Data communication Hardware
The transfer of data over a communications circuit requires appropriate hardware and software. Once these are working you can use various applications for the following services and operations:-
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Internet
Having registered with an Internet service provider (ISP), you can use the World Wide Web (WWW), send messages via electronic mail (e-mail), convey files using file transfer protocol (FTP) or use Internet telephony to speak to other Internet users for the cost of a local call, irrespective of distance. However, to talk to others that aren’t on the Internet you must register with an internet telephone service provider (ITSP).
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Peer-to-Peer (Point-to-Point) Communications
This lets you transfer data between computers using a communications application, but without using the Internet. Unfortunately, the call charges are expensive over long distances.
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Terminal Emulation
This is similar to peer-to-peer operation, but lets you communicate with an old-fashioned mainframe computer or a more modern system that uses a compatible terminal.
Hardware Options
A wide range of hardware is available for interconnecting computers, most of which is designed for the Internet. As well as the hardware itself, you’ll need to deal with the cost of installation and any associated cables. And for Internet access you’ll need to subscribe to a service provider, although some companies can provide all that you need in a single package.
The choice of hardware is a compromise between cost and speed. The latter, measured in kilobits per second (kbit/s), must be considered in two directions. First, there’s the upstream speed, the rate at which you can send data or upload files to a remote computer. Secondly, there’s thedownstream speed, the rate a which you can receive data or download files from another machine. Of the two, the latter is more important, since most people receive more data than they send.
The following table shows the various options available in the United Kingdom, in order of mass popularity. The speeds shown here are typical, although higher rates are possible.
| Connection Method | Access | Downstream (kbit/s) | Upstream (kbit/s) |
|---|---|---|---|
| Standard modem | Dial-up | 56 | 56 |
| ADSL | Permanent | 512 | 256 |
| SDSL | Permanent | 512 | 512 |
| Cable | Permanent | 128/512 | 256 |
| ISDN | Dial-up | 64/128 | 64/128 |
| Leased line | Permanent | 64/128 | 64/128 |
| Satellite | Permanent | 400 | 56 |
| Wireless | Permanent | 128/512 | 256/512 |
- A permanent connection is essential if you want to operate your own Internet server.
Here’s a quick summary of what’s available:-
Standard Modem (56 kbit/s)
This lets you convey digital data over a normal phone circuit, also known as the public switched telephone network (PSTN) or plain old telephone service (POTS). Both the caller and the recipient must have a modem connected to their computers. As with a normal telephone call, the link is operated as adial-up service, only providing a connection when required.
The modem at the sending end modulates the data into an audio signal which the modem at the receiving end demodulates back into data. Speed is seriously limited, since the phone system is designed for speech signals of restricted bandwidth.
- Some modems support multilink operation, sharing data over several phone circuits and giving increased speed.
ADSL (512 kbit/s)
An Asymmetric Digital Subscriber Line requires special wiring from your telephone company, as well as an ADSL terminal adaptor (ADSL TA) or an ADSL modem. ADSL is faster and more reliable than a dial-up circuit. When used with a router, it gives a permanent connection to the Internet, requiring you to use personal firewall software for protection against hackers.
SDSL (512 kbit/s)
A Symmetric Digital Subscriber Line, also known as G.SHDSL, is similar to ADSL, but offers the same speed in both directions, as required by some professional users. This makes it an ideal alternative to a leased line or ISDN connection.
Cable (128/512 kbit/s)
Cable-assisted television (CATV), also known as cable TV, employs coaxial cables to carry TV pictures, but can also provide a permanent connection to the Internet. This requires a CATV splitter box for feeding your TV and a special cable modem.
- In some parts of the United Kingdom you can use blueyonder, a cable-based system provided by Telewest that offers improved rates of 512 kbit/s, 1 Mbit/s or 2 Mbit/s.
ISDN (64/128 kbit/s)
The Integrated Services Digital Network (ISDN) predates ADSL, but is well-established in professional circles. It uses one or more circuits from your local telephone exchange, normally operated as a dial-up service. However, instead of a modem, you’ll need an ISDN terminal adaptor (ISDN TA), ISDN cardor USB-to-ISDN adaptor. Such devices support peer-to-peer communication while some TAs also accommodate multilink operation.
Leased Line (64/128 kbit/s)
This option, sometimes known as a T1 connection, is similar to ISDN but provides a permanent connection, which means you’ll need firewall software to protect yourself against hackers.
Mobile Phone (9.6 kbit/s – 2 Mbit/s)
You can use your mobile phone for sending and receiving data, preferably in conjunction with a portable computer. Although GSM and other current systems are very slow, the second generation of phones operate at a similar rate as PSTN, and the third generation (3G) are even faster.
Satellite (400 kbit/s)
Satellite communication offers rates of 400 kbit/s or higher, although early systems used a telephone modem for sending data ‘upstream’. More recent offerings download at 512 kbit/s and upload at 128 kbit/s, both via satellite, with an option for downloading at 2 MB/s. Most parts of the UK can use a 890 mm satellite dish, although a 980 mm version is needed in Northern Ireland and Scotland.
- The time-lag introduced by satellite systems makes them unsuitable for real-time games.
Wireless (128/512 kbit/s)
This technology is still emerging, although it will undoubtedly become popular.
