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Fiber fiber fiber...
April 2, 2012 4:09 PM   Subscribe

I need some advice on best hardware / best practice when running ethernet over fiber optic.

So, I've been tasked with connecting a satellite office to our main network. The run is well over 400 feet long, so ethernet-over-fiber makes the most sense to me. There are 5x workstations in the satellite building and we need to support a decent amount of bandwidth, say equivalent to at least 100-base.

I've found these boxes on Amazon, which seem to be a legit starting point and fit the budget well.

What type of cable must I purchase? Any special considerations? Are the ethernet-to-fiber boxes I've found adequate?

Many thanks, hivemind! This will be my first fiber run and I want to do it right.
posted by roygbv to Computers & Internet (12 answers total) 4 users marked this as a favorite
 
You want to accurately measure your run, and then purchase a pre made 50 micron, 850nm multi mode cable with ST connectors. These are widely available. I wouldn't buy 62.5 micron simply because the signal degrades quicker in the bigger core.

The boxes you have found are fairly uncomplicated and there are a ton of variants on them out there, I would make sure you plug them in to full gigabit ethernet interfaces on either end.

Depending on the gear at either side you can often just shove an sfp or gbic in the device to get the same effect.
posted by iamabot at 6:03 PM on April 2, 2012


Make sure you keep a 3-5 meter service loop at either end, and always run 2 cables when running one for this kind of stuff.
posted by iamabot at 6:04 PM on April 2, 2012


Check out single mode fiber. You can get gig and 10 gig over single mode.
posted by roboton666 at 7:35 PM on April 2, 2012


Yikes. Stop. Do not use ethernet-to-fiber boxes UNLESS THERE IS NO OTHER CHOICE.

First, figure out whether you want gigE, 2x gigE, or 10gE. 2x gigE is a particularly clever choice because you can run two fibers and have the potential for automatic recovery from failure if you want it...

Pick some inexpensive managed switches. We happen to like the Dell 5324's around here. They support generic SFP optics, and for $125/each used, you can pick up two plus a spare and you've simultaneously solved your switch issue in the remote building. If you don't need vlan's, the 5224 are less expensive. You can opt for redundant power on either of those.

You need optics and fiber then.

For 400 feet? SX on 62.5 is rated for 220 meters. SX on 50 is rated for 550 meters. And that's *rated*. Fiber is full duplex; you're sending on one and receiving on the other. As long as the light gets there without being scrambled, it's fine. Many people have shot 62.5 far more than 220 meters, and I believe I recall a kilometer for 50. 400 feet? Don't get all freaked out and spend a lot. You probably do NOT want LX (singlemode) because there are complications with mode conditioning and attenuators that need to be considered at short distances. The cheap advice is to get 62.5 micron unless 50 is available at an acceptable cost, which it almost always is these days.

For optics? If you choose SX, and the switches above, use cheap FDDI-grade optics. Finisar FTRJ-8519-7D-2.5 is known to work, and they're like $10 each on eBay. Get one spare, and one or two for each end, depending on what you decide you want for a link speed.

For fiber? Is this going to run outdoors? Buried? Inside? If inside, get a suuuuuuper long patch cable if you want it to be cheap. Check with your local inspector to make sure they won't have an issue with it. Outdoor or buried is a little more complicated. Probably beyond the scope of this little note.

Suggest terminating the fiber on each end, rather than running it direct into each switch (a little ghetto but people do it). Terminating to SC is very common, then you'd need some SC-to-LC patches to connect to your switch.

Now if you've decided for 2x gigE, then you make sure you have turned on spamming tree...
posted by jgreco at 8:55 PM on April 2, 2012


Furthermore, over multimode you could get gig out of 400+ feet, you won't get 10 gig. Also, when fiber is run, ask to get 6 or 12 "strands" pulled.

The cabling company will put fiber patch panels on both sides. You need to make sure you know what kind of termination they are giving you in the patch panel:

SC Fiber "Stubby Connector" is a mnemonic I use
LC Fiber "Little Connector" is the other mnemonic I use.

"ST" fiber (I call it stab and twist) is a type that I consider to be going out of favor. I'm not sure why, but all the new installs of fiber tend to use SC or LC these days.

You don't specify if the office is outside, but if so be prepared for permits and trenching.

