Become a fan of Slashdot on Facebook

 


Forgot your password?
Close
typodupeerror
×
Technology

Fiber Optic World Records Broken 148

Posted by jamie from the excelsior dept.
Thousands of miles of existing fiber still lie dark, but as schnucki writes, "Bell Laboratories believe they have broken two world records in the use of optical fibres to transmit information." They sent 160 gigabits/sec on one wavelength, and then in a separate experiment sent 1,022 separate wavelengths down one fiber. You do the math. Check it out.
This discussion has been archived. No new comments can be posted.

Fiber Optic World Records Broken More

Fiber Optic World Records Broken

Comments Filter:
  • I am getting 21600 on my 56K modem at my new apartment? Did I win anything?

  • This just in... (Score:1)

    by Anonymous Coward
    a third record has just recently been broken. Bell Laboraties has finally succeeded in using fibre optic cabling to send pjorn at speeds until now unkown to many scientists. Guys were actually cumming before the pictures hit their screens...not to mention something else that did a second or two later!
  • Bandwidth boys and girls? I knew you could!

    Can you say really amazing pornography? I thought so.... It seems like any technology improvement is sucked up there anyway. That's OK. Let the perverts drive the cost/unit down.

    On a personal note, I was pretty pumped to get 115K a second on a download on my cable adapter (I refuse to say cable MODEM!) the other day :)
  • The first record promises to increase speed.
    Woohoo! No more poxy 299,792,458m/s! According to relativity, this means that the data can go backwards in time. Soon we'll all be complaining about anti-latency.

    Normally I wouldn't nitpick the BBC[1], but seeing as they split an infinitive in the last paragraph, I felt I had no choice.

    [1]This is a lie.

  • Re:can you say .... (Score:1)

    by Anonymous Coward
    If you don't have digital cable, it should be called a modem. All it would be doing is demodulating analog signals to digital and modulating digital to analog. Or am I just talking out of my ass. That seems pandemic to slashdot these days. I better submit this under Anonymous before I lose my precious karma points ==== last sentence provided as a joke, in case some of you tight asses get your panties in a bunch (that statement always makes me laugh).
  • Each experiment is highly impressive, but why don't they try to do both at once? Yes, logic (and the theory of fo) says that it will work, but they should still test it.

    Anyhow, this is something else that still needs to be implemented over a wide area. Many of the main phone carrier lines here are fo, but most buildings still have 20 year old copper, so it doesn't do the user much good. Hopefully telco's will (are?) encouraging the use of fo in new buildings. How much of the U.S. telephone systems have been replaced with fiber?
  • I'd like to have that running into my home. Perhaps we could use SimCity to demonstrate the traffic surge that will generate? The subways could be the fibers, put some commerce, here, there. Cram the schools in the lower corner, Why does SimCity insist that there have to be power generators inside the internet?
  • Well, it has always been my understanding that Fibre Optics transfered data by sending "light" through "glass fibre" hence the name "Fibre Optics." From this explanation I would imagine that light traveling through glass fibre would travel at the speed of light. Pretty logical I think.

    -Al-
  • Just a little thought should tell you this isn't so. If the speed of light were directly correlated to datarate, that would indicate that all fiberoptics trasmitted the same amount of data, and thus the feat that Bell Labs performed wouldn't be very interesting.

    To give a bit of background, fiberoptics is just a small glass (or other clear substance) thread, which provides a container for light to bounce through. The light always goes at the same speed (I know that isn't quite true, but close enough for this discussion).

    The data rate achieved is based on the frequencies that are transmitted. So, in order to get the higher data rates, higher frequencies are needed. (Generally.)

  • Also does this mean a faster internet? I have a cable modem and many sites are just soooo slow.


    hehe, i'm on a 2mbit link, and yes the internet is sooo slow. :)

    but as long as i stay on the backbone, it just soo fast

  • Stability? (Score:3)

    by nevets ( 39138 ) on Monday November 15, 1999 @07:34AM (#1531045) Homepage Journal
    I'm just curious what the error rate is. Can you send that much data without loosing a few bits. I'm impressed with the numbers regardless, but if you have a 50% error rate is that good? Also if you loose one bit per byte, can you clam anything? Did they only count the good bits sent?

    Also, what is the speed to transfer the light signals to electrical. I don't have (or have I ever heard of) an optical computer, would be nice though ;). If you send 160 Gb/s (20 GB/s), can you convert that to electrical data without making a bottleneck. I'm not an expert in this area, but I'm curious to know.

    Steven Rostedt
  • I thought that was one of the advantages of fibre, that it didn't have any interference such as crosstalk on copper wires.
  • 160 gigabits/sec * 1022 wavelengths = 163,520 gigabits/sec on a single piece of fiber.

    Which reminds me, I need more fiber in my diet, if only for the bandwidth alone.

    --
  • 299,792,458m/s

    Just to join in the nit-picking, this isn't in a vacuum, but in a dielectric, so the speed of light won't be c necessarily. I don't think there is a huge difference (been a long time since I have done the calculations), but there is a difference, that's how the light is kept inside the cable!
  • You are thinking of RF interference. Fiber optics are immune to radio emmisions from outside sources becuase their medium is light instead of bouncing electrons.

  • It's great news (and I submitted it a week ago and got rejected - grrrrrr.... :) but note that the experiment requires Lucent's new optical cables.

    I doubt the mass market is going to re-lay their existing, im-pure cables anytime soon. So Doom fans take it easy.

    However new corporations should look with interest. And investors may want a bet on Lucent: first a record fast switch and then a record fast cable. These guys are on to something.

  • I'm most positive that bandwidth will not be a "buzzword" for future generations. I remember living in a house (as a child) with a T.V. antenna on it. Every neighbor had one too. We got Maybe 4 channels on a good day. We had a clicker on the table that actually went ~click~. Now, I have cable TV. There are over 200 channels, and everyone I know has this or a sattelite. The only place I've seen rooftop antenna's this year, is a trailer park. There's gonna be a day, in the not-to-distant future where bandwidth will be endless (in comparison to now). The Bandwidth Blues will be just another Golden Oldie.

