Just how long are telephone lines in the UK?
ADSL2+ which is filling a fair number of press releases of late with its promises of 24Mbps is not going to deliver this to all but a handful of people who perhaps live in the telephone exchange. The Point Topic group has added some data to the picture of the average UK local loop length, which can be viewed here.
Point Topic believe they have reverse engineered the loop lengths from various sources of data, and suggest that 45% of lines are less than 3km long - which in ADSL2+ terms equates to the cross-over point where ADSL2+ performs very like ADSL giving a maximum speed of 8Mbps. What is interesting is that the Point Topic data seems to differ from that previously published by the Broadband Stakeholder Group (see our news back in June 2005) which suggested that 80% of lines are under 3km long. Of course the differences are to some extent immaterial, since knowing your loop length is only part of the story, to get a good estimate of your lines capability you need to know the thickness and type of cabling used between you and the exchange. Additionally the level of noise in the 25kHz to 2.2MHz frequency range in your area will be crucial in determining what speed the rate adaptive ADSL2+ services will give you.
One crucial point very rarely mentioned is that the 24Mbps maximum speed of ADSL2+ is the ATM cell rate, the maximum throughput users would get even if connected at that speed will be around 22Mbps. Additionally ADSL2+ tends to only give this speed on lines under 300 metres long, and once you allow 100-200m for the cabling inside an exchange building, you can see you would have to live on top or next door to an exchange to get this speed.
As a final comment on ADSL2+ it is interesting to see the services rolling out in the UK, and users reporting very variable reliability, some of which seems to be down to choice of ADSL2+ hardware. In short it seems while the ADSL standards have had years of ironing out the bugs, ADSL2+ hardware is still in its infancy. Is it possible that the deployments of ADSL2+ in other countries have not been as widespread, and that the UK is not that far behind so is seeing the problems of deploying a relatively new technology?