As BT starts installing high-speed residential asymmetric digital subscriber line (ADSL) services this week, experts have warned that a fast connection at home doesn't necessarily mean unlimited internet speed.
From today, BT will start installing ADSL in the homes of 100,000 pre-registered customers. The service offers an 'always on' connection at 500Kbps downstream and 256Kbps upstream for around £40 per month.
While BT is starting with 500Kbps, ADSL is capable of speeds up to 6Mbps. But experts in the US, where ADSL has been available for several years, say that no matter how fast the connection to the home, bottlenecks on the internet will always limit surfing speed.
Rex Cardinale, chief technology officer at Covad, a Silicon Valley-based wholesale provider of digital subscriber line (DSL) services, said: "Very few users need more than 1Mbps. Once you get above dial-up speed [56Kbps] you start to run into other bottlenecks on the internet."
Since 1997, Covad has kept its downstream speed to a maximum of 1.5Mbps, partly because of the limited speed of the internet at large, but also because of the limitations of DSL technology. Put simply, DSL speed decreases as customer distance from the local exchange increases. Copper quality can also affect data speed.
"It turns out that the technology will run faster than [1.5Mbps], but only on certain telephone lines. We could offer 6Mbps to 10 to 20 per cent of the market, but would have 80 per cent of the market unhappy. So we decided to offer 1.5Mbps, because it enables us to offer it to the majority," said Cardinale.
Glenn Madsen, senior systems marketing manager at Nokia's networking division in Silicon Valley, said the average speed of accessing a website using a residential DSL connection in the US is just 300Kbps to 400Kbps.
Service providers are now working to accelerate download times by storing temporary copies of media files within their own networks, thereby accelerating download speeds for users. According to Cardinale, users could pay a premium for a faster and more reliable connection.
Another solution is to move the exchange equipment closer to the customer. US telecoms giant SBC is co-ordinating a trial in the US of technology that shortens the length of the local loop. The so-called 'neighbourhood broadband gateways' are boxes containing DSL electronics that sit between customers and central exchanges, reducing the distance barrier.
However, Cardinale said that widespread use of these gateways is at least five years away. He said they would enable faster types of DSL, such as VDSL, which can increase download speed to 20Mbps. Over the next 10 to 20 years, he said the equipment would move even closer to homes, creating local area networks in residential sectors. Beyond that, fibre to the home is the logical progression, but is not yet being considered seriously.
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