  • the number of simultaneous calls that can be carried using 32 colours on a fibre to be increased from 30,000 to millions

    That's a lot of calls at the same time. Maybe someday we'll be able to watch digital TV while bungee jumping. But who cares.

    Everyone on earth will soon be able to call everyone at the same time (to just talk about nothing).

    The world needs the new optical technology

    They mean a small part of the world needs optical technology (nerds). :-|

    The rest of the world needs water, electricity and food.

    Solutions for a small part of the planet. a.k.a IBM's motto

    Just thoughts

  • You're right, of course; it won't be c. But the beeb mentions that they (say they) increased the speed by changing the transmitter, not the cable. So they got light to go faster through the same medium. Can you die of cherenkov radiation poisoning?
  • What they are doing here is called WDM (wave division multiplexing). There has been a standard for a while on WDM. But the thing is this only allows you to cram more information down one pipe it doesn't shrink the equipment on either end. They need to stick in and OC-48 for each wave length, so you would need about 1 foot ball field of space to stick all of the equiptment for this one piece of fiber. To sum it up don't expect to see any dramatic speedups anytime soon
  • actually, it seems that tons of investors ARE betting on it.

    Lucent's stock has nearly tripled in the last year/year and a half.

    (I bought last september with a cost of $28.50/share... it's now in the $70's)

    Now if only their software backed up their hardware so we don't have a repeat of the MCI-Worldcom problem of a few months ago with the frame relays crashing for about a week.
  • They claim all 1022 wavelengths were transmitted at the same time with an ultra fast laser. I thought lasers emitted coherent light at one wavelength. I have seen adjustable lasers, but it was one wavelength at a time and depended on tube geometry and the die used. How do they tune their laser to transmit multiple frequencies at the same time? It sounds unbeleivable to me.
  • According to my networking teacher, IBM pretty much stopped looking for maximum bandwidth with fiberoptic because their equipment became the bottleneck. In other words, if you can build a machine that can transmit 163 Terabits in one second and a machine that can recieve 163 terabits in one second, then you can do the full test.

    This is a serious value multiplier. They don't need to add any more fiber where there is already a line. Why aren't I excited? You think Bell Labs is going to share this tech with ANYONE? Hell no.

    Later
    Erik Z

  • That's more colors than there are colors for the new "PalmGlove" cases!

    And boy, will that ever give us more bandwidth to support the increasing numbers of cellular phones!

    (Um, oops... How do you get the fibre cables out to the phones?)

  • They should be researching new cable INSTALLING techniques. Who cares how much bandwidth the trunk a half mile away has if I can't have any of it? Until it cost about 3 orders of magnatude less than $450K per mile (number based on unreliable recollections) for fiber I'll be stuck in the bleak world of copper.

    Vacuous futurist idea: Imagine a very small machine that burrows from a central office/switch to your basement with very little operator attention. As it burrows it's dragging along a strand or two of lovely fiber.

    Listen to me whine! I'm lucky enough to have a cable modem and I'm STILL not content!

  • Light can indeed cancel itself. Think of defraction patterns caused by coherent light mixed 180 degrees out of phase with itself. My physics is a little rusty, but I'm interested in fundamental harmonics created by other modulated wavelengths.
  • Umm. Doesn't electricity also travel through copper at roughly the speed of light?
  • "Vacuous futurist idea: Imagine a very small machine that burrows from a central office/switch to your basement with very little operator attention. As it burrows it's dragging along a strand or two of lovely fiber. "


    As it burrows it also cuts lovely little holes through existing fiber lines oops :)
  • "Vacuous futurist idea: Imagine a very small machine that burrows from a central office/switch to your basement with very little operator attention. As it burrows it's dragging along a strand or two of lovely fiber. "


    As it burrows it also cuts lovely little holes through existing fiber lines oops :)

    (the successor to the backhoe of doom)

  • the big news (Score:3)

    by Haven ( 34895 ) on Monday November 15, 1999 @08:06AM (#1531068) Homepage Journal
    I think the most impacting news is that optic "router". That is going to have the biggest effect. We dont' need 160gb/s if it has to be converted into an electronic signal everytime it switches fiber lines.
  • I have a similar problem..is it caused by a bad phone line or bad isp anyone know? I get a slightly better speed with one isp, but still way below what I'd expect.

    ------

  • Sampling rates, digital, and misc cool stuff (Score:5)

    by Signal 11 ( 7608 ) on Monday November 15, 1999 @08:09AM (#1531070)
    Just incase you guys didn't know - the reason fiber optic can go so fast is because it transmits analog signals. That means you can layer several hundred harmonics on a single frequency and create a very complex waveform. The trick is in the decoding - converting it to digital. That's where all the sample-rate jazz comes into play.

    This isn't really revolutionary new technology.. we've known about stuff like this for awhile. There's a nearly infinite number of ways to encode frequencies, and stack things onto each other.

    I find myself wanting of the ability to insert IMG tags here. :( In short, picture a sine wave. Now along the slope of one, picture another sine wave attached to it. And so on. I suspect they're doing something like that. Actually, TVs do something like this - it's how the sync pulses and whatnot work. Very facinating technology. Also very old by today's standard, but still very useful.



    --
  • Qwest [qwest.com] has their fiber-optic lines setup so you don't need to dig them up to replace them. They just yank them out of the conduit. They have 2 conduits set up, one is full right now, the other is empty (if I recall), so they can string the fiber in it, with no digging up the lines.

    Older companies like AT&T have to do more work to redo their fiber lines.

    BTW, a post further down the line here there is a post which implies that Lucent makes fiber-optic lines for sale. I know they do optical research, but Corning makes the majority of the optical lines sold. Corning's [corning.com] symbol is GLW [nasdaq-amex.com] for interested investors.
  • okay, I am dropping off into the theoretical here, but bear with me...

    We all know the speed of sound. Well, that is the speed of sound at sea level. The speed of sound in water is quite a bit faster. Something about closer particles transmitting a wave form faster.

