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JoelC707
Premium
join:2002-07-09
Lanett, AL
kudos:5

T568B ethernet wiring standard deprecated?

I'm looking up things on cat 6 cabling and I see a mention on Wikipedia about 568B being deprecated as an official wiring standard. I click over to the TIA/EIA 568 page and see the same thing. Both entries have [citation needed] tags so I'm leery of believing it (I'm leery of believing it anyway). Has anyone heard anything about this before?

»en.wikipedia.org/wiki/T568A/B#T5···mination

It even mentions this: The United States National Communication Systems Federal Telecommunications Recommendations explicitly forbid T568B, as does all US Federal guidance on new construction for the US Government.

If that's true then what is so bad about 568B? Sure 568A lines up better with lines 1/2 on a standard RJ11 jack for phone service but that's about all I can think of. Plus you STILL need 568B for a crossover cable. I've always preferred 568B personally and I've noticed many of the pre-made patch cables I have are wired as 568B.



jeffmoss26

join:2002-07-22
Beachwood, OH

First I've heard of it. I was trained using B and I see it everywhere.


bdnhsv

join:2012-01-20
Huntsville, AL
reply to JoelC707

wikipedia is great, but you you can't always take everything on there at face value. That's referring to FIPS 174 which was withdrawn in 1997. To your other question - there is nothing wrong with 568B.


JoelC707
Premium
join:2002-07-09
Lanett, AL
kudos:5

Yeah I don't usually put much stock into many things I find on Wikipedia. I was looking around Google this morning for further proof one way or the other and still saw mention of it being deprecated. That said, like all these rumors that start about various actors being dead, there was little evidence to support their claims.

Given that 568B is flat out required in order to make a crossover cable, even if it does get deprecated, it's not fully going away anytime soon. Thanks for your help guys on confirming what I already suspected.



tschmidt
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reply to JoelC707

The reason T568A is preferred is exactly the reason you mentioned. The first two pair match the Line 1 and Line 2 USOC designation for phone system wiring using Type 66 or 110 punch-down blocks for cross connect and 6-postion modular jacks.

The reason T568B is so popular in the US, and why it is even in the specification, is because it matches the AT&T 258A wiring used for Merlin phone system that was very popular when the spec was introduced.

This trivial difference in pin out has been a source of tremendous confusion. Electrically it does not matter, it is simply a matter of backward compatibility to preexisting cable color coding.

The TIA specs requires T568A for greenfield construction, T568B is allowed if building is already wired with AT&T 258A/ T468B.

/tom



tschmidt
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reply to JoelC707

said by JoelC707:

Given that 568B is flat out required in order to make a crossover cable, even if it does get deprecated, it's not fully going away anytime soon.

Just to clarify. The EIA/TIA-468 specification is independent of how the cabling is used. I realize that only happens in a perfect world hence the reason we have Cat5e and Cat6A. But the goal was to create a wiring standard independent of how it is used. Now that speed is pushing the upper limits of copper that is no longer the case and cabling specs have to be closely tailored with the hardware.

The fact an Ethernet 10/100 Mbps crossover cable is T568A on one side and T568B on the other is an accident due to the pairs chosen for transmit and receive. If other pairs had been chosen by IEEE 802.3 the pin out would have been different. At Gig and higher speed all four pairs are used so there is no notion of a crossover cable. With the advent of Auto-Mdix crossover cables are pretty much of historical interest.

/tom

JoelC707
Premium
join:2002-07-09
Lanett, AL
kudos:5

All very true, and I even forgot all about gigabit+ using all four pairs. Thanks for clarifying