Erasure codes have the property that for a file N packets long, you calculate some number K of coded packets, and the receiver needs only to receive N of any combination of coded or source packets to be able to recreate the original file.
For instance, I could have a file 100 packets long, and calculate 25 coded packets, then I could receive, for example, 80 packets of the original file and 20 coded packets (80+20=100) and recalculate the entire original file. Or 90 original and 10 coded packets. Or 75 original and 25 coded packets...etc.
Before Tornado codes, this was computationally difficult to do in practice for large files. Typical use of Tornado files is to just send all coded packets, and receivers can "fill their cup from the fountain, dipping it into the stream whenever they want" to get any N number of packets to recreate the original file. Obviously, this makes a lot of sense in a multicast domain.
But for distributed file transmission, I'm not sure this makes sense. You would need to collect N different packets. If you got the same coded packet more than once, it would not help you.
Keeping track of which unduplicated coded packets you have and need is just as difficult as keeping track of which unduplicated original packets you have and need.
Packet loss is not really much of a problem if you are using TCP. On the other hand, it is a problem when you are doing multicast UDP over the Net or satellite.
So overall I'd say file-level FEC using erasure codes is pretty much useless for distributed file transmission.
Nope, the battery worked fine for a half an hour. The problem was that nobody knew the power had gone out, because the lights stayed on till the battery died...
This has been my experience as well. I've met several people from the local goth scene whom I don't think I really would have met without LiveJournal (which is really the key social network site, although it doesn't sell itself as such).
I've also met some fellow classical liberals through Friendster and Tribe, and have actually hung out with them.
Clearly this is most empowering for people like me who are not naturally highly outgoing. I can meet someone at a venue, exchange LiveJournal names, and an online conversation can start (aided with IM as well). The next time I see them we are slowly becoming virtual friends.
Moreover, some of these people would probably freak out if complete strangers tried to have in-depth communication with them at public venues anyway. So it is a way of reaching people who wouldn't normally be reached, as well as a way of helping people make contacts they normally would not initiate.
The most powerful things of humanity are driven by social networking. The use of computer technology to order and drive these, like the PDA/Outlook/email/etc., is going to make for a better humanity.
No, the issue is that India and China have been backing away from socialism and state control of industries for the last 20 years, and no big surprise, are having massive economic growth where for 40 years before that there was little.
There is no recession in the US now. We are gaining jobs now, not losing them. The economy is not overheated now like it was during the Dot-Com boom because investors are now looking for real returns and revenues from companies. Unemployment is not particularly high.
I do agree that there are some mildly deflationary effects of offshoring that are beneficial to the US in keeping our core inflation rate low. The other thing is that offshoring is reducing global poverty at the same time.
I also agree that US government spending is not on a sustainable course, and needs a correction fast.
I work in an environment that is 100% mission critical. Yet we took a power hit. The control center is powered by UPSes until the generator can take over. Because of that, no one in the center even noticed that the power went out, because the UPS kept the center going. Until the UPS ran out and the lights turned off.
The generator never started. Why? The generator battery was dead. Someone had accidently kicked a switch from 12V to 6V to charge the battery immediately after the last weekly test.
So power was out for a few minutes while people raced to drive their car around to the generator and "jump-start" it.
Don't assume that 720p uses 14Mbps. Uncompressed HD video of any sort takes over 1Gbps. Compressing it down creates artifacts. HDCAM at a little over 200 Mbps is the standard for acquisition and contribution these days.
720p at full ATSC bandwidth (~19Mbps) will look better than 720p at 14Mbps. Same with 1080i. Note that motion is the killer, not still image resoltuion. It is all a matter of "how bad do I want it to look".
From my perspective, any chance for DTV broadcasters to get some money and recoup the tremendous cost of the DTV transition will be grabbed at. Besides, almost no one is watching over-the-air free DTV today. For that matter, only about 20-30% of people watch over-the-air television of any flavor, including analog. DBS and cable are the majority delivery mechanism.
You can obtain an 8VSB demodulator for DTV broadcasts with ASI output (asynchronous serial interface, generally on coax @ 270 Mbps).
Then you can take the MPEG-2 transport stream on ASI and run it into MPEG-2 video decoders, IP de-encapsulators, etc. MPEG-2 transport streams can contain multiple program streams addressed by PIDs (program identifier).
