Thursday Nov 23
Feb
15/08
What You Should Know: 568 A vs B
Updated on Tuesday, 12 August 2008 03:43
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Why you need to know what your cabling standards are.

There are a few (okay, several) points of networking I’m working on understanding better. One of those is being able to succinctly explain to customers the difference between 568A and 568B and help determine which they’re using. I’m not at the point I can walk into a closet, glance at the patching, and tell you how it’s punched. I certainly don’t consider myself an expert on this (talk to your cabling provider) but here’s some good information to help you understand when it’s important, and what questions you should be asking.

So, to get started- what we have to understand is there are are two ‘levels’ of the 568 cabling standard. The first ‘mothership’ 568 standard is the all-encompassing EIA/TIA 568-B Telecom Standard (2001). (FYI- TIA, Telecommunications Industry Association is an assoc of the EIA, Electronics Industry Alliance).

Here’s where the A and B come in. Within the EIA/TIA 568-B Standard are a few pages dedicated to the pinouts, or Termination Standards – T568A and T568B which describe the pin/pair assignments for the cabling (Cat 3, 5, 6).

What’s the difference? Physically, pairs 2 & 3 (Green/Orange) are swapped. Functionally, because of the pair-swapping, the T568B is not backwards compatible with many legacy systems and telephony cabling. (FYI, 568B is not even recognized as a standard by several national telecomm organizations).

Why does it matter? In addition to not being backwards compatible, connections terminated with differing standards on each end will not function properly (or at all). This is extremely important if you’re going to be moving from 100-T to 1000-T, since Gig uses all 4 pairs.

To sum it up: EIA/TIA 568-B is the overall telecom standard, and T568A is the recommended termination, or pin out.

If you’re already setup with T568B throughout, then its recommended you stick with that. All new implementations should go with T568A, and we recommend ANYONE upgrading from 100T to 1000T double-check the cabling standards in patch panels when planning an upgrade (it’s part of our Layer 1 checklist). You may be running 10/100 over mixed-ends and it’s working, but when you slap that new Gig switch in the rack you could get a nasty surprise if you’re not paying attention.

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