fibre optic explanation needed

(probably white (not clear), blue, red, green)

They gave you 4 incase one of the pair was bad. Generally, you'll be running Gigabit Ethernet over two individual fibers.

Sounds normal.

No, you shouldn't need another module. Sounds like you have everything that you need to have. Did you swap around the pair of fiber end-to-end such that the Transmit of one switch is going into the Receive port of the other? If not, try flopping over one to the other at one of the panels.

If your cable has only four strands of fiber, their colors leave me in wonderment: it's been years since I saw anyone using non-standard colors for fiber. I mean, those that differ from the de-facto standard:

#1-blue #2-orange #3-green #4-brown #5-slate (grey) #6-white #7-red #8-black #9-yellow #10-violet #11-rose #12-aqua

It may also be the case that you have a 12 or 8-strand cable of which only

4 are terminated, namely #7, #3, #1 and #6 (assuming white is clear). In this case you may need to try eight combinations of pairs (like, red-green, white-blue, red-blue, red-white and so on) because you would not know which combination makes a pair on the other end. Actually, this is the reason why people use standard colors: you always know the sequence on the other end.

Oh dear, i wasnt aware of that i think the company may be a bit dodgey.

We think we have got the idea though because looking at the cabinets there are 3 fiber patch panels/links, one from the new building i am trying to sort on from another cabinet that already works and one that links to a cabinet with the servers in, this final one has a fiber switch in so we have ordered another patch cable to finish the chain, then its just a case of getting them the right way round. This is my next bit, i assume if i see a light on one cable this is the reciever and the one with no light is the transmitter. is there a standard for which is left and right on the patch panel????

Thanks for all the help so far

Phil Sigley

If "light" means a flashlight beam, then you should see that on every fiber. If you mean a "light" from a switch or other device, you should not be looking at the end of the fiber. It may be a laser beam. You could get eye-damage.

Actually, I think Phil was referring to an interesting phenomenon that has to do with the way human eye senses the light. By saying that I'm assuming that he does not have a visual fault locator, which would explain it little easier ;-) If I'm wrong in that assumption, Phil, please correct me. So, getting back to a human eye: It has been observed that some (most? myself included) people have some degree of sensitivity to lower end of the infrared spectrum. Anything above 700 nm is considered infrared (invisible to humans). Most of the infrared light is absorbed by the eye, however, peripheral areas of the retina can still catch some light energy in the lower infrared spectrum. The trick only works on 850nm multimode fibers. 1000BASE-SX would be one example. When you look at your fiber switch with a live connection and dust cups/cords off so that the fiber is in the corner of your vision, you can see dim red light on the "receive" end of the fiber. The key is: YOU SHOULD NOT TRY TO FOCUS YOUR EYES ON THE FIBER END. Focusing your eyes greatly increases the risk of laser burns, so never do that. Besides, focusing on the fiber end defeats the whole purpose of the exercise because at the center of the retina you'll see nothing in the infrared part of the spectrum anyways.

One other reason why you can possibly (with caution, of course) look at the fiber is because the light leaves the fiber end at some angle of aperture (about 16 degree for general multimode), so the energy starts to dissipate. All the laser safety is based on assumption that you might look at a COLLIMATED beam, and the light, escaping fiber does not qualify. One thing is for sure though: you should never look at a fiber with a tool that focuses the light.

With that said, one should never look at fiber AT RANDOM! Except for the particular case with multimode fiber and 850 nm sources you will see nothing anyways AND may get your eye permanently damaged, so what?s the point?

A great reading on the laser safety is Laser Institute of America laser safety information bulletin here:

Always know what you are doing, and you?ll be fine! There is no reason to be afraid of fiber optics.

Thanks for that link, we will be careful. Unfortunatly we work in a school and the chances of being bought any equipment for testing a fiber is non existent due to financial restraints. As would be paying a pro to do this job.

We know have the thre cabintes linked up and in the fiber switch, a

3com 3300fx, we get a green light on the LEDs on the front but no flashing orange light to indicate packets beign sent or recieved. Swapping the fibers knocks the green led out as well so im assuming something needs doing to the switch. Anyone got any ideas what this all means.

Phil Sigley

Well, if you try to connect the 1000BaseSX(?) module mentioned in your original posting to a 100BaseFX Port you will be definitly out of luck.

Steady on link light and no activity light usually means that the receiver end senses some signal coming in, but either one of the three conditions is present: #1 The signal transmitted from the local end does not reach the other end (mis-patch, break or disconnect of the fiber, connected to the local transmit end) #2 The devices on the pair of fibers have incompatible protocol and hence can't establish a connection #3 Hardware failure, including wrong GBICs or other plug-in fiber modules.

If you flip fibers in the pair, then you'll observe following changes:

#1 - the link light will go off on the local end and on the remote end #2 and #3 - the link lights will go off on both ends.

Of these three #2 is easy to rule out when armed with datasheets on both units. #3 can possibly be ruled out by swapping units with those known as working.

For further drilling down on #1 a visual fault locator makes an indispensable tool. It's basically a laser pointer (635nm red LED) with precisely aligned and collimated light output that can be efficiently coupled with fiber to observe visible light as far as couple miles of fiber. The tool can be had for around $150~$200 on the Net, and it will save literally thousands of dollars worth of fiber service calls over couple years. In my estimate at least 60% of fiber service calls are caused by accidental swap of fibers in a pair and well as wrong patching. These problems are easily identified and fixed with a VFL.

Good luck with the troubleshooting.

Manfred is right i think, our new switch is gigabit and the old is

100mb so they cant be linked. Will take all i now know to the powers that be and see if they can find the money to go gigabit over all the fiber backbones. Knowing the good old uk education funding system that will be a no and it will be april beofre i get my library working. Suppose i could lay a copper wire instead.

Id like to thank everyone for their advice and patience with me while trying to work through this problem. Thanks very very much as good advice is hard to come by.

Regards Phil Sigley

No good idea, especially between buildings. You could get a 100BaseFX mediaconverter for some 50 pounds and forget about Gbit for awhile. A single Gbit link is not too beneficial unless you have very a special traffic pattern. And even in this case a trunk with a second converter would probably suffice and is only 10-20% of a Gbit interface in your old superstack.

I think i may have persueded the management to take all the fiber up to Gbit in one go and at some time soon. What i need to know is to take the whole lot up to 1000base-SX from 100base-FX will i have to get new fiber laid around the building or can we just upgrade the switches in each cabinet. I seem to remember someone from the cable company saying our system was 'capable' of Gbit, however after several bodged jobs we have broken links with this company.

Phil Sigley

It depends on the length and the kind of fiber. The specs for 50/125u fiber are 500-550m and you can expect it to work for about 1km.

62.5/125 carries much less (220m) and I have no experience on how far you can push it.

220m. We've got old FDDI grade 62.5 MM in the ground and when we went to 1Gig back bone, there were several buildings that had to switch to single mode. We've basically found that the 220m is a brick wall.

Another way to allow for greater distance over the same 62.5/125 multimode fiber would be to purchase 1000BASE-LX GBICs instead of 1000BASE-SX. It's a different price range, of course, but it may still be less expensive that to re-pull the fiber cable.