    Light is also a wave, just electro-magnetic. The medium the wave is passing through will also affect the speed of transmission.

    That is yer lesson in pseudophysics from a former chem major. heh.

    -Steve
  • no. The information carried electrically travels at the speed of light, but the speed of the electrons themselves depends on the field (and hence the voltage), and the mobility. The formaula is normally written as = mu.E
    or average speed = electron mobility times field

    It is not the "real" speed that is an issue, but the amount of data you can cram down a line per second - normally referred to as bandwidth, and it is this barrier that the boys and girls at bell labs have raised.

  • Re:Using *one* laser (Score:3)

    by dej05093 ( 7707 ) on Monday November 15, 1999 @08:15AM (#1531076) Homepage
    If you have a really short pulse length of e.g.
    10 fs (= 10^-14 s!) the spectral range of this
    puls covers the whole visual spectrum. If you
    pick out a small range of this spectrum using
    a grating you will enlarge the length of the
    pulse (if you have a pulse with a length of one
    ns you can't determine the frequency of this
    pulse with a higher precision than one GHz and
    vice versa).
    With fibre gratings you might be able to pick
    out a large number of different spectral ranges
    which can then be modulated individually before
    they are once again combined and put into the
    fibre. With 1550 nm wavelength the required spectral range should be at least about +- 100 nm!
    for a data bandwidth of 20 TBits/s

    Nevertheless it is really amasing!
  • (20440gigabytes/sec)/(1024Gigabyte/TB)=

    _______________19.961TB/s_______________

    Now some body add in some EC code, say we use up 10% of the traffic for EC, stil have 19TB/sec!!!
  • I always call it a cable router, but that's just me. And I usually get 2,000+ kbps according to the Computingcentral.com Speed Test [computingcentral.com]
  • The error rate would be almost nil. Most errors on standard wires are caused by surrounding data inadvertantly manipulating the bits, known as 'bursts'. Light, on the other hand, isn't succeptable to such manipulations. The only error that I can think of that would happen in the fiber optic line would be an error in the process of making the cable, and would manifest itself every single time, instead of in the random way standard errors appear. Granted, there could be all sorts of errors converting data to light and back, but that certainly can't be written off as a fault of the cable. As long as you are able to accurately and quickly convert your data to light and back again, you should see almost no errors at all.
    Additionally, one could use Hamming code (certainly appropriate for Bell to use), for error correction. Granted, this would slow conversions, but it is the current error-correction on computers anyway.

  • At 163 Tbps, it is capable of handling 105,496,774 T1 lines!!!

    you could also calculate that since each T1 has 24 channels (right?) that's 2,531,922,576 channels available! (1 channel = 1 normal telephone line.)

    I can't wait.

    Bob.

  • No, not at todays processing speeds. You could though push electrons through copper at roughly the speed of light. Think of it like this. You have marbles(electrons), and a pipe(copper or any other conductive medium). You can push the marbles through the copper to near the speed of light, but due to laws of relativity the electrons will never be able to be transmitted the speed of light.
  • Lasers emit coherent light, but not necessarily of one wavelength. A CO2 laser I once used for atmospheric sounding emitted 72 distinct and separately detectable frequencies.

    The real question is how you're going to transmit data over all those frequencies at once. The frequencies of the CO2 laser spectrum were set ratios of one another. To have each frequency transmit independant information, you'd either have to use multiple lasers or have some very interesting frequency gate optics. I do not work with fiber optics or data transmission...perhaps gate optics of that sort already do exist.
  • technically, according to the newest published editions of a very respected book on english grammar (oxford, i think), split infinitives are now alright to use. my english teacher was a bit annoyed at this realization.
  • That's the refractive index difference between the fiber's core and the cladding, which is much smaller.

    Furthermore, most communications fibres have a graduated difference between the refractive index of the core and the cladding, so that the light doesn't "bounce" but is "bent" instead, in a curved fashion. These fibres are called graded-index fibres. The advantage is that all paths through the fibre are of approcimately equal length, so synchronisation is easier than for step-index fibres

  • Does this mean that Feel-O-Vision is about to come to public release ?

    (Feel free to modify words in that sentence so as to provide bad jokes. There are ample options available...)

  • 160,000,000,000 * 1022 = 163,520,000,000,000 bits
    163,520,000,000,000 / 8 = 20,440,000,000,000 bytes
    20,440,000,000,000 / 1024 = 19,960,937,500 kbytes
    19,960,937,500 / 1024 = 19,493,103.02734375 Mbytes
    19,493,103.02734375 / 1024 = 19036.233425140381 Gbytes
    19036.23342514038 / 1024 = 18.590071704239 Tbytes

    That is some bandwidth on ONE FIBER....

    -- iCEBaLM

  • math (Score:2)

    by Haven ( 34895 )
    can it do 160gb/s over all 1022 channels?
  • Actually, I've got no problems with split infinitives at all at all. It's like that silly rule about a preposition being something you shouldn't end a sentence with. The argument was along the lines of 'if it can't be done in latin, it shouldn't be done in English.'
    BTW I've got no respect for Oxford. They spell realise with a 'z'. And they're not even American. A big red Chambers is your only man. Or dictionary.

    Yeah, it's offtopic. But I've karma to spare, so I don't care.
  • Just provide the link to such a pic. If we are interested we could go look. And if we really don't care we won't. Ya gotta figure it'd be abused if we were allowed to post img. Imagine the load times if first psoters were allowed to put pics of the acclaims....
    -cpd
  • Right...not unlike modems except on a phone line there is a very limited number of sine waves that can be fit and there amplitude and frequency are quite limited...early modems were 110 bps, then 300 then faster...the max speed of the medium never changed (POTS are limited to 33,600 bps) only the encoding techniques changed ...

  • What they're probably doing is electrically changing the laser's index of refraction (at very high speed, of course). Doing this changes the effective length of the optical cavity, and thus the lasing frequency. Semiconductor lasers are not spectrally pure in any event, and being able to switch among several of the different resonant modes is one way to do the multi-color trick.