Any one-way data can be encapsulated into the MPEG-2 transport stream. There have been a lot of examples of encapsulated UDP IP multicast packets delivered over DTV, including Windows Media streams.
You can also get DVB-S (a digital satellite standard) receivers with an ASI output as well.
My impression (I work in the industry) is that broadcasters have to deliver at least one free in-the-clear video service over their DTV bandwidth. The rest of the bandwidth of the ATSC MPEG-2 transport stream can be used in any other way.
Just to make it clear, the whole shutting down the DOI Internet access thing is 100% BS, driven by lawyers looking for money who do not have the best interests of Native Americans in mind.
Right, Gallager worked out LDPC codes in 1963. Then they were forgotton for 20 years until people realized that Digital Fountain's "Tornado" codes were LDPC codes.
LDPC codes will be behind DVB-S2, the new transmission system for digital satellite video distribution. Since they approach the Shannon limit so closely, there will be no DVB-S3.
I should say that the IEEE article is a little over-hyped, in that these codes really only buy about 2-4 dB additional gain, concatenated RS and convolutional coding were pretty close to the Shannon limit in AWGN, but those last couple of dBs were nice, but the remaining 0.5-1 dB beyond LDPC & Turbo Codes isn't worth much.
Much more important now are ways to handle "fast fading" channels found in mobile environments, this is what is driving OFDM.
Also, both Turbo Codes and LDPC codes are really computationally intensive to decode. They are currently only decoded at speeds below 20 Mbps, generally implemented as (expensive) FPGAs. We won't see real cheap ASICs for another year or two.
I don't have the most recent version, but Audacity is simple, but still pretty cool!
I am working on an art project where I need to synchronize touch tones in the right channel with spoken speech in the left channel. While I have to generate the DTMF tones in Sound Forge, I bring them into a multi-track editing session in Audacity to actually get the synchronization correct, then just export out the final stereo sound file.
Yes, the laser was capable of vaporizing a man-sized object from space. The perfect "peacetime weapon." And let me tell you, there hasn't been a new working weapon since Korea.
Unfortunately, on its first test shot, the laser went off target and accidently destroyed a house by setting off a large charge of popcorn, then it melted down. Everybody wants to the rule the world!
I'd like to believe that, but prove it. If a craft is filled with helium to achieve neutral balance, very small amounts of work are required to compress an decompress the gas to move it up and down.
If we assume a nearly infinite height of air (and thus minimal pressure differential), it is clear that you can have a buoyant object accelerate the whole way up and then the whole way down with very small amounts of work done on each end. The maximum amount of energy you can extract would be equivalent to the kinetic energy of the buoyant object at the bottom and top, imagine it hits a giant piezoelectric crystal at the top and botton.
I'm sure some of you are breaking out your ideal gas law to see if this is a perpetual motion machine. However, please take this into account: buoyant acceleration is actually = g*(m-md)/(m+md) where m is the mass of the buoyant object and md is the mass of the diplaced gas.
This is interesting: "Wyant is quick to point out PUC won't be using power lines to deliver Internet access directly into the home. Instead, the company is installing wireless access points along its medium-voltage lines in densely populated residential areas."
Of course, it took 40 years from independence until India decided to open up their economy, and they also were starting from a position of being a true democracy with much greater levels of freedom of speech.
After the recent elections in Iran, I think the country will now face another 10 years at least of government cronyism (most of the economy is in the hands of a small number of conservative clerics) and repression of oposition.
I second this. In the current era, why should employers PAY to have an ad on Monster? For things like web design and development where you can expect 1,000 resumes to come over your desk, just post to Craigslist. My wife regularly does this when she is hiring, and gets excellent candidates (once the wheat and chaff are separated).
Also the job sites of potential employers is a good idea as well. I got my current job from the company's career section of their web site.
Specialized organization web sites are good as well. When my wife was looking for an architecture job, she found it on the American Institute of Architects career web site.
Here is a bigger question - has anyone gotten a job through Friendster/Tribe/Linked-In?
If you look closely at the site, you will see that to effectively get the eyeglass lens molders into work in third-world countries, they will depend on "microentrepreneurs" in those countries selling glasses for about $5 each. These people will, of course, be motivated by the almightly dollar (or rupee or whatever).
Slashdot Mirror
Plenty of geeky chicks go to night clubs - try the gothic clubs.
Here is a paper that describes using chaotic gates as "universal gates".
Erasure codes have the property that for a file N packets long, you calculate some number K of coded packets, and the receiver needs only to receive N of any combination of coded or source packets to be able to recreate the original file.
