LAN Connectors (terminology) - Page 1
Forum section: electronics / beginners

author: metrologist
author_rank: Super Contributor
timestamp: February 26, 2019, 03:28:16 pm
content: What is the proper term for the ethernet connector on your PC or laptop? Are these always referred to the same? I read some info that makes me wonder if the wiring to the PCB is always the same or could be different? Say if one instrument says it is an RJ45 connector vs and RJ48C connector (and I think the RJ spec just talks about the cable wiring).For an Ethernet connection, is it wrong to call it an RJ48C connector?Quote

author: tooki
author_rank: Super Contributor
timestamp: February 26, 2019, 03:36:47 pm
content: Yes, that’d be wrong, too. (RJ45 for Ethernet is technically wrong, too.) It’s properly an “8P8C modular connector”, with the wiring being either T568B or T568A (same pinout on both ends of a cable for straight through, one end of each pinout for crossover). T568B is by far the dominant type, so that’s what I follow when terminating Ethernet cables. And then there’s the Category rating of the cables and connectors themselves, which specifies performance (and in the cables, the pair twisting).In practice, calling it an Ethernet connector is usually sufficient, especially since many of the jacks on Ethernet endpoints (routers, switches, computers, etc) contain the Ethernet transformer right inside the jack, making it a special jack exclusively usable on Ethernet.

author: metrologist
author_rank: Super Contributor
timestamp: February 26, 2019, 03:42:47 pm
content: Well, it's confusing still because have this idea that RJ45 is was the old standard - how my 40 year old phone was wired to pins 4,5.Then we have Ethernet and it is not wired to pins 4,5. I guess that is different than the WAN port, which is wired to pins 4,5? It must because that WAN is on my old phone line in the walls.

author: tooki
author_rank: Super Contributor
timestamp: February 26, 2019, 03:54:30 pm
content: Huh?Few people have actual RJ45 (8P8C) phone jacks at home. They are usually RJ11 (6P2C for a single line), RJ14 (6P4C for two lines) or rarely RJ25 (6P6C for three lines).None of the above has much relevance to Ethernet. (Though pins 4 and 5 most definitely are used, they’re Pair 1, which is why an Ethernet wall socket can be pressed into service for POTS use.)WAN vs LAN has no relevance. That’s a logical (data-level) distinction, not one of wiring.Please review the T568B wiring standard.And maybe you can clarify what it is you’re trying to learn — cuz it seems to me it wasn’t just the names of the connectors.

author: Nusa
author_rank: Super Contributor
timestamp: February 26, 2019, 04:09:00 pm
content: The RJ (Registered Jack) standards were established as standard network interfaces between customer equipment and carrier equipment. The RJ number specifies both the physical connector andhow it is wired. Ergo, if your modular jack/connector isn't intended to connect to the outside world, it technically is not an RJ connector/jack, even if it uses exactly the same modular connector.RJ48 is 8p8c used for modem connections like ISDN, T1, and others.RJ48C is an RJ48 specifically wired for a T1 circuit using pins 1,2,4,5

author: tooki
author_rank: Super Contributor
timestamp: February 26, 2019, 04:11:02 pm
content: I was going to add thathttps://en.wikipedia.org/wiki/Modular_connectoris a really good article that covers all the basics quite well.

author: metrologist
author_rank: Super Contributor
timestamp: February 26, 2019, 04:40:16 pm
content: Quote from: Nusa on February 26, 2019, 04:09:00 pmOK, RJ48 is for T1 and RJ48C is specifically for T1. I presume there is a difference there?It is a socket on an instrument. It says it is RJ48C. What is it for? I plug my network cable into it and connect to my LAN.Can it do more than just LAN and it can do some sort of T1 testing?QuoteWhat that last port do?in wiki, they say Ethernet is governed by TIA/EIA-568-B:In Digital Signal 1 (T1) service, the pairs 1 and 3 (T568A) are used, and the USOC-8 jack is wired as per spec RJ-48C.Note the only difference between T568A and T568B is that pairs 2 and 3 (orange and green) are swapped.https://en.wikipedia.org/wiki/TIA/EIA-568But I am talking about the socket that solders to the PCB. Where do those 8 pins go? It must make a difference.

author: metrologist
author_rank: Super Contributor
timestamp: February 26, 2019, 05:12:19 pm
content: OK, so I was looking at this again and the port is actually E1 T1 test port. I think the MFGrs are incorrect to specify the bare metal socket receptacle or plug as an RJ45 connector.