    The thing that gets me is that the 1022-wavelength laser and the 160 GB/sec carrier are probably incompatible; the laser almost certainly cannot be modulated anywhere near the 160 Gb/sec rate. Assuming one system can do both is not much different from assuming that because you can get a 20-ton garbage truck, and you can get a Mach 2 SST, that you can make a 20-ton Mach 2 garbage truck.
    --
    Advertisers: If you attach cookies to your banner ads,

  • So, does this beat the proverbial stationwagon barreling down the highway, full of data tapes, in terms of "bandwidth"?

    For those of you unaware, it's often been said (though I'm not sure how true it is now) that current data transfer methods may seem fast, but they still don't beat the "data transfer rates" of simply filling a stationwagon full of data tapes, and driving it yourself to the destination ;).

    Alex Bischoff
    ---

  • What's wrong with cable modem? It modulates and demodulates, right?
  • You think Bell Labs is going to share this tech with ANYONE?
    Yes, I do. Selling the technology is how they make their money; if they kept it to themselves, the next company to get a product out there would lock up the market and eat Bell's lunch.
    --
    Advertisers: If you attach cookies to your banner ads,
  • That's not entirely correct. the free electrons in a conductor will still hit the fixed positive ions fairly frequently, stopping them dead. They will then accellerate again as the electric force acts on them. for example the mobility of copper is 0.0035 M^2/(V.s), and say the field was 1 V/m, then the average speed of an electron would be ~3.5 mm/s. clearly this is not anywhere close to the speed of light. As I stated above, it is the speed at which the knock on effect passes information on that is important. Think of it like one of those eighties-tastic executive desk toys that has a row of ball-bearings suspended by thin threads. Th balls individually don't move fast, but the information is passed through very quickly.
  • yup...99% of all cable is carrying analog waves, which makes it a cable modem (MODulator/DEModulator)

  • Hmm, Lucent bought a company, nexabit networks, earlier this year that sells a 1TB/s router. Not 100 TB but still pretty fast geach

  • Someone flunked Fourier analysis (Score:4)

    by Tau Zero ( 75868 ) on Monday November 15, 1999 @08:56AM (#1531108) Journal
    Vary the single wavelength's amplitude (intensity) alone, and it's still single frequency while carrying data too.
    I see you never studied for a ham radio license or anything else of the sort.

    Varying the intensity of a light source creates "sidebands", the same as it does for RF. These "sidebands" are wavelengths slightly longer and shorter than the "carrier". What you see as an amplitude variation is really the interference of the carrier and the sidebands, as they slip in (high amplitude) and out (low amplitude) of phase over time. If you have a carrier frequency of F and a modulation frequency of M, you'll create sidebands at F+M and F-M. If you have really good filters you can suppress one of the sidebands and still carry all the information, and if you have really good frequency references as well you can ditch the carrier and only bother sending one sideband (you can use the frequency reference at the receiving end to supply the "carrier" for demodulation); this is how SSB radios work.

    What does this mean for optical fiber? It limits how close together your "colors" can be based on how fast each one is modulated. The sidebands get farther and farther from the carrier as the modulation gets faster, and if the sidebands start clashing you get crosstalk and data errors.
    --
    Advertisers: If you attach cookies to your banner ads,

  • Depends on the speed of the CPU and particularly the data bus. On most PC hardware, even direct memory transfers aren't THAT fast. You need the speed in the I/O bus which is even slower....you simply wouldn't NEED that much bandwidth.
  • This has to make it through slashdot, so I thought I'd post it here.

    link [yahoo.com]

    "The 50-nanometer transistor - roughly 2,000 times smaller than the width of a human hair - is known as a ``vertical'' transistor because all of its components are built on top of a silicon wafer and its current flows vertically. In today's conventional transistors, which typically measure 180 nanometers, the current flows horizontally and the transistors are formed within the wafer itself."

    "Although many researchers have tried to build vertical transistors during the last 25 years, the Bell Labs approach has several advantages over previous designs; it can accommodate ultra-thin insulating layers, and the channel and gate are closely aligned. Because the Bell Labs vertical transistor provides a solid foundation, it may be possible to add additional layers of transistors to silicon chips, resulting in so-called high-rise chips -- one of the holy grails of semiconductor manufacturing."

    ..we need a Lucent logo for articles.

    /me
  • should have been "this hasn't made it..."

  • Re:speed of light == c only in a vacuum! (Score:3)

    by Otto ( 17870 ) on Monday November 15, 1999 @09:05AM (#1531113) Homepage Journal
    The speed of light through any medium is less than the speed of light in a vacuum. Sometimes light can be made to travel through a medium faster than it's natural rate. This results in a nifty "light shockwave" which I believe is called cherenkov radiation.

    Yep. You can see some cool pics of this effect at http://www.nuc.umr.edu/Reactor/Reactor.ht ml [umr.edu], along with a pretty good explanation of how. It's pretty neat the way it actually happens..

    Furthermore, the light in a fiber actually zig-zags down the fiber channel and does not travel straight down it. This also reduces the signal's speed from c.

    Actually it increases the distance of travel which gives an appearent speed difference from c, which is just as good as slowing it down. :-)



    ---
  • Thanks for the vote of confidence, but do I get moderated up for being right? NO

    does the other guy get moderated up for being wrong? YES

  • it's often been said (though I'm not sure how true it is now) that current data transfer methods may seem fast, but they still don't beat the "data transfer rates" of simply filling a stationwagon full of data tapes, and driving it yourself to the destination.

    True, but the thing that this approch doesn't take into account is latency. (which, depending on the length of the drive, and how long it takes to load/unload the stationwagon, can range from ~5 minutes, to several days..)