For instance, I could have a file 100 packets long, and calculate 25 coded packets, then I could receive, for example, 80 packets of the original file and 20 coded packets (80+20=100) and recalculate the entire original file. Or 90 original and 10 coded packets. Or 75 original and 25 coded packets...etc.
Before Tornado codes, this was computationally difficult to do in practice for large files. Typical use of Tornado files is to just send all coded packets, and receivers can "fill their cup from the fountain, dipping it into the stream whenever they want" to get any N number of packets to recreate the original file. Obviously, this makes a lot of sense in a multicast domain.
But for distributed file transmission, I'm not sure this makes sense. You would need to collect N different packets. If you got the same coded packet more than once, it would not help you.
Keeping track of which unduplicated coded packets you have and need is just as difficult as keeping track of which unduplicated original packets you have and need.
Packet loss is not really much of a problem if you are using TCP. On the other hand, it is a problem when you are doing multicast UDP over the Net or satellite.
So overall I'd say file-level FEC using erasure codes is pretty much useless for distributed file transmission.
Anyone care to differ?
Nope, the battery worked fine for a half an hour. The problem was that nobody knew the power had gone out, because the lights stayed on till the battery died...
This has been my experience as well. I've met several people from the local goth scene whom I don't think I really would have met without LiveJournal (which is really the key social network site, although it doesn't sell itself as such).
I've also met some fellow classical liberals through Friendster and Tribe, and have actually hung out with them.
Clearly this is most empowering for people like me who are not naturally highly outgoing. I can meet someone at a venue, exchange LiveJournal names, and an online conversation can start (aided with IM as well). The next time I see them we are slowly becoming virtual friends.
Moreover, some of these people would probably freak out if complete strangers tried to have in-depth communication with them at public venues anyway. So it is a way of reaching people who wouldn't normally be reached, as well as a way of helping people make contacts they normally would not initiate.
The most powerful things of humanity are driven by social networking. The use of computer technology to order and drive these, like the PDA/Outlook/email/etc., is going to make for a better humanity.
No, the issue is that India and China have been backing away from socialism and state control of industries for the last 20 years, and no big surprise, are having massive economic growth where for 40 years before that there was little.
There is no recession in the US now. We are gaining jobs now, not losing them. The economy is not overheated now like it was during the Dot-Com boom because investors are now looking for real returns and revenues from companies. Unemployment is not particularly high.
I do agree that there are some mildly deflationary effects of offshoring that are beneficial to the US in keeping our core inflation rate low. The other thing is that offshoring is reducing global poverty at the same time.
I also agree that US government spending is not on a sustainable course, and needs a correction fast.
I work in an environment that is 100% mission critical. Yet we took a power hit. The control center is powered by UPSes until the generator can take over. Because of that, no one in the center even noticed that the power went out, because the UPS kept the center going. Until the UPS ran out and the lights turned off.
The generator never started. Why? The generator battery was dead. Someone had accidently kicked a switch from 12V to 6V to charge the battery immediately after the last weekly test.
So power was out for a few minutes while people raced to drive their car around to the generator and "jump-start" it.
The issue here is that encrypted broadcast is not "broadcast".
Don't assume that 720p uses 14Mbps. Uncompressed HD video of any sort takes over 1Gbps. Compressing it down creates artifacts. HDCAM at a little over 200 Mbps is the standard for acquisition and contribution these days.
720p at full ATSC bandwidth (~19Mbps) will look better than 720p at 14Mbps. Same with 1080i. Note that motion is the killer, not still image resoltuion. It is all a matter of "how bad do I want it to look".
From my perspective, any chance for DTV broadcasters to get some money and recoup the tremendous cost of the DTV transition will be grabbed at. Besides, almost no one is watching over-the-air free DTV today. For that matter, only about 20-30% of people watch over-the-air television of any flavor, including analog. DBS and cable are the majority delivery mechanism.
You can obtain an 8VSB demodulator for DTV broadcasts with ASI output (asynchronous serial interface, generally on coax @ 270 Mbps).
Then you can take the MPEG-2 transport stream on ASI and run it into MPEG-2 video decoders, IP de-encapsulators, etc. MPEG-2 transport streams can contain multiple program streams addressed by PIDs (program identifier).
Any one-way data can be encapsulated into the MPEG-2 transport stream. There have been a lot of examples of encapsulated UDP IP multicast packets delivered over DTV, including Windows Media streams.
