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History Question

History Question

History Question

Okay, it's Friday, and I'm waiting for 5:00. This is a cabling history question. Why is it that the 568A and 568B standards used 1,2,3,&6? Why did they "jump" over 4&5? was it because telephones on Cat3 used 4&5? That's the only reason I can think of. Why didn't they use 1,2,7,&8 instead? Some theoretical reason? Would the EMFs caused problems?

Iolair MacWalter
Network Engineer

RE: History Question

This would seem like a logical answer to your own question, but back when this standard was put in place, there were a lot of phone systems out there that used 2 pairs for each phone. Maybe they actually looked to the future and saw that phones were going to one pair ....
It would really be interseting to know the answer for sure!

RE: History Question

Back then to protect Ethernet equipment from -48V battery of the phone line, it was thought better to use pairs other than pins 4&5 of an 8P8C modular jack.


RE: History Question

568B is exactly an earlier Bell 'standard', so involves no change.  This is why B is more common than A, it involves no change.

I tried to remain child-like, all I acheived was childish.

RE: History Question

Thanks for the answers. Funny how things evolve, isn't it?

Iolair MacWalter
Network Engineer

RE: History Question

the answer is because 99 percent of the time you will find dial tone on pins 4 and 5

RE: History Question

It probably has something to do with the config of RJ (Registered Jack) terminations. Everybody calls this connector an RJ45 but that is actually incorrect! Before the IT world decided to latch on to the 8P8C connector (the true technical name for this connection) it was a connector used to connect both phone and data connections to the PSTN. You can lookup the different versions of the 8P8C connector on wickipedia, which may give an insight to why things are the way they are! Most people don't even realise that the terms RJ45 and Cat5/6 are totally incompatible!

RE: History Question

That is nothing new to me, I have been pointing out this misinformation about MODULAR PLUGS & JACKS, since I have been a member of the forum. I complained to several manufacturers back in the 1980s when I discovered the wrong designation in their literature or manuals. So the journey continues...

I worked at Western Electric in the 1970s, when the Modular Plugs & Jacks were designed and introduced as a cost cutting measure for phone equipment in the Bell System along with the "kit program" for 500/2500, 700/2700, and Trimline™ phones.



RE: History Question

Kit program?  Like 616's and 623's smile

In the independent system we had that ugly wall plate that was designed for a 554 phone to convert a 1654 (your basic wall compact) to touch tone and not have a big ugly unpainted spot on the wall.  It came in the same colors as the phone.  Pastels were in back then so pink, avocado, harvest gold, and robins egg blue were the colors of the day.  F'ugly.

Ahhh, the beauty of working in both the Automatic Electric and ITT/Stromberg-Carlson world.


RE: History Question

I worked on those too, growing up with an ICO in the 1950s & 60s. California Water & Telephone used primarily Stromberg-Carlson sets, although they had their share of AE 40s, to me those were very ugly! The Stromberg-Carlson stuff was superior to AE. S-C had the MiniWall™, 1654 rotory & 2554 for ToneDial™ (S-C's Touch-Tone™). S-C expanded the color offering with orange, and lime green, not to mention the SWIRL colors for the Slenderet™, S-C's Trimline™ set.

Those were interesting times. CWT was acquired by GTE in 1967. The first thing they did was "improve" the Director™ SxS SATT system. We had one of the original Type 48 Director™ systems, that was installed in Monrovia, CA in 1949.

The "Kit Program" was started by Pacific Telephone in an effort to reduce costs and inventory. How successful it was I don't know, and I don't know if other Operating Companies used the concept.


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