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This is the support site for Andrews & Arnold Ltd, a UK Internet provider. Information on these pages is generally for our customers but may be useful to others, enjoy!

How broadband works: Difference between revisions

How broadband works (view source)

Revision as of 08:33, 1 September 2024

747 bytes removed ,  1 September 2024
Significantly rewrote FTTP. Removed 20cn->21cn, the work is all done and I don't the Wiki is intended as a full history lesson. Added rate ranges for the various technologies to make the antique technologies more obvious. Link to the James Harrison EMF Talk
m (Mention the term 'baseband' (as opposed to broadband))
(Significantly rewrote FTTP. Removed 20cn->21cn, the work is all done and I don't the Wiki is intended as a full history lesson. Added rate ranges for the various technologies to make the antique technologies more obvious. Link to the James Harrison EMF Talk)
 
 
==ADSL1==
In the early 2000s, ADSL has been defined for use alongside normal phone service as well as alongside ISDN. The different frequency for ISDN means it is a different standard. In the UK we use ADSL over POTS (Plain Ordinary Telephone Service) following ITU G.922.1 Annex A which allows in theory up to 12Mbit/s downstream and 1.3Mbit/s upstream. However BT offer only 8.128Mbit/s downstream and 832kbit/s upstream maximum using ADSL1.
 
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+==
In the late 2000s, A new standard for ADSL called ADSL2+ providesprovided extended bandwidth. This follows ITU G.992.5 and provides up to 24Mbit/s downstream and 1Mbit/s upstream.
 
A variation of the ADSL2+ specification called Annex M allows up to 24Mbit/s downstream and up to 3.5Mbit/s upstream. In the UK we cannot achieve the full 3.5Mbit/s upstream as there is a frequency plan that must be followed on all phone lines to avoid interference. Therefore, in the UK, Annex M allows around 2Mbit/s uplink.
 
==VDSL==
In the 2010s, Openreach started to offer 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 100Mbit/s on very short lines. The speed available drops off quickly with distance - but this is not usually an issue as cabinets are usually close to premises. There are cases where FTTC can be slower than ADSL all of the way from the exchange.
 
 
==Fibre==
In somethe 2020s, Openreach and many Altnets are casesdeploying fibre optic cable (glass) can be used to provide a service to a customer premises., generally using PON (Passive Optical Network) technology, Fibre is usually a single frequency using a laser, so not actually broadband at all. Whilst speeds to change with distance on fibre services, they are so high that services are sold with specific speeds which do not vary. Various services are available, see each service description for the speeds that are offered, typically between 80Mbit/s and 1000Mbit/s.
 
The Openreach FTTP rollout is progressing, with 25 million premises (80%+ of the UK) expected by December 2026
 
[https://media.ccc.de/v/emf2024-305-the-last-miles-of-the-internet James Harrison provided an excellent talk PON/FTTP at EMF 2024]
Most services sold by other companies as fibre are not, in fact, fibre optic services to your premises. All Internet access services, even ADSL from the exchange, make use of fibre optic cable for part of the service, but what matters for speed and reliability is the weakest link, which is normally the bit to your home.
 
Some companies have previously branded coax based services as Fibre, which can muddy the water a little.
==Upgrade to 21CN==
Existing lines on 20CN will be upgraded to 21CN and so allow ADSL2+. This is part of an ongoing programme. The upgrade may be some months after ADSL2+ is available on the exchange, and so customers can pay a small fee to upgrade sooner if the exchange is ready. Upgrades as part of our upgrade programme are free of charge and we email you several weeks in advance with details. When we upgrade we initially keep your line on ADSL1 on the new 21CN kit, and then change to ADSL2+ a few days later.
 
==Beyond the exchange==
Wishy
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