    If I'm playing a game of quake, I'll get my ass whopped if I rely on the stationwagon method :o)

    I think that (although the bandwith is considerably smaller) this is a step in the right direction. :o)
  • I work in a biophysics lab that uses short-pulse lasers.
    here is part of a paper that talks about short pulses:
    ----
    Infinitely short pulses of one particular wavelength would be ideal [for bio purposes]. However, from the Heisenburg uncertainty priciple (deltaE*deltaT > h/2) it is immediately clear that these cannot be obtained.
    ----
    however, another part of the paper says:
    A completely different method was developed and applied to study ultrafast processes [in bio]. Pulses from a CPM laser were amplified, and then the light was chirped in an optical fiber. With the use of pulse compression ultrashort pulses of 6-12 femptoseconds were obtained. The ultashort pulses correspond to a broad specral range because of the Heisenberg uncertainty principle.
    -----
    So, we can create ultrashort pulses, but encoding 100 million waveforms for a 20Tbit/s connection would take 100 million individual modulators to encode the signal.



  • Of course, they don't have a working product.
    Still, neither is this fibre.
    www.annovation.com [nanovation.com]

  • as well as Gowers and others, the fear of splitting infinitives has always been a superstition and rarely justified. Yes, you should try to avoid splitting your infinitives if you can convey the same meaning by restructuring your sentence, but avoiding the splitting of infinitives at all costs leads to much greater sins like splitting direct objects from transitive verbs, as well as even sillier superstitions like fearing to split helping verbs from their infinitives.

    In any event, rules of grammar are not beholden to any single authority; either something is correct or it isn't, and incorrect things eventually become correct when enough of the population is using them. Of course, I will likely continue to assert the difference between "owing to" and "due to" until I die.
  • www.nanovation.com [nanovation.com]

    The article I wanted (http://www.nanovation.com/news_story.cfm?article= 3) was in a frame. *sigh*
  • It sounds better if you write ".05 microns".
  • so now windowsNT and 2000 can crash at the speed of light?
  • Correct me if I'm wrong (/. is good for that :-), but I don't think you build up a complex waveform like that... you superimpose them.

    i.e. take a sine wave of frequency 'x' and amplitude 'y'. now take a sine wave of 3x and 1/3y and "add" them. i.e. along the horizontal, take the amplitudes and add 'em. Excel is good for this :-)

    Now keep going. 5x with amplitude 1/5y, 1/7th the 7th, 1/9th the 9th... you'll notice that the rising and falling edges start to get steeper and steeper and the tops start to flatten out... you're building a squarewave.

    I'm not quite sure what you meant by "attach another sinewave along the slope of the first"...

  • Huh? (Score:1)

    by Mr Z ( 6791 )

    Bzzzt.... try again. The UART's speed setting has nothing to do with the actual data rate on the wire. And don't say "but I have compression turned on." Doesn't help where you need it most -- downloading huge files. Also, 115kbps is far below even ISA's bandwidth.

    Next time, do some research before you post.

    And to make this post marginally on-topic: It's doubtful that these optical developments will speed up POTS modems at all, except in the cases that they cause old, crufty analog lines to be bulk-replaced with new digital lines. These optical developments are more important for backbones and long-haul connections, not connections between you and your CO.

    --Joe
    --

  • "At 163 Tbps, it is capable of handling 105,496,774 T1 lines!!!

    you could also calculate that since each T1 has 24 channels (right?) that's 2,531,922,576 channels available! (1 channel = 1 normal telephone line.)"

    ...this is very good for the internet commoner to.

    AOL would only have to buy 5 or 6 of these to not have to hang up on their cutomers every 10 minutes.

  • I don't think Brave New World had any computer networks in it...

  • Re:Fibre Optics vs speed of light. (Score:3)

    by Mr Z ( 6791 ) on Monday November 15, 1999 @10:20AM (#1531132) Homepage Journal
    I'm curious, can the speed of light be measured in Gb/s?

    *sigh* People keep getting rate of propogation confused with rate of transfer. This is latency vs. bandwidth folks.

    For instance, consider the ancient communication method consisting of two people atop hills signalling with lanterns and shades. The latency is really low because the light propogates at near 3e8 m/s in air. The bandwidth sucks. Now consider a freight-train loaded to the gills with DVD-ROMs. The bandwidth is enormous, but the latency sucks.

    The speed of light governs how quickly a packet of data gets from point A to point B. Bandwidth measures the total number of packets of data that you can send from point A to point B at a given time. The two are different, unless you somehow treat each photon as its own packet of data, and we're not there yet.

    --Joe
    --
  • We need to run fiber to every home in the nation with gov't footing a large chunk of the bill (otherwise no one would do it).

    We'll run fiber to the homes shortly, if something isn't developed soon that's even better. (Take a look at the recent Scientific American articles on the current candidates.)

    Individual fibers to the home are a lot of bux. But a multiwavelengh fiber to the neighborhood and a passive wavelength divider (think prisim) and a bunch of short fibers to the house look like a good cost-tradeoff.

    But having the government pay for it means you get to pay for whichever solution they chose at least three times - once for the install, twice more for the administrators. And the government will chose the wrong one. And the government won't even chose the best price/performance combo for the data rate they do chose.

    Sure the government built the Interstates (kinda). And then they installed a 55 MPH speed limit - city, prarie, or deserted desert. Let them wire your home (or your kid's school) and they'll do it badly, expensively, and use it as a wedge to control the content.

    The fact that I can plug in a *crank* telephone (not pushbutton, not rotary,... a crank phone) from 189x and *still* use it to make and receive calls on POTS lines should say something about the state of telephone tech in supposed advanced nations like the US.

    Actually, it says more about good standards lasting a long time. Just like the Roman's choice of wheel spacing affecting cars, trains, and spacecraft components (that are shipped on trains) to this day.

    The POTS standard is about getting audio from the switch in the city to the houses in the city and to the farms around it. The last mile of the audio part of that job hasn't changed materially since Bell and Strowager. A cheap low-tech solution does it, so why pay a bunch of bux to replace it with something that doesn't interact? Especially when doing so creates an administrative nightmare for no advantage.

    Data is now hitting the wall on the capacity of the infrastructure designed for voice, so you need to replace part or all of it to go beyond.

  • That press release sure implied that the two methods can be multiplied together, but I'd bet good money that it just ain't so. The 160Gbps test used a laser that was tuned for sending very quickly on a single frequency. The 1022 channel test used a DIFFERENT laser that was tuned for shifting rapidly between frequencies.

