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network cable


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#1
vally

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Hi there


I am trying to understand the way the network cable connected to a RJ45 is suppose to be connected.
Now I know how to to connect it parallel or crossed and that crossed is needed for a direct connection between two computerese, or for connecting between older switches and/or hubs.

I have read and seen that to connect computerese in a 100Mb network you only need a 4 wire cable (pins 1 2 3 6) but the protocol calls for a full connection that you need all 8 wires. I have seen printers that need all 8 wires to be connected to run in full duplex (on a 100mb net) even though the computer sending the data only has 4 wires.

Another question is I understand that a cat5 cable is only good for a network up to 100mb. Now knowing that to connect a gig network you need all 8 wires and also a ground\earth wire inside. When the network is working at a gig speed it means that the speed between the bytes is 1Ghz and does not slow down the speed of the bytes just the time between sending the packets.
So you need a cat7 wire and not cat5 because the bytes are slowed down till it is sent correctly.?


Sorry - This may not be written up correctly but I am trying to understand how it works.
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#2
dsenette

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I have read and seen that to connect computerese in a 100Mb network you only need a 4 wire cable (pins 1 2 3 6) but the protocol calls for a full connection that you need all 8 wires. I have seen printers that need all 8 wires to be connected to run in full duplex (on a 100mb net) even though the computer sending the data only has 4 wires.

this is correct...for gigabit connectivity you need all 4 pairs connected on both ends of the cable. with 10baseT or 100baseT you could get by with just 2 pairs because there was no need for auto negotiation and you could achieve full duplex across the 2 pairs, but 1000baseT requires auto negotiation and thus needs the extra 2 pairs for communication

Another question is I understand that a cat5 cable is only good for a network up to 100mb. Now knowing that to connect a gig network you need all 8 wires and also a ground\earth wire inside. When the network is working at a gig speed it means that the speed between the bytes is 1Ghz and does not slow down the speed of the bytes just the time between sending the packets.
So you need a cat7 wire and not cat5 because the bytes are slowed down till it is sent correctly.?

this is actually incorrect...you CAN use cat5 for gigabit networks, you'll just experience higher instances of crosstalk and attenuation at longer distances. it's suggested to use cat5E or cat6 (or higher) for use with gigabit networks.

the ONLY real difference between any of the categories of cables above cat4 is the thickness and construction of the insulation. the higher levels (5e, 6, etc..) also have more twists per inch to reduce crosstalk and interference....other than that the cables are basically the same

and you don't need the "ground" wire...that's called shielding, which is only used in STP (shielded twisted pair), UTP (unshielded twisted pair) is PERFECTLY fine for gigabit transmission. the purpose of STP is to reduce interference when you're running cables in a high interference area (such as around spinning electrical motors or if you're running your cables down a cable tray that also houses 3 phase electrical lines)

the cable itself has no bearing on the speed of transmission of the packets, the cable ONLY effects crosstalk and other interference
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#3
vally

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So based on what you posted about cat5 cable if I have a line to between 2 switches that is cat5 (set up 9 years ago) I can connect two gig switches and will see that they are working at gig or they will decrees automatically to 100baseT. It is in a building and not next to motors or 3 phase elec.
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#4
dsenette

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yes...it will operate at gigabit speeds if you're using cat5...however depending on the length of the run you'll have increases susceptibility to crosstalk, collisions, and other interference since the insulation isn't as good as 5e or 6...

if you've got the ability, it's best to run 5e or 6 for gigabit. but in a situation where you've got a short to medium run of cat5 you can run gigabit with few to no issues
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#5
vally

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Well tomorrow we will find out.

In the morning we are going to change a few switches that lately stopped running smoothly (9 yr. old and have not been touched in that time :) . But don't worry they are HP and have warranty for life :) )
If all goes well we will change some of the cat5 with cat7 depending on how things run before people show up. You never know what will happen.....

Thanx allot
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