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Not so fast Broadband 

This article was first written in 2006 when broadband MAX products were first introduced. It has been updated for the currently available products.

Hype
Don’t be misled by the hype, you may not receive a full 20Mb/sec connection with your broadband product. This article attempts to set out why.

Connection speeds
Broadband ADSL connectivity used to be purchased at fixed speeds of 512Kb/s 1000Kb/s and 2000Kb/s. In 2006 the new Max products were introduced which can today reach 16000Kb/s. However, just like everything else in this world the figures only tell part of the story. Broadband ADSL is what is known as a contended service, to understand this requires an understanding of bandwidth (try using Capacity in place of the word Bandwidth). The Max products also rely on what is known as Rate Adaption.

Contention
When connected through ADSL broadband every connection is monitored through a number of groups called contention groups (these are defined and managed by BT) Each of these groups have a fixed amount of bandwidth which is distributed to the connections within it.

Consider a user connected to the internet and downloading a large file. If this users connection is the only one in the contention group the user will have the full bandwidth of his connection available to him. However if a second user is also trying to download a large file at the same time, both users will only have 50% of the total bandwidth available to them. If these two users are the only 2 in the contention group then this is the worse case scenario and we state that the service has a contention ratio of 2:1. Unfortunately the normal domestic product offering is 50:1 with businesses being offered 20:1 as standard with options of 15:1, and 5:1 in some instances.

This isn’t as bad as it seams, most users aren’t downloading large files all the time and the available bandwidth is quite adequate. If you own a broadband account you will know that most of the time you get very good browsing performance and mail update speeds. None the less it is quite possible that if all users in a contention group started to require continuous high speed downloads then the available bandwidth to individuals in that group would be compromised. It is theoretically possible for broadband performance to drop to below dialup speeds of 56Kb/s, this would be exceptional and unlikely to be sustained for very long.

Rate adaption
In addition to contention your broad band service is reliant upon such things as line quality, distance from the exchange, and exchange capacity. Until the Max products were introduced, these parameters determined what broadband speeds would be offered to you (IE 512,1000,2000Kb/s). So if the wire from your exchange was very long (in excess of 8Km) or had poor quality connections or cable in it, then you would be offered lower speed products. The Max products use rate adaption technology to dynamically assess the maximum possible connection speed that can be acheived on your line.

When you are first connected to a Max product some software at the exchange determines your initial maximum connection speed. At one time the assessment of your Maximum Stable Rate (MSR) took upto 10 days and the service was very hit and miss but now the initial connection speed is more or less what you can expect as your MSR. Your accounts operational service agreement is defined in terms of your MSR.

Your ISP will not be able to forward fault or complaint reports to BT if your service is operating within the service agreement. Remember too that Max products are also contended services which may limit your connection speed as described above.

We recommend that you arrange for any existing router, modem, or firewall hardware to be checked for operation at 16000Kb/sec and that this hardware is running with appropriate revisions of firmware. Please Contact us if you need any help.