If you have to trench, check out Vertical Inlaid Fiber

Pretty much any transceiver will work. I like to use Transition Networks when I am forced to use transceivers (most of my fiber is terminating into Cisco gear at 10Gb speeds these days, so it's been a while since I bought a standalone transceiver). If you have switches that support fiber GBIC's even better.
posted by roboton666 at 8:58 PM on April 2, 2012


"ST" fiber (I call it stab and twist) is a type that I consider to be going out of favor. I'm not sure why, but all the new installs of fiber tend to use SC or LC these days.

Uh, because ST sucks? It hasn't been in style since the days of 10Mbps.

Pretty much any transceiver will work. I like to use Transition Networks when I am forced to use transceivers (most of my fiber is terminating into Cisco gear at 10Gb speeds these days, so it's been a while since I bought a standalone transceiver). If you have switches that support fiber GBIC's even better.

I meant to note in my previous post that many switches that support GBIC's or SFP's can be picky about the specific ones they'll take - especially most of the name brands. Cisco is easier because there are so many knockoffs out there, but these come at some risk. If you are able to just load optics in your existing switches, that's great, but I suspect from your examination of ethernet-to-fiber boxes, you don't have SFP/GBIC slots. And you probably need a switch for your satellite office anyways.
posted by jgreco at 9:29 PM on April 2, 2012 [1 favorite]


Thanks jgreco and robotron666, awesome guidance.

Indeed, our switches do not support optics at this point, but eventually they will. Hence the ethernet-to-fiber boxes... Why are these so bad?

Incredible bandwidth isn't the goal - we're just attaching 5 minor workstations to a group of servers that would be expensive/complicated to replicate in the 2nd building. The existing cat5 run is god-awful. Seeking a simple, affordable and stable solution until time comes to build something truly fancy.
posted by roygbv at 11:27 PM on April 2, 2012


Actually, those Dell 5224s look like a perfect fit for my application. Any recommendation on a used hardware vendor?
posted by roygbv at 11:35 PM on April 2, 2012


The ethernet-to-fiber boxes represent just another dumb thing to fail. Consider, for example:

http://www.newegg.com/Product/Product.aspx?Item=N82E16833156017

By all accounts, a well-thought-of product. First off, it's about as expensive as the route I've suggested. Next, it has a separate wall wart; in my experience, these can and do fail, and there should be a special place in hell reserved for an engineer who builds a product with a 7.5VDC hard-to-replace wall wart. Further, diagnostic information is sketchy; as one of the reviewers noted, status lights are minimal. If you pick a more recent switch like the 5324, you can access any onboard diagnostics on your SFP's, which could help identify the trouble. For example:

Port Temp Voltage Current Output Input LOS
[C] [Volt] [mA] Power Power
[mWatt] [mWatt]
----------- ------ ------- ------- ------- ------- ---
g21 N/A N/A N/A N/A N/A N/A
g22 32 3.36 9.43 2.62 2.22 No
g23 N/A N/A N/A N/A N/A N/A
g24 33 3.34 10.32 3.7 2.1 No

Temp - Internally measured transceiver temperature
Voltage - Internally measured supply voltage
Current - Measured TX bias current
Output Power - Measured TX output power in milliWatts
Input Power - Measured RX received power in milliWatts
LOS - Loss of signal
N/A - Not Available, N/S - Not Supported, W - Warning, E - Error

Well, that sucked, it lost the formatting. But anyways, that only works if both your switch and your optics support it. I don't recall if the 5224 does, but the 5324 with the aforementioned Finisar optics do.

# sho int st
Flow Link Back Mdix
Port Type Duplex Speed Neg ctrl State Pressure Mode
-------- ------------ ------ ----- -------- ---- ----------- -------- -------
[...]
g21 1G-Combo-C Full 1000 Enabled Off Up Disabled On
g22 1G-Combo-F Full 1000 Enabled Off Up Disabled Off
g23 1G-Combo-C Full 1000 Enabled Off Up Disabled On
g24 1G-Combo-F Full 1000 Enabled Off Up Disabled Off

And then knowing whether or not your ports are set up properly is just a question of chatting with the switch, rather than having not one, but TWO black boxes in-between your switches, where you could have a problem between your copper switch and the media converter, between the media converters, or between the far media converter and the far switch, a problem in any leg of which would just cause the link LED's to fail. Is it a bad patch cord? Did one of your media converters die? Maybe a little dust got caught in the optics of the SC connector, causing a bad signal? You suddenly have a lot of things to be verifying.

