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Trying to get gigabit speed thru cat5 cabling

Hi - I'm in the beginning stages of upgrading switches to gigabit and wifi for an older building that has turned into an office building. From what I have been told, some parts of the building were wired 15 years ago and are only running Cat5, which as it was wired, doesn't support gigabit, like Cat5e does. Someone told me that it could possibly work "if we switch the A and B wire at the punch down" for the cat5 - can someone clarify this for me? Would this work?
4 Solutions
JohnBusiness Consultant (Owner)Commented:
I cannot say if that works or not.   But the faster cable is not a function of switching wires, it is a function of the twisting and the inter pair capacitance (must be reduced).
Mal OsborneAlpha GeekCommented:
It will probably work, but may not be reliable. Maybe only some runs will work, while other ones sometimes drop out, or run slowly, or only work with certain brands of NIC.  

Cable length will be a big factor, if you are close to 100M expect problems, if 10M you should be OK. Gigabit also uses all 8 conductors, while 100Mb only uses 4 of them. Thus, if any of the previously unused wires were not terminated, or have been damaged later, Gigabit will not be possible.

Having worked on a site with dodgy cabling, I would be very hesitant to try this. It is a real PITA when cabling is unreliable and occasionally and intermittently fails.
JohnBusiness Consultant (Owner)Commented:
It is a real PITA when cabling is unreliable and occasionally and intermittently fails.

Especially if the cable is buried in the walls. Cheaper to pull new cable than 10x the cost to fix bad cable.
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Andrew LeniartSenior EditorCommented:
Would this work?
No, at least not reliably. I recall a job I was involved in several years ago where a licensed electrical tech tried this and the network issues that followed just ended up costing more money to fix and do what should have been done in the first place. Installing new cable is far preferable and in the long run cheaper. I'd also recommend pulling down CAT6 rather than CAT5e cabling. The cost difference per metre is fairly small and CAT6 is far more reliable in my experience.

I hope that's helpful.

Regards, Andrew
If it is truly cat5, not cat5e, just replace it. No point in creating an unstable scenario. Do it right the first time and your life will be much easier.
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