Technology Primer


ADSL is a typical technology for bringing broadband to homes and businesses over standard (copper) telephone lines. ADSL splits a single telephone line into separate voice and data channels, allowing you to make a phone call while surfing the Internet at the same time.
ADSL is a ‘best effort’ broadband service, with highly variable connection speed. The length of the line to the exchange will determine the maximum speed that a line is capable of. The further away from the exchange a property is the slower the broadband speed.
Superfast broadband uses fibre optic lines, which allow information to be transmitted in the form of light. Fibre lines are incredibly fast and reliable.
Ofcom and the EU define super fast broadband as connections with download speeds greater than 30Mbps.

Unfortunately it would be incredibly costly to install fibre cables to every home and office. As a result telecoms operators, such as BT and Virgin Media, have preferred to adopt a more cost effective approach by mixing existing (old) cables with the latest fibre optic lines. This is known as FTTC (Fibre-to-the-Cabinet).
The advantage of this method is that related services are usually both significantly cheaper and easier to install because the last part of the connection into properties does not need to be replaced (i.e. the fibre optic cable is taken to a local street cabinet - but no further).

BT requires an existing green cabinet for its FTTC service and will install a new cabinet, with a fibre link back to the exchange, near the existing cabinet. The new cabinet basically houses the ADSL technology from the exchange. Telephone calls go down the copper wire to the exchange in the normal way but data is split off at the fibre cabinet and uses the fibre to the exchange.

As the distance of copper wire from the ASDL equipment and the home is much shorter, much greater broadband speeds can be achieved. Speeds of up to 80Mbps download and 20Mbps upload are the current standard, which could rise to 100Mbps+ in the near future.
Virgin and BT are two main providers of superfast broadband.
Virgin has cabled an area of Rotherhithe around Elephant Lane and have some cabling around other parts of the peninsular. This was done many years ago.
BT has been able to install superfast broadband to a few of parts of Rotherhithe. These are areas around Elephant Lane and Rotherhithe Station, Globe Pond Rd and Russia Dock Rd and the Water Gardens development on Surrey Quays Rd. BT were able to do this without too much trouble as these are the only areas in Rotherhithe that had existing green cabinets. The presence of green cabinets is essential for BT to install their current superfast broadband service.
Most of Rotherhithe doesn’t have these green cabinets as they are linked directly to the Bermondsey Exchange. BT has decided that, unless they are able to obtain additional external funding to reduce this investment, an upgrade for Rotherhithe is not commercially viable.
There are also companies who can provide superfast broadband to multi-residents properties. Hyperoptic provide services to several developments in the area. They currently do not provide services to individual homes.


Asymmetric Digital Subscriber Line: Broadband delivered down your telephone line through copper wires. It works well – with speeds of up to 20 Mbps download and 3 Mbps upload. You have to be very near to the telephone exchange to get these speeds. The maximum disstance for ADSL is around 5km where speeds drop to less than 2 Mbps.
When uploadand and download speeds are different. Upload is much slower than download in ADSL and FTTC broadband.
The part of the network that links your local exchange or hub to the core network or the Internet Exchange.
The speed at which data travels to and from your computer. Measured in Mbps (megabits per second) or Kbps (kilobits per second). Just as a wider water pipe will deliver more water, more quickly, broader bandwidth delivers more data, more quickly.
Internet connection between 2 and 24 Mbps. When a onnection more than 24 Mbps its classed as 'Superfast' braodband. Connections around 1 Gbps (gigabait) and more loose the broadband name and are now called 'Next Generation Access'.
A green box that you might see on a street corner in a town or city that connects telephone lines to the exchange. Also known as a primary connection point. In some fibre nextworks this is called a hub.
A Community Interest Company (CIC) is a type of limited company created for people who want to conduct a business or other activity for community benefit, and not purely for private advantage. Some existing community broadband initiatives are set up as CICs.
The number of people who share backhaul capacity. A contention ratio of 50:1 means that you may be sharing that capacity with up to 49 other people. Imagine a rush-hour train with only two carriages. Some passengers may have to stand. With four carriages there is a lower contention ratio – everyone gets a seat and travels in comfort. Some people pay more for a lower contention ratio so their broadband is faster. Some internet service providers put up to 400 people on one connection to keep costs low.
The backbone of the communications network, carrying voice and data services around an area.
Distribution point: the point near to a premises where the main cable is split to provide service at one or more localised premises. A DP can be at the top of a telegraph pole (Overhead DP), under a walkway (Underground DP) or on the side of a building.
Underground pipes that hold copper or fibre cables.
Optical fibres are thin, flexible, hair-sized fibres that transmit data in the form of light signals. They can be bundled together, often encased in cable similar to an ordinary computer cable, and can transmit data millions of times faster and more reliably than metal wires.
Fibre to the cabinet. This is a possible model for broadband delivery in which the final portion of the access network, from the cabinet to the home, continues to use your existing copper line. ‘Up to’ 40 Mbps is possible, but not likely. You have to be within 300 metres of the cabinet for it to work. You also have to have a good line to the cabinet. FTTC does not usually work in rural areas, where a large proportion of customer lines are too long.
Fibre to the home (or FTTP, fibre to the premises). This is true next generation access where the fibre connection reaches the home or business. There are no bottlenecks to stop the flow of data. Data is symmetrical, with the same upload speed as download speed.
Internet service provider: the company that supplies your broadband. Also known as an SP – Service Provider
Kilobits per second, a measure of the rate of data transfer. 1,000 Kbps = 1Mbps.
Megabits per second, a measure of the rate of data transfer. 1Mbps = 1,000 Kbps.
Primary connection point: A green box, that you might see on a street corner in a city, which connects telephone lines to the exchange. Also called a cabinet.
The box that connects your computer to the internet and pushes broadband out to other computers in your building. Often installed with firewall protection. Also called a gateway.
Where uploadspeeds are the same as download speeds. True Next Generation Access will be symmetric. Video conferencing requires symmetric upload and download speeds. Current broadband is asymmetric.
Very-high-bitrate Digital Subscriber Line is a DSL technology that offers speeds of up to 76Mbps downstream and 16Mbps upstream over a single flat untwisted or twisted pair of copper wires – over short distances. This is the technology BT uses with it's 'Infinity' service.