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Technological Studies
Computer Network Technology
Computer Network
Technology
1 Computer network technology .................................................................... 2
(a) The importance of computer network ......................................................................... 2
(i) Sharing hardware ............................................................................................................................. 3
(ii) Communication ................................................................................................................................ 3
(iii) Shared message ................................................................................................................................ 3
(b) Network transmission protocol ................................................................................... 3
2 Types of network ........................................................................................... 5
(a) Local Area Network .................................................................................................... 5
(b) Wide Area Network .................................................................................................... 5
(c) Information highway ................................................................................................... 6
3 The structure of network.............................................................................. 6
(a) Star network ................................................................................................................ 7
(b) Ring network ............................................................................................................... 7
(c) Bus network................................................................................................................. 8
4 Commonly used network components ........................................................ 8
(a) Network interface card ................................................................................................ 8
(b) Modem ........................................................................................................................ 9
(c) Hub ............................................................................................................................ 10
(d) Router ........................................................................................................................ 10
5 Internet ......................................................................................................... 11
6 Electronic communication facilities .......................................................... 12
(a) Coaxial cable ............................................................................................................. 13
(b) Optical fibre cable ..................................................................................................... 13
(c) Microwave ................................................................................................................. 14
(d) Satellite...................................................................................................................... 14
7 The applications of electronic communication ......................................... 15
(a) Fixed network telephone ........................................................................................... 15
(b) Mobile telephone....................................................................................................... 16
(c) Electronic mail .......................................................................................................... 16
(d) Office network .......................................................................................................... 17
(e) Video conferencing ................................................................................................... 17
8 The future of the technology of telecommunication ................................ 18
(a) The third generation of mobile phone system (3G) .................................................. 18
(b) Household local area network ................................................................................... 19
(c) Short distance wireless communication protocol ...................................................... 19
(i) Connecting network transceiver..................................................................................................... 19
(ii) Replacing cables ............................................................................................................................ 20
(iii) Establishing personal temporary network ...................................................................................... 20
Exercise ........................................................................................................... 21
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Computer Network Technology
Computer Network
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1 Computer network technology
(a) The importance of computer network
As computers are broadly used, one organization may have to use several or even hundreds of
computers at the same time. If every computer has to install a scanner and a printer, this will lead to
a great wastage (Fig. 1). Besides, if a user wants to copy a file from one computer to another
computer, he must first copy the file to a floppy disk or CD. This will also waste a lot of resources
and time. Therefore, many organizations use computer network to increase communication
efficiency.
Fig. 1 Independent computer system
A computer network is a system that connects two or more computers and some peripheral
devices (e.g. a printer and a scanner) together. It allows independent computer accounts to share the
same hardware or even software, and communicate with other computers and share information.
This can increase the overall performance of the computer system.
Fig. 2 Computer network
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(i) Sharing hardware
After the establishment of a computer network, every computer account on the network can
share all peripheral devices, including the printer, scanner, plotter, CD ROM, large storage device
and backup storage device (e.g. magnetic tape machine). This method can reduce the high cost of
installation and repairing of the devices. It also saves space for storing this device at the same time.
Some of the computer network also connects to the internet, so that all users on the network can log
on to the internet.
(ii) Communication
Computer network allows users to transmit and receive files or messages, and communicate
more easily, for example, electronic mail (Email), communication software (e.g. ICQ), video
conferencing, etc. The advantages of using computer network for communication are fast and that
we can simultaneously transmit and receive files, including document files, programs, images,
photos and videos, etc.
Some offices will encourage the staff to use the computer network more, and reduce the use of
paper, so that they can become ‘paperless offices’. For example, when a meeting is held, the holder
of the meeting can first prepare the agenda and document in the form of computer files, then send to
members through the computer network immediately. After the meeting, minutes can be delivered
through the network. This method not only can reduce both expenditure and space, but also can
save paper which requires chopping down of trees. This is a kind of environment conservation.
(iii) Shared message
Different departments of organisations always require sharing certain data and messages. For
example, all EPS machines of banks need to share the same account information of the clients;
every computer in the library can check the book records of the library; the government can check
the basic details of a citizen. All these tasks require a computer network to connect client
computers to one or more database.
