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can someone tell why UTP 10/100 is wired 1236? why not 1234, 3456, 5678? (i know that on old adapters only 1236 pins were connected) which was the rationale of 1236?

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    Unfortunately, historical trivia is off-topic. – Ricky Beam Jul 1 '19 at 15:11
  • @RickyBeam its not only trivia.. i wired all my cables 1-2,3-4,5-6,7-8; they work for short distances.. that i needed since 20 years.. not so for long distances; so given this huge mistake i wander of the rational of 1236; i kept my question short and on point.. don't assume its pointless – user688056 Jul 2 '19 at 10:27
  • @RickyBeam btw.. google doesn't know.. from 1 day searching i can only assume it came from 4 pins phone line.. but why didn't they put ethernet 1-2, 7-8, assuming 3-4,5-6 were phone line arrangements, and why did they wire phone line 1-4,2-3 instead of 1-2,3-4; in the same order visible spectrum is ..green.. orange.. but UTP pair2 is orange and pair3 is green; whats the catch? i'm asking proffessionals.. they should know.. lol section – user688056 Jul 2 '19 at 10:47
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EIA/TIA-568 defined the pairs 1-2, 3-6, 4-5, and 7-8 long before twisted-pair Ethernet came up in the form of StarLAN which was designed to utilize the already existing cable plants.

Possibly, StarLAN developers left the 4-5 pair out to simplify coexistence with the previous twisted-pair application POTS. Unless there's a good source that is guesswork and off-topic here.

10BASE-T and 100BASE-TX inherited that pinout. 1000BASE-T onwards uses all pairs, not just 1-2 and 3-6.

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  • regarding 1000BASE-T the pairs still persist 1-2, 3-6, 4-5, 7-8, only difference .. it uses all of them; i'll also look into EIA/TIA-568 standard for rationale; ty for the hint – user688056 Jul 1 '19 at 10:46

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