UK Broadband information and advice

     Details on UK Broadband, and a look at what the UK Broadband providers have to offer

What is Broadband?

A broadband connection (ADSL) provides high-speed Internet access over a standard phone line. The advantage of a broadband connection over the older dialup service, is that Broadband is considerably faster, and is 'always-on', meaning that once you're logged on, your PC is online until the PC is turned off again.

Broadband offers high-speed Internet access and allows telephone calls and a permanent Internet connection to share a single phone line simultaneously.

What do I need?

• Broadband coverage in your area. Each broadband provider allows you to enter your phone number or postcode to check availability. A basic test is done on your line, and when you sign up, a more comprehensive test is carried out.
  
• A Broadband (ADSL) modem or router. These cost from around £50 (PC World) - although many Internet providers, including BT Broadband, provide you with a free router when you first sign up to their service. If it's offered, try to get a free wireless router with your Broadband package.
  
• Microfilters. When Broadband is enabled, the broadband signal is available via any extension socket in your home as well as the main point. You'll need to use a filter to cut out the Broadband "crackle". You need a filter on every phone socket that has something plugged into it - this includes phone handsets, fax machines and your Sky box.

A few years back in many places, accessing the web was something challenging due to lack of internet sources, and people had to settle with the very slow telephone line dial-up connections of the internet. The dial-up internet connection used to come with a modem which dials a network number and connects, providing a slow speed of 56 Kbps, but then the new form of Internet connection was introduced, called the Broadband internet service in which the minimum internet speed was recorded to be 256 Kbps.

The speed of 256 Kbps is defined for the download rate, as the different networks provide lesser upload rates than the download speeds. The broadband technologies in most areas are DSL, ADSL and cable modems. However, there are some new technologies which are being used, and they are termed VDSL and optical fiber connections.

A few abbreviations -  

VDSL – Very High Speed Digital Subscriber Line

DSL – Digital Subscriber Line

ADSL – Asymmetric Digital Subscriber Line

Through VDSL, the internet data is transferred through single twisted pair of copper wires. And this enables very high speed Internet access.

India ranks #18 in the total number of Broadband subscribers, and China tops the list, followed by the United States.

Every non-possible thing of dial-up internet can be possible with broadband as broadband internet connections provide and carry heavy packets of internet. Activities like watching videos, downloading heavy files, downloading songs, voice chat, web-cam chatting are possible uninterruptedly with broadband services.

Asymmetric Digital Subscriber Line

Asymmetric Digital Subscriber Line (ADSL) is one form of the Digital Subscriber Line technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. It does this by utilizing frequencies that are not used by a voicetelephone call.^[1] A splitter, or DSL filter, allows a single telephone connection to be used for both ADSL service and voice calls at the same time. ADSL can generally only be distributed over short distances from the central office, typically less than 4 kilometres (2 mi),^[2] but has been known to exceed 8 kilometres (5 mi) if the originally laid wire gauge allows for farther distribution.

At the telephone exchange the line generally terminates at a Digital Subscriber Line Access Multiplexer(DSLAM) where another frequency splitter separates the voice band signal for the conventional phone network. Data carried by the ADSL are typically routed over the telephone company's data network and eventually reach a conventional Internet Protocol network.

Operation

Currently, most ADSL communication is full-duplex. Full-duplex ADSL communication is usually achieved on a wire pair by either frequency-division duplex (FDD), echo-cancelling duplex (ECD), or time-division duplex (TDD). FDD uses two separate frequency bands, referred to as the upstream and downstream bands. The upstream band is used for communication from the end user to the telephone central office. The downstream band is used for communicating from the central office to the end user. 

With standard ADSL (annex A), the band from 26.000 kHz to 137.825 kHz is used for upstream communication, while 138 kHz – 1104 kHz is used for downstream communication. Each of these is further divided into smaller frequency channels of 4.3125 kHz. These frequency channels are sometimes termed bins. During initial training, the ADSL modem tests each of the bins to establish the signal-to-noise ratio at each bin's frequency. The distance from the telephone exchange and the characteristics of the cable mean that some 

frequencies may not propagate well, and noise on the copper wire, interference from AM radio stations and local interference and electrical noise at the customer end mean that relatively high levels of noise are present at some frequencies both effects the signal-to-noise ratio in some bins (at some frequencies) may be good or completely inadequate. A bad signal-to-noise ratio measured at certain frequencies will mean that those bins will not be used, resulting in a reduced maximum link capacity, but with an otherwise functional ADSL connection.

The DSL modem will make a plan on how to exploit each of the bins, sometimes termed "bits per bin" allocation. Those bins that have a good signal-to-noise ratio (SNR) will be chosen to transmit signals chosen from a greater number of possible encoded values (this range of possibilities equating to more bits of data sent) in each main clock cycle. The number of possibilities must not be so large that the receiver might incorrectly decode which one was intended in the presence of noise. Noisy bins may only be required to carry as few as two bits, a choice from only one of four possible patterns, or only one bit per bin in the case of ADSL2+, and very noisy bins are not used at all. If the pattern of noise versus frequencies heard in the bins changes, the DSL modem can alter the bits-per-bin allocations, in a process called "bitswap", where bins that have become more noisy are only required to carry fewer bits and other channels will be chosen to be given a higher burden. The data transfer capacity the DSL modem therefore reports is determined by the total of the bits-per-bin allocations of all the bins combined. Higher signal-to-noise ratios and more bins being in use gives a higher total link capacity, while lower signal-to-noise ratios or fewer bins being used gives a low link capacity.

The total maximum capacity derived from summing the bits-per-bins is reported by DSL modems and is sometimes termed sync rate. This will always be rather misleading, as the true maximum link capacity for user data transfer rate will be significantly lower; because extra data are transmitted that are termed protocol overhead, reduced figures for PPPoA connections of around 84-87 percent, at most, being common. In addition, some ISPs will have traffic policies that limit maximum transfer rates further in the networks beyond the exchange, and traffic congestion on the Internet, heavy loading on servers and slowness or inefficiency in customers' computers may all contribute to reductions below the maximum attainable.

The choices the DSL modem make can also be either conservative, where the modem chooses to allocate fewer bits per bin than it possibly could, a choice which makes for a slower connection, or less conservative in which more bits per bin are chosen in which case there is a greater risk case of error should future signal-to-noise ratios deteriorate to the point where the bits-per-bin allocations chosen are too high to cope with the greater noise present. This conservatism involving a choice to using fewer bits per bin as a safeguard against future noise increases is reported as the signal-to-noise ratio margin or SNR margin. The telephone exchange can indicate a suggested SNR margin to the customer's DSL modem when it initially connects, and the modem may make its bits-per-bin allocation plan accordingly. A high SNR margin will mean a reduced maximum throughput, but greater reliability and stability of the connection. A low SNR margin will mean high speeds, provided the noise level does not increase too much; otherwise, the connection will have to be dropped and renegotiated (resynced). ADSL2+ can better accommodate such circumstances, offering a feature termed seamless rate adaptation (SRA), which can accommodate changes in total link capacity with less disruption to communications.