Thursday Feb 22

Posts Tagged ‘568B’

Layer 1: Mr Bump and the Bad Wire
Last Updated on Tuesday, 12 August 2008 03:52
Written by JJ
Wednesday, March 19th, 2008

No, not a bad Mr Bump, or a bad Bump in the Wire… But one of the Bumpster’s recent posts brings about a good topic for mention- bad cable (or wire, as is more appropriate for his post).

In his friendly KISS-it note, he shares a story to remind us of our Layer 1 woes. I can’t TELL you how many times there’s a mystery problem… which almost always later surfaces as a physical dis-connect or mis-connect along the way.

In fact, just last night a certain someone called me from the road while setting up a demo… after hours of agony (and fixing some other issues) the final problem was- YEP- a cable in the wrong spot.

It’s something that happens to all of us- certainly nothing to be ashamed of. And it doesn’t always work out to be a misplaced cable… quite frequently we see bad cables, older cheap Cat 5 that’s not behaving well, home-made ends that corrode or break and even the occasional patching mis-match (see my previous post on 568A vs B).

Don’t we feel stupid after hours (or days) of puzzling, only to find out there’s a piece of metal, plastic or fiber to blame?

Here are a few Tips & Tricks to check Layer 1 and possibly eliminate frustration when you have your next ‘mystery’ problem:

  • Cable placement. Obvious one, but check and double-check, then have someone else check. It’s like proof-reading your own writing.
  • Cable REplacement. If you’re not sure- just replace the cable when possible with a known good. (Note the ‘known good’, I’ve seen batches of lemons more than once).
  • Ditch Home Mades. This little gem comes from my father- many years ago, he started noticing home-made cable ends (even those made with the BEST crimping tools) would eventually deteriorate. It may be fatigue, corrosion or little aliens- you can’t always be 100% sure of the cause, but it happens more often than not.
  • Don’t Bend It. If you are working with fiber, be nice to the fiber… wrap it gently in loose coils. Don’t bend it, squish it or let it get crimped in the cable management. You may know this, but others rummaging in your closet may not.
  • Check Negotiation. Hop in the switch or device interface and see what speed and duplex it auto-negotiated to. This culprit is probably a close 2nd behind finding bad cables.
  • Check Neighbors. A good way to dig around and investigate a possible Layer 1 issue is to jump back in that switch interface and do a show arp or show neighbors (clear old first) and see if you what you think should be there is actually there.( Pings can work too, but it’s possible ICMP is disabled, so I prefer the former method personally.)
  • Check Patching Termination. Instead of repeating myself, I’ll direct you to the recent post on 568A vs B. You’ll usually see this when you upgrade from 10/100 to Gig.

Layer 1 is the FIRST thing we check for when doing a site survey or network migration plan. If you don’t get that one right, the others are surely to fail… which may take you to Layers 8 & 9… and as we know- we like to stay a 7 and below. ;)

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What You Should Know: 568 A vs B
Last Updated on Tuesday, 12 August 2008 03:43
Written by JJ
Friday, February 15th, 2008

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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