Broadband Download Speeds

Broadband advertised download speeds have been a high profile subject over recent months. The Chairman of Ofcom sent an open letter to the chairmen of the 6 top Broadband suppliers [pdf opens in new window] in December 2007 expressing his concern. Several magazines and the Gadget Show on Channel 5 have written about or campaigned on the consumers behalf.

The issue boils down to the advertised speed on many high speed broadband packages, that's "up to 8Mb/sec" and faster, not being the same as a customer recieves once signed up to the service. Often quite a bit less than advertised.

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ADSL+ is the technology behind the common "up to 8Mbps" speed broadband packages. It has a maximum possible download speed of 7.2Mbps and a more likely real world range of between 2-5Mbps.

ADSL2+ is behind the new faster broadband packages offered at 16Mbps to 24Mbps. If you live close to the exchange (less than 500m) you could get a top speed of around 22Mbps. However the higher frequency used by ADSL2+ means that once you get to 3 or 4 kilometres away speeds are unlikely not to be any faster than ADSL+.

Optical Cable Only offered by Virgin Media who have a 20Mbps package and are trialing 50Mbps. A cable connection does not slow down the further away you are from the exchange.

Use our broadband checker to see the straight line distance to your local exchange.

Theoretical maximum

The advertised speed seen on many broadband deals is actually the theoretical maximum. Most telephone exchanges have been upgraded with equipment that gives a theoretical maximum speed of 8Mb/sec, known as ADSL+. 2008 was ADSL2+ enabled exchanges that has a maximum speed of 16Mbps to 24Mbps. ADSL2+ exchanges are now quite widespread, with many of the unbundled exchanges having been upgraded.

The headline download speed using ADSL is never actually possible because there is an overhead involved in making a connection and sending the data along the wire. The fastest possible speed for ADSL+ is around 7.2Mb/sec. However this is only possible if the line is of top quality with no degradation of the signal. There are several factors that can affect the line quality including:-

  • distance from the exchange (the most likely cause)
  • quality of the wiring
  • your modem settings.

Real World download speeds vary considerably but are usually in the region of 2Mb/sec - 5Mb/sec for a product advertised as up to 8Mb/sec. Unfortunatly it is not possible to work out your download speed until you have signed a contract and started to receive a service from an ISP.

It's also worth noting as mentioned before that the quality of the line from your house to the exchange and also the distance to the exchange affect the download speed. Therefore changing from one ISP who is a BT Wholesale customer to another who also resells BT Wholesale will make no difference to your connection speed as they will using the sme equipment.  Broadband supplied by an ISP who has unbundled your exchange would be using their own equipment and the speed could change in that case.

Broadband over a cable connection

Broadband over a cable connection is not affected by the distance of the exchange from your home or office. Upload speeds are also generally higher. Virgin Media, the UK's cable provider, use fibre optic cables to transmit the data, sometimes using copper wires just for the last section into your home.

However download speeds over cable like ADSL can slow down from their maximum speed due to other factors like contention ratio which essentially means how many people are connecting at once and using the available bandwidth.

See Virgin Media cable broadband deals.

Other Reasons Your Download Speed may slow down.

Cable and ASDL service providers use several methods and techologies to share their available bandwidth amongst their customers and limit those who use the most. Your broadband connection could be subject to traffic shaping, download limits and bandwidth management with a resultant reduction in download speed.

Traffic Shaping
Software used by your ISP to control their network traffic.
Download Limits
Several broadband packages have a monthly limit for the amount of data downloaded.
Bandwidth Management
Similar to traffic shaping, banwidth management is carried out by an ISP to share out the available resources evenly. Some ISP's have fair use policies that throttle back a customers connection speed once a certain threshold has been reached in a day.