§ Value-Added Network (VAN): although not relating to size (but it rhymes with the others!), it refers to the provision of a network infrastructure service to other businesses.
The service goes beyond the physical cabling and includes “value-added services” such as limited data and transaction processing or message routing. An example for the banking
industry is the provision of an inter-bank Electronic Funds Transfer (EFT) and clearing 66 [Free reproduction for educational use granted]
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service, linking the computers of different commercial banks (and, possibly, retailers)
together.
6.1.2 Network Topologies.
The network topology refers to the physical and logical way in which the computers in a network are connected together. Although there are a number of proprietary ways, the
following three are the main topologies in common use (refer Figure 7-1). Note that these topologies usually refer to a LAN configuration.
§ The star network is driven by one central computer to and through which all other computers communicate. Although this allows for central co-ordination and control, it
requires a very reliable central computer and lots of cables.
§ The ring network consists of a continuous loop connecting all computers. Signals travel in a given direction and all computers have equal access to the data. A special version of the ring network is the token ring whereby a special code, the token, is passed around the ring. This token serves as the data holder and computers can send information only after grabbing an available i.e. empty token, adding their data and passing the token back onto the network.
§ The bus network is currently the most popular configuration. A central data cable is used, to which each computer (and other devices such as printers and routers) can be attached.
Although bottlenecks can occur, its popularity stems from its inherent robustness: devices can be added or removed without affecting the rest of the network. Data clashes (two
computers attempting to send information simultaneously) can prevented by a variety of
means.
Rin g
net-
w ork
Star
netw ork
Bus netw ork
Figure 6-1: Network topologies
6.2 Telecommunication Devices
Regardless of the network topology that has been implemented, the same basic equipment is Discovering Information Systems
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used to connect the different computers and to ensure error-free data transmission between them.
• Network cables are the physical wires by which computers are linked together. The most common types are:
o Twisted pair: thin insulated copper wires, combined in one single cable. This is similar to the wire used for voice telephone connections.
o Coaxial cable: (or coax) a thin copper wire inside a tube of insulation material, surrounded by a sheath or mesh of conducting wire, again insulated on the outside.
This is similar to the wire used to connect antennas to video or TV equipment.
Because there is less possibility of interference, it allows greater volumes of data to be transmitted in a given time – the amount or volume of data that can be transmitted
over a network connection is referred to as bandwidth.
o Optical fibre or fibre-optic: a translucent and flexible material through which laser light can travel over long distances. This fibre is much more difficult to work: it
requires special connectors as well as lasers and sensors (with electronics-to-light
converters) at each terminal. Although this technology is more expensive, laser light
can be switched on and off a lot faster than electricity (and it travels ten times faster), resulting again in a much greater bandwidth.
o Wireless: not all computer devices need a physical cable connection. Because of the cabling costs and hassles, engineers have explored many methods of transmitting data
without the use of wires. For short distances, infra-red signals work well albeit slowly
– the same technology as your VCR remote control. For longer distances and higher
bandwidths, radio frequencies or other parts of the electro-magnetic spectrum are
used. Satellite technology is increasingly being used for digital data transmissions,
especially in conjunction with Global Positioning Systems (GPS).
• Network interface cards (NICs) are necessary when computers are connected directly to other computers by means of digital network cables (as opposed to the situation when two computers are connected to each other via a telephone link). Their primary function is to make sure that there are no transmission conflicts with the other computers linked to the network, since data may be simultaneously sent and received by many different
computers all linked to the same network. In addition, the network card usually fulfils an error-checking function, to ensure that uncorrupted data is received at its destination.
• Multiplexers allow a single channel to carry data transmissions simultaneously from many sources, by merging them at one end of the channel and then separating the individual
transmissions at the receiving end of the channel.
• Front-end processors (FEP) are used in bigger networks that are centrally controlled by large computers – often mainframes. In order to give the expensive mainframe more
“time” to concentrate on application processing, it needs to be relieved from the rather mundane task of network control. FEPs handle all or most communication processing
such as error-checking, data conversion, packaging and transmission control.
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• Routers and bridges are computers dedicated to the translation of network protocols and standards between different networks. They are becoming important as more and more
organisations are linking their own networks to those of other organisations. They may be using
o different operating systems (Novell, Unix or Windows NT),
o other technologies (coax or fibre-optic),
o or different protocols (proprietary or public standards set for computer
communications).
