It is simply called BANDWIDTH. You can only shove so much down a "voice" channel, and you have to remember that the typical telephone "voice" channel is certainly not "HI-FI" quality to begin with. The limit wasn't set so much by the FCC as it is just a standard to prevent cross talk on other circuits. DSL is sent over a special 'phone circuit, and in essence, amounts to sorta the same thing, but special lines and equipment has to be used, you can't just go out 'an hook 'er up with y'er 'ol alligater clips on the 'ol farm-farm fence-line/phone. You people oughta be glad they're THAT fast, I can show you friends of mine, NOT VERY FAR from the Spokane downtown area, that routinely have to put up with 20xk, and a friend of mine in the Rural's of Montana is darn lucky to EVER get above 22k. The phone company never has, never will, make any guarantees about digital transfer rates on a VOICE line.

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>> My friend in England gets about 56-58K so that means the 56K Modem is capable of transferring data at speeds higher then 56K. << I think your friend in England is either getting a little confused or is telling porkies. 56 kbps is a theoretical maximum and theoretical maximums are hardley ever achieved outside a lab. BTW I'm in England as well. The best I have ever achieved is 51.5K and thats on a brand new copper pair half a mile from the exchange. Dialup technology has reached its limit on a PSTN system. The PTSN was desighned for audio frequencies of up to 3.5KHz Try and put frequences higher than that down the PSTN and they will be filtered out. DSL uses frequencies of up to 100 Khz. Stuart

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Actually phone links could theoretically do up to 64K, but that's a theoretical maximum with cleanest best phonelines. It is a limit to how the line technologically works. MCSE, MCSA Messaging, baby!

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Name is spot on. I was trying to avoid using that dreaded word Bandwidth, it is so misunderstood that it will create more questions than it answers. In the UK, BT will guarantee a digital transmission rate of 9600 baud over the PSTN. That is good for fax and not a lot else. A 56K modem uses a baud rate of 14, 000 Stuart

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If you look at the development of data communications, in the early days speeds were very low. To achieve higher speeds, often 4 wires were used (2 for tx, 2 for rx) when using either dialup or direct connection. Here in the UK around 25 years ago a 9600baud modem cost thousands of £'s and was half the size of todays pc base cabinet. While over the years line quality has improved, generally it is advances in modem technology (compression/error correction etc.) that have made possible todays high speeds on a normal 2 wire phone line. I felt these advances should have continued, but to do so requires matching technology both ends, which equates to cost. It is also about profit as the phone companies want their share of the cake. Here in the UK, despite their much pushing, broadband has not taken up as much as they would like. Although we are told the max speed is 56kb, ever noticed the line from your house to the exchange is able to support broadband and a telephone call at the same time without upgrading. Good luck - Keep us posted.

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>> Although we are told the max speed is 56kb, ever noticed the line from your house to the exchange is able to support broadband and a telephone call at the same time without upgrading. << Of course it will. The limiting factor is not the copper wire, but the euipment the copper wire is attached to. When your wire goes into the exchange it is split. The voice frequencies go to the voice equipment and the DSL frequencies go to the DSL equipment. Try and put frequencies higher than 3.5Khz through the voice quipment and they wont get through. Stuart

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Well done stuart - there is "no" limit to what you can get through a modem - all you need to do is apply more and more compression - the tricky but is to compress and decompress fast enough to make the increased throughput worthwhile. A quoted modem speed is not the speed it transfers at but it's uncompressed equivalent Techy n Welsh

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Its you that is getting a little confused rayok. The quoted transmission speed is the actual speed of data regardless of compression. Compression doesn't enter into it. If you want the uncompressed data it will be measured in bytes not bits as data transmission speeds are. The uncompressed equivalent will vary almost second by second as the compression will vary on the type of date being transmitted. We are talking about data transmission speeds. Bugger all to do with compression. Stuart

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stuart is right. although there is a limit on the line, most of the speed is achived by compression. if you widen the bandwidth (and for those of you that are lost on the meaning of it bandwidth is the range of frequencys for example 20hz - 20khz as used in most hi fi audio equiptment) then you get more room for more data to be passe d through therefore the compression will also make it more effective. the reason dsl is so much faster than dail up, is because it doesnt use voice transmittion, or frequency variations to transmit. the system sticks to one frequency (that is decoded at the switching station) the frequency sends a digital signal, a voltage is applied and cut, accordingly to the datta being transfered. so in essence the modem pulses the frequency extreamly fast. this is fater because a voltage can be switched on and off faster than a voice frequency can variate, due to inductance and wave refraction. now that is not all that makes dail up fast. because it is digital and not voice it makes compression and decompression faster because computers use digital interface. so the modem receiving a frequency that is slightly differed than the one it transmits (so you dont get interferance) it hears the "sounds" pulsing as 00110100111010111010010101 in digital code. since it is alreay in digital it doesnt need to go through the voice-digital conversion that dail up does do it cuts decompression and compreaaion a grat deal, so it only needs to decompress the actual data part, as compared to dail up wich needs to do both. hope that helped anyone who is lost understand a bit more. My Pathetic System ------------------ AMD K-6 II 500Mhz 384 MB PC-100 RAM 10 GB + 3 GB HDs 52x CDR/W 24x CD-ROM Soundblaster AWE 64 10-100 Ethernet 8 MB VRAM

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Isnt it also true that DSL uses more than one communication channel to transfer data, requiring a mux/demux on each end?

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Isnt it also true that DSL uses more than one communication channel to transfer data, requiring a mux/demux on each end?

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Originally posted by: 180MHz "00110100111010111010010101 in digital code" It's binary code. Digital codes are something like this "&â⌂♫ u♥Θ! ─^♠&ïG♀&ïW♫ëF÷ëV°ïF÷ïV°RPÜ v◘ v♠Ü≥♣■♥=  t♥Θâ â· t♥Θ{ ─^♠&ïG◘&ïW ^♠&9W☻}♥Θ* ~♥Θ◘ &9•s♥Θ↔  v◘ v♠Üû♠2♦ë" Expert™

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"Isnt it also true that DSL uses more than one communication channel to transfer data, requiring a mux/demux on each end?" Yes, this is one method used by DSL providers called DMT: http://computer.howstuffworks.com/dsl5.htm All data sent over a telephone line is analog, not digital. DSL DOES use frequency variations to transmit data. All phone line and cable modems, modulator and demodulator combinations send information over a channel that is represented as an analog quantity, today we use variations in voltage to represent information for DSL and voice communication. Modern DSL technology uses Quadrature Amplitude Modulation (http://www.pcquest.com/content/broadband/201030103.asp). The process of demodulation takes the analog signal and converts it into a digital signal. A digital signal is not sent directly over the communications medium. DSL does work similar to how 180 described, it is digital in the sense that a frequency or group of frequencies are switched on or off to represent 1s and 0s, but modulation is still taking place. The digital information 1s and 0s are still being represented in the form of an analog signal. Avoid Intel Celeron CPUs, buy an AMD instead. Avoid Nokia, go Motorola instead.

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