WHAT IS DSL...?
Digital Subscriber Line is basically the technology behind "broadband through a telephone line", it does this by utilizing frequencies not used by telephone calls, there are many variations of DSL like ADSL (adsl1, adslmax, adsl2, adsl2+), SDSL , VDSL (vdsl, vdsl2) etc and speeds can range from as low as 128Kbps to as high as 100Mbps+ depending on the type of DSL thats used, the way its set up and the length, type and quality of the customers telephone cable.
Current UK broadband connections consist mostly of DSL services, usually ADSL1 (fixed rate 512Kbps , 1Mbps or 2Mbps), ADSLmax (upto 8Mbps) or ADSL2+ (upto 24Mbps) packages, although there are some FTTC (Fibre-To-The-Cabinet upto 40Mbps) connections going live across the country which are essentially VDSL over a longer fibre connection / shorter copper connection, but these are mostly in cities and large suburbs. Other than regular DSL Broadband there is also 'Cable' broadband like Virgin Media which essentialy uses the DOCSIS protocol (as opposed to DSL) using Fibre Optic cable to the Hub then Co-axial copper cable to your home - this is covered more in our 'What is Fibre Optic' Guide.
ADSL1 (or simply ADSL) was the first orignal 'Broadband' through a telephone line in the UK, this service over BT's network consists of fixed rate speeds, namely 512Kbps , 1Mbps or 2Mbps download speeds with 288Kbps upload speeds.
ADSLmax is a 'rate-adaptive' technology that works out the maximum speed your line can support and sets it at that, speeds are "up-to" 8Mbps although in reality the maximum speed you can get is 7.2Mbps on ADSLmax due to profiling, on this system a connection rate and profile speed is set by the DSLAM in the telephone exchange and depending on your distance from the exchange, quality of telephone line and other factors it would determine what is the correct connection speed for your line.. the further away you are the slower the speed/connection rate is, ADSL1 utilizes frequencies 25kHz to 1.1mHz.
ADSL2ADSL2 was created to improve on the current ADSL1 services, mostly by improving the modulation techniques.. It also has a theoretical max speed of 12Mbps and upload speed of 3.3Mbps. ADSL2 also utilizes frequencies 25kHz to 1.1mHz.
ADSL2+ADSL2+ is an improvement on the earlier profiles, it allows for a max speed of 24Mbps download and a max speed of 3.3Mbps upload, connections started going live around the country at around about the same time as ADSLmax did but ADSL2+ was much more costly to implement as it meant new hardware had to be installed in each telephone exchange for each ISP (Internet Service Provider) that wanted it -(this is known as Local Loop Unbundling or 'LLu'). This type of service is limited to users living in citys or suburbs, telephone exchanges in rural areas rarely get any LLu providers as its not cost effective to spend tens or hundreds of thousands of pounds to install the equipment only to sign up a handfull of customers. ADSL2+ utilizes frequencies 25kHz to 2.2mHz.
VDSL2 (Very high bitrate DSL) is the new DSL profile thats used in conjuction with FTTC (Fibre-to-the-Cabinet) , it allows for connection speeds in excess of 100Mbps for both upload and download, this setup differs from regular connections where instead of your telephone line consists of twisted pair copper cable from telephone exchange all the way to your home - they replace it with Fibre Optic cable from the Exchange to the Patch Point (you know those green cabinets you see at end of roads or entrances to estates? well thats a patch point - sort of a halfway point to your home) ...from the patch point to your home is just your regular 'untouched' twisted pair copper cable, this results in speeds of around 40Mbps depending on distances, in some cases co-axial copper cable can be used from the patch point/green cabinets to the home which would yield speeds of about 60Mbps. VDSL2 utilizes frequencies 25kHz to 30mHz.