• Finally, the modem allows a computer to communicate
with another computer by means of the public voice
telephone network, rather than by using digital
cabling. This requires the conversion of digital computer
signals (used inside the computer) into analogue sound signals
(that can travel over the voice telephone lines) – this process is called modulation. At the other end of the line, these sound signals are converted back into digital signals – or demodulated. The word modem refers to this modulation / demodulation process. You may have heard this “modulated signal” when listening to a fax machine, which is really a
scanner/printer/modem in one. Since the modem replaces the network card, it usually
carries out similar error-checking functions to ensure the correct transmission of data.
Trivial fact: More than 5000 satellites are orbiting the earth and most of them are involved in telecommunications.
6.3 SA Public Telecommunications Services
Because telecommunication services are a critical part of any country’s infrastructure, most governments have been very protective towards their telecoms. Paradoxically, this
protectionism often resulted in high tariffs (monopolies!), thus reducing the overall
competitiveness of local businesses. Recently more and more countries have started to
privatise these services and allowed competition to drive prices down. The South African public telecommunication services are controlled by Telkom, although its legal monopoly is being phased out. The following are the main data network services provided by Telkom.
6.3.1 Public Switched Telephone Network (PSTN) Services
The oldest data service provided by Telkom is the Datel service, which provides a connection between computers by means of the standard Public Switched Telephone Network (PSTN) i.e.
the same as the normal voice telephone traffic. This requires the use of built-in or external modem equipment that modulates the digital signal into an analogue audio signal (and demodulates it back at the receiving end). This service is quick and easy to set up since it is available anywhere where there is an ordinary voice telephone point. The main drawbacks are the limited transmission speed, high error rate and the lack of security. Customers may choose between a dial-up or leased line connection.
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6.3.2 Diginet
Diginet is a dedicated digital data service from Telkom that provides reliable and efficient point-to-point (i.e. not switched) data connections. It differs from the Datel network in that the transmission path is entirely digital: a combination of fibre-optic, microwave and coaxial cable. Because the signal does not have to be translated into analogue form, no modem is required, resulting in a cost saving. However, its main advantages are the higher transmission rates and a substantial reduction in transmission errors. The standard Diginet service allows for 64 kpbs ( kilobits per second) though an enhanced service called Diginet-Plus has been designed to transfer up to 1920 kpbs, which allows slow-scan TV and video conferencing
signals to be transmitted in real-time.
6.3.3 Public Switched Data Network (PSDN) Services
Saponet is Telkom’s Public Switched Data Network (PSDN). The Saponet-P service relies on a packet-switching mechanism whereby all data transmissions are broken up into smaller, standard-size units or data packets. Each of these packets is then routed independently to their destination. The path travelled by the packet depends on the available capacity and
bottlenecks. At the destination, the original transmission is reassembled out of the constituent packets. A Packet Assembler & Disassembler (PAD) is responsible for the breaking up of a message into packets and the opposite process of reassembling packets into a message at the destination. This PAD can be a separate hardware device or a software program.
6.3.4 X.400 and Telkom400
Telkom400 is a VAN on top of the X.400 infrastructure. It supports electronic message
handling and electronic data interchange (EDI). EDI is the automated computer to computer application exchange of structured business data between different organisations. An
international standard defines common business documents such as order forms, invoices or electronic funds transfer documents that are exchanged directly between the computers of the respective business partners.
6.3.5 ISDN and ADSL
Now that most of Telkom’s telephone exchanges have become digital, Telkom is able to
provide new functions and services. One all-digital connection that has sufficient capacity ( bandwidth) to support speech, video conferencing, facsimile, data and image transfer. This connection is called an ISDN line (Integrated Services Digital Network) and is currently available in selected metropolitan areas. Much more popular is the newer Asymmetric Digital Subscriber Line (ADSL) which allows a broadband connection (at least several hundred
kilobits/second) over your standard telephone line while keeping the line available for voice telephone calls. It is called “asymmetrical” because the standard allows for much greater
“download” than “upload” speeds; this reflects the typical home user pattern. Higher volumes and transmission speeds of up to 150mbs – typically needed by mid-size and larger businesses
– are available through Telkom’s ATM Express service.