On the power topic, I'll note that the Dell switches have a redundant power supply option. I've seen switch power supplies go flaky, but not frequently, and usually not for newer gear. You can plug a RPS into a different UPS, though, and gain the potential for better network uptime. Compare that to the addition of a point of failure in the form of a wall wart.

I had a bunch of other things to rail on but I got derailed a bit following that thread of thinking. In Trendnet's defense, a good percentage of my complaints can be fixed by sticking these units in a 16-bay chassis they sell. But then you're looking at pretty hefty expensive.

Anyways, economically, the incremental cost of the method suggested here is rather low. These switches can aggregate up to four fiber ports as a single trunk group, meaning that if you were to run four pair of fiber, you could run up to 4Gb/sec just by adding more cheap SFP optics. I see the average price on eBay is about $130 for the 5324 and $10 for the Finisar's, so $170 per end for 4Gb/sec capabilities (though I *strongly* encourage the purchase of a spare of everything).

I can't recommend a particular used hardware vendor. While we actually do sell the stuff, and actually have everything mentioned here available, the ethics of it all don't let me turn this into a sales pitch. So I will offer you some good advice instead about eBay and 5324's:

1) Purchase something with rack ears. It doesn't always mean that it was used in a rack, but earless models often mean that they were stuffed behind someone's desk or something, poor/dusty airflow. Not all machine rooms are clean, but many have much better airflow, so a tendency for eared gear to be in better shape.

2) Purchase something that looks clean. It's obvious: it means it was handled by staff that cared. Labels are good, labels come off, and again mean that it was maintained by staff that cared. The units with scratches all over the place? Not so cared for.

3) Purchase units, where possible, from someone selling in quantity. They'll tend to be retiring gear out of a data center or telecom closet, stuff that was probably installed out of the box, never moved, and then deinstalled and put up for auction.

4) Do not buy units that look like one of the SFP ports might have been damaged. Look at, for example, port 24 on this unit:

http://www.ebay.com/itm/Dell-PowerConnect-5324-24-Port-External-Managed-Switch-w-4-Gigabit-SFP-Ports-/251032838579?pt=COMP_EN_Hubs&hash=item3a72b921b3#ht_1400wt_1145

It probably works but why take the risk.
posted by jgreco at 5:36 AM on April 3, 2012 [1 favorite]


The school I netadmin runs gigabit over both 62.5μm (with ST terminations) and 50μm (with SC) multimode fibre for building-to-building networking, using these D-Link switches (cheap!) and their accessory mini-GBIC fibre interfaces (not so cheap). In the three years those have been installed I've seen one fibre interface fail out of ten, and that was replaced under warranty. Before those switches were installed we used to run 100Mbit over the same fibre using standalone Ethernet-to-fibre adaptor boxes at each end; in the three years we had those, three out of six failed.

So whatever fibre interfaces you end up using, it couldn't hurt to lay in a couple of spares.
posted by flabdablet at 7:02 AM on April 3, 2012


Those D-Link switches aren't that cheap.

As a note, "mini-GBIC" is another term for "SFP", just to avoid any terminology questions.

And just to make one more point: you may not be able to use generic optics like the Finisar modules I listed with arbitrary switches. Many switch manufacturers see SFP's as a value-added upsell. Once you're locked in having bought their switch, you may find out you're locked in to buying their optics - so be sure that either you can pocket the cost of the total solution as provided by D-Link, or be careful to do some research to make sure that your selected switch will accept unbranded SFP's. Don't even buy a newer Dell switch and assume that since the 5324 works with generics, that newer ones will too. It doesn't work that way.

Sorry for the repeated revisits to topic, there's a lot of information to dump and a lot of angles to consider. Everybody here has given you great advice, even where contradictory. You can do this many ways, each has pros and cons, and there is no one magic right way. But all the stuff you've heard more than once, that in particular, pay attention, it's the voice of experience.
posted by jgreco at 7:48 AM on April 3, 2012


I love you, metafilter! Thanks to all for the killer advice.
posted by roygbv at 9:15 AM on April 3, 2012


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