Why 4 pairs in 100Base-T|
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Posted by Charles Lindsey on June 4, 2009, 10:32 am
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copnnectors and cat5 cable carrying 4 twisted pairs. But, AIUI, only 2 of those pairs are used for the protocol, so what are the other two for? given that cat5 cable does not come cheap, surely 2-pair cable would be far more economical. So why not use 2-pair cable and leave the other RJ45 pins unconnected? Would that work? -- Charles H. Lindsey ---------At Home, doing my own thing------------------------ Tel: +44 161 436 6131 Web: http://www.cs.man.ac.uk/~chl Email: chl@clerew.man.ac.uk Snail: 5 Clerewood Ave, CHEADLE, SK8 3JU, U.K. PGP: 2C15F1A9 Fingerprint: 73 6D C2 51 93 A0 01 E7 65 E8 64 7E 14 A4 AB A5 | ||||||||||||||||||||||||||||
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Posted by Conor on June 4, 2009, 1:09 pm
Please log in for more thread options Telephony and Power over Ethernet. -- Conor I only please one person per day. Today is not your day. Tomorrow isn't looking good either. - Scott Adams | ||||||||||||||||||||||||||||
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Posted by glen herrmannsfeldt on June 4, 2009, 1:11 pm
Please log in for more thread options < Connections between desktop computers and hubs/routers customarily us RJ45
< copnnectors and cat5 cable carrying 4 twisted pairs. < But, AIUI, only 2 of those pairs are used for the protocol, so what are < the other two for? given that cat5 cable does not come cheap, surely < 2-pair cable would be far more economical. < So why not use 2-pair cable and leave the other RJ45 pins unconnected? < Would that work? I have some patch cables with only two pairs that came with 100baseTX cards. Otherwise, they are pretty rare. You need all four pairs for gigabit, though. It may cost a little more now, but saves the cost of replacing all the cables when updating to gigabit. I have some patch cables with only two pairs. Otherwise, they are pretty rare. You need all four pairs for gigabit, though. It may cost a little more now, but saves the cost of replacing all the cables when updating to gigabit. Otherwise, I don't think you can easily buy two pair Cat 5. The cables I have might only be Cat 3, though if short enough will likely work for 100baseTX. -- glen | ||||||||||||||||||||||||||||
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Posted by Charles Lindsey on June 8, 2009, 9:25 am
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>< So why not use 2-pair cable and leave the other RJ45 pins unconnected?
>< Would that work? >I have some patch cables with only two pairs that came with
>100baseTX cards. Otherwise, they are pretty rare. OK, so if I'm making up my own cables, for whatever reason, then I may as well use just two pairs (assuming I can find someone to sell me such cable in bulk). >You need all four pairs for gigabit, though. It may cost
>a little more now, but saves the cost of replacing all the >cables when updating to gigabit. Sure, but most applications (including mine) would be happy on 10BASE-T, so I don't think I need worry about gigi-stuff. -- Charles H. Lindsey ---------At Home, doing my own thing------------------------ Tel: +44 161 436 6131 Web: http://www.cs.man.ac.uk/~chl Email: chl@clerew.man.ac.uk Snail: 5 Clerewood Ave, CHEADLE, SK8 3JU, U.K. PGP: 2C15F1A9 Fingerprint: 73 6D C2 51 93 A0 01 E7 65 E8 64 7E 14 A4 AB A5 | ||||||||||||||||||||||||||||
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Posted by glen herrmannsfeldt on June 8, 2009, 1:07 pm
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<>< So why not use 2-pair cable and leave the other RJ45
<>< pins unconnected? Would that work? <>I have some patch cables with only two pairs that came with
<>100baseTX cards. Otherwise, they are pretty rare. < OK, so if I'm making up my own cables, for whatever reason, < then I may as well use just two pairs (assuming I can find < someone to sell me such cable in bulk). As I understand it, Cat 5 requires four pairs. For short patch cables you can probably get away with Cat 3 cable. That would be fairly likely if that was the only cable in the connection, and much less likely if there was 90m in between. <>You need all four pairs for gigabit, though. It may cost
<>a little more now, but saves the cost of replacing all the <>cables when updating to gigabit. < Sure, but most applications (including mine) would be happy < on 10BASE-T, so I don't think I need worry about gigi-stuff. You originally asked about 100baseT (that should have been more specific, as 100baseTX or 100baseT4. 100baseT4 uses four pairs of Cat 3 cable, but is very rare.) I believe that two pair 10baseT patch cables were not that rare. My favorite is one that came with a 3com PCMCIA NIC with a very small outer diameter. -- glen | ||||||||||||||||||||||||||||
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> Connections between desktop computers and hubs/routers customarily us RJ45
> copnnectors and cat5 cable carrying 4 twisted pairs.
>
> But, AIUI, only 2 of those pairs are used for the protocol, so what are
> the other two for?