Broadband Connections by Phoebe Barnett

Satellite

phoebe_mb — 2016-01-22 15:27:25 UTC

Satellite broadband is used in remote areas where physical and wireless connections are not available. These areas could include some locations in the countryside or ships at sea. There are two types of satellite broadband:

One-way satellite broadband uses a satellite connection for downloading data from the internet, but uses a modem and telephone line for uploading data.
Two-way satellite broadband allows both downloading and uploading of data through the satellite connection. It is asymmetric meaning downstream has a higher bandwidth than upstream (like ADSL).

Satellite broadband uses geosynchronous satellites which are approximately 37,000km above Earth. This means that there is a latency between data being sent and data being received of about 0.7 seconds. This is not too much of a problem for downloading data and sending/receiving emails, but it means interactive applications, such as internet gaming, are not practically possible. Using this method for video conferencing can also be very frustrating due to the delay.

Line of sight is required, so low Earth orbit satellites cannot be used as they do not remain in a fixed point above the Earth.

The table below compared the different types of broadband connection using 2009 data.

Leased Line

phoebe_mb — 2016-01-22 15:27:29 UTC

A leased line exists between two locations only. There are no contention ratios as the line is a direct connection between one router and another router. This means the bandwidth is guaranteed. The line must be installed especially for an organisation and so this makes leased lines very expensive. Leased lines are symmetric, meaning that there is the same amount of upstream bandwidth available as downstream bandwidth. Therefore leased lines are preferred by large businesses and organisations providing access into their own networks using an extranet.

Many local education authorities have a 'Grid for Learning', which provides each school with a leased fibre-optic line that connects to the local authority. In 2009, the Birmingham Grid for Learning was providing 10Mbps leased lines to all of its schools. Secondary schools have hundreds of computers that could be accessing the internet at the same time, including multimedia applications that use up a lot of bandwidth. Some local authorities are now looking at the possibility of upgrading the 10Mbps connections to 100Mbps. A bottleneck can still exist between a local authority and the internet through, particularly if lots of schools are downloading lots of data at once.

Wireless

phoebe_mb — 2016-01-22 15:27:33 UTC

Since the introduction of 3G on mobile telephone networks, wireless broadband access has become far more popular. 3G was introduced to enable video calls and high bandwidth internet connections. In 2009, mobile telephone networks were offering bandwidths of up to 7.2Mbps, although 3G is capable of providing up to 14.4Mbps downstream and 5.8Mbps upstream, meaning that it is asymmetric.

Wireless broadband enables users to use the internet while not at home and also while travelling. However, it does require a good 3G signal to be available. A computer can connect to a wireless broadband connection by either connecting through a mobile phone using Bluetooth®, a USB cable or by using a USB modem stick.

Cable

phoebe_mb — 2016-01-22 15:27:38 UTC

Broadband internet access can be provided by cable television companies. The main infrastructure uses fibre-optic links meaning that higher bandwidths are available. In 2009, in the UK, downstream bandwidths of 50Mbps were available for business users and 20Mbps were available for home users. Cable, like ADSL, is asymmetric because it has different upstream and downstream bandwidths. While some cable television providers claim that there are no contention ratios with cable broadband, this is not actually true because there may still be a bottleneck when a number of households share the same fibre-optic link from the street to the cable company.

Asymmetric Digital Subscriber Line

phoebe_mb — 2016-01-22 15:27:40 UTC

Asymmetric digital subscriber line is when a range of frequencies are used on an existing copper telephone line to provide a broadband connection to the internet. Asymmetric means that the downstream bandwidth is different to the upstream bandwidth. As the vast majority of ADSL connections are used for downloading data from the internet, more frequencies are allocated to downstream bandwidth than to upstream bandwidth. A typical ADSL line with 8Mbps downstream bandwidth may only have 512kbps or 1Mbps upstream bandwidth. This is why it takes longer to upload a file to a web page than to download a file and why it takes longer to send an email than receive an email. A much smaller range of frequencies is left available for the public switched telephone network (PSTN).

ADSL provides 'always on' internet access and does not prevent the telephone from being used at the same time. In 2009, ADSL was available at up to 24Mbps. In order to be able to use ADSL, a subscriber needs to be connected to a compatible telephone exchange within a workable distance. A number of factors can affect the available bandwidth:

Distance from the telephone exchange.
Local AM radio stations causing interference (this may reduce the number of usable frequencies and thus reduces the bandwidth).
Other devices, such as fax machines, connected to the telephone line.
Electrical interference on the copper cable.

ADSL is mainly used in homes as no extra installation of cable is required. While it is used in business, it is not favoured in large businesses where more upstream bandwidth is required. A common problem with ADSL is the contention ratio, which refers to the number of subscribers that are sharing a bandwidth. A larger contention ratio means that there is more chance of not being able to download data using the full bandwidth.