--A thanks to Compwiz for his help in research and fact-checking for this
We've all seen the commercials, a communications company saying their new DSL service is available "up to" a certain speed, or with speeds "potentially as high as" But why is that? Surely if their hardware can handle those speeds, then it should be available to everyone, right? Well, it's annoyingly wrong because of the X-factor of an aging infrastructure in the United States and a behavior of copper wire known as "signal attenuation" which is, in its basest explanation, the loss of signal over distance.
Data sent by DSL modems is an electrical packet, which is power. Power running through copper wire, or any metal wire for that matter, will entropy over distance due to resistance and interference causing attenuation (decay) of the signal. If you think of a wire like a hose and electricity like the water, resistance is the friction in that hose which makes it harder to pump it over longer distances. Sending data packets is like sending pulses of hot and then cold water down that hose. The worse the attenuation in the line, the faster the hot water cools down and the cold water warms up. To get data from one end to the other, it has to not only arrive, but still be the right temperature.
In a smooth, featureless hose, that would be simple, but that's not the case. Old and worn out networks, different gauges of wire used, and splices made improperly are like kinks, connectors, and different size hoses on the line, and with each of those the water passes through, the hot and cold are going to get a bit harder to pump and a bit more mixed together.
A single packet could be: 1110010110101011010110110010110
But how can you know it's still the packet that was sent with all these things affecting the line?
The answer is with checksums. All of the "1" data in that packet adds up to 18, so a checksum would be sent with it that says "18" If the packet gets damaged, then the data will no longer add up to 18, and it's considered corrupted. Likewise, if the checksum gets damaged, it could suddenly read "7714" and the same applies.
When a modem connects to an ISP's server, it performs something known as a "handshake" tossing packets with these checksums back and forth at ever-faster rates until they begin failing. When the failure point is reached, the modem backs up a little bit, sending the packets slower, with longer 1's and 0's at a higher power level, to ensure they won't be lost.
If the interference in the line increases, though, then it can begin dropping packets. if the packet loss gets above a threshold, then the modem severs the DSL connection and performs the handshake again, to calibrate itself to the new speed limits. This is what's usually happening when a DSL connection goes out for a few minutes at a time.
Fiber lines, which have already replaced copper in the nation's backbone infrastructure solve this by using light signals inside a fiber optic cable. Fiber optic still suffers from attenuation and resistance, but at radically lesser values. Also, the data is being sent with light, which travels...at the speed of light. This is why most landline internet connections will have low latency, because the bulk of their travel distance is now handled by these high-speed, high-reliability lines and very few checksums fail due to interference.
So why isn't fiber available everywhere?
Well, running aerial cables is expensive, and there's a lot of cable in the United States. A government article covers just how expensive it is maintaining the grid, let alone upgrading it. In the past, when one electrical system was being phased out by another it was as simple as waiting for a section to need repairs then taking that opportunity to upgrade it cheaply, but with the leap to fiber optic that can't be done, as it uses an entirely different method for transmission and whole regions need the upgrade at once, or it fails to deliver.
It all boils down to how expensive it is to deliver fiber optic service to an end-user, and sadly there's simply not enough motivation for the companies with the money to afford it to go and make that kind of investment.
There's good news to be had, though; As computer usage continues to expand and the demand for high-speed, high-reliability internet continues to grow there will be a turning point when companies start seeing it as being worth the expense, and delivering the next generation of high-speed service to the end-user.
If you'd like to learn more about this topic and get into the technical nitty-gritty of it, there's a very informative blog by Directcom and an article on HowStuffWorks that both get into the science behind this.
Wise words of the day:
"Eloquence is the power to translate a truth into language perfectly intelligible to the person to whom you speak."
~Ralph Waldo Emerson
We've all seen the commercials, a communications company saying their new DSL service is available "up to" a certain speed, or with speeds "potentially as high as" But why is that? Surely if their hardware can handle those speeds, then it should be available to everyone, right? Well, it's annoyingly wrong because of the X-factor of an aging infrastructure in the United States and a behavior of copper wire known as "signal attenuation" which is, in its basest explanation, the loss of signal over distance.
Data sent by DSL modems is an electrical packet, which is power. Power running through copper wire, or any metal wire for that matter, will entropy over distance due to resistance and interference causing attenuation (decay) of the signal. If you think of a wire like a hose and electricity like the water, resistance is the friction in that hose which makes it harder to pump it over longer distances. Sending data packets is like sending pulses of hot and then cold water down that hose. The worse the attenuation in the line, the faster the hot water cools down and the cold water warms up. To get data from one end to the other, it has to not only arrive, but still be the right temperature.
In a smooth, featureless hose, that would be simple, but that's not the case. Old and worn out networks, different gauges of wire used, and splices made improperly are like kinks, connectors, and different size hoses on the line, and with each of those the water passes through, the hot and cold are going to get a bit harder to pump and a bit more mixed together.
A single packet could be: 1110010110101011010110110010110
But how can you know it's still the packet that was sent with all these things affecting the line?
The answer is with checksums. All of the "1" data in that packet adds up to 18, so a checksum would be sent with it that says "18" If the packet gets damaged, then the data will no longer add up to 18, and it's considered corrupted. Likewise, if the checksum gets damaged, it could suddenly read "7714" and the same applies.
When a modem connects to an ISP's server, it performs something known as a "handshake" tossing packets with these checksums back and forth at ever-faster rates until they begin failing. When the failure point is reached, the modem backs up a little bit, sending the packets slower, with longer 1's and 0's at a higher power level, to ensure they won't be lost.
If the interference in the line increases, though, then it can begin dropping packets. if the packet loss gets above a threshold, then the modem severs the DSL connection and performs the handshake again, to calibrate itself to the new speed limits. This is what's usually happening when a DSL connection goes out for a few minutes at a time.
Fiber lines, which have already replaced copper in the nation's backbone infrastructure solve this by using light signals inside a fiber optic cable. Fiber optic still suffers from attenuation and resistance, but at radically lesser values. Also, the data is being sent with light, which travels...at the speed of light. This is why most landline internet connections will have low latency, because the bulk of their travel distance is now handled by these high-speed, high-reliability lines and very few checksums fail due to interference.
So why isn't fiber available everywhere?
Well, running aerial cables is expensive, and there's a lot of cable in the United States. A government article covers just how expensive it is maintaining the grid, let alone upgrading it. In the past, when one electrical system was being phased out by another it was as simple as waiting for a section to need repairs then taking that opportunity to upgrade it cheaply, but with the leap to fiber optic that can't be done, as it uses an entirely different method for transmission and whole regions need the upgrade at once, or it fails to deliver.
It all boils down to how expensive it is to deliver fiber optic service to an end-user, and sadly there's simply not enough motivation for the companies with the money to afford it to go and make that kind of investment.
There's good news to be had, though; As computer usage continues to expand and the demand for high-speed, high-reliability internet continues to grow there will be a turning point when companies start seeing it as being worth the expense, and delivering the next generation of high-speed service to the end-user.
If you'd like to learn more about this topic and get into the technical nitty-gritty of it, there's a very informative blog by Directcom and an article on HowStuffWorks that both get into the science behind this.
Wise words of the day:
"Eloquence is the power to translate a truth into language perfectly intelligible to the person to whom you speak."
~Ralph Waldo Emerson
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