6.4 The Internet
The Internet is probably the most exciting, the most popular, most visible and definitely the 70 [Free reproduction for educational use granted]
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“coolest” information systems development of the decade.
6.4.1 What is the Internet?
The origins of the Internet can be found in the early sixties, when the US Department of Defence sponsored a project to develop a telecommunications network that would survive a nuclear attack. It had to link together a diverse set of computers and work in a decentralised manner so that, if any part of the network were not functioning, network traffic would
automatically be re-routed via other network nodes. This project quickly grew into a popular academic network linking virtually all major research institutions and US universities. Soon other countries jumped onto the bandwagon, thus linking academics and researchers across the globe. True to the academic ethos, it quickly became a means for global information
sharing. By now, businesses also got a piece of the action. This was spurred on by the trend to network the personal computers in home and business environments and the development
of more user-friendly, graphical interfaces: the web-browser and the Windows operating
system.
The Internet (or, more colloquially, the Net) consists of a huge and fast-growing number (hundreds of thousands) of inter connected net works linked together. Currently more than 100
million users are connected to the Internet. The popularity of the Internet can be explained by the amount of information it makes available: the equivalent of many libraries of information is stored on millions of computers ( Internet hosts), much of it free of charge to all Internet users. This information is provided by educational institutions, governmental agencies and organisations, individuals, and increasingly by businesses. Hence, the Internet is frequently referred to as the Information Highway or the Infobahn.
But the Internet is more than just a huge information resource. Its initial purpose was to act as a communications network and it fulfils that role well. It is the transport mechanism for electronic mail, the transfer of computer files, remote computer access and even allows for voice calls. Businesses quickly realised the potential of the multimedia-enabled Internet for marketing purposes. Of late, more and more business transactions are being conducted via the Internet: electronic commerce (e-commerce) is the latest revolution to be embraced by the Internet community.
6.4.2 Electronic mail
Probably the most popular Internet service is electronic mail, more commonly known as email. This consists of the sending of messages composed on the computer, via a network, directly to the computer of the recipient who reads the message on his/her computer.
Knowledge workers with access to e-mail write five to ten times as many e-mail messages as hand-written notes. The following are just some of the advantages of e-mail.
• Reliability: although there is no guarantee, you will normally receive quick feedback if the address does not exist or there is a similar delivery problem.
• Efficiency: many short-cut tools exist to increase your efficiency when composing messages. You can use your computer’s cut-and-paste function, you can have
managed address books and lists, when replying to another message you can
automatically incorporate any part of the message to which you are, etc. And it is just Discovering Information Systems
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as easy to send a message to one as to a whole list of addressees. (Admittedly, this
results in a lot of abuse and information overload on the recipient’s side.)
• Digital: e-mail is composed on a computer and remains in computer-readable format all the way to its destination. Thus one can also easily incorporate other computer data such as graphics or document files.
• Cheap: because the capacity of the Internet and disk storage is increasing all the time, the cost of a sending and storing a one-page e-mail message is negligible.
• Speed: messages are generally delivered across the world in a matter of seconds.
The e-mail address
Just like with ordinary postal mail (now usually referred to as snail-mail), you need to know the recipient’s address before you can send your message. Internet e-mail addresses have a standard format: username@domain. The username is often the name that your addressee uses to connect to the network, e.g. “jvanbelle” or sometimes a long number. This username is allocated by the LAN administrator. The domain identifies the file server, which acts as the local post office for your recipient’s e-mail. The domain consists of several parts, separated by full stops or dots. The international standard for domain identification is <name of LAN
server>.<name of organisation>.<type of organisation>.<country code>.
• The country code is the international two-letter code for the country e.g. au for Australia, za for South Africa, sa for Saudi-Arabia, uk for Great Britain, etc.
• The two most common types of organisations are co for a commercial organisation and ac for an academic institution . Less frequent are org for (not-for-profit) organisations, mil for military, net for networks and gov for government agencies.
• Each country has a national Internet naming body that allows its organisations to
chose their own name, as long as no one has claimed the same name before.
Examples of South African domain names are anc.org.za, uct.ac.za, fnb.co.za.
