Wires-only ADSL

Wires-only was one of the first of many BT initiatives during 2002 designed to kickstart the adoption of broadband, appearing on a wholesale basis at the start of the year and reaching consumers via ISPs over the following months.

Also referred to as "self-install" - because there is no need for a BT engineer to visit the subscriber's premises at install time - wires-only instead requires that the subscriber purchase and fit a microfilter on every phone socket of the phone line with ADSL. Installed in pairs, these ensure that both signals - telephony and ADSL - can reside on the telephone line without interfering with one another. The low-pass filter separates the bottom 4KHz of the spectrum for conventional voice calls, faxes, modems and any other system that previously used the old audio system. The high-pass filter separates off everything between 4KHz and 1.1MHz for use by the ADSL digital channels.

ADSL Micro-filters

When the only option was for a BT engineer to install ADSL, these microfilters were fit at the primary linebox, making it necessary for the socket to be located close to the equipment to be connected to it if RJ11 extension cable runs were to be avoided. Modifying the primary linebox isn't necessary with wires-only. Instead, the ADSL capability is carried to all sockets on a line, with each requiring the installation of a microfilter in order to use it.

As well as being a lower cost option, wires-only packages afford technically competent subscribers with significantly greater flexibility. Not only do they not have to commit to a particular range of equipment or local network topology at the time they sign up for a service, but minimum contract terms are reduced to as little as a month, providing the opportunity to test drive broadband without having first to make a long term commitment to it.

The choice of ADSL modem depends on the type of ADSL "presentation" required. USB presentation - an ADSL modem connected to a single PC via a USB socket - is the cheapest option. Ethernet presentation is more expensive, an ADSL modem/router providing a standard RJ45 Ethernet socket for connection to an existing or planned LAN. Such devices may also include some form of firewall protection. Where cabling is a problem, a wireless Ethernet modem/router can be used. G.DMT is a ratified standard which defines a common interface for ADSL devices, ensuring interoperability. Whilst USB presentation doesn't prevent sharing an ADSL connection across several networked PCs, Ethernet presentation is the more conventional choice for such scenarios.

Satellite broadband

Whilst the advent of its RADSL variant may have increased the range of ADSL from 3.5km to 5.5km, the fact is that the technology will always be literally "beyond the range" of many living in rural areas. In theory, satellite communications can reach almost anywhere, and satellite broadband is becoming an increasingly feasible solution for those for whom ADSL and cable are not options.

Satellite Braodband

The technology is well established and typically all that's needed is a dish on or near the subscriber's home and a modem/router unit inside. This needs to have an unobstructed view of the satellite in order to work. This means that no buildings, trees or other permanent obstruction should block the path between the dish and the satellite. Inside the premises, the dish is typically connected by two standard coaxial cables to a modem/router, which in turn connects to a PC via either a USB or Ethernet port. Some systems provide two-way satellite communications and so require no telephone connection, dial-up account or other ISP. Others are hybrid, combining a conventional narrowband ISP dial-up connection for uploading information to the Internet with a broadband satellite downlink.

The equipment needs to be installed professionally, but once fitted, the hardware is no more difficult to set up or use than a standard ADSL or cable modem. Some systems provide only a USB connection on low-end systems, with Ethernet costing more. A basic system allows a single PC only to be connected. Higher-end systems allow multiple PCs to be hooked up by establishing a network in which the satellite modem/router connects to the LAN through an Ethernet port.

Maximum download/upload speeds for two-way systems are in the region of 500/120 Kbit/s respectively. This translates to typical operational speeds of the order of 250/70 Kbit/s. However, there are no service level guarantees and although higher speeds are possible, contention issues mean that performance may be slower at busy times. Of course, performance can also be affected by weather. Heavy rain can temporarily impair reception and strong winds may potentially knock a dish out of alignment.

Long distance satellite communications are unavoidably subject to a slight delay (or latency) in transmission of at least 750ms. To achieve high speed downloads and mask the effect of delay over the satellite link, the service "accelerates" certain protocols that control the transmission of internet data. Notwithstanding this, such latency can have noticeable effects, making some applications impractical. These include: