

>     The problem is that the cable is straight from the machine to the
> switch.........

This isn't a problem, all straight cables (not talking about the
crossover cables here) will do this.

> I am not sure whether the twist in the cable is okay or not..... How to
> check for this problem?

This is an experience things, "cat 5" or whatever not only describes the
conductors and insulators, but how each pair is twisted, around itself
and the other pairs, it's quit complicated. On the other hand I knew a
cable monkey who could feel the outside insulation and tell you what
category the twisting was.

> Perhaps it is the noise but still not sure..... Maybe all cables are not
> equally made even with the cat 5E stamp!

The twisting is _supposed_ to take care of noise (don't ask me how) the
5e stamp is only for the cable, but the connectors etc should be 5e too.

I just supe'd on an install of cat 6, where the orange pair had a
significantly higher diameter insulator, 15 boxes of various colours all
of them...

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2004\03\28@225912 by Anand Dhuru

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> 3. If connection is right, likely the twist pair is wrong.  You need to
have
> the twisting right, else the noise-effect of long cable would become a
> problem.  This caught me, once or twice.
>
> > the floor's switch located in the server room. *The cable tested okay
> > for connectivity when using a
> > multimeter *
> >

This does indeed indicate a wrong pairing. Electrically (from a DC
viewpoint) if the cable is as per specs, and yet does not work reliably, it
*must* be the pairing. Also, if you have crimped the ends yourself, make
sure the twisting is intact right upto the point the cable enters the RJ45
plug.

Regards,

Anand Dhuru



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2004\03\28@230327 by john chung

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Anthony Toft wrote:

>>    Yeap the cable is matching the equipment.
>>
>>
>
>Matching the equipment? what does that mean? Is this a self built cable?
>What does each end look like? which pair goes to which pair?
>
>
>
    The cable is self built. Exactly the same order for wire color at
both ends.

{Quote hidden}

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2004\03\28@230740 by Liam O'Hagan

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The twisting means that each cable in the pair receives the same noise, at
the receiving end the signals from both cables are combined in such a way
that where x = signal and y = noise, you get x + x + y - y = 2x...

{Original Message removed}

2004\03\28@231608 by john chung

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Wrong pairing? Do you mean the order of the wire must follow the exact
specification
of cat 5e? I always believe that all the wire electrical characteristics
are equal?

here is the order of wire for my network cable

1st jack
1)white + orange
2)orange
3)white +green
4)blue
5)blue + white
6)green
7)white + brown
8)brown

2nd jack
1)white + orange
2)orange
3)white +green
4)blue
5)blue + white
6)green
7)white + brown
8)brown



John



Anand Dhuru wrote:

{Quote hidden}

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2004\03\29@000453 by info

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part 1 2817 bytes content-type:text/plain; charset="ISO-8859-1"John,

The signals travelling in your cable are balanced in nature. Unbalanced signals (such as noise) are
cancelled at twist "nodes" in the cable. As long as the pairs of balanced signals from your
equipment is transmitted down a twisted pair (and not 2 conductors on different pairs), then the
performance should be fine)

Personally, I would adhere to the colour convention to save having to figure out which terminal
pairs connect to which twsited wire pairs.


Refer to : http://www.incentre.net/incentre/frame/ethernet.html for convention.



Kind Regards
David Huisman (CEO)
Orbit Communications Pty Ltd
Wireless Solutions that Work
Ph: +61-2-4393-3627
Fax: +61-2-4393-3685
Web: http://www.orbitcoms.com

{Original Message removed}

2004\03\29@001352 by Anand Dhuru

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Hi,

This is the connection I use in my house; its been working well for a long
time.

This is for a PC-to-PC connection, without a hub.

Connector1                                                        Connector2
     1 Orange+White 3
     2 Orange 6
     3 Blue+White 1
     4 Green+White 4
     5 Green 5
     6 Blue 2
     7 Brown+White 7
     8

    Brown

    8




Regards,

Anand Dhuru




{Original Message removed}

2004\03\29@001946 by Anand Dhuru

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Sorry, the formatting went haywire in my earlier post.

This is for a PC-to-PC connection, without a hub.

Connector1                Connector2
      1 - Orange+White - 3
      2 - Orange - 6
      3 - Blue+White - 1
      4 - Green+White - 4
      5 - Green - 5
      6 - Blue - 2
      7 - Brown+White - 7
      8 - Brown - 8

Regards,

Anand Dhuru

>
>
> {Original Message removed}

2004\03\29@003023 by Russell McMahon

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> The signals travelling in your cable are balanced in nature. Unbalanced
signals (such as noise) are
> cancelled at twist "nodes" in the cable. As long as the pairs of balanced
signals from your
> equipment is transmitted down a twisted pair (and not 2 conductors on
different pairs), then the
> performance should be fine)
>
> Personally, I would adhere to the colour convention to save having to
figure out which terminal
> pairs connect to which twsited wire pairs.
>
>
> Refer to : http://www.incentre.net/incentre/frame/ethernet.html for
convention.

I have seen commercial cables which were physically "straight through"
without the division of the second pair onto either side of the centre pair.
This causes pair splitting when connected to properly terminated equipment.
You can tell how a cable is wired by looking at the plug. If you are me then
you need a magnifying glass :-). Some plugs have very little of the wire
colours showing BUT you can (in all the many cases that I have seen) see
some indication of the colours.

Usually it's the A version in the above reference.

When the cable is "split" so the two wires of the circuit are on two
different pairs you may be exposed to the effects of resonant lengths of
cable. This MAY explain the effects you are getting. A similar result used
to occur when other than short stubs of coax were used to connect PC to
Ethernet coaxial T connections.

Best of all was including a short length of wrong impedance cable in a
coaxial ethernet installation.Guess how I know :-( .


       RM

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2004\03\30@160244 by Howard Winter

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Russell,

On Mon, 29 Mar 2004 16:28:52 +1200, Russell McMahon wrote:

> Best of all was including a short length of wrong impedance cable in a coaxial ethernet installation.Guess
how I know :-(

Ah, memories!  I remember getting a call from a secretary at our office, who said "Get here and fix this
(expletive deleted) thing before I throw it out of the window!"

Never being one to underestimate a threat like this, I headed back (from a client's) and found that
Wordperfect would take 5 minutes to load, then another 5 to open a file, etc.  It was a network wide problem
so I set to with the time-domain-reflectometer (praising the accounts department that I'd been allowed to buy
one!) and it showed some odd readings - usually you open the termination at the one end end of the 10-base-2
(50-ohm coax) and connect the TDR at the other end and it gives the length of cable to the open end of the
network segment, then you work along and as you exclude a length of cable the remaining length shown reduces
accordingly.  This didn't!  It intermitently showed a much shorter length, and it wasn't consistent from the
two ends,  so I did a "binary chop" to locate where the problem was.  I found that someone had inserted a
piece of coax they'd found in a cupboard, to add their machine to the network, and it was (I think) IBM
terminal cable: 75-ohm instead of 50.  I replaced it with some of the right stuff, and harmomy was restored.
I'd like to say that the secretary was eternally grateful and demonstrated it... but sadly not  :-(

I'm rather glad that 10-base-T (twisted pair) caught on and replaced coax - it's much easier and more reliable
to use all round.

I wonder who got custody of the TDR?

Cheers,

Howard Winter
St.Albans, England

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2004\03\30@200520 by john chung

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Thanks to all that replied to my question. I found a very resourceful
site that
would be fluke! There are plenty of resources for me to read about
networking
and cabling.

Thanks,
John Chung

Anand Dhuru wrote:

{Quote hidden}

>>{Original Message removed}

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