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pico1180

Gigabyte LAN drops to 100BASE-TX

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So, I have a windows home server running cat5e everywhere in my house. All the runs are full gigabyte but one. It keeps dropping to 100BASE-TX (12MB/s). Process of elimination has indicated the problem is in the CAT5e drop somewhere. Either on the keystone jacks, or somewhere in the wire itself.

I was wondering if anyone has experience with this. I was hoping someone could tell me exactly what wire(s) I'm having trouble with (loose, not making contact, etc.). If I can’t get it isolated, I'm going to have to rip the whole drop out of the wall and replace it. I don’t want to do that. At all.

I'm confused as to how it can cary a 100BASE-TX signal, but not a 1000BASE-T. It has carried a 1000BASE-T signal in that past, but its intermittent. Now it won’t do it all. To someone who knows this kind of stuff, it may be very clear and apparent. I just simply don’t know enough about it to understand why it will carry a 100BASE-TX, but not a 1000BASE-T.

Any suggestions would help.

Thank you.

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Since you've narrowed it down to the wiring run, try reterminating it and see if that helps.

100mbit ethernet is much less demanding than gigabit ethernet. It only uses two pairs instead of the full four (1/2, 3/6) that GigE does, and while the bandwith requirements are similar (standard Cat5e is rated only to 100Mhz), the higher bitrates mean a marginal quality cable or marginal termination (or both) mean that there are many cases where a piece of cat5e will not do 1000Base-T, even if it should if everything properly meets spec. (attenuation, crosstalk, delays, skew requirements are all tighter for 1000Base-T vs. 100Base-TX...)

http://en.wikipedia.org/wiki/Category_5_cable

http://en.wikipedia.org/wiki/Ethernet_over_twisted_pair

Someone out there can probably post fancy frequency analyzer shots if you need a graphic depection, but unfortunately I'm not finding any off the top of my head.

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Yea if its runs you have wired yourself, you probably have a loose or not so great connection somewhere. As continuum mentioned, you are hitting an interference level that is too great for 1G and its dropping to 100Mb since that is what the standard will do in that scenario.

I'd focus on any RJ45 terminations in that loop (if you aren't using pre-made cables) from the keystone to switch or keystone to desktop, and then swap out keystones as the next step.

Now hopefully its not this, but did you have any snags pulling that drop that needed any really forceful tugs? Maybe you have a serious kink in the line.

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Aside from just a kink, if the cable was stretched too much during installation, that could also cause issues.

Since the only real fix short of pulling a new cable is to reterminate it, reterminating it usually is the first place to start...

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