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Posts Tagged ‘cabling’

Fiber: Review of Optics, Cables & Connectors
Last Updated on Tuesday, 12 August 2008 04:18
Written by JJ
Saturday, April 5th, 2008

When I started this blog, I said I wanted to give you useful information, sometimes in the form of lengthy technology overviews, and sometimes in short snippets. I like to dig around the search terms, comments and emails to see what you want to know more about, and I’ve seen a lot of interest in fiber information.

The fiber types (such as multi-mode, single-mode), standards (SX, LX, LH) and  connectors (LC, ST, SC) seem to be topics that need clarification about 80% of the time when we’re working with customers on networking equipment or site surveys.

Here’s a brief review of the various types of fiber, optics, connectors and when to use what. Let’s start with the basic stuff, and move down the line.

Multi-mode vs Single-mode
First of all, we have multi-mode and single-mode fiber. Multimode has a larger diameter ‘core’ or the area in the middle the light travels through. The larger diameter- think of it as a big tunnel- lets the light take different paths, creating multiple rays, or modes (hence multi-mode). The light bounces around more, which means the connectors and splices for multimode are more forgiving than for singlemode, but the bouncing causes dispersion and fidelity loss. On the other hand, singlemode has a much smaller diameter core, giving the light one straight path, or mode, through the cable. Because of this, singlemode offers higher throughput and longer distance, but the light equipment and connectors are much more finely-tuned. Which, of course, means singlemode is much more expensive.

When you’re adding or surveying multimode fiber, you should know what core size you’re working with. The core size affects bandwidth and the maximum distance you can reliably run it. Multimode usually comes in 50- or 62.5-micron, which is the core diameter. The larger the core size, the more bouncing, so the shorter distance you’ can go. To give you a general comparison, most singlemode comes in 9-micron core, which is about 1/6th the diameter of multimode. The smaller the diameter, the more precision you get.

When to use what. In short, the fiber type you choose will depend on 1) budget and 2) distance. Mostly, you’ll use multimode for short fiber runs, between switches, to servers and possibly between buildings, if they’re adjacent. You should use singlemode when you need higher throughput or a longer distance. Here’s a quick look at the types and maximum distances for each. I’ve also included a proprietary rating, for connectors using 1550nm wavelength over singlemode fiber, to get increased distance. (Standard for singlemode is 1310).

  • Multimode – up to 220m with 62.5 micron core
  • Multimode – up to 550m with 50 micron core
  • Singlemode – up to 5km-10km (standard, using 1310nm optics)
  • Singlemode – up to 70+km* (proprietary, using 1550 nm optics)

Fiber Optic Standards
You’ll need to know the type of optic to specify for your network equipment. Some vendors have their own proprietary fiber optics, but the standards are 1000Base-SX for multimode, and 1000Base-LX for singlemode. You can use multimode with 1000Base-LX with the addition of a mode-conditioning cable to set the light along the correct path down the cable. LX, which is standard, uses the ~1310nm wavelength. Vendors have created 1000BASE-ZX and 1000BASE-LH, which use the 1550nm optics to obtain longer distances. Note, here we’re talking about 1-Gig fiber, not 10GbE, hence the 1000Base. We usually just refer to these as SX, LX and LH, leaving off the 1000Base– when talking about the optics.

  • 1000Base-SX – multimode
  • 1000Base-LX – singlemode standard (can be used over MM with mode-conditioning cable)
  • 1000Base-LH – singlemode non-standard (proprietary for longer distances at 1550nm)

Here’s the fun part, and no one remembers what connectors they have (if they even knew in the first place!). There are several out there, but you’re probably going to only ever run into three – LC, ST and SC.

I’ll start with LC since that’s usually found on switches and other network equipment these days. LC stands for ‘Lucent Connector’ (the creator) and is the connection type on SFPs (Small Factor Pluggable) or Mini-GBICs. They’re small, and were designed to replace the SC connectors.

Since I mentioned SC, let’s go there next. SC, or ‘Standard Connector’ are the predecessor to LC, and are similar in shape, but quite a bit larger. We suggest using the mnemonic ‘Square Connector’ to remember SC.

Last- and possibly least- we have ST, which really means ‘Straight Tip’, but many folks have a better time thinking of ‘Stab and Twist’. You stick it in and lock it in place by turning the outer barrel, sort of like BNC did. And yes, I’m old enough to remember the BNC days ;)

Duplex and Simplex
Most often, you’ll be using duplex fiber, which consists of a pair of fiber for bi-directional communication. Then- of course- you would use simplex fiber cables if you only need to send data a single direction. Those applications are more specific, but they do exist. On duplex cables, you’ll noticed connectors that aren’t fixed-form will be marked or color-coded, one for transmit, one for receive.

Ordering Fiber Cables
If we’re translating all our acronyms and numbers into something we can use, then let’s talk about how you put it all together when you’re looking for the right cables.

For example, let’s say you’re purchasing short fiber jumpers for connecting your patch cable to your switch. Most likely, you’ll want multimode, in a short length (2meters), with LC on the end going to the switch and let’s say SC on your patch panel. In our example, we’re assuming we have 62.5micron mm fiber.

What you’ll ask for is: Fiber jumper, 2 meters, duplex, 62.5-micron multimode, LC to SC.

fiber_LC_2.jpg fiber_SC_2.jpg fiber_ST_2.jpg

These are the best images I found to demonstrate the shapes and orientation of the various duplex fiber connectors we talked about. You can find these images and descriptions at Cables To Go.


Wowzers, I said this was going to be a short one. In fact, this post was originally titled “Fiber: A Very Brief Review of Cables & Connectors” but I had to rename it ;) Oh well- now you have all the information in one place for future reference.

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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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