Symmetrical Digital Subscriber Line (SDSL) connections, which have been around for a number of years, are gaining popularity. SDSL is a halfway house between ADSL (suitable for residential use), and frame-relay or leased line connections (for large corporate users – high data transfer rates but also very expensive). SDSL internet connections do cost more than ADSL, but for some small to medium sized businesses, the restricted upload speed of the latter is just not enough.
If you are interested in SDSL for your business, here are some things you need to know.
* SDSL connections are very stable.
* Availability is quite good in many parts of North America, Europe and Asia.
* SDSL utlises telephone landline twisted pair copper wires, though it cannot share lines with voice data.
* SDSL requires a specialised modem.
* The closer to a telephone exchange, the faster the connection will be.
* The difference between SDSL and its predecessor ADSL (asymmetric digital subscriber line) is that the upload capacity of SDSL is the same as the download capacity, whereas with ADSL, the upload capacity is a fraction of the download (25% or less).
* ADSL has a higher maximum download capacity than SDSL (theoretically up to 9Mbps) but much smaller maximum upload (up to 640Kbps). SDSL works in the range of 1-3Mbps.
* SDSL uses better contention ratios, up to a maximum of 10:1, whereas ADSL ratios are up to 20:1.
* VoIP (voice over IP) requires substantial upload capacity and will experience sound issues if it is too narrow. VoIP (also known as web phone or Internet phone) is emerging as an alternative to fixed line and mobile telephony.
* Video conferencing requires large data up- and download capacity to stream real-time video images and sound. If there is upload delay, video images will become choppy.
* SDSL can provide sufficient bandwidth for live webcasting to a limited audience. However, reliable streaming to a wide audience requires specialised servers, so is probably best handled by web hosting companies.
* SDSL is sufficient for limited forms of website hosting, though, if your website is mission critical it is probably safer to use a web hosting company with a dedicated line connection.
* Web services or Services Oriented Architecture (SOA) can work well using SDSL to connect, and standardised communication methods such as XML to carry data.
Virtual Private Networks (VPN) also operate well over SDSL, as more people elect to work from home. SDSL is cheaper than other high capacity upload options.
* There are other types of Digital Subscriber Line available – HDSL (High bit-rate SDL), RADSL (rate-adaptive SDL), VDSL (very high-speed DSL).
You can find more information about SDSL on various broadband news sites.