• Large organisations often refine the domain further by adding the name of their LAN
servers, e.g mail.uct.ac.za.
Examples of possible e-mail addresses are: JaneDoe@stats.uct.ac.za (Jane working in the statistics department at the University of Cape Town in South Africa); info@anc.org.za
(information department at the ANC, a political party) or SoapJoe@marketing.bt.co.uk (Joe Soap in the marketing department of British Telekom in the U.K.).
The US Americans, having “invented” the Internet, use a slightly different way for their addresses. They leave off their country code ( us) and use com for commercial organisation or edu for educational institution. Since the majority of Internet users hail from the US, you will encounter many addresses such as JWood@mit.edu or Bill@microsoft.com.
Netiquette
Just as in any other social interaction environment, there are some rules and guidelines for appropriate social behaviour on the Net: Netiquette (etiquette on the Internet). The following 72 [Free reproduction for educational use granted]
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are some illustrative examples pertaining primarily to e-mail.
• Shouting¸ THE PRACTICE OF TYPING ENTIRE SENTENCES IN UPPER CASE is
generally seen as novice ( newbie) behaviour and frowned upon. Perhaps it stems from the disgust with old teletypes and mainframe terminals that did not have lower-case
characters.
:-)
Happy face
• The use of emoticons to indicate emotive content of a :-(
Sad or sorrow
sentence is highly recommended. Typed text does not
;-)
Wink
:-0
Shock
reveal any body language and a joking remark can easily
:-\
Sarcasm
be interpreted the wrong way. Whenever one writes :^]
Wide grin
something in jest or with humorous intent, it is advisable
:-x
Blowing a kiss
:’(
Teary-eyed
to add an emoticon. An emoticon (an icon indicating
:-P
Sticking tongue out
emotional content) consists of a series of text characters
8-)=
Beard & glasses
which are meant to be rotated a quarter turn and represent
:--)%
Boy on skateboard
a laughing :-) (i.e. equivalent to J or the smiley) winking <g>
Grin
<w>
Whisper
;-) or sad face :-( L.
{{}}
Hug you
• Flaming is the carrying on of a heated
BTW
By the way
IMHO In my humble opinion
personal emotional debate between two or
FWIW For what it’s worth
more individuals on a public Internet forum. A
SO
Significant other (partner)
flame war is generally a sign of immature
BRB
Be right back
FAQ
Frequently Asked Questions
behaviour by individuals who cannot take
RTFM Read the f*** manual
perspective and should really take the
TTYL Talk to you later
discussion off-line.
IRL
In real life
F2F
Face to face
LOL
Laughing out loud
• Netizens (inhabitants of the Internet i.e.
frequent net surfers) often use standard but, to
the non-initiated, cryptic abbreviations. Examples are: BTW = by the way ; ROFL =
rolling on the floor with laughter ; TPTB = the powers that be ; BRB = Be Right Back.
This vocabulary has been adopted and expanded with the growth of Short Message
Service (SMS) use on cellular phones.
6.4.3 The Web
The Internet service that has received the most attention from the public media is the WorldWide Web or the Web for short (sometimes also called WWW or W3). The Web is a vast collection of multimedia information located on Web servers attached to the Internet.
Its popularity is due to a number of reasons.
• Information links are transparent. Links to any other piece of information located
anywhere on the Internet can be inserted in a web document. A simple click of the mouse
takes the reader completely automatically from one Web server to another, quite possibly in another country.
• Information can be presented in a hypertext link format whereby one can jump immediately from one concept to a related concept or explanation. No need to read text in Discovering Information Systems
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the traditional top-to-bottom sequential way.
• It allows for multimedia information. A Web document can incorporate rich and colourful graphics, animation, video clips, sound etc. Just think of the marketing opportunities!
• The Web supports interactive applications. Web applications can request information
from visiting users and documents can include programming instructions. Users can even
download small programs (often written in Java) that could perform some processing on the user’s computer or display special visual effects.
Reading or accessing information on the Web is called surfing the Net because one jumps from one hypertext link to another following whatever takes your fancy. In order to surf the Net you need some special browser program that understands the Web protocols and formats and presents the information to suit your computer monitor. You also need an access point or connection to the Internet. Your Internet connection ma