Common operational misconceptions

"Ethernet/Token Ring/Cisco Console/whatever uses an RJ45 connector"

RJ45 defines a keyed 8P8C type connector, wired in a specific
manner, for a specific 2 wire telco service. Incompatible with the
above on several levels. "RJxx" == specific connector/wiring pattern
for specific telco applications. Non-telco uses need not apply.

One of these days I'm going to start carrying around some actual RJ45
type cables to hand out to those who ask.


DB defines a D series subminiature connector with a size "B" (nominal 25 pin)
shell. DE defines a size "E" (nominal 9 pin) shell. DA15, DB25, DC37, DD50,
DE9, etc.. Also DB13W3 (old Sun monitors), etc. If in doubt, refer to
ITT/Cannon catalogs. (my oldest is from 1971).

RJ45 is really an example of what was originally a misconception
became so widespread, so universal, that reality has actually shifted
so the misconception became reality. When was the last time you ever
heard anyone say "8P8C connector?"

Joe public caught on to "RJ45", so now that word means something
different in common usage than what it was specified to be. When
was the last time you heard someone say 8P8C connector in reference to

Nowadays it is technically ambiguous to say "RJ45"; are you talking about
[a] The original standard, Registered Jack 45, which was a specific
connector together with a specific pinout (which is not Ethernet
over UTP)? Usage of the connector is exceedingly rare, and will
hardly ever be referred to.

[b] "Ethernet" connector; The generic 8P8C connector (which has a
certain resemblance to RJ 45) is specified for use with TIA/EIA 568
compliant cable termination ?

Now instead of [a] being correct and [b] being always the
misconception..... [b] is "correct" in common usage.

And you have to decide based on context of the conversation which
defintion of RJ45 is intended, but [b] will almost always be the
correct definition.

And then there's the 10C variant used on some serial port interfaces (like those from Equinox).....

'8 pin modular plug' is reasonable, though, and is what I'll typically say, with the modifier 'for stranded' or 'for solid' conductors, as it does make a difference. I haven't said 'RJ45 plug' in years.

Yeah, it's a bummer that the keyed RJ45 plug got genericized to the unkeyed variant; at least the unkeyed plug used for TIA568A/B will work in a true RJ45 jack.....

At least "RJ45-X" is still unambiguus. <wry grin>

WADR: horseshit.

I, in fact, just wrote a cabling RFQ yesterday for a new building, and
*I* write "8P8C male modular connector". So, in short: if you *actually
need to be saying it*, you actually need to be saying it correctly, because
you're talking to people who know the difference.

They won't say anything, mind you, and you'll get what you want; they'll
just think you're a clueless dilettante.

-- jr 'yes, I'm a prescriptivist[1]' a

[1] The *point* of language is communication; this is impossible if
words "mean what people want them to mean, no more, no less".