Difference between RJ11 and RJ12?

Discussion in 'Networking, Telephony & Internet' started by Roman209, Nov 10, 2003.

  1. Roman209

    Roman209 Member

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    What is the difference between an RJ11 connector and RJ12 often i would see reference made as RJ11/12. I was wondering what the difference actually was?
     
  2. caspian

    caspian Member

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    Technically, the RJ11 is a 4P4C connector, the RJ12 is a 6P4C.

    If you compare an RJ45 network connector to an RJ12 phone connector, you will notice the RJ12 is narrower by 2 pins (regardless of whether the copper contacters are actually fitted or not). The RJ11 is 2 pins again narrower still.

    RJ45 - 8 pins
    RJ12 - 6 pins
    RJ11 - 4 pins.

    You can physically connect the smaller plugs to the larger sockets, as long as you are careful to get them lined up correctly.
     
  3. OP
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    Roman209

    Roman209 Member

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    Thanks for the reply.

    Another thing im just curious about, do phones only use 2 pins of those 4? Are they Bi-Polar?

    Thanks


    EDIT: My bad, i understand now. Those other questions still stand though. :)
     
    Last edited: Nov 10, 2003
  4. caspian

    caspian Member

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    All analogue phone gear (dialup modems, faxes, phones etc) uses only the centre 2 pins of the connector. Equipment that uses 4 pins is digital.

    Often you will see 4-wire cords or sockets with 4 wires attached, the cords are multi-porpoise (still only 2 conductors used), the socket most likely simply has 2 lines wired to it. (all cables into houses have 4 wires, 2-pair is the smallest cable used.)
     
  5. OP
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    Roman209

    Roman209 Member

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    Got it thanks.

    Are those 2 wires bi-polar? That is there is no positive or negetive.
     
  6. Whisper

    Whisper Member

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    What I want to know is what happened to RJ13 through to RJ44 :)
     
  7. aXis

    aXis Member

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    AFAIK, the two phone wires are "Tip" and "Ring". I think you're supposed to get them in the right order.

    But that said, you shouldnt have to guess, because you're going to get a licensed professional to do it properly, arent you?
     
  8. OP
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    Roman209

    Roman209 Member

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    Im not installing anything.
    I just wanted to know because there is not much information i could find online.
     
  9. aXis

    aXis Member

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    I have seen an RJ twenty something. It's a big telco connector for aggregating many lines - sometimes used on high density switches.
     
  10. sciencewhiz

    sciencewhiz Member

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    Do they fit into various species of porpoise? Like just dolphins and not whales or are they truly multi-porpoise?

    Greenpeace will have you caspian, if you're advocating putting sockets in seafaring mammals!
    They get pretty pissed about massaging baby harp seals with long wooden objects and practicing acupuncture from a distance on those whale type animals.
    Personally, I believe not giving dolphins network access is a crime.... :D
     
  11. caspian

    caspian Member

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    you should have seen me when I got my new crimpers the other week, everything in sight had an RJ45 crimped onto it. the cat still won't come with 10 feet of me...
     
  12. OP
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    Roman209

    Roman209 Member

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    lol this has gotten totally off topic, espically talking about the porpoise.

    With an RJ45 connectors 8 pins only 4pins of those are actually used with a computer?
    So its quiet possible to use standard telephone cable to wire a network? Of course it will be more exposed and get more signal degradtion because of the lack of quality of the wire?

    Why do we have RJ12 connectors when we will only even use at max 4 pins for the digital equiptment such as commanders?

    Iv seen phone networks wired with cat5 and only 2 of those pins being used.So i was curious how it all fell together.



    Another question ill put which might be suitable to another thread, since commanders are digital, they convert the analog phone line into digital.
    You carnt use dialup or adsl on a line which comes off a commanders since modems also do this analog/digital conversion.

    Would there be any need for a modem at all if the line you are using comes off a commander?

    Sorta fuzzy with me here, im sure theres something else to it, something stopping it or some other special equiptment necessary. But i dont know if its even possible?
     
  13. aXis

    aXis Member

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    With 10 base T and 100 base TX, yes. With GigE, I think all conductors are used.

    Possible for 10 base T, but would fail completely with 100 base TX due to the lack of quality.

    Dunno - future compatability maybe? I have a modem which operates in leased line mode using the outer pins of a 6p6c RJ12 connector.

    Modems are common, proprietarty PABX interfaces are not. You can get Analogue cards to suit most PABX equipment, allowing you to use a modem. Often the link to the telco will be ISDN, so you can patch a channel to an ISDN modem/router.
     
  14. OP
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    Roman209

    Roman209 Member

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    ok thanks all
     
  15. GenoCyber

    GenoCyber Member

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    You should always connect all 8 pins with ethernet and fast ethernet as they are needed to reduce cross talk between pairs.

    Also gigabit ethernet needs all 8 pins to work.
     
  16. dakiller

    dakiller (Oscillating & Impeding)

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    also it isnt just the middle 4 pins that are use for normal 10/100 either

    the network card will use pins 1, 2, 3 and 6 with 1 and 2 being a twisted pair and 3 and 6 another pair

    so you need an 8p8c connector anyway
     

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