You can also get DVB-S (a digital satellite standard) receivers with an ASI output as well.
My impression (I work in the industry) is that broadcasters have to deliver at least one free in-the-clear video service over their DTV bandwidth. The rest of the bandwidth of the ATSC MPEG-2 transport stream can be used in any other way.
Just to make it clear, the whole shutting down the DOI Internet access thing is 100% BS, driven by lawyers looking for money who do not have the best interests of Native Americans in mind.
Be careful, there are some specific LDPC codes that have been patented (such as the Digital Fountain "tornado" codes).
VMSK debunked
Right, Gallager worked out LDPC codes in 1963. Then they were forgotton for 20 years until people realized that Digital Fountain's "Tornado" codes were LDPC codes.
LDPC codes will be behind DVB-S2, the new transmission system for digital satellite video distribution. Since they approach the Shannon limit so closely, there will be no DVB-S3.
I should say that the IEEE article is a little over-hyped, in that these codes really only buy about 2-4 dB additional gain, concatenated RS and convolutional coding were pretty close to the Shannon limit in AWGN, but those last couple of dBs were nice, but the remaining 0.5-1 dB beyond LDPC & Turbo Codes isn't worth much.
Much more important now are ways to handle "fast fading" channels found in mobile environments, this is what is driving OFDM.
Also, both Turbo Codes and LDPC codes are really computationally intensive to decode. They are currently only decoded at speeds below 20 Mbps, generally implemented as (expensive) FPGAs. We won't see real cheap ASICs for another year or two.
That would have come in handy for the chat with Iraq I organized between a coffeehouse near Washington, DC, and the Baghdad Internet Cafe.
I don't have the most recent version, but Audacity is simple, but still pretty cool!
I am working on an art project where I need to synchronize touch tones in the right channel with spoken speech in the left channel. While I have to generate the DTMF tones in Sound Forge, I bring them into a multi-track editing session in Audacity to actually get the synchronization correct, then just export out the final stereo sound file.
Yes, the laser was capable of vaporizing a man-sized object from space. The perfect "peacetime weapon." And let me tell you, there hasn't been a new working weapon since Korea.
Unfortunately, on its first test shot, the laser went off target and accidently destroyed a house by setting off a large charge of popcorn, then it melted down. Everybody wants to the rule the world!
I'd like to believe that, but prove it. If a craft is filled with helium to achieve neutral balance, very small amounts of work are required to compress an decompress the gas to move it up and down.
If we assume a nearly infinite height of air (and thus minimal pressure differential), it is clear that you can have a buoyant object accelerate the whole way up and then the whole way down with very small amounts of work done on each end. The maximum amount of energy you can extract would be equivalent to the kinetic energy of the buoyant object at the bottom and top, imagine it hits a giant piezoelectric crystal at the top and botton.
I'm sure some of you are breaking out your ideal gas law to see if this is a perpetual motion machine. However, please take this into account: buoyant acceleration is actually = g*(m-md)/(m+md) where m is the mass of the buoyant object and md is the mass of the diplaced gas.
This is interesting: "Wyant is quick to point out PUC won't be using power lines to deliver Internet access directly into the home. Instead, the company is installing wireless access points along its medium-voltage lines in densely populated residential areas."
Of course, it took 40 years from independence until India decided to open up their economy, and they also were starting from a position of being a true democracy with much greater levels of freedom of speech.
After the recent elections in Iran, I think the country will now face another 10 years at least of government cronyism (most of the economy is in the hands of a small number of conservative clerics) and repression of oposition.
I second this. In the current era, why should employers PAY to have an ad on Monster? For things like web design and development where you can expect 1,000 resumes to come over your desk, just post to Craigslist. My wife regularly does this when she is hiring, and gets excellent candidates (once the wheat and chaff are separated).
Also the job sites of potential employers is a good idea as well. I got my current job from the company's career section of their web site.
Specialized organization web sites are good as well. When my wife was looking for an architecture job, she found it on the American Institute of Architects career web site.
Here is a bigger question - has anyone gotten a job through Friendster/Tribe/Linked-In?
If you look closely at the site, you will see that to effectively get the eyeglass lens molders into work in third-world countries, they will depend on "microentrepreneurs" in those countries selling glasses for about $5 each. These people will, of course, be motivated by the almightly dollar (or rupee or whatever).