Electronics > Beginners

LAN Connectors (terminology)

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tooki:

--- Quote from: metrologist on February 27, 2019, 03:28:44 pm ---The point is figuring out what an 8P8C socket is used for, because there are standards for that if not used for proprietary purposes.

3-pin 3.5 mm jack does not seem analogous to RJ45. I would not expect Motorola to call their transceiver's 8P8C mic port an RJ45 port, but maybe they do and that is OK. I'm not sure those jacks aren't RJ11, RJ14, or RJ25 though...

--- End quote ---
Whether you like it or not, “RJ45” is what everyone calls the 8P8C physical connector, even if it’s technically wrong.

As for “what it’s used for”... um, whatever low-voltage purposes the engineer wants? Ethernet is without a doubt the most common application, but it was also widely used for ISDN, PBX phone systems, as the serial console port on various network gear, etc. It’s not a connector that was purpose-designed for a single application (like the connectors for USB, HDMI, FireWire, etc.), and indeed predates its now-dominant application. The handful of standardized applications of the 8P8C connector are explained well on the wiki page I linked to in an earlier reply. Everything else is a proprietary use.

I mentioned the 3.5mm because of your question of where the pins inside the device go, to illustrate that they go wherever they’re needed.

I still think we haven’t really pinned down what it is you want to know. Perhaps you’re operating from assumptions that aren’t correct, in which case maybe you can elaborate?

metrologist:
I see an 8P8C socket on some instrument. It has the typical three-terminal-screen as a label. The document says it is an RJ48C port for connecting LAN.

I wasn't familiar with RJ48C, so I looked it up and could not figure out how an RJ48C port could possibly support regular old Ethernet since the wiring is different. That is what I posted in my OP.

Then I started looking at other equipment with this connector and saw a lot of references to RJ45, which like RJ48C, is said to support T1. I knew the issue with referencing RJ45 incorrectly in a general use sense, but I always took the standards to mean something more than just the physical socket and plug dimensions. Having an actual RJ48C connector and calling it an RJ45 seems just as bad as calling an RJ45 connector an RJ48C connector.

I was looking for the actual RJ45 specification, or the database of RJ specifications so I know what they say. You can't find that on the FCC.gov site, or at least I can't and their search returns 0 results. Maybe it is a payed standard? Anyway, I though these standards were implemented originally for a specific purpose and application.

I am the type to honor the difference between Velcro and Hook and Loop.

Nusa:
You're not finding an RJ45 spec because there isn't one. There's an RJ45S and a RJ45M, but not RJ45. That hasn't stopped people from adopting RJ45 informally for Ethernet jacks, simply because they use the same 8p8c modular. RJ48C is real, however, and has a different pin-out than Ethernet.

See https://en.wikipedia.org/wiki/Registered_jack

--- Quote ---Unofficial plug names
The following RJ-style names do not refer to official ACTA types:

RJ9, RJ10, RJ22: 4P4C or 4P2C, for telephone handsets. Since telephone handsets do not connect directly to the public network, they have no registered jack code.
RJ45: 8P8C, informal designation for T568A/T568B, including Ethernet; not the same as the true RJ45S
RJ50: 10P10C, often used for data
--- End quote ---

Current standard details are on a paywall at the ACTA site. You can find some of the older ones on archived copies of the FCC part 68 regulations, where the details were actually in the regulations. But that all got privatized and now part 68 just points you at ACTA for details.

tooki:

--- Quote from: metrologist on February 27, 2019, 06:32:47 pm ---I see an 8P8C socket on some instrument. It has the typical three-terminal-screen as a label. The document says it is an RJ48C port for connecting LAN.

I wasn't familiar with RJ48C, so I looked it up and could not figure out how an RJ48C port could possibly support regular old Ethernet since the wiring is different. That is what I posted in my OP.

Then I started looking at other equipment with this connector and saw a lot of references to RJ45, which like RJ48C, is said to support T1. I knew the issue with referencing RJ45 incorrectly in a general use sense, but I always took the standards to mean something more than just the physical socket and plug dimensions. Having an actual RJ48C connector and calling it an RJ45 seems just as bad as calling an RJ45 connector an RJ48C connector.
--- End quote ---
I think this maybe explains the confusion: There’s no such thing as an “RJ48C connector”, because the RJ48C standard means the combination of the 8P8C connector and the specific pinout/application.

Though as Nusa said, “RJ45” is shorthand, and not the actual name of any specific standard.

As for the manual referenced, if it said that the RJ48C jack or T1 port is for a “LAN”, then it’s probably an error, since a T1 is a WAN technology, not a LAN one. I googled some of the quotes from the manual you posted, and I’m guessing it’s an Anritsu spectrum analyzer, perhaps the MS2724C. And while the Anritsu MS2724C’s data sheet says RJ48C for the LAN jack, it’s a mistake: the user’s manual says it’s an RJ45.

Probably some marketing intern tasked with writing the data sheet did some googling and found the wrong name.

metrologist:
Nusa, It gets even more confusing if there is no RJ45 spec. For example, the RJ45S spec seems to include a physical key, so you can't use those dimensions. How is this tribal knowledge to be perpetuated once the wiki and connector mfgs change with the wind?

tooki, There is no such thing as an RJ48C connector? Sometimes nuance of language is irritating. Maybe it is a Port rather than a connector? It is labeled as "E1/T1 Test Port" and in the document it says RJ48C, but that is under a larger heading of all instrument connectors listing their type (USB, HDMI, PCIe, RJ48C, BNC, SMA, etc.). It looks totally the same as the "RJ45" port you'd see for your laptop Ethernet, but that is not what it's for. I presume this square hole meets the combined requirements you've mentioned? There was a mistaken reference to RJ48C for the LAN port that instigated this.

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