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View Full Version : Some basic Fiber questions.

kilowatt
September 8th, 2009, 02:47 PM
Greetings,

Due to an overwhelmingly high amount of RFI (radio interference) being generated by my wired ethernet network, I have decided to switch some of it over to fiber optic medium. This question isn't mac-specific obviously, but I think the folks here will know the answers faster than anywhere else on the web (so far that's been my experience here!. :-)

Switching to wifi isn't an option in this location because we are in a broadcast facility that actually uses that frequency spectrum for other uses.

I currently use a single Cat-5 ethernet cable going from my router computer (an intel box running FreeBSD) to my VoIP server (an intel box running linux). I would like to replace this with something optical.

Questions:

1) which of the several optical mediums is best? My usable outside bandwidth is about 20mbit, although in this application only a few mbit is really needed. I'll need supported PCI cards on both ends obviously.

2) is there an optical concept similar to an ethernet crossover cable? Or can I just rotate the plug so that the RX and TX are swapped at one end? I don't want to buy an optical hub/switch for a single connection if I don't have to.

Sorry to ask such noobie-ish questions, but I've had a hard time finding "basic technical" answers. Especially the second one.
bitlord
September 8th, 2009, 03:04 PM
There is single mode and Multi mode fiber. There is no crossover cable for fiber. last time I checked they had 10G. Not sure it has been a while. There are conversion kits. these are little boxes that connect to the Ethernet you are already have installed on your PC's and then you connect the fiber to these boxes. You can get new fiber cards for your Pc's instead but, I was thinking you would have less configuration issues with the converter boxes. You will have to get new switches though.

I hope this was useful
kilowatt
September 8th, 2009, 03:12 PM
Yeah, I saw those converter boxes, but they cost more than the NICs. And, I'd still have a short ethernet cable -- something I have to avoid.

So there are no crossover cables. Does that mean I have to go into some kind of hub or switch? Or can point-to-point links just swap the TX and RX?
bitlord
September 8th, 2009, 03:31 PM
You maybe able to connect directly PC to PC but I have never done it. My 1st computer job was running the fiber cables in the building I worked at. I always hooked up to switches or routers. I always connected the PCs to Switches.

I only mentioned the boxes so you would not have to reconfigurer your router.
If you mix up the TX and RX the card will not work.
I guess I will have to ask one of the network guys next time I see one. I'm sure they would know.

Sorry I don't know more
simbalala
September 8th, 2009, 05:50 PM
Yes, you just switch the tx and rx to get the connection. The plugs are not physically polarized, there's an indication on the cable so you know which fibre is which.

Multimode is fine for your application, which is short and slow for fibre. If you can get single mode hardware and cable for about the same price then I'd go for single mode just to have the better stuff.
Satcomer
September 8th, 2009, 10:48 PM
The cheapest wired you could use is Shielded Cat 5E cables. The shielded will prevent bleed over but they do cost a little more then regular unshielded. The shielded cables is what used in most network shops because it really prevents bleed over.
kilowatt
September 9th, 2009, 10:07 AM
From what I've heard, the shielded cat 5 is better but not as quiet as I need it to be. There are other solutions too, like placing ferrite filters every few meters. But I don't think anything will be as quiet as optical fiber ;-)

Thanks!
simbalala
September 9th, 2009, 10:48 AM
From what I've heard, the shielded cat 5 is better but not as quiet as I need it to be. There are other solutions too, like placing ferrite filters every few meters. But I don't think anything will be as quiet as optical fiber ;-)

Thanks!
Fibre is terrific, it solves all kinds of problems which one runs into with metallic cabling, EMI just completely goes away as an issue. I know you don't care about distance but even with multi mode fibre runs of thousands of feet are not a problem, single mode takes you to miles.

It sounds like you know what you want and why, the only downside with fibre is the cost.