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Kn1ght
Frequent Member
Joined: Nov 09, 2003
Posts: 163
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 Posted: Tue Jan 27, 2004 9:29 pm Post subject: Cabling concepts |
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I was reading your site about cable. Cat 5 Cat 3 exc.
You are talking about twisting, but I didn't get the concept behind twisting. Why the more twists the faster the cable?
I'm stupid I know... But hey I'm at this site so I'm trying to get un-stupid. 
Knight the confused. |
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tfs
Retired Team Member
Joined: Jul 22, 2003
Posts: 521
Location: Orange County, California
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| Posted: Tue Jan 27, 2004 10:43 pm Post subject: |
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The twisting is to prevent crosstalk between pairs of wires.
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In fact, one of the main differences between Cat5 and Cat3 cable is avoidance of crosstalk and other interference. Cat5 is much more tightly twisted than Cat3, and the twists are more tightly controlled to be uniform in distance
Crosstalk is an issue whereby signals traveling along one pair of wires interfere with those on another. The more twists per inch of cabling, the less susceptible the wiring is to both EMI and crosstalk. |
The above is from a couple of articles.
Here is a page from this site that talks about it under network/cabling - http://www.firewall.cx/cabling_utp.php
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Tom |
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Kn1ght
Frequent Member
Joined: Nov 09, 2003
Posts: 163
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| Posted: Wed Jan 28, 2004 12:34 am Post subject: |
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| could you repost? Because your link isn't working and I can't find that sentance anywhere! |
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Chris
Founder & Senior Editor
Joined: May 25, 2002
Posts: 1231
Location: Thessaloniki, Greece
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| Posted: Wed Jan 28, 2004 12:44 am Post subject: |
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There was an unwanted dot '.' at the end of the link tfs posted. I've fixed the link so you can now click on it and go directly to the page!
Cheers,
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Chris Partsenidis.
Founder & Senior Editor
http://www.firewall.cx |
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Kn1ght
Frequent Member
Joined: Nov 09, 2003
Posts: 163
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| Posted: Wed Jan 28, 2004 1:46 am Post subject: |
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| what is EMI? |
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tfs
Retired Team Member
Joined: Jul 22, 2003
Posts: 521
Location: Orange County, California
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| Posted: Wed Jan 28, 2004 3:54 am Post subject: |
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There are 2 types of electrical interference:
1) EMI - Electomagnetic Interference
2) RFI - Radio Frequency Interference
This is interference by electrical motors, power cables, flourescent lights, transformers, radio transmitters etc.
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Tom |
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Neon
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Joined: Oct 28, 2003
Posts: 101
Location: Victoria, Australia
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| Posted: Wed Jan 28, 2004 6:41 am Post subject: |
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I'll just add my 2 cents here...
As tfs quoted “the more twists per inch of cabling, the less susceptible the wiring is to EMI and crosstalk...” this is important why you should NEVER (and I know a lot of people do) stretch the cable. If it isn’t long enough make another cable (You can use the cable somewhere else), the more you stretch the cable the more it untwists, therefore eliminating the purpose of Twisted Pair cable! Thus making it susceptible to EMI and crosstalk (slowing your speeds of course)
Just thought I would like to add that in cause all too often at gaming LANs I see people jerking their cable around the place to make their cable reach their computers… Not a good thing to do |
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sahirh
Associate Editor & Security Advisor
Joined: Aug 14, 2003
Posts: 1699
Location: Mumbai, India.
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| Posted: Wed Jan 28, 2004 8:37 am Post subject: |
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and then they complain that they lost because the latency was too high 
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Sahir Hidayatullah.
Firewall.cx Staff - Associate Editor & Security Advisor
http://tftfotw.blogspot.com |
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Kn1ght
Frequent Member
Joined: Nov 09, 2003
Posts: 163
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| Posted: Wed Jan 28, 2004 6:59 pm Post subject: |
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okay I'm with you so far. Maybe I am just really stupid but I'm not finding out WHY twisting it is going to make it so that Cross over doesnt happen and EMI and RFI.
Thanks!
COnfused |
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tfs
Retired Team Member
Joined: Jul 22, 2003
Posts: 521
Location: Orange County, California
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| Posted: Wed Jan 28, 2004 7:25 pm Post subject: |
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Here is an explanation I found that might help clear it up:
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Each cable pair forms a complete electrical path for signal transmission. The currents flowing through the wires in each pair are equal, but flow in opposite directions. These currents produce electromagnetic fields that could transmit electrical noise to nearby wires. However, the fields surrounding the two wires have opposite polarities. Twisting the wires together causes the fields to cancel out, which minimises the electrical noise, or crosstalk, generated by each cable
pair.
There are two types of twisted pair cable: shielded twisted pair (STP) and unshielded twisted pair (UTP). STP cable, which may also be referred to as ScTP (screened twisted pair) or FTP (foil-screened twisted pair), contains a conductive shield that is electrically grounded to protect the wires inside from electrical noise. STP cable is more expensive and more difficult to install than UTP
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Tom |
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