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Broadband:

This section will explain the different types of broadband connections including ADSL, DSL and Cable (T1, T2, T3...):


ADSL:


ADSL (Asymmetrical Digital Subscriber Line) allows the transmission of digital data over plain telephone lines. ADSL carries signals to the network (upload) at speeds of up to 640 Kbps, and it can deliver data from the network (download) at speeds of up to 8.1 million bits per second (Mbps).

An ADSL modem seperates an ordinary telephone line into 3 separate data channels, each with different capacities and speeds. The lowest-capacity channel transmits analog voice data for telephones; the second, medium-capacity channel, transmits data to the network for uploads; and the third, highest-capacity channel, transmits data from the network for downloads. This seperation of upload and download channels means that upload and download speeds will be different. The download speeds are faster than the upload speeds, thus the term 'Asymmetric'.
adsl_diagram.gif

(Source: http://www.answers.com/topic/asymmetric-digital-subscriber-line)


DSL:

DSL (Digital Subscriber Line) is similar to ADSL but equal in its download and upload speeds. DSL does this by also splitting the telephone line channels into 3 channels: telephone, upload and download; but it does this equally so that the distributed bandwidth for each channel is equal.

DSLdiagram.gif


Cable -T1, T3:


When you use a normal copper phone line modem, it can transmit data at perhaps 30 kilobits per second (30,000 bits per second).
With the T1 line, it means that there is a fiber optic line in place (a T1 line might also come in on copper although not quite common because copper phone lines are slower and cannot carry as much data at a time as a fibre optical line can handle). A T1 line can carry 24 digitized voice channels, carrying data at a rate of 1.544 megabits per second. If the T1 line is being used for telephone conversations, it plugs into the users' phone system. If it is carrying data it plugs into the network's router.
A T1 line can carry about 192,000 bytes per second -- roughly 60 times more data than a normal residential copper modem. A T1 line can generally handle many people sharing the line at time. For general browsing, hundreds of users are easily able to share a T1 line comfortably. A T1 line might cost between $1,000 and $1,500 per month depending on who provides it and where it goes/what it's used for. The other end of the T1 line needs to be connected to a web server, and the total cost is a combination of the fee the phone company charges and the fee the ISP charges.

Speeds/Capacity:
  • T1 - 1.544 megabits per second
  • T3 - 43.232 megabits per second (28 T1s)
(source: http://computer.howstuffworks.com/question372.htm)