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DSL Concept

DSL uses the non-voice frequencies of the telephone line to transmit data. So, natural voice conversations are not affected by DSL, unlike the annoying Dial-Up, where if your grandma picked up the phone while you were connected to the internet, she would be greeted by the deafening tones over a hoarse telephone line, or with a roar from you, because your internet line got disconnected!

Getting a DSL connection most often requires you to enter into a commitment for at least a year, if you wish to get good rates; I mean the money in this case. Services are also partitioned by the maximum achievable data rates. So, if you wish to get higher speeds, you have to pay more. 

There are several kinds of DSL services which are offered. At the time of this writing, the ADSL family is in vogue and we are tending towards the VDSL market. Before this piece gets to become a cluster of abbreviations, I will stall it right here. ~S ~T stands for Asymmetric and V stands for Very High Speed. DSL, as you may remember is, Digital Subscriber Line. 

Asymmetric DSL is based on the premise that while surfing the internet, you get a lot more data coming into your browser than what you send to it. Even if you are typing a huge post to a blog, what you type is considered as an offline activity, since everything you type is stored locally until you hit the send or post button. The optimal approach for someone would be to type everything into a local editor and then cut-paste onto the 'Blog This' window. I have already mentioned that in the days of dial-up internet, especially in places where it is really tough to get the connection over noisy lines, it would be to your advantage to do as much homework before connecting on to the internet. With DSL, which is a dedicated, always ON connection, this is not so much of a problem. The data rate in the receiving side is about 10-30 times the data rates you can get while sending. 

Another example is, if you are watching a live football game over the internet, you are receiving much more than you send. Whereas if you consider a Voice over Internet (VoIP) or Voice chat over Yahoo or MSN messenger, the amount of data you send and receive are more or less the same, assuming that both the sides in the conversation are equally talkative. This is a case for SDSL, the symmetric counterpart of DSL, where the data rates are similar in both directions. For extensive Video based applications, the case for VDSL comes into the picture. 

Most of our discussion will revolve around ADSL, since that is the technology which I am most familiar with. As I mentioned earlier, in ADSL, we make use of the frequencies over the phone line, above the voiceband, which are inaudible to the human ear. There happens to be much more of the band that we cannot hear when compared to the band we can actually perceive through our occular nerves. Thus DSL is an innovation that uses this part of the frequency band that can be used to transmit data.



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