Broadband and ADSL Information

Broadband and ADSL Information - Introduction

Broadband, ADSL, ADSL-Max, ADSL2, Cable, NTL, Fibre - Are these all the same? - What do I need to know?

The terms 'Broadband' and ADSL are generally used interchangeably, however ADSL is a specific type of Broadband service, as opposed to ADSL2  or Cable. 

Most home users have ADSL Broadband provided over a physical BT telephone line, except the Virgin Media (Ex NTL) customers who have 'Cable' broadband.  ADSL is provided over a standard telephone 'cable' while a 'Cable' broadband connection is provided on a Co-axial cable, together with the other cable services from the cable provider.

Even if you have move away from BT to another (non-cable) telephone provider, your telephone and broadband are still connected via the original BT supplied telephone cable to your property.

In the future, faster broadband services will involve a move away from traditional copper cable connections (of any type) to optical fibre to provide much higher data rates, although this is a long way off as the cost of providing this is currently prohibitive.  At present, the upgrade path to faster broadband services will continue to be via upgrades to the existing infrastructure over copper cables, which will mean newer modems and routers to connect to those services as new standards evolve.

Where we need to differentiate between types of Broadband (ADSL, Cable etc) we will specify it - otherwise, when we refer to 'Broadband' we mean any generic broadband service.

ADSL - What does it MEAN?

ADSL stands for Asymmetric Digital Subscriber Line - The Asymmetric part referring to the (often overlooked or glossed over) fact that the speed usually quoted is the maximum download speed - the upload speed being much lower, typically 256Kb or up to 442Kb on a ADSL-Max line - or possible 832Kb on a business class connection.

Why "Up to 8Mb" ? - and why is it Never 8Mb?

The attainable download speed depends on a number of factors - however the most important is the line attenuation - i.e. the signal loss of the telephone line from the exchange to your property.  This increases with cable length, as well as poor quality cable (Aluminium compared to copper), the number of joins in the cable and poor quality internal extension wiring. This line loss broadly determines the maximum "Line Sync" speed you might see.  The maximum actual download speed to expect will be between 10% and 20% less than this, due to protocol overheads and other issues.

The actual speed can be limited by the connection you have been provided - some Cheap Broadband ISPs still provision 0.5Mb or 1Mb connections rather than ADSL-Max.  The contention (the number of people downloading at the exact same time as you) greatly reduces overall throughput.  Almost all  'home' class services have a quoted contention of 50:1 - meaning you could be sharing your quoted download speed with 49 others.  In the worst possible case, a 0.5Mb connection could legitimately give a maximum throughput of 0.01Mb - or 10Kbps, much slower than a 56Kb modem! - In reality, this seldom occurs as the majority of users 'idle' allowing contention to do it's job of allowing a large number of users to share a very expensive connection from BT to your ISP - more on this later...

As well as contention, the site you are transferring from could be busy - or on another ADSL connection, where your download rate is limited by the UPLOAD speed at the other end of the connection.

Summary

As you can see - Broadband suppliers quoted download speeds have too many variables to allow an end user to easily choose the best value broadband provider.  Read on to learn more about the hard facts about broadband and why you Don't want to follow the masses with the latest cheap broadband offer...