    Also notice that Bell didn't mention a damn thing about the bit rate on the multichannel test. For all we know, those 1022 signals could be running at 2400 baud. And both tests were based on single lasers. Can they convince hundreds of these lasers to play nice and merge signals onto a single fiber? What the press release DIDN'T say leaves much to be desired, so far.
  • I think that they called them feelies in Brave New World...
  • But funny! so please don't mark this down :-)

    Winston Churchill is reputed to have answered, when accused of ending a sentence with a preposition, "That is something up with which I shall not put".

    --

  • Re:Sampling rates, digital, and misc cool stuff (Score:3)

    by tzanger ( 1575 ) on Monday November 15, 1999 @10:43AM (#1531138) Homepage
    not unlike modems except on a phone line there is a very limited number of sine waves that can be fit and there amplitude and frequency are quite limited...early modems were 110 bps, then 300 then faster...the max speed of the medium never changed (POTS are limited to 33,600 bps) only the encoding techniques changed ...

    Not quite...

    Modern modems use QAM to send data, not discrete sine waves. If I'm not mistaken "raw" sine waves haven't been used since 300 baud modems... You know the ones where you had the switch to select originate or answer. :-)

    POTS is limited to 2400 baud. You achieve everything faster by encoding more than one bit per "transition" or baud. Modems these days aren't. They are "just" DSPs which don't actually modulate based on a carrier, rather just output what is necessary to achive the symbol.

    Picture a graph centered at the origin. x is phase and y is amplitude. You don't just have +1 and -1. you have (if I'm not mistaken) 6 or 8 levels along each axis. you can choose any of those phases with any of those amplitudes. Essentially you end up with 64 or 256 possibilities per symbol. (I'm pretty sure it's 256)...

    Anyway what I'm trying to describe is a constellation pattern... They're usually illustrated like this:


    . . . . | . . . .
    . . . . | . . . .
    . . . . | . . . .
    . . . . | . . . .
    --------+--------
    . . . . | . . . .
    . . . . | . . . .
    . . . . | . . . .
    . . . . | . . . .


    Each dot represents a possible symbol. You can only spit out 2400 symbols per second over POTS but you can send multiple bits per symbol, or baud, giving you speeds faster than 2400bps.

    The 56k limit on POTS has its roots in how T1s are actually set up and transmitted. T1s are actually transmitted as 193-bit-long frames, 8000 times per second. One of those bits is required to keep frame sync, leaving a payload of 192 bits per frame, giving you 1.536mbps. T1s originally carred voice, sent as 8-bit PCM data. Twelve 193-bit-long frames are logically grouped together and called a super frame. The 6th and 12th frame in the larger super frame had 1 bit used for frame sync as usual, but then instead of the remaining 192 bits being used as 24 8-bit channels, 24 7-bit channels were sent, with the LSB used for line status for each channel (busy, off-hook, etc.). This loss of the LSB every 6 frames wasn't very noticable for voice, but over data it just isn't cool. ESF is similar to SF but 24 193-bit frames were grouped instead of 12 so that 4 bits of framing could be used instead of just 2, on the 6th, 12th, 18th and 24th frame. AFAIK those extra two bits weren't ever really used, they just duplicated the info in the original 2 line status bits.

    Since every 6 frames you're missing a bit and it's not possible for the modem to know which frames will be missing the bit, the modem only relies on the 7 bits being clean. So now you've got 7 bits sent 8000 times a second for 56000bps instead of the theoretical 64000bps per channel over a 'clean' T1 channel.

    This concludes your lesson. If you want to know more, just email me. Hopefully this isn't too far off topic, but it *is* some history about how POTS works with digital transmission. :-)
  • When you change the amplitude of a sine wave at zero crossing, you'll create a kink there since the slope of a sine at zero is proportional to it's amplitude. This discontinuity in the slope put energy in all frequency range.
  • Let see... Typical mainframe Tape: 4 inches on a side, one inch thick. Holds 50 gig uncompressed, 100 gig comrpessed (STK redwood). figgure the back of your station wagon is 5 feet long, 3 feet high, and 5 feet wide. Thats 75 cubic feet. Now the tapes take up 16 cubic inches. Convert units, and you get 675 tapes in the back, for 675 Terabytes. Remember that fibre typically is talked about sending teraBITS, and things look even better for our old station wagon. I wonder how big a station wagon really is? I guessed, figguring the passanger seats would take up any slack from my estimates being off, and probably have room left over for more tapes. Course if your talking about those old (and unreliable) floppy attached tapes this is a different story.
  • Amplifying a pure sine wave "exactly at the zero crossings" to eliminate sidebands is not possible because the amplification or deamplification cannot happen instantaneously without an infinite amount of power and since the amplitude change would always take some non-zero amount of time, the sine wave will deform over that period. The deformarions show up as other frequencies.
    Actually, it's worse than that. You can view any waveform as a collection of pure sinewaves at various frequencies and phases (integral from 0 to infinity of e^(i*omega*t) f(t) dt). The wave you're describing would have a corner, an instantaneous change in slope, there at the zero crossing. (Exactly where, zero crossing or otherwise, doesn't matter.)

    But since this is all put together from sinewaves, which are nice and continuous, how the heck do you get a corner? In practice you can't, because it requires frequency components out to infinity (and infinite bandwidth!). But even an approximation of that "corner" requires other frequency components which add during the high-amplitude section, and then they all come together at the "corner" and suddenly they all subtract from the "carrier" for the low-amplitude section. All of these different frequency components mean lots and LOTS of sidebands. You can hear this in Morse code communications; if a keying network isn't set correctly and it cuts the signal off abruptly, you can hear the sidebands (key clicks) far away from the sender's carrier frequency. An over-modulated AM signal that "flat-tops" (clips)or cuts off completely causes broadband "splatter" which can be heard well off the channel too.

