SDSL Leased Line – Getting Symmetric Connectivity Fast
An SDSL Leased Line provides a symmetric dedicated connection over standard copper phone wires.
SDSL is similar to ADSL, except that its upload speed matches its download speed.
The maximum speed you can get is determined by how far away you are from your local telephone exchange. The further away you are, the longer will be the copper phone line linking you to your exchange, and the slower will be your connection speed.
In most of the country, the fastest SDSL leased line you can get is 2Mbps. That's quite slow given that fibre leased lines can run at speeds of up to 10,000Mbps.
Is an SDSL Leased Line Available in Your Area?
Even if you'd be happy with a 2Mbps SDSL leased line, you may not be able to get one.
Less than 900 of the UK's 5500 telephone exchanges have the equipment necessary to offer Symmetric Digital Subscriber Line circuits. You're unlikely to be on an SDSL-enabled exchange, unless you're in a dense urban area.
If your exchange is not yet SDSL-enabled, it's unlikely to be enabled in the future. The commercial roll out of SDSL leased lines stalled, due to a lack of market demand. As a result, BT and most of the local loop unbundlers decided to focus on rolling out rate-adaptive ADSL (up to '8 Mbps' etc) or ADSL2+ ('Up to 20Mbps') instead.
Some providers sought to get around this by 'bonding' several dedicated ADSL connections together. However, these are usually inferior to standard leased lines.
Thankfully, there is now a better SDSL Leased Line alternative. It's called 'EFM'.
Ethernet First Mile is Rapidly Replacing Traditional SDSL Leased Lines
BT Wholesale have a product, which you can buy through resellers such as hSo. It's called Ethernet in the First Mile, or EFM for short.
EFM bonds several DSL connections together to create a symmetric dedicated connection of up to 35Mbps. The maximum speed depends on how far away you are from your local telephone exchange.
It overcomes the capacity limits of SDSL by using several phone lines simultaneously, bonding them together, and using enough of them to provide a reliable service.
EFM Isn't Always Better Than Fibre
A fibre-optic circuit may be cheaper than an SDSL leased line in some areas of the country
In much of the country, fibre leased lines are cheaper than leased lines delivered over copper BT Wholesale EFM circuits.
And frankly, that's a preferable option, as unlike EFM, fibre leased lines easily scale up to beyond 35Mbps, should you ever need more bandwidth.
Services provided over fibre are slightly more reliable than services that are provided over copper (EFM, SDSL, ADSL etc). This is because copper wires suffer from 'cross-talk' from currents induced from nearby phone lines.
Although error correcting codes can be used to detect and correct almost all of these errors, it's obviously preferable not to have any errors in the first place.
But If Fibre Isn't Available, EFM Could Be Ideal
However fibre isn't always a cost-effective option.
Digging up the pavements of Britain proved to be ruinously expensive for many of the original cable franchisees, and much of their subsequent investment went on maintaining their networks (and merging them with those of other franchisees), rather than extending the reach of their networks.
Some areas of the country can't get fibre at all.
Some can get it but only at speeds of 2Mbps.
Some of these areas that are poorly served by the fibre networks will be close enough to a BT 21CN enabled exchange to be able to get a leased line that's built using a BT Wholesale EFM circuit.
EFM copper circuits may also be far quicker to install than a fibre leased-line. So they are popular with organisations that can't afford to wait several months for their leased line circuit to be installed.
Find Out How Much a Leased Line is Likely To Cost You
To check how much an EFM or Fibre leased line is likely to cost, visit our online leased line price checker.