Study question...

jadams

2[H]4U
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Mar 14, 2010
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TL;DR: WTF are pins 4,5 and 7,8 used for? Which is TX and which is RX?

So I'm working towards CCNA. Just started a study book and the first few chapters are pretty basic review stuff from college.

Anyway its said pins 1,2 on your PC (and routers, etc... for that matter) is for transmitting and 3,6 is for receiving. Opposite on a switch/hub. Alls good....

The book then goes into introducing the other two pairs for 1000Base-T but doesnt specify what 4,5 and 7,8 are used for. It doesnt mention which is for tx and which is for rx. The assumer in me wants to say 4,5 is for transmitting like 1,2 and that 7,8 are used for receiving like 3,6. this assumption is based strictly off the adjacent pins.

I cant seem to answer this question on the internet. Surely someone here knows.

SO WHAT IS IT?!
 

Liger88

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Is it asking you which pins are used for what with 1GbE or is this just a personal question? I know in CCNA Academy they leave a lot of these details out and I remember this one. Another one for me was how the frequency of the cable affects things like bandwidth.

This question got me curious again and googling around the best answer I found was that it depends. It seems as though 1GbE hardware has a kind of "negotiating" feature built-in (not sure if it's it relates directly to MDX/MDIX). Once both devices on the other end establish a 1GbE communication the signaling is bi-directional for the pins. That's about as far as I could get with things.
 

jadams

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The question is actually my question, not so much the book's question.

They introduce the two additional pairs and the corresponding pins but do not say what they're used for.
 

Liger88

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The question is actually my question, not so much the book's question.

They introduce the two additional pairs and the corresponding pins but do not say what they're used for.


Oh, yeah then in that case they are definitely used for transmitting and receiving to make 1GbE throughput, hence with each pin @ 1GbE and above they're just referred to as "Bi-Directional". In other words they negotiate with other 1GbE devices which to use for send/receive, so you probably wouldn't find an answer to which is send/receive out of the 8 pins because it would no longer be relevant.

Would be nice if a CCNP/CCIE or the equivalent had a more in-depth answer to this.
 

vr.

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TL;DR: WTF are pins 4,5 and 7,8 used for?

They're a packing barrier to keep the bits from flying off the conductor as they zip around the twists, whizzing down the track.
 

WHITE80

n00b
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Nov 27, 2012
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you won't need to know this for ccna. just make sure you know stp,eigrp,ospf, and frame relay really well.
 
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