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ADSL explained

Written By : Dale Hurwitz | 2009-09-21

ADSL (Asymmetric Digital Subscriber Line) is an internet connectivity technology that within South Africa enables an ordinary telephone line to reach speeds of up to 4096kbps (over 73 times that of a dialup connection).

Although ADSL is not a guaranteed service it does offer a high level of reliability and is always online, without the cost implications associated with services such as leased lines.

There are two components required to complete an ADSL solution;

Firstly the ADSL line. In South Africa the ADSL line is supplied by Telkom. You can acquire the line through your ISP, but it is the same line from Telkom irrespective of whether your ISP bills it or Telkom. The lines are available in three speeds currently Fast (384kbps), Faster (512kbps) and Fastest (4096kbps). In a follow up article we will discuss “Choosing the correct ADSL solution” where we will cover which line will be the best for your specific requirements. The ADSL line runs through the same cable as your regular telephone line. A device called POTS filter will ensure that you can make a call and be on the internet at the same time. This device must be plugged into the phone line between the telephone socket on your wall and an actual telephone.

Secondly the ADSL account. You have many choices for accounts and these vary in terms of quality, speed and usage limits.

The best quality accounts are generally ones where the international bandwidth is sent and received via fibre optic cables rather than satellites. Fibre optic cables are faster and less prone to errors. It is important to note the contention ration of your account. The contention ratio is the amount of users that share the same amount of available bandwidth. An acceptable contention ratio is between 15:1 and 25:1, however many lower quality services have ratios in excess of 50:1 and even as high as 100:1.

The speed of the account is influenced by the maximum speed of your ADSL line, the quality of you account and finally may be limited by your ISP (especially prominent in uncapped accounts). The speed of the account is an important factor to consider when choosing the correct ADSL solution.

Usage limits are placed on most regular ADSL accounts. The usage limit is generally classified as a “cap”. The ADSL account cap is a total of bandwidth that can be sent and or received over the account in a calendar month. When looking at uncapped accounts there is often a “rolling threshold” in place. This helps to mitigate the risk of abuse that may impact the quality and speed of service for other users of the service. Typically when the rolling threshold on an uncapped account is reach the service will not stop working, but will continue at a slower speed. ADSL usage in a home or business environment has no specific usage limits that are “normal”. What account will be best depends on what the application of the account is. When asked what usage limits are acceptable for businesses we always say that as long as the bandwidth is used productively there is no maximum. The biggest issue is when staff waste bandwidth on unproductive or unhealthy websites or applications.

One last facet you will require for ADSL is a router. A router will allow for your line to connect to your ISP account. It controls your connection to the internet and allows one or more computers to be connected to the internet simultaneously. There are mand different brands of ADSL routers that offer functionality such as wireless, firewalls and quality of service that may be useful depending on your exact requirements.

In the next article we will go into detail on “Choosing the correct ADSL solution”. Click here to view our ADSL options



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