Symmetric Digital Subscriber Line (SDSL) services promise cost-effective broadband links. Service concerns and lack of availability have limited uptake, but suppliers are now tackling these issues.
SDSL delivers more bandwidth than Asynchronous DSL (ADSL), potentially up to 8Mbit/s, over existing copper telephone connections. SDSL has a number of other advantages over ADSL, not least of which is that it provides the same level of bandwidth upstream as downstream, a critical consideration for firms that need to send large files to or from branch offices or remote workers; perform data backups; or host web sites, applications and other services.
SDSL services may also be attractive to business users that are currently renting 2Mbit/s E1 leased lines, which can be twice as expensive. The downside is that SDSL services are usually contended or shared links, rather than the dedicated private virtual circuits (PVCs) that E1s provide. And few of the SDSL services now available come with any kind of service level agreement (SLA), which guarantees minimum levels of bandwidth and stipulates compensation for customers if the service falls short of its promise.
Analyst company Point Topic estimates that the number of SDSL lines could be up to 650,000 worldwide by the end of the year. In a recent report it also pointed out that there are huge differences in the price and availability of SDSL services in countries across Europe.
"SDSL will bring proper business-strength broadband services down to a price that more firms can afford," said the author of the Point Topic report, Tim Johnson. "For example, they will be able support teleworkers much better than before, with direct access to the company network, running Ethernet over SDSL."
Martin Saunders, head of product marketing for UK SDSL provider EasyNet, commented, "In the last six months there has been a huge swing to symmetric services. The concept is finally being understood and a lot of companies are switching from leased lines."
The last few months have seen BT upgrade more of its local telephone exchanges to support SDSL services, bringing the estimated total to 180.
Companies within range of an SDSL exchange should now be able to sign up to faster symmetric services. BT's 2Mbit/s SDSL links are leased to other service providers at a fixed price of £200 per month, plus a connection fee of £250 per customer.
In the UK, Easynet offers 2Mbit/s SDSL connections to end-users in a small number of UK cities, including London, Manchester and Birmingham, priced at around £300 per month, plus a £950 customer connection fee.
The Point Topic report says there are wide variations in the prices that businesses pay and in service level agreements (SLAs). For example, a basic 2Mbit/s connection can cost only £65 per month from QSC in Germany but £846 per month from Cybernet in Switzerland. The terms of SLAs also vary enormously and some suppliers are still not offering them.
Easynet's Saunders commented, "As for SLAs, there have been some very dodgy agreements out there. We use our experience to set meaningful SLAs within the constraints of infrastructure."
Another ISP, Tiscali, has said it will introduce SDSL services based on BT's wholesale services later this year. "We will be able to offer whatever BT is offering on its DataStream service, initially up to 2Mbit/s upstream," said Tiscali's chief operating officer, Stephane Huet.
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