dsl

2

2scoops0406

I'm sure one of you can clear this up for me (sorry about the hijack BTW) if you have a DSL (digital subscriber line) why do you need a modem (modulator demodulator) which is used to convert analogue signal into a digital signal.

I now the difference between hubs, switches, reapeater, bridges, brouters, gateways BTW, but I can't get my head around a lot of stuff that's talked about WRT to broadband technology, a lot of it seems contradictory.

Hopefully an explanation will help with the original question anyway.
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Lynda, moderator

please don't hi jack posts, I have split this one

Me head, good grief.
 
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DSL uses a wide range of frequencies (hence broadband) to carry the digital data. Although you have one physical modem, it actually consists of a number of virtual modems, each monitoring a subset of the frequencies available. Data is switched between these logical modems as an when required in order to maintain quality and high speeds. It's the combination of these virtual modems that allows the high speeds to be achieved.
 
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What Igorian said is correct except that the reason a modem is required is because the bandwidth of the copper tail circuits used is very poor.

Modulation is used wherever you need to change the bandwidth characteristics of the signal you want to send to the bandwidth characteristics of the transmission channel you have available. The DSL scheme frequency multiplexes a number of channels on to the line and a clever modulation/demodulation scheme is used to greatly enhance the data carrying capacity of each channel.

The DSL modem is just used to get your data to your local exchange where a device called a DSLAM demodulates it and chucks it into a proper network with loads of bandwidth.
 
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