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Fiberless Optical Networks
Alien54 writes "According to this Forbes Magazine article, the time for Fiberless Optical Networks may have arrived. Wireless optics have been given up for dead until very recently. But now better technology and lower product costs have enabled some to solve most of the problems. AirFiber (a company mentioned in the article above) is emerging as one of the favorites in wireless optics, and seems to have a set of good answers for the inevitable "bird and fog" questions: Can a flock of birds take down a network by flying through the lasers? Can a heavy fog send your precious information into the ether?"
Hi, just want to tell you that this laser thing really is old. Here at Aachen (in the very western part of Germany) the student hostels "Die Türme" (the towers, called so for being the four heightest buildings here in Aachen) of the technical university RWTH use such a laser to connect their local network via the laser with the main computer facililty of the RWTH and the web. The laser is about 4 years old and has a max. bandwith of 40Mbit. And yes, fog and heavy rain is a problem. Have a look at: http://www.oph.rwth-aachen.de/ag/netzwerk/technik/ laser.html
for the technical data and here, you'll get a picture: http://www.oph.rwth-aachen.de/ag/netzwerk/technik/ laser.bilder.html
(No, that's not me on the picture)
. Sorry, all pages are in german.
Not the birds or the fog. But if this is takn up by a lot of ppl/companies, will we not see bandwidth pollution similar to what is/happening with devices that operate in the 3G spectrum? The portable (not mobile) phones, the radio lan cards that are made, the airport (from apple)(yeah bastratdised radio lan cards), [perhaps the previous could be summed up as 802.11].??
What you are thinking of is the RF (radio) spectrum. Since it is broadcast, it is regulated, and yes it is being used up.
This, however is a point to point laser beam... (as in light... a totally different part of the EM spectrum) the only other station receiving the beam is where it is pointed.
People may use wireless optical stuff to simply avoid dealing with awful phone companies. Our t1 is upheld by the Verizon fiasco (may be in Fri) now. Att *could* do frame relay for us, as it is 2k for the drop and 1900 a month, in 30 to 45 business days. To expedite the delivery to 15 days, they want to bump us up to national service, so that would be 7k for the drop, and 5300 a month on a 36 month term = a 200k over 3 yr. commitment. We are actively looking at the lucent wireless gear, but building height on our new site is a problem.
Its misery like this that will help push people to find new high bandwidth solutions.
matt
const double MAX_POWER=500.0*ONE_MEGAWATT
const double NORMAL_POWER=500.0*ONE_MILLIWATT
if (flockOfBirdsDetected()) {
setLaserOutputPower( MAX_POWER);
wait(1);
collectCookedDinner();
setLaserOutputPower( NORMAL_POWER);
}
Donte Alistair Anderson Roberts - hi son!
Karma: Chameleon
Can a flock of birds take down a network by flying through the lasers?
;)
Well, if you increase the power of the lasers, you could then only need to pose this question:
Can a network take down a flock of birds flying through the lasers?
Problem solved.
From the article:
"And, with asynchronous transfer mode technology (ATM), the lasers have become intelligent enough to track the laser beams between the two optical transceivers, so they never get off target."
How the heck is ATM going to keep the lasers on target? I think the author confused this with ATM signallig setting up SVC's on the fly to provide reliable data transfer through the network in the case of a link going down.
Bit rate is proportional to bandwidth times the logarithm of the signal-to-noise ratio. To maximize bandwidth, you go up to higher and higher transmission frequencies. To maximize signal to noise ratio, you step up the transmission power. But in a wireless laser network, both of these steps have their disadvantages.
The first problem is essentially that the higher frequencies (e.g. infrared, which is on the order of microns, as opposed to microwave, which is on the order of centimeters) are more susceptible to various scattering phenomena. The most frequently mentioned is, of course, fog, dust, smog, etc. These scatterers are far to small to have any significant effect on, for example, cellular communications (transmitted signal has a wavelength of tens of centimeters, not microns), but they are excellent scatterers in smaller wavelengths. In addition, the atmosphere itself scatters visible light more and more effectively as you go to higher and higher frequencies, reaching a maximum somewhere in the ultraviolet. This is due to the electronic properties of diatomic nitrogen and oxygen and cannot be avoided. (As a side note, it is also why the sky is blue and sunsets are red). So, one cannot step around the fog problem by going to even higher frequencies. I believe, but am not certain, that fiberless lasers still operate in the IR.
The second problem, of course, is that stepping up the power output of the transmitter is expensive. A tenfold increase in bandwidth requires a thousandfold increase in signal to noise ratio. To see why this is so, imagine that with a given signal to noise ratio, you can resolve 16 signal strengths with a bit error rate of less than, say, 10^-8. This means that you can transmit 4 bits of information per symbol. To get twice as many bits per symbol, or double the bit rate, you need to be able to resolve 256 signal strengths - i.e. square your signal to noise ratio. To get 12 (three times as many) bits per symbol, you need to cube your S/N, and so on. Essentially, you have to double your S/N for each additional bit per symbol you wish to be able to resolve at a certain bit error rate. Hence the need for enormously increased power to achieve relatively modest increases in bandwidth.