    The way to limit bandwidth is to vary things smoothly, with no edges or corners. It may not be intuitive, but this is an area where your intuition doesn't get much experience.
    --
    Advertisers: If you attach cookies to your banner ads,

  • By that argument, any interface which converts digital signals into an analog transport and back with some form of modulation should be called a modem. Like your Ethernet card, for instance. We all call them Ethernet Modems don't we? Didn't think so. That said, the term "cable modem" is a reasonably accurate name for what it is/does, and since it replaces a traditional POTS modem, its name matches its intended purpose pretty well. --Joe
    --
  • I thought signals propogated at c/6, at least in SI. My CS prof metioned this once in connection with the importance of keeping die size small as clock rates rise. You have to give the clock signal enough time to reach the end of your data path before you send another one. I could be way off on this, but I'd assume that it would apply to copper as well.
  • Changing amplitude only at zero crossings rather than at other places changes the details of how the energy is smeared among frequencies, but doesn't change the fact, or amount, of the smearing.

    You can derive the result of amplitude modulation from the trignometric identity:

    sin(a) * sin(b) = sin(a+b) + sin(a-b)

    By treating the carrier as a sine wave and the modulation as a sum of sine waves, and using the normal properties of real-number multiplication and addition you can work out the spectrum that results from amplitude modulating a carrier with any periodic waveform. It gets slightly more complicated for aperiodic waveforms, but the basic result is the same: A pair of sidebands, on either side of the carrier, that reproduce the spectrum of the modulating signal.

    To send more bits on an AM carrier you essentially have to either modulate the signal faster (spreading out the spectrum of the modulating signal and thus that of the modulated signal) or modulate it more finely (using more bits to control the amplitude). The number of bits you can cram into the second is limited by the signal-to-noise ration of the channel (i.e. when you get near the noise your least significant bits get corrupted).

    The Nyquist sampling criterion gives you a quantitative limit on this: If you have a band-limited signal, you can encode it with a number of bits-per-second equal to 2 times the bandwidth times the base-2 log of the signal-to-noise ratio, and reproduce it to within the the noise threshold. So that's the absolute maximum number of bits the signal can carry.

  • Read bell labs blurb on their web site here [bell-labs.com] they do get a /bit/ more technical...not much though i'm afraid...
  • precisely. for a change i know the facts, yet someone who says something that is indisputably physically incorrect gets moderated up.

    oh well, such is life.

  • There's more than that in-flight in the wire, since, as someone else pointed out, the speed of light in fiber is about 0.7C.

    BTW, you accidentally inverted your fraction in there. The correct equation is:

    speed = 0.7 c = 0.7 * (299792458 m/s) = 209854721 m/s
    dist = 300000m
    bps*nbsp; = 160000000000 bits/sec


    bits_in_wire = (dist / speed) * bps
    bits_in_wire = (300000m / 209854721 m/s) * 160000000000 bits/sec
    bits_in_wire = 228729664 bits = approx 27 MegaBytes

    BTW, your final result (19MBytes) looks about right from your original equation, since my adjusted result is the same as yours divided by 0.7. It looks like you just typed in the substitution incorrectly when you said "299792458/300000".

    Incidentally, this phenomenon is why Linux allows you to allow large TCP windows. Look at the Configure.help entry for CONFIG_SKB_LARGE. It points out that "[a]t 45 MBit/second there are alot of bits between New York and London ...".

    --Joe
    --
  • Thank you, that was very informative. I wish I could score you to +5, you deserve it. And I will e-mail you off slashdot - I find such material facinating in the extreme. Kudos!

    --
  • The speed of light through any medium is less than the speed of light in a vacuum. Sometimes light can be made to travel through a medium faster than it's natural rate. This results in a nifty "light shockwave" which I believe is called cherenkov radiation.

    Light cannot be made travel through a medium faster than its natural rate. A subatomic particle can be made travel faster than the speed of the light in that medium. When that happens, you get the Cherenkov effect.

  • Kind of off topic but my University contratcted with @home to intall cable modems on campus, problem is, 30mbs/4000 connects = a 14.4 is just about as quick sometimes.

    God, I wish Al Gore would Hurry Up and Invent the Internet 2

  • Sort of a tangent to what you were saying, but somewhat on-topic too... :)

    There is actually another way of installing fibre that is a bit more future-proof than the traditional way that they are installing it in most situations today. I'm not sure of the name for the technique, but the company(ies?) that markets it calls it 'Air Blown Fiber'.

    Installers bury conduits that have sub-conduits inside (looks like honeycomb when you look at the cross-section). Each internal conduit is independent of the other. After the conduit is laid out and in-place (buried etc), the installer shoots a 'BB' through each mini-conduit to make sure it is clear (using a big air tank and some special equipment).

    Once it is determined clear and safe, the installer places a strand of fibre (protected but very light-weight - no kevlar!) into one of the conduits and 'blows' it through. Air pushes the strand(s) of fibre to the other side. It does this *very* fast, somewhere between 50-100FPS if I remember correctly. I was amazed to find that damage to the fibre strand is not an issue when they do this... it's actually quite rare. Installers I talked to said it was much more rare than the damage that occurs to the fibre in a conventional installation.

    The idea behind it is: yes, you have to dig the initial hole and bury the conduit. But you'll never have to do it again. The conduit has many extra mini-sections for later expansion if you ever want to add more fibre (you can buy conduits with 2-72 mini-conduits, and each holds up to 6 strands of fibre), and if the fibre becomes outdated or destroyed for whatever reason, you just yank it out (using the same method in reverse if you want) and blow different fibre through. You can even blow a fibre through, remove it, then reinstall the same one multiple times with no problems.

    I worked with a project at the National Department of Energy (Fermi) where this technique was used, as well as at the J. Paul Getty Museum in Southern California. Some universities are also adopting this method.

    The amazing thing is that it's actually considerably less expensive than the conventional installation technique. Where's the catch? I don't know /that/ much about fibre installations, but I haven't found any.

