Two keystone/rj45 chacks on one network cable/connection?

Discussion in 'Computing and Networks' started by prometei, Mar 14, 2016.

  1. prometei

    Thread Starter Well-Known Member

    Apr 13, 2008
    56
    0
    Hi,

    I've connected two keystone/rj45 jacks to a cable that's plugged into a LAN port on a router, like this:

    Router-----Jack1------Jack2.

    If I connect my pc to Jack2, it works, i.e. I get a connection with the router, but I it does not work with Jack1, i.e. the computer and the router show that nothing is connected to their LAN ports. Any suggestions?

    Thanks
     
  2. prometei

    Thread Starter Well-Known Member

    Apr 13, 2008
    56
    0
    I've done some searching and if I understand correctly the problem is most likely that the cable going to Jack2 inserts noise/reflections in the whole length of the cable (Router to Jack2) because it's not terminated with resistors.
     
  3. andrewmm

    Active Member

    Feb 25, 2011
    30
    6
    how long is the cable between the two jacks ?
    has the cable ever worked,

    are you certain its wired correctly ?

    the PC / switch should try to negotiate a speed it can work at,
    at 10 Mb's a link has to be very bad not to work...
     
  4. BR-549

    Well-Known Member

    Sep 22, 2013
    2,002
    389
    Are you saying that you built a jumper with a jack on both ends?

    Sometimes that can be Bad Juju. Look at the data sheet of the jack and compare it with the data sheet of the PLUG. Recheck pin wiring.

    Usually a jumper has a plug on one end and a jack on the other. Helps to keep wiring straight forward and mates the other cables, without more adapters.

    In a jack to jack jumper, or a plug to plug jumper, sometimes a pair gets inverted, or doesn't get inverted, but needs to.

    People used to run into this when making their own serial cables to link computers.

    I am not familiar with CAT protocol, maybe this doesn't apply.

    Check for intermittent cable or faulty jack. Be sure to use recommended tools.
     
  5. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,146
    204
    Bad Juju

    These are constant impedance transmission lines, not "just wires". The wire has a characteristic Z of about 120 ohms and the ends are terminated at 120 ohms. The middle can't go off in space somewhere.
    **************************************************************************************************************jack1
    You can put a hub/switch in the middle if you want. So it;s route/hub/switch - wire - jack - hub
    ***************************************************************************************************************Jack2

    The "switch" is an Ethernet Switch.
     
  6. prometei

    Thread Starter Well-Known Member

    Apr 13, 2008
    56
    0
    Hi, yes I know about switches but I don't want/need one since I only have one PC which I want to use in different parts of the room.

    ----

    The setup works only if the PC is connected to Jack2. Or it works with Jack1 only if the cable that goes to Jack2 is disconnected from Jack1.

    Here is the schematic again: Router-----Jack1------Jack2. The ----- is the Cat5 cable.
    The jacks I used look like this:
    [​IMG]

    I'm pretty sure it does not work at Jack1 since the cable going to Jack2 is left "open".

    These are constant impedance transmission lines, not "just wires". The wire has a characteristic Z of about 120 ohms and the ends are terminated at 120 ohms.
    So, I how would I properly terminate the TX and RX lines at Jack2? With 60 ohm resistors to ground, between the pairs, or?

    thanks
     
  7. prometei

    Thread Starter Well-Known Member

    Apr 13, 2008
    56
    0
    The length between Jack1 and 2 is about 3 to 4 meters.

    Yes the cable works.

    Yes it is wired correctly.
     
  8. tom_s

    Member

    Jun 27, 2014
    285
    333
    either too early in the morning or this makes no sense at all
    you trying to run 2 devices off the same cable?
     
  9. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,146
    204
    The TS said one at a time in the same room. What's permissible in telephone is not permissible in Ethernet. Daisy chaining jacks even if only one is used.
     
  10. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,146
    204
    You should AT LEAST get a link light. The punch down block won't support two wires. You should maintain the twiists and use CAT4 minimum wire for 10/100 base T.

    If one of the devices are not Auto-MDIX, you'll have to use a crossover cable.

    Remove the plug at the router and the other end, Short the pairs and measure continuity at the other ends.
     
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