"The 'speed' of a broadband service is dependent on several factors. First, there's the speed of the line itself - this depends on the quality and overall length of the user's phone line and will drop the further away you are from the serving exchange," said Steve Powell, product manager for Connectivity & Security Services at Viatel. "The maximum line rate will drop with the length of the copper wire on the individual phone line - 10kms away from the serving exchange this will drop to a maximum of less than 0.5Mb/sec."
ADSL1 is the technology employed on the majority of ADSL services available within the UK and can provide a maximum line rate of 8Mb/sec, while ADSL2+ the later version of ADSL being rolled out as part of BT's 21CN network and by many LLU providers can link up at a maximum of 24Mb/sec. However under both ADSL versions, line speed is set by the quality of an individual user's telephone line.
"Another factor to consider is that many service providers are forced to squash more and more end users onto the available bandwidth in order to maintain a cost effective service as there are huge costs involved in moving data from the user's connection to the service provider," continued Powell. "There's also the level of contention or congestion that may hamper the flow of data over the established ADSL circuit - this can be within the serving exchange, within the national BT backhaul network, within a service provider's own network or out on the Internet itself. Broadband users need to be aware of all these issues in order to avoid further confusion and understand why providers can only offer an 'UP TO' ADSL service."