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Telecoms providers: SDSL - DSL for those who want to have it both ways?

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After ADSL and VDSL, meet SDSL, the third instalment in the digital subscriber line internet connection technologies. Much less know by the general public, this technology has been specifically developed for business users who do not care so much about ever-growing download speeds, but rather more on fast upload speeds.


What is SDSL

Symmetrical digital subscriber line is based on fundamentally different technological frameworks than other digital subscriber line technologies.

Technological digest

SDSL primarily may refer to two different concepts:

- all types of DSL technologies providing symmetric bandwidth - as fast for downloads as for uploads -, like IDSL or HDSL,

- a proprietary technology using this name.

One major similarity of these technologies is that although it also uses traditional copper wires, it cannot coexist with a voice service, and requires a specific installation at the user’s premises, with a specific modem.

Development and enhancements

One of the first symmetrical digital subscriber line technologies invented was IDSL, or IDSN-based Digital Subscriber Line. Popularised in the early 1990s, it provided 144 kilobits per second upstream and downstream connections. More recent so-called “bonded” symmetrical line technologies may be as fast as 2x8 megabits per second.

Advantages and disadvantages

This technology has several advantages over ADSL... but are they still relevant?

Advantages of SDSL

While ADSL was deliberately developed with the idea of prioritising downstream, as private user would largely only surf the web and therefore upload little data, SDSL is meant to deliver similar performance for downloads and uploads. It is therefore much more indicated to business users. Moreover, as channels used by this technology are not shared with voice service, users are guaranteed to get maximum performance for their data use, at any time, without any interference with voice conversations.

Finally, performance remains rather stable even if the user is far from the node, with distances up to 5,000 feet supported.


Disadvantages include the facts that:

- A specific installation, with specific cabling, splitter, modem and gateway has to be implemented. Users don’t simply plug their router into the telephone socket,

- Most technologies are proprietary and have never been distributed by many ISPs,

- Only a small minority of telephone exchanges in the UK support this technology,

- Price is significantly higher than ADSL,

- And finally, ADSL had finally managed to overtake SDSL in upload speeds (albeit often only slightly), while allowing much faster download speeds.

SDSL plans and prices in the UK

Because of all these shortcomings, providers are getting hard to find in the UK.

Very few providers...

Most popular names have stopped proposing plans using this technology. However, several small, B2B-only ISPs are still marketing SDSL plans. They include:

- Spitfire,

- Macintosh electronics,

- Hotchili communications,

- EMNet

... at relatively expensive rates

Prices for these plans are significantly higher than DSL plans, never going lower than £99 per month, and more usually around £150 per month.