author: tooki
author_rank: Super Contributor
timestamp: February 27, 2019, 03:14:37 am
content: Quote from: metrologist on February 26, 2019, 05:12:19 pmYeah, I kinda said that in my initial reply... But, pedants notwithstanding, it’s the terminology that everyone actually uses.Quote from: metrologist on February 26, 2019, 04:40:16 pmAs best I can tell, “RJ48” is a blanket term for a few specific wiring standards, especially RJ48C and RJ48S, with the C variant being the norm for T1 lines.Quote from: metrologist on February 26, 2019, 04:40:16 pmQuite a departure from your initial question...Quote from: metrologist on February 26, 2019, 04:40:16 pmUhhh, it’s product-specific. Or am I not at all understanding what your question is? (It sounds as generic as “where do the pins from a 3-pin 3.5mm jack go inside a device?”)In an Ethernet device, if the 8P8C socket includes the Ethernet transformer, then the outputs go straight to an Ethernet transciever IC. If the socket doesn’t include the transformer, then the socket pins go to a separate Ethernet transformer, and from there to the Ethernet transciever IC.Generically speaking, it’ll go to... whatever circuitry it needs to go to. And from there the signals route to/from where they need to go.

author: metrologist
author_rank: Super Contributor
timestamp: February 27, 2019, 03:28:44 pm
content: 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...

author: tooki
author_rank: Super Contributor
timestamp: February 27, 2019, 04:46:24 pm
content: Quote from: metrologist on February 27, 2019, 03:28:44 pmWhether 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?

author: metrologist
author_rank: Super Contributor
timestamp: February 27, 2019, 06:32:47 pm
content: 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.

author: Nusa
author_rank: Super Contributor
timestamp: February 27, 2019, 10:03:09 pm
content: 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.Seehttps://en.wikipedia.org/wiki/Registered_jackQuoteCurrent 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.

author: tooki
author_rank: Super Contributor
timestamp: February 28, 2019, 03:21:17 am
content: Quote from: metrologist on February 27, 2019, 06:32:47 pmI think this maybe explains the confusion: There’s no such thing as an “RJ48Cconnector”, because the RJ48C standard means thecombinationof the 8P8C connectorandthe 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.

author: metrologist
author_rank: Super Contributor
timestamp: February 28, 2019, 07:19:31 am
content: 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.

author: Nusa
author_rank: Super Contributor
timestamp: February 28, 2019, 03:00:27 pm
content: I guess RJ45 is tribal knowledge, because the tribe invented it. It's not a standard, so the name is fair game, I guess. Even if it confuses people who stop to make sense of it.If it WAS a standard, then you would be able to say that the designation was misused when it's not connected to the carrier network. But the tribe does this all the time. Since they are already wrong in those instances, why would we want to perpetuate this knowledge?This is like getting people to stop using Kleenex and Xerox as generic names, even though the manufacturers would prefer you only use them to refer to the actual brand name. Ain't gonna happen.

author: tooki
author_rank: Super Contributor
timestamp: March 01, 2019, 04:05:34 am
content: Quote from: metrologist on February 28, 2019, 07:19:31 amWhat makes you think the “wind” is changing? We moved to twisted-pair Ethernet in the early 90s, and there’s no evidence whatsoever of this changing any time soon.Quote from: metrologist on February 28, 2019, 07:19:31 amNope. I don’t know any way to explain it other than what I’ve said already: RJ48C uses the 8P8C connector. But the 8P8C connector is NOT limited to RJ48C, so it’s not an “RJ48C connector”.Quote from: metrologist on February 28, 2019, 07:19:31 amI’d word it as “it’s an E1/T1 test port wired to the RJ48C standard”. “Port” indicating the function, and the “standard” defining the implementation, namely the connector and pinout.Quote from: metrologist on February 28, 2019, 07:19:31 amYup, because, as we’ve said repeatedly, the 8P8C connector has many different uses.Quote from: metrologist on February 28, 2019, 07:19:31 amIf it’s for a T1, it’s going to be RJ48C, if it’s for Ethernet, it’ll be T568B (or A). But since Ethernet is extremely consistent in using the T568B (and A) standard, saying it’s an [insert link speed here] Ethernet jack is sufficient to know what it actually means in practice.Please, please, please, carefully read the “registered jack” wiki article I linked to earlier. I feel it explains all of your questions quite well, and we are all clearly going in circles.Quote from: metrologist on February 28, 2019, 07:19:31 amSo the device has both a T1 port and an Ethernet port? Then it probably explains the marketing intern’s confusion.They saw the T1 port correctly labeled as conforming to RJ48C, and they mistakenly assumed this was the connector name, and so when they looked at the Ethernet port with the same connector type, they assumed it was also RJ48C, which it isn’t.