Network Cable

Unanswered Question
Feb 5th, 2007

hi, can anybody tell me what is the need of 4 pairs of cable in cat 5 while only 2 pairs are use.



I have this problem too.
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scottmac Mon, 02/05/2007 - 10:19

Four pair (of copper)is the specification for "Structured Cabling."

The concept is that the cabling can be used for many things, including Networking.

For example:

* Token-Ring uses 3&6, 4&5

* 56KDDS (and ATM) uses 1&2, 7&8

* Video frequently uses 3&6 (and possible other pairs for audio)

* Serial can use a few as three conductors, or as many as eight ... and it's not standard ... each vendor uses their own layout.

Specifically for Ethernet and Fast Ethernet, it's true that only 1&2, 3&6 are used: However, for Gigabit Ethernet, all four pair are used (both directions at the same time on all four pair .... it's Magic!).

So, the idea is that you can use the cable plant for many things, up to and including networking. All you need is the proper adapter / BALUN / UNUN / pigtail / "thingy"

Hope this helps

Good Luck


adnan.zafar Mon, 02/05/2007 - 22:47

I'm totally agreed with Scott

Basically 2 pairs are used for supporting purpose and 2 pairs contain data (1,2 and 3,6 )

in which 1,2 used for sending and 3.6 used for receiving You can say that transmitting and receiving the data

You can use remaining 2 pairs to connect another pc on the network or if your 2 pairs are not working then you can use these 2 pairs....

Telecom cables like RJ11 use only 1 pair but 2nd pair used for supporting

In STP we have 1 more wire which use for grounding so that surge can ground if it comes..

Hope this will clear your concepts......

Jitez1234 Wed, 02/07/2007 - 04:44


please what is the pinout for 1000BaseT i.e gigabit over ethernet cable connection.

guessing it may be like pin 1-4 send, pin 5-8,


Thanks in advance.



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