In ADSL (‘asymmetric digital subscriber line’ - the most common form of DSL), the total available capacity of the high speed digital subscriber line is split asymmetrically between downstream and upstream directions of transmission – there is a much higher bitrate made available for downstream transmission – at the expense of the upstream transmission rate. The advantage of this is that information transferred downstream (e.g. delivery of webpages, software downloads etc. out of the Internet to the user’s PC) can be delivered much more quickly. Since little information is sent upstream by the typical Internet surfer (e.g. only the odd ‘click’ message or short email), the asymmetry of ADSL benefits the user.
ADSL is a particular type of DSL: indeed ADSL is often referred to simply as ‘DSL’, since ADSL is the commonest form of DSL. (Note: All ADSL lines are ‘DSL’ lines – and many ADSL services are simply marketed as ‘DSL’. E.g. T-DSL, Deutsche Telekom’s german version of DSL is actually an ADSL service. But remember that not all DSL is ADSL). ADSL is a technology used to provide a digital highspeed internet access line over a ‘normal 2-wire telephone line’. Over an established telephone or IDSN (digital telephone) line, the public telephone company uses ADSL technology to provide the high speed ADSL internet access line sharing the same 2-wire connection to the public network.
The fact that the ADSL line can share the same 2-wire connection as the user’s (analogue) telephone or ISDN (integrated services digital network) telephone line is important, since it affects the equipment which must be provided for the ADSL service (DSL splitter/filter and DSL modem) and the economics (price to the user).
What is.... ADSL2+?
Your ADSL connection... What do I need for DSL / ADSL?
Choosing the right ADSL connection type... ADSL connection types
Deciding on ADSL service... Choosing your ADSL service provider
Setting up & operating your ADSL connection... ADSL Network configuration
Internet or Broadband Telephony... Introduction to VOIP (voice-over-IP)