As new Asymmetric Digital Subscriber Line (ADSL) services become available this summer, more telecoms carriers will offer access to the Internet over traditional copper phone wires with download speeds of 2Mbit/s and upload speeds of 512kbit/s. However, the same period will also see some operators offering Symmetric Digital Subscriber Line (SDSL) technology to business users, with both upload and download rates set at 2Mbit/s.
Most operators and commentators see two main uses of SDSL: to support Internet access for small to medium-sized companies; and to support teleworkers or branch offices connecting remotely to larger corporate networks. Many smaller firms that have traditionally found broadband solutions too expensive will be able to afford SDSL. 'Where end users previously could not justify the cost of a leased line, always-on broadband [DSL] services will be ideal for email and Web hosting,' said Neil Armstrong, BT's product marketing manager for SDSL. For teleworkers, SDSL provides the ability to send large files quickly back to the central office Ã, unlike ADSL, where the slower upload speeds can make such operations tedious.
Another possibility is that corporate users of leased lines will eventually switch to SDSL. Although pricing has not yet been announced, Armstrong says that StreamLine Direct will have a "significantly lower cost than traditional leased-line solutions". Competition from other operators is likely to force the price down further. Tim Johnson of analyst firm Ovum said, "There's no fundamental reason why SDSL should be more expensive than ADSL. Looking ahead two or three years, an SDSL modem should be cheaper and better than an ADSL modem, giving you more bandwidth."
Redstone Telecom, which will start offering its SDSL service in April, said it will be able to reach half of the country's small and medium-sized businesses by the end of the year, and is also targeting teleworkers and mobile users, such as sales staff. Its solution includes a voice over DSL component Ã, SDSL enables between four and 16 distinct voice lines to be run over the same copper cable Ã, meaning it could provide savings for smaller businesses, which will not have to pay for several individual voice lines.
The advantages of SDSL for larger corporates are likely to be less clear-cut. Although the low cost of SDSL is a big attraction, there are still concerns about the limitations of copper cabling, compared with fibre-optic. And while the adoption of the new Symmetric High Bit-Rate Digital Subscriber Line (G.SHDSL) standard has greatly improved the reliability of SDSL over single lines, there is still some degradation of quality for users more than two kilometres away from the phone exchange.
Axel Lagerborg, director of product management at broadband supplier XO, which is taking part in the BT trials, believes that most corporates will stick to leased lines, but will use SDSL for their home users and satellite offices. "You might be in a chain dealing in car parts and your head office in London might determine that you have a 2Mbit/s leased line, but all your little dealerships throughout the country might only need SDSL. So before you only had a choice of ISDN, or leased line. Leased line is too expensive, ISDN isn't good enough and SDSL comes in the middle," said Lagerborg.
SDSL is good news for corporates, says Johnson, because it will drive down the cost of fibre leased lines. "[Corporates] are not going to go back to copper. But they'll certainly be going to their supplier and saying, 'People are offering us copper lines for Ã,£100 a month or less, and you're still charging us Ã,£1,000. It won't do.' I think it will put a lot of pressure on prices for leased circuits."