    Pretty neat stuff, sorry no URL. I'm sure a Google search on 'air blown fiber' would return some good results. :)

    --SONET
  • Error Correction on SONET. SONET is set for simple error detection. On the slower data rates (OC 3, 12, 48) this is enough. If errors start to occur the data is switched to the protect channel and the problem is determined. (Tech out to site to replace a bad pack or do fibre cleaning). Why fibre cleaning is necessary, There are at least 8 connections between two terminals. Any dirt or grim that makes it into these connections causes slow degeration of the light levels and when the signel gets low enough errors begin to happen. For long fibre runs the data (on off) also begins to merge because the light can take multiple paths from transmiter to receiver (single mode fibre helps reduce this). Getting a consistent clean signel at the OC-192 rate is hard to do (10 Meg/Sec) (hamming code is a vender option to help with the error rate it is not SONET standard). I would like to know what type of signel they sent and what the error rate was.
  • Could you point me towards more information on this subject, the Cherenkov effect? Would a Tachyon qualify?

  • This technology will enable 1/3 of the end to end system. If we look at the flow of information, it goes:

    Content Server -> BackBone -> User

    This technology will enable the backbone to move the bits between the server and the user. The day of evaluating your backbone provider by how many wavelengths they have in use, and how many are spare are coming fast. Optical switches, and one day optical routers will push this to speeds we can only dream of today.

    The other two thirds are not keeping up though. Servers tend to be overloaded. If you work for an ISP where you have 100Mbps or 1000Mbps desktop connections to the network you know this already. Most servers, particularly big sites, couldn't fill a 10Mbps connection sending content. We're at a point where faster backbones carry more connections not faster connections .

    The end user is even worse. Last mile problems persist, and will for a long time. The installed base of low quality copper is huge, and preventing even DSL from reaching many areas. New developments and business parks are not buring fiber during construction, even though the investment would be minimal. We should all be worried about how we are going to get high bandwidth to the home or small office.

    Looking forward to the "killer apps" of the next 10 years, like Video on Demand I just don't see how it can happen. Care to dream of a server, or server complex that can deliver 2-5 million streams of video on demand? Will there be 20 million households with >= 10Mbit/sec access to watch those 5 million streams? I have my doubts. Will be Internet backbones be able to carry that traffic? I think so, that I'm not worried about.

  • I dare say that the PHY layer behaves more like an analog layer than a digital one. Hence the term Carrier Sense, Multiple Access / Collision Detection. Pure binary digital signals are mutually exclusive with the concept of a "collision".

    Also, Manchester encoding is a very light form of modulation, in that it ensures a transition during every bit period (a bit like XORing the data sequence with the clock -- looks alot like AM modulation).

    See this online guide [techfest.com] for more details.

    --Joe
    --

  • It's not ludicrous. Check your facts.

    Of course an ethernet card is "not the gateway to the communication infrastructure," at least if you define that as the POTS network or the Internet backbone. Neither is a cable modem. Cable modem networks actually behave alot like Ethernet in that it's a broadcast medium within each segment. Where it differs is in the fact that segments are arranged hierarchially, and all nodes on the network are not peers as they are in ethernet. (Apparently, nodes that are nearer to the top of the hierarchy cannot report collisions to nodes beneath them on a cable network, if I recall correctly. On Ethernet, everyone's a peer -- there is no above/below.)

    In both cases, you need a separate gateway device which hooks your network segment up to the Internet or whatever "communication infrastructure" you're conceiving. They really aren't very different AT ALL.

    --Joe
    --
  • Photons can and do leak out of fibers. And they can leak in. At the moment, crosstalk isn't an issue, but remember when they ran the first AC powerlines it wasn't either. Look what that stuck us with.

    Briefly: The longer a path light takes, the longer it takes to reach its destination. So if some photons go right down the middle of the fiber, while others take a bouncy route off the sides, the edges of each pulse get stretched and blurred. Over short distances (under a kilofoot?) or at low speeds (under a gigabit/s) this isn't an issue, but it quickly becomes a problem when you move from the pansy-ass glass campus Ethernet into the serious bit-pumping that today's telcos do.

    Each path that photons can take is called a "mode". I don't know why they picked that word. The fibers that a typical datamonkey is familiar with are "multimode", which means a wide core (125 microns?) of glass, which accomodates lots of bouncing. The fibers that your friendly telcos are burying are "singlemode", which is a much narrower core surrounded by more glass of different refractive indices. The idea is to straighten the light out and get it all traveling along the same path, so that pulse stretching is minimized. Still, the quality of your glass has a lot to do with it.

    Now think about the construction of a typical optical cable. The stuff has to be somewhat flexible, to allow for installtion. In order to allow for some curving, the fibers/bundles aren't laid straight in the cable, but they spiral a little bit. This relieves stress when the cable is curved.

    The problem here is that the photons are being asked to travel down this several mile long helix of glass, while remaining in as tight a group as possible. You can have one or the other, folks. Every time a fiber bends, a few photons wander off and do mischevious things.

    Want to see something nifty? Go see EXFO [exfo.com]'s "live fiber detector" tool. Next time your phone service actually works, thank these folks for making sure the wrong fiber wasn't cut/disconnected by some technician working from outdated paperwork.

    Errors happen for all sorts of reasons. Stray photons are actually the least of them. Imagine the sensitivity of the poor receiver that gets to turn all those bursts back into electricity. Can we say "sensitive to interference"? I thought we could. Most SONET systems achieve an in-service bit error rate well under 10E-10, and some are guaranteed better than 10E-13. How's that stack up against the consumer market, eh?

    I need to go learn more about the funky laser those Bell folks used, it sounds like it's more of a color generating toy than a data pumping tool, and I bet the actual bitrates it achieves are laughably slow on each individual wavelength. I don't see DWDM disappearing any time soon.

    Besides, none of it matters if the world ends next month. Tee-hee! You should see the disaster plans the telcos are putting together. Stock tip: Buy Dunkin Donuts shares, because telco techs are gonna buy 3 days worth of munchies on the 30th, because they can't leave their appointed sites after that.

Slashdot Top Deals

If you didn't have to work so hard, you'd have more time to be depressed.

Close