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How broadband works: Difference between revisions
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Broadband provides high speed data carried over a normal phone line without affecting the telephone service.
==Interleaving==
The margin on the line sync helps accommodate general changes in the performance of a line over time. However, there can be interference that is more like "pops and clicks". Impulse interference that causes corruption of data. This causes packets to be lost and resent and so has the effect of making the overall performance of the line slower.
To accommodate this type of interference a system of error correction is used. This means extra parity data is sent, and if data is corrupted then this can be identified and corrected. It uses a small amount of the available bandwidth to provide this extra parity data but makes the line much less prone to errors. At the same time the data is interleaved. This means overlapping each block of data with the next and is the same trick used on CDs to make them resist the effects of scratches on the surface. The effect is higher latency (the time taken for data to get through the ADSL).
==ADSL1==
ADSL has been defined for use
It is important to realise that the above is a technical statement about the ADSL1 technology. An actual service will achieve a sync speed (which includes various overheads) depending on the line length and quality and other factors, and may even change over time. To assess the likely speed of your service, please use the availability checker.
==ADSL2+==
A new standard for ADSL called ADSL2+ provides extended bandwidth. This follows ITU G.992.5 and provides up to
A variation of the ADSL2+ specification called Annex M allows up to
It is important to realise that the above is a technical statement about the ADSL2+ technology. An actual service will achieve a sync speed (which includes various overheads) depending on the line length and quality and other factors, and may even change over time. To assess the likely speed of your service, please use the availability checker.
==VDSL==
Fibre To The Cabinet (FTTC) operates using VDSL from a street cabinet rather than ADSL all the way from the exchange. VDSL uses different frequencies and powers to ADSL but is otherwise very similar technology. VDSL can provide speeds over
It is important to realise that the above is a technical statement about the VDSL technology. An actual service will achieve a sync speed (which includes various overheads) depending on the line length and quality and other factors, and may even change over time. Services are available with speed caps set at
==Fibre==
The ADSL/broadband bit connects between your premises and the local telephone exchange, at which point the line is split between voice (for telephone calls) and ADSL. The local exchange is connected via fibre to one of 20 main interconnect points where a large fibre back-haul network connects back via gigabit fibre links to our rack in a data centre in Docklands. We are then connected by fibre so that we can communicate directly with hundreds of UK based ISPs as well as international (transit) links to the rest of the world.
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