Whatever professor is teaching this curriculum should be shot. Telephone lines were upgraded to digital almost twenty years ago. And the speeds can range from 110 symbols per second upto 3429 symbols per second (analog). Or 110 bit/s upto approximately 34000 bit/s (analog).
>>>Uh no. Pretty much all landline telephones are already digital
Dear Anonymous Coward: You committed a STRAWMAN ARGUMENT. Nowhere in my message did I say phonelines or 56k modems were not digital. I am well aware that modern phones are almost-universally digital in nature.
>>>Phone signal used all of the bandwidth in a rather wide range
4000 hertz is not wide. Your compact disc player has more width (20,000).
>>>Even if DSL operated in the 0-4000 Hz range, it would use the spectrum much more efficiently than would an analog signal sampled at n times a second. >>>
56k modems are not analog; they are digital. (33k modems are analog.) If DSL was confined to 4000 hertz like your 56k digital dialup modem, it would still be limited to the same 7 bits * 4000 hertz * 2 == 56000 bits/second.
>>>technology is not limited to the techniques you are familiar with.
No it's limited by the universe. Just as you cannot exceed 186,000 miles per second, neither can you exceed a certain datarate within a fixed width. You would understand my point if you had bothered to read your PHYSICS 101 textbook about Shannon's Limit or Nyquist's Theorem. Or as Scotty would say, "You cannae change the laws of da universe!"
>>>Kind of reminds me of the predictions that 9.6, then 14.4, then 28.8 were the fastest possible modem throughput on copper because it was physically impossible to squeeze any more information onto the available bandwidth. Yet each time someone makes this assertion something else comes along. >>>
False history. There were three speed limits - one was due to lack of knowledge, and the other two were imposed by the universe:
14k - based upon QAM with 4 bits per symbol - engineers didn't know any other method of modulation and believed this was the maximum they could do. Once they discovered trellis modulation, they realized they could reach the Shannon Limit: 35k - analog limit per Shannon's Theorem 56k - digital limit per Nyquist
Note that the last limit has stood for 15 years and will never be broken, unless we discover some alternate universe with different laws. In *this* universe the limit has been hit.
>>>I disagree with the fact "we need" cell phone service.
Me too. I have a prepaid cellphone that automatically adds $5 each month. It's now over $100 since I rarely use it. One of these days I'll go on a vacation and make lots of long-distance calls, but for now the money just keeps accumulating.
>>>I thought of a solution. Have cell towers and data towers be much much closer together
Heck just give everyone a cell tower, right on top of their roof. And then run the cable from each tower, through the owner's home, and out to the street....... wait a minute! That's just like wiring everyone directly. You don't need wireless.
>>>older techniques, but how does that relate to whatever spec is going to be rolling out
Alright. Well technologies improve, yes, but there's still a physical maximum imposed by our universe. 21 megahertz == ~330 Mbit/s according to Nyquist's Theorem. So killing-off AM and FM would free-up enough bandwidth to serve three maybe four users.
>>>>>>>>technology will evolve to give you more bandwidth. >> >>No. There's a limit to how much technology can do. That's why phone lines are maxed-out at 56 kbit/s - there's no more room for expansion since it's already at the physical limit (4000 hertz).
(Score:0, Troll)
Unbelievable. The moderators on this forum would fail basic PHYSICS 101. They can't even understand the simplicity of Shannon's Limit or Nyquist's Theorem (which state a limited bandwidth has a maximum data rate).
>>>I work at a university and we use phone lines to move audio from building to building.
Since telephone lines are bandlimited to 4000 hertz, what you are claiming is impossible. You would have to remove that 4000 hertz limit to carry the full 20,000 hertz audio spectrum, at which point the lines cease to be telephone wires...... they no longer meet the international specifications for POTS.
What you have is twisted-pair copper. Basically ethernet, but carrying analog audio instead of data.
>>>So you're saying it wasn't a physical limitation of the broadcast medium at all, it was a hardware limitation of the receiver.
No it was an EXAMPLE to illustrate what happens when bandwidth is limited. Imagine that every cellphone user is assigned 4000 hertz of space for his usage. How much data can be sent over that width? The answer is not "as much as we want". The answer is defined by the physical limits of the universe.
