What is ADSL?

What is DSL..?
•A new technology came on the scene in recent years called DSL. 

•Digital Subscriber Line (DSL) is the generic name for a technology that allows digital data to


 sent over an ordinary copper telephone line at high speed.

•It is much faster than ISDN. For example in the UK it is common to have a 512Kbs service.


 Compare this to a dial-up service at 56Kbs or ISDN at 64Kbs

•There are more than one type DSL service. For example

–ADSL (Asymmetric Digital Subscriber Line)

–SDSL (Symmetric Digital Subscriber Line)

ADSL

>Providing bandwidth is expensive – it needs special  equipment at the exchanges and your

 telephone line has to be of good quality .

>Telephone companies realised that most domestic customers would be downloading far

 more than they would be uploading. And so it made sense to develop a DSL technology that

 provided fast download speeds but slower upload speeds.

>This service is called Asymmetric Digital Subscriber Line (ADSL) otherwise known

‘Broadband’

ADSL connections are becoming more and more widely available and can provide an 

excellent internet connection.

The connections work by splitting your phone line into two separate channels, one for data

 (internet) and one for voice (phone calls) which means you can talk on the phone and be

 connected to the internet at the same time.

• You will often see ADSL connection services advertised as having different speed

 specifications, below are some common configurations:

256Kbps/128Kbps

512Kbps/128Kbps

1Mbps/256Kbps

Notice there are two values to each configuration, the first figure states the download speed

 and the second figure is the maximum upload speed. 

ADSL – Typical performance

Average Web Page (50 Kilobytes including images)

•256kbps download speed - roughly 1.56 seconds to view page

•512kbps download speed - roughly 0.78 seconds to view page

Average MP3 file (music file) (4 Megabytes)

•256kbps download speed - roughly 2 minutes and 8 seconds to download.

•512kbps download speed - roughly 1 minute and 4 seconds to download. 

Advantages of ADSL

•Faster downloads compared to dial-up or ISDN

• No need for a second phone line - by allowing voice and data transfer at the same time

 (you can use the phone as normal while connected to the internet).

•Because ADSL transfers data digitally it doesn't need to convert the data from digital to

 analogue and back again.

•ADSL connections are Always on, which makes the usual long wait to connect a thing of

 the past. 

Disadvantages of ADSL

•ADSL connections are not available to everyone, you need to be within 3 miles of an

 ADSL enabled exchange.

• The hardware costs can be quite significant as you will need a special ADSL modem

 and ADSL filters to use the service, most ISPs allow you to hire these items which can

 reduce the initial cost.

•Because ADSL connections are Always on you will need a firewall to protect your PC