ethernet jack

Possibly because the *plugs* are different ?? :-)

One reason is so you don't plug a PC's NIC cable into a phone jack and destroy it when the NIC gets hit with the 90 volt ringing signal of a phone call.

BTW, the use of the term "RJ-45" for LAN jacks and plugs is, was, and always will be technically incorrect. The entire RJ-series of Registered Jacks and Plugs are telephony applications. The early LAN builders liked the 8 pin 8 conductor form of the mini-modular series so much they usurped it for their use, apparently not being imaginative enough to label it something appropriate to LAN applications. I suppose they were tired of the grief they got over the infamous AUI slide-lock connector they decided not to risk their own design again.

If you are curious, RJ-45 correctly means a "data modem with programmable transmit level" operation. The installing telco would install a resistor within the jack, after selecting a value that would tell the attached modem what transmit level to use to insure the modem's signal reached the local telco CO at a -12dB level, accounting for the loop loss of that specific installation.

If you get the impression that I have been on a 20+ year, Don Quixote-like, crusade against the usurpation of the term RJ-45, you are most correct.

--reed

I admire your persistence but I think it's a battle lost. Go into a store and ask for an 8p8c jack and the clerk will have no clue what you want. Ask for an RJ-45 and he'll point you to a whole rack full of 8p8cs.

To prevent people from plugging things into the wrong jacks?

Ethernet and POTS are completely different electrically, and it makes sense to try to keep people from connecting them together and damaging something.

S

Sure. It makes sense. But keyed connectors are rare. If you see an RJ45 socket, it can be anything. Ethernet, ISDN (S-bus), Token Ring, POTS, you name it.

Phone jacks are used allover. Probably because they are cheap. And they moved from RJ11 to RJ45 because you cannot crimp a

8-wire cable to a RJ11 :-)

OK, then maybe we can all start calling them RJ-48 connectors ;-P

(or we could call them "ya know, those 8 pin modular jacks used for ethernet"?)

wasn't as much of an issue until 1000base-t.

Before then, the blue pair which phones would use was not used by ethernet.

So no chance of getting equipment zapped by ringer voltage (ssuming the equipmemnt didn't do somethong dumb, like wire the unused pins to signal ground)

Not to mention RJ48C and RJ45 look the same...

Now don't get me started on T-1 access jacks ;-)

Sadly today, no one would know what you meant....

In most businesses these pins were used by the phone systems of the day. (80s & 90s). And putting the wrong device into the jack could upset the equipment at the far end. :(

The question was why not use RJ-11 for Ethernet; that would have required putting Ethernet data on the same pins as POTS voltages.

This wasn't so bad a strategy prior to 1000BaseT, but there were still problems since (a) you can fit a RJ-11 plug into a RJ-45/RJ-48C jack, and (b) doing so would put POTS line 2 on Ethernet's data pins.

Also, if Ethernet had used RJ-11 cables, people would have been tempted to use standard phone cables instead of Ethernet ones, leading to all sorts of problems (insufficient twists, only one pair connected, etc).

I've seen many, many laptops smoked when power is applied on pins 4&5 or

7&8. It doesn't seem so common on desktops, but that might just be the relative frequency of reattachment. S