In the world of telephone modems 4000 hertz hits that universal maximum at just 56k. In the world of Digital AM radio, it's a mere 20k. QED the comment "technology will evolve to give you more bandwidth" is flat wrong because bandwidth is a fixed quantity, and how much information you can send in that fixed width is limited by the universe.
(And I really wish people would stop modding me "troll" when I am trying to EDUCATE you. No wonder my old Physics professor is sick of teaching - the students don't listen, he said.)
>>>technology will evolve to give you more bandwidth.
People didn't like my 56k/4000-hertz-wide telephone example, so I'll try a different tactic: Bandwidth is FIXED. You can change the datarate inside that fixed bandwidth, but that is limited by Shannon's Limit (analog) and Nyquist's Theorem (digital). Engineers can not violate the physical maximums placed upon us by the universe.
I meant to say "4000 hertz" not 8000 hertz. Ooops. .
>>>is using the same physical lines (although they may have to be cleaned up to remove loading coils or branched circuits)
Yes but the whole point of this discussion is your have a *fixed* bandwidth or spectrum. If DSL was forced to fit inside the same 4000-hertz-wide telephone line as a dialup modem, it would be no faster than 56k (7 bits timed 8000 samples/second with bit 8 reserved).
If it were possible to exceed 56k over POTS, someone would have already done it.
Ever heard of the Shannon limit? On an analog phone line, you cannot exceed 35 kbit/s (V.34). Ever heard of Nyquist theory? On a digital phone line, the 4000 hertz bandwidth sampled at 8000 times per second, times 7 bits per sample == 56000 maximum.
As Scotty on Star Trek would say, "You cannae change the laws of physics!"
>>>phone lines are inherently limited to 2400 bits/second (bps). Better compression algorithms got us up to 56 kbps. >>>
False. The physical limits on an analog phone line are 3,429 SYMBOLS per second, with approximately 10 bits represented by each symbol, to achieve 33,800 bits per second (V.34)
The physical limits on digital phone lines are 8000 SAMPLES per second, and 7 bits each, to yield 56,000 bits per second. The 8th bit is reserved by the telephone company, otherwise we would see 64000 bit/s.
Using V.92 data compression, you can achieve an *apparent* speed of ~400 kbit/s for text, ~150 for executables, and ~56k for incompressible JPGs, GIFs, and other datafiles.
>>>I think kevinmenzel illustrated the point quite well. Analog phone lines are indeed no faster than 56 kbits/second. That's why we went to a new technology, and now have DSL. >>>
Yes but if DSL was forced to fit inside the same bandwidth as the old dialup phone modems (4000 hertz wide), it would still only be 64 kbit/s speed. *That* was the point I was making... you can only squeeze so much data into a FIXED width of space. The universe places physical limits in what engineers can do.
Another example is Digital AM Radio, which is limited to just 4500 hertz in Europe, or ~20 kbit/s.
No... same line, different bandwidth. The bandwidth is the key. 4000 hertz for the phone dialup modem versus ~200,000 hertz for the DSL connection. If the DSL was forced to limit itself to the same bandwidth as a dialup modem, it would only be 64k. (This is called a "DSzero" or "DS0" line by the telephone company, also called ISDN.)
DSL also terminates your line only a few hundred feet from your house, and upgrades it to fiber or coax, whereas the original telephone line could travel many miles with no apparent degradation of the 4000-hertz-wide signal.
>>>I'm getting about 7 Gbits from the phone line that used to be maxed out at 52k or so
No you're not. When you upgraded to DSL, the company disconnected the telephone line (bandlimited to 4000 hertz) with a standard twisted-pair wire (no upper limit). Furthermore they disconnected your house from the old phone service, and connected it to a DSLAM which converts the short ~500 meter cable to higher-quality coaxial or fiber.
So my previous comment about the 4000-hertz wide telephone service still being limited to just 56k is still true.
No DSL is *not* over telephone lines. POTS (plain old telephone service) is defined as having a 0 to 8000 hertz bandwidth, hence the 56k dialup limit. The engineers have squeezed as much data as they can into that limited range.
DSL disconnects the POTS line, and replaces it with a central box (DSLAM) that converts the incoming twisted-pair and passes it along to higher-quality fiber or coax.