IPstream is the term used for BT's provision of DSL over their network, simply put when you sign up with an ISP and they dont have any equipment in your local telephone exchange (LLu) then your simply on a re-sold BT package 'of sorts', as BT own just about all the telephone exhanges and telephone connections to a customers home they control the broadband networks and act as 'supplier' to other ISPs, simply put if your not on LLu then your on a re-badged BT connection and you share this network with all other ISPs that are on it, these services consist of ADSL1 (upto 2Mbps) and ADSLmax (upto 8Mbps) and in some locations (WBC) ADSL2+ (upto 24Mbps). These services tend to have a very large user base and therefore have tendencies to slow down at peak times on most providers, there are a select few (NewNet, IDnet, Fast) who manage their networks with monthly usage limits and charge a little more but the end result is a better service, these ISPs tend to use the extra charges to pay BT to expand their part of the networks allowing for less/no bottle-necking, cheaper and larger ISPs fall fowl to bottle-necking at peak-time mostly for two reasons.. first one is they are cheap and so have the larger user base and thus more users online at peak time, second one is they are cheap so dont have money to expand their networks and stick as many users as they can on the system, probably to the extent where its doesnt meet OFCOM requirements. If IPstream is your only choice of service then your best with one of the afore mentioned services.
Local Loop Unbundling
LLu is where ISP or Telecom Providers install their own equipment into BT's telephone exchanges, this means the ISP has total control of the line and supplys its own network rather than over BT's network and backbone, these 'LLu' services are ADSL2+ 'up-to' 24Mbps connections, LLu ADSL2+ connections are considered better to have as they can be provided much cheaper as they cut out the middle man (BT) and also up to 3 times faster than most IPstream connections (except where WBC is available where 24Mbps can be had), because they are on their own dedicated network and not bundled together with other ISPs like on IPstream means there is even less network traffic and faster speeds constantly with little to no chance of bottle-necking, only those living in city or suburbs will be lucky enough to sign up to a decent LLu service like BE* or SKY
Wholesale Broadband Connect
WBC (Wholesale Broadband Connect) - WBC simply put is BT installing their own ADSL2+ equipment in their telephone exchanges so that their customers can receive up to 24Mbps connections too, but like LLu providers only those that live in a city or suburb will be lucky enough to receive such a connection. BT use the name 'Wholesale Broadband Connect' to describe this generation of networks, they also allow other ISPs to provide services over these connections, where your exchange may be WBC enabled you will be able to go with BT or other suppliers for upto 24Mbps speeds.
21st Century Network
21CN (21st Century Network) - This is BT's next generation network, discussed earlier on the VDSL2 section this is essentially BT extending the reach of their fibre network from the telephone exchange closer to your home thereby shortening the copper connection which is responsible for loss of speed, these connections are known as FTTC (Fibre-to-the-Cabinet) or FTTP (Fibre-to-the-Premises), a typical FTTC connection would consist of fibre cable from telephone exchange to a 'patch point' (usualy a green cabinet you see at entrances to estates) and from that patch point is just the regular copper cable untouched, this type of connection is going live in citys up and down the UK and yields speeds of up to 40Mbps download and 10Mbps uploads. FTTP connections are reserved more for new builds or businesses that require and will pay for it, a typical FTTP connection would consist of Fibre Optic cable running completely from the exchange to the premises and this would yield speeds of up to 100Mbps up or down.
Other DSL protocols
There are a whole range of other DSL services and protocols which are listed below, but just about all of the connections in peoples homes in the UK will be one of the above that we have already discussed and why we have not gone into great detail about them, you can click on the links below to find out more about those types of connections on Wikipedia.
HDSL, HDSL2, IDSL, MSDSL, PDSL, RADSL, SDSL, SDHSL, UDSL, VDSL
What Can I get?
Find out exactly what services your local telephone exchange has by using our guides on the left, using the exchange search and modem/router statistics from your current connection you can work out which ISP would be best for you and what speeds you will/should get, even if you are unable to get your modem stats we have a table that shows the average 'speed-per-distance' from the exchange, although these figures are 'average' so could be a little more or less as those guides cant account for the exact quality of your line whereas your modem statistics will.