So, with these constraints in mind, it will be interesting to see what optimum is achieved by TeraBeam et al, and how resilient their systems turn out to be.
Dave Bailey
Ibag
"Me fail english? That's unpossible!" --Ralph
This reminds me of something more than 20 years back: Datapoint's "ArcLight", for their Arcnet.
Arcnet was a token-ring based network with a broadcast topology. Cut the connection between two parts and it immediately reconfigures into two nets. Plug it back in and it reconfigures into a single net.
Ran on 8080-based terminals.
To get between buildings they used a gadget with an infrared laser diode (which had just come out) and a photodiode - each behind a lens about 6 inches in diameter. The device looked somewat like a weatherproof half-height-full-width monitor case with a little bit of a lightshade and the screen replaced by a couple of big glass eyes.
In a city where most buildings weren't skyscrapers (so a little defocussing could deal with building sway and clear-air turbulence without too much energy loss and interference acceptance), clouds and fog were rare, and at a time when high-speed data lines were 300 baud, it was great. A LAN that spanned multiple buildings. If the fog rolled in the network partitioned until it went away (no data between the head office and the branch for a couple hours, but the nets WITHIN the buildings were still up. Birds were handled by retransmissions that were part of the normal protocol.
Something similar would be easy with IP these days: Run a low speed (56k, T1, whatever) between the buildings AND put up the high-speed link. On foggy days your bandwidth drops but your connection is still there. IP also understands flakey connections and rerouting around them, and TCP understands using retransmission to make a reliable connection over unreliable links.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
It's amazing. Take a perfectly normal concept, like meshed networks, and apply it to wireless, and suddenly, you have made some kind of great advancement of science.
I don't see how this is any different than normal problems. Ther are using a wireless PHI.. fine.
The only point the article has made is that the price of optical open-air laser networking gear has come way down, so now it is feasible to build meshed networks with it, and hence, overcome some of the inherent problems with it.
And if the equipment used to cost $150,000.. how much do you think the monthly rental for that DS3 cost anyway? Not cheap. It will quickly dwarf the cost of equipment.
Of course, when we talk about canned networks for corporations (which *IS* a big deal these days), this gets more interesting.
Can a flock of birds take down a network by flying through the lasers?
Maybe they could adapt RFC 1149 - A Standard for the Transmission of IP Datagrams on Avian Carriers and, instead of seeing the birds as a potential problem, use them as carriers. Sure, a device would have to print the scrolls of paper, and attach it to the birds. It would probably decrease bandwidth, as the mentioned RFC mentions: "Avian carriers can provide high delay, low throughput, and low altitude service.". It's worth a good read.
To deal with this, they could also use RFC 2549 - IP over Avian Carriers with Quality of Service .
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Roses are #FF0000, Violets are #0000FF, find / -name '*base*' |xargs chown -R us && mv zig greatjustice
The purchasers of bandwidth understand:
- "Fiber" to mean very fast data sent via light (in something called "fibers" or "fiber optics" or something like that...)
- "Wireless" to mean signals sent between two stations without any hardware spanning the distance. (Just install a box at each end and maybe an antennaish thing on the roof.)
So "wireless fiber" produces the idea of sending high-speed data via light between two sites with gadgets on the roof without anything but open space in between them.
Even if the words don't really make sense when you look at them closely.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
25 years ago, the carrier I was on had a big honking radar. We used to hear scuttlebutt that the techs would get seagulls off the mast by mircowaving them. We figured it explained mystery meat and scab steak.
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Infuriate left and right
"With new eFog, your point-to-point wireless optical data communications link can be enhanced into a local area network!"
Next quarter, analysts forecast the public release of eClouds which will allow for a wide area network with a range of approximately 7 miles.
Kevin Fox
Kevin Fox
Most of Dave's comments are relevant to RF communication, not to optical.
Capacity is proportional to the logarithm of (1+signal to noise ratio). A small but significant difference. The result is that for a given power budget it is always better to use as much bandwidth as possible unless you are limited by arbitrary constraints such as the FCC's dumb frequency management practices.
There's no need to go to higher optical frequencies to increase capacity. The carrier frequency of a 1.3 micron infrared laser is 230 terahertz. It's easy to see that a few hundreds of megabits per seconds barely scratch the theoretical capacity.
You've got so much bandwidth in optical that more than one bit per symbol makes absolutely no sense. In fact, you want LESS than one information bit per symbol by using forward error correction codes.
The right frequency to choose is in the atmospheric window wavelengths - those least absorbed by water vapor.
In fog conditions the cumulative attenuation per meter is so high that even a hundredfold increase in laser power will not make a significant increase in the effective range. You are stuck with a few hundreds of meters. Deal with it. AirFiber's architecture looks like the right way to do it. Even if you ignore the bird problem, with a relay every few hundreds of meters the end-to-end reliability drops exponentially with the number of hops the signal has to go through. A mesh architecture can cover long distances while still maintaining adequate availability.
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Stop worrying about the risks of nuclear power and start worrying about the risks of not using nuclear power.