BTW thanks for modding me "troll" kevinmenzel. -1 I disagree is not why moderation exists.
>>>allow devices to find frequencies that are and aren't being used
Yeah there's already been tests using these devices on the TV Band. What they found was the device could detect strong local stations, but not the low-level signals from 40 miles or more distance, so they started broadcasting over top existing TV stations, thereby interrupting viewers' reception. The idea was rejected by the FCC in early 2008.
Okay - FM is 20 megahertz wide and AM is about 1 megahertz wide, so we're talking the equivalent of 3.5 television channels.
According to the ATSC spec, that's just 70 Mbit/s of datawidth. According to the HDR spec, you get 300kbit/s per 0.2 spacing, or about 32 Mbit/s. Trivial.
If there's no radio in my car, what am I supposed to listen to? And before you say "iPod" I don't want to hear the same music over and over. I want to hear new stuff. Also traffic and weather reports ("warning: tornado coming") are nice to have. I like my radio and if they take away both AM and FM, then I'm going to hurt somebody.:-| At the very least leave me AM.
>>>I turned on a shortwave and between huge swaths of static,
What? You need to get rid of that old unit, because they have digital shortwave now. It sounds almost as good as a CD, and still remains popular in Europe, Asia, and Australia.
>>>Today, we still are wasting a significant portion of bandwidth on broadcasting when the future is point to point communications along with some form of P2P crowdcasting. >>>
Soooo..... it will take about 1000 times more wireless/cellphone spectrum to do what broadcast TV does in just 300 megahertz. Point-to-point sounds horribly inefficient to me?
>>>technology will evolve to give you more bandwidth.
No. There's a limit to how much technology can do. That's why phone lines are maxed-out at 56 kbit/s - there's no more room for expansion since it's already at the physical limit. Same applies with wireless.
Slashdot Mirror
http://www.computing.dcu.ie/~humphrys/Notes/Networks/physical.phone.html "Basic speed 2400 bps. Clever coding used to get up to 56 kbps. The last mile is (usually) analog."
Whatever professor is teaching this curriculum should be shot. Telephone lines were upgraded to digital almost twenty years ago. And the speeds can range from 110 symbols per second upto 3429 symbols per second (analog). Or 110 bit/s upto approximately 34000 bit/s (analog).
Here read this list of speeds for better understanding:
http://en.wikipedia.org/wiki/Modem#List_of_dialup_speeds
>>>Uh no. Pretty much all landline telephones are already digital
Dear Anonymous Coward: You committed a STRAWMAN ARGUMENT. Nowhere in my message did I say phonelines or 56k modems were not digital. I am well aware that modern phones are almost-universally digital in nature.
>>>Phone signal used all of the bandwidth in a rather wide range
4000 hertz is not wide. Your compact disc player has more width (20,000).
>>>Even if DSL operated in the 0-4000 Hz range, it would use the spectrum much more efficiently than would an analog signal sampled at n times a second.
>>>
56k modems are not analog; they are digital. (33k modems are analog.) If DSL was confined to 4000 hertz like your 56k digital dialup modem, it would still be limited to the same 7 bits * 4000 hertz * 2 == 56000 bits/second.
>>>technology is not limited to the techniques you are familiar with.
No it's limited by the universe. Just as you cannot exceed 186,000 miles per second, neither can you exceed a certain datarate within a fixed width. You would understand my point if you had bothered to read your PHYSICS 101 textbook about Shannon's Limit or Nyquist's Theorem. Or as Scotty would say, "You cannae change the laws of da universe!"
>>>Kind of reminds me of the predictions that 9.6, then 14.4, then 28.8 were the fastest possible modem throughput on copper because it was physically impossible to squeeze any more information onto the available bandwidth. Yet each time someone makes this assertion something else comes along.
>>>
False history. There were three speed limits - one was due to lack of knowledge, and the other two were imposed by the universe:
14k - based upon QAM with 4 bits per symbol - engineers didn't know any other method of modulation and believed this was the maximum they could do. Once they discovered trellis modulation, they realized they could reach the Shannon Limit:
35k - analog limit per Shannon's Theorem
56k - digital limit per Nyquist
Note that the last limit has stood for 15 years and will never be broken, unless we discover some alternate universe with different laws. In *this* universe the limit has been hit.
