Comment by anyfoo | Hacker News Reader

Comment by anyfoo | Hacker News Reader

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True, the plastic tab can be annoying, but I guess the sheer abundance of patch cables nowadays means the cheapness of the connector, while retaining pretty good ease of use (better than many others), makes up for that drawback. Maybe something slightly more resilient could have been designed within the same parameters, had people known just how ubiquitous that connector would become.

Maybe M12 is that, but it looks way more expensive at first glance. Possibly more laborious to connect/disconnect, too, with its screw-locking? Seems to be better for applications where a secured connection is more important (transportation is mentioned).

And yeah, the 1000base-T pin ordering seems unusual. I'm curious about the history there, because even 10base-T (where I thought Ethernet for Twisted Pair begun) had this really weird pinout, which does not support my initial theory that it was because Ethernet kept progressively adding more differential pairs: https://www.arcelect.com/10baset.htm It may well be because they added the original two pairs to a pinout that already carried something else, but the diagrams don't say what those other lines were for, so if anyone knows...

According to those same diagrams, though, it seems to be more common to split up the pairs than not, which now makes me wonder if there is any benefit to that?

> but the diagrams don't say what those other lines were for, so if anyone knows...

Telephones. Telephones are why. Those other two pairs were often used for voice communication. If you had four-pair station cabling, the pairs were provisioned on the modular jack from the inside out. So line one was the blue/blue-white pair on the inner pins, line two was the orange/orange-white pair on the next two pins, and so on.

Ethernet comes along and lots of places where you'd want a network connection already had a phone jack with two pairs unused, so for signal integrity reasons those are moved to the outside and used for data, leaving the inner two pairs where they were to be used for voice.

But why 4 pairs in the first place?

Just about the time that Ethernet was transitioning from coax to twisted pair, the digital PBX was taking over from key systems (1A2) and reduced the number of wires required for a business telephone from 25 pairs (or more ... secretarial sets often had 100 or more pairs) per station down to 4 (for HORIZON[0]) and later two pairs (DIMENSION and eventually Merlin, Definity, etc.). So if you're wiring a new building, you can just run one CAT-3[1] cable to each desk and use the first two pairs for voice and the second two for data[2].

[0] OK, for the pedants out there, HORIZON wasn't ever very popular and really pre-dated Ethernet, but the telecom world moves kinda slow [1] Wasn't really CAT-3 until the early 90s [2] Not on the same jack, but by using pins 1, 2, 7, and 8 for data, you can plug the wrong cable in without risk of hurting the phone or your computer's network card

>Ethernet comes along and lots of places where you'd want a network connection already had a phone jack with two pairs unused, so for signal integrity reasons those are moved to the outside and used for data, leaving the inner two pairs where they were to be used for voice.

But 10BASE-T uses pins 1, 2, 3, 6, thus green and orange pair.

That makes perfect sense now, thanks.

> so for signal integrity reasons those are moved to the outside and used for data

I'm not sure about that bit, though. Would keeping the pair together not help with signal integrity?

I think the advantage of ethernet pinout vs always having adjacent pairs is that it can also be used for a two-line phone or token ring which both use the two inner pairs nested.

I've seen somewhere that a pair of the two outer lines didn't have sufficient performance, so the outer pairs needed to wired side by side instead, but I don't have a reference. Also, there's a reasonable question of why use one inner pair and one outer pair, and not both inners or both outers.

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