>>>I disagree with the fact "we need" cell phone service.
Me too. I have a prepaid cellphone that automatically adds $5 each month. It's now over $100 since I rarely use it. One of these days I'll go on a vacation and make lots of long-distance calls, but for now the money just keeps accumulating.
>>>I thought of a solution. Have cell towers and data towers be much much closer together
Heck just give everyone a cell tower, right on top of their roof. And then run the cable from each tower, through the owner's home, and out to the street....... wait a minute! That's just like wiring everyone directly. You don't need wireless.
>>>There's a better case for re-using the old analogue TV spectrum
The old analogue spectrum has already been reassigned for use by digital TV. It isn't available.
>>>older techniques, but how does that relate to whatever spec is going to be rolling out
Alright. Well technologies improve, yes, but there's still a physical maximum imposed by our universe. 21 megahertz == ~330 Mbit/s according to Nyquist's Theorem. So killing-off AM and FM would free-up enough bandwidth to serve three maybe four users.
>>>>>>>>technology will evolve to give you more bandwidth.
>>
>>No. There's a limit to how much technology can do. That's why phone lines are maxed-out at 56 kbit/s - there's no more room for expansion since it's already at the physical limit (4000 hertz).
(Score:0, Troll)
Unbelievable. The moderators on this forum would fail basic PHYSICS 101. They can't even understand the simplicity of Shannon's Limit or Nyquist's Theorem (which state a limited bandwidth has a maximum data rate).
>>>I work at a university and we use phone lines to move audio from building to building.
Since telephone lines are bandlimited to 4000 hertz, what you are claiming is impossible. You would have to remove that 4000 hertz limit to carry the full 20,000 hertz audio spectrum, at which point the lines cease to be telephone wires...... they no longer meet the international specifications for POTS.
What you have is twisted-pair copper. Basically ethernet, but carrying analog audio instead of data.
>>>So you're saying it wasn't a physical limitation of the broadcast medium at all, it was a hardware limitation of the receiver.
No it was an EXAMPLE to illustrate what happens when bandwidth is limited. Imagine that every cellphone user is assigned 4000 hertz of space for his usage. How much data can be sent over that width? The answer is not "as much as we want". The answer is defined by the physical limits of the universe.
In the world of telephone modems 4000 hertz hits that universal maximum at just 56k. In the world of Digital AM radio, it's a mere 20k. QED the comment "technology will evolve to give you more bandwidth" is flat wrong because bandwidth is a fixed quantity, and how much information you can send in that fixed width is limited by the universe.
(And I really wish people would stop modding me "troll" when I am trying to EDUCATE you. No wonder my old Physics professor is sick of teaching - the students don't listen, he said.)
>>>technology will evolve to give you more bandwidth.
People didn't like my 56k/4000-hertz-wide telephone example, so I'll try a different tactic: Bandwidth is FIXED. You can change the datarate inside that fixed bandwidth, but that is limited by Shannon's Limit (analog) and Nyquist's Theorem (digital). Engineers can not violate the physical maximums placed upon us by the universe.
I meant to say "4000 hertz" not 8000 hertz. Ooops.
.
>>>is using the same physical lines (although they may have to be cleaned up to remove loading coils or branched circuits)
Yes but the whole point of this discussion is your have a *fixed* bandwidth or spectrum. If DSL was forced to fit inside the same 4000-hertz-wide telephone line as a dialup modem, it would be no faster than 56k (7 bits timed 8000 samples/second with bit 8 reserved).
If it were possible to exceed 56k over POTS, someone would have already done it.
>>>Then they KNEW 56000 bps was the max, etc..
Ever heard of the Shannon limit? On an analog phone line, you cannot exceed 35 kbit/s (V.34). Ever heard of Nyquist theory? On a digital phone line, the 4000 hertz bandwidth sampled at 8000 times per second, times 7 bits per sample == 56000 maximum.
As Scotty on Star Trek would say, "You cannae change the laws of physics!"
>>>phone lines are inherently limited to 2400 bits/second (bps). Better compression algorithms got us up to 56 kbps.
>>>
False. The physical limits on an analog phone line are 3,429 SYMBOLS per second, with approximately 10 bits represented by each symbol, to achieve 33,800 bits per second (V.34)
The physical limits on digital phone lines are 8000 SAMPLES per second, and 7 bits each, to yield 56,000 bits per second. The 8th bit is reserved by the telephone company, otherwise we would see 64000 bit/s.
Using V.92 data compression, you can achieve an *apparent* speed of ~400 kbit/s for text, ~150 for executables, and ~56k for incompressible JPGs, GIFs, and other datafiles.
>>>I think kevinmenzel illustrated the point quite well. Analog phone lines are indeed no faster than 56 kbits/second. That's why we went to a new technology, and now have DSL.
>>>
Yes but if DSL was forced to fit inside the same bandwidth as the old dialup phone modems (4000 hertz wide), it would still only be 64 kbit/s speed. *That* was the point I was making... you can only squeeze so much data into a FIXED width of space. The universe places physical limits in what engineers can do.
Another example is Digital AM Radio, which is limited to just 4500 hertz in Europe, or ~20 kbit/s.
>>>Same line, different signal.
No... same line, different bandwidth. The bandwidth is the key. 4000 hertz for the phone dialup modem versus ~200,000 hertz for the DSL connection. If the DSL was forced to limit itself to the same bandwidth as a dialup modem, it would only be 64k. (This is called a "DSzero" or "DS0" line by the telephone company, also called ISDN.)
DSL also terminates your line only a few hundred feet from your house, and upgrades it to fiber or coax, whereas the original telephone line could travel many miles with no apparent degradation of the 4000-hertz-wide signal.
Correction: Replace "8000 hertz" with "4000 hertz"
>>>I'm getting about 7 Gbits from the phone line that used to be maxed out at 52k or so
No you're not. When you upgraded to DSL, the company disconnected the telephone line (bandlimited to 4000 hertz) with a standard twisted-pair wire (no upper limit). Furthermore they disconnected your house from the old phone service, and connected it to a DSLAM which converts the short ~500 meter cable to higher-quality coaxial or fiber.
So my previous comment about the 4000-hertz wide telephone service still being limited to just 56k is still true.
No DSL is *not* over telephone lines. POTS (plain old telephone service) is defined as having a 0 to 8000 hertz bandwidth, hence the 56k dialup limit. The engineers have squeezed as much data as they can into that limited range.
DSL disconnects the POTS line, and replaces it with a central box (DSLAM) that converts the incoming twisted-pair and passes it along to higher-quality fiber or coax.
BTW thanks for modding me "troll" kevinmenzel.
-1 I disagree is not why moderation exists.
>>>allow devices to find frequencies that are and aren't being used
Yeah there's already been tests using these devices on the TV Band. What they found was the device could detect strong local stations, but not the low-level signals from 40 miles or more distance, so they started broadcasting over top existing TV stations, thereby interrupting viewers' reception. The idea was rejected by the FCC in early 2008.
Okay - FM is 20 megahertz wide and AM is about 1 megahertz wide, so we're talking the equivalent of 3.5 television channels.
According to the ATSC spec, that's just 70 Mbit/s of datawidth.
According to the HDR spec, you get 300kbit/s per 0.2 spacing, or about 32 Mbit/s.
Trivial.
If there's no radio in my car, what am I supposed to listen to? And before you say "iPod" I don't want to hear the same music over and over. I want to hear new stuff. Also traffic and weather reports ("warning: tornado coming") are nice to have. I like my radio and if they take away both AM and FM, then I'm going to hurt somebody. :-| At the very least leave me AM.
>>>I turned on a shortwave and between huge swaths of static,
What? You need to get rid of that old unit, because they have digital shortwave now. It sounds almost as good as a CD, and still remains popular in Europe, Asia, and Australia.
>>>Today, we still are wasting a significant portion of bandwidth on broadcasting when the future is point to point communications along with some form of P2P crowdcasting.
>>>
Soooo..... it will take about 1000 times more wireless/cellphone spectrum to do what broadcast TV does in just 300 megahertz. Point-to-point sounds horribly inefficient to me?
>>>technology will evolve to give you more bandwidth.
No. There's a limit to how much technology can do. That's why phone lines are maxed-out at 56 kbit/s - there's no more room for expansion since it's already at the physical limit. Same applies with wireless.