Some shared information allows the clients to search through the network easily. For example,
investors can check the stock market through the computer network; the public can also check the
government news, notices and video clips and enquiring documents, etc.
(b) Network transmission protocol
In the network communication, different computer systems must have certain rules, so that
information can be transmitted accurately. These rules are called network transmission protocol.
Take the internet as an example. When the users visit different homepage using browsers, they may
have to connect to the internet in order to take the documents. Every connection must provide the
browser with an URL. It indicates the name, path and filename of the computer which store the
document. Fig. 3 shows an internet homepage, the label part provides the URL that connects to the
document, i.e. http://www.ctphk.com/tf-ts. The first part HTTP of the URL is the network
transmission protocol used to access the internet homepage. Its name is “hyper text transmission
protocol”. The above URL shows that the server storing that document is called www.ctphk.com;
the remaining part is the path and filename to that document.
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Fig. 3 Internet homepage
To open a document, the user has to start the related connection (Fig. 4a). The browser will
first enquire the regional computer in order to find the address of the computer that contains the
document (Fig. 4b). The regional computer keeps the records of the address name and the
corresponding digital address. Once the regional computer finds the required digital address, it will
send the digital address to the user’s computer. Otherwise, it will search the address from other
regional computer.
When we get the digit address, the browser will first connect to the computer that contains the
required document (Fig. 4c). Then, the browser will execute the client version of HTTP in order to
send out a document file request, at the same time it states the filename and the format that can be
processed (Fig. 4d). The computer that contains the document will run the server version of the
HTTP, and respond to the request made by the HTTP of the browser, finally send back the correct
document file back to the browser together with HTTP reply (Fig. 4e). After receiving the
document file, the browser can finish the connection, and display the suitable document (Fig. 4f).
(a) Start the related connection
(b) Find the address
(c) Connect to the computer
(d) Send out the request made by the HTTP
(e) Respond to the request made by HTTP
Fig. 4 Receive the homepage by HTTP
(f) The homepage is displayed
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There are different types of network transmission protocols. Besides HTTP, other examples
include FTP, TCP, IP, etc. Each of the network transmission protocol provides specific service. For
example, file transmission protocol (FTP) is used for the transmission of files. Transmission
control protocol (TCP) is used for providing connection service. Internet protocol (IP) is used for
transmitting and receiving data on the internet, etc.
2 Types of network
According to the area covered by the computer network, it can be classified into three types:
local area network, wide area network and information highway.
(a) Local Area Network
A Local Area Network (LAN) is a network used in smaller area. For example, a room, a
classroom, a laboratory, schools and buildings, etc. It uses communication cables to connect two or
more computers together (Fig. 5). In Local Area Network, usually one of the computers will work
as the server that controls the network system, while the remaining computers are called
workstations. All client computers can then use shared hardwares, communication with each other
and share information through the server.
Fig. 5 Local Area Network
In a Local Area Network, the distance between computers is shorter, so communication cable
with a high transmission speed is usually installed. Thus, it will not be affected by other
communication networks (e.g. telephone network). Since every workstation in a local area network
is a computer, every user can work independently even when the network is out of order.
(b) Wide Area Network
If local area networks of different regions are connected together, then a wide area network
(WAN) will be formed (Fig. 6). For example, different police stations have installed with local area
network. If all the local area networks in different police stations are connected, a wide area
network will be formed. Since wide area networks need to connect several regions that are farther
from each other, some public electronic communication networks, for example, telephone line,
microwave communication, satellite and coaxial cable, etc. have to be installed.
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Fig. 6 Wide Area Network
(c) Information highway
With the development of the computer network, the transfer of data among computers has
become more frequent. In order to tackle the increasing amount of data transfer, many countries
and regions start to build communication cables which have high transmission speed, large capacity
and large area coverage, these cables are called information highways. (Fig. 7).
Information highway can transfer sound, data, images and information that exist in other forms,
this enables users in different regions to transmit and receive email, listen to the online news,
commercial, government and educational information. It not only can be used for connecting
computers, but also can connect telephone and cable TV. Since the internet can already provide
most of the above functions, so this is why it is called information highway also.
Fig. 7 Information highway
3 The structure of network
The method that connects computers in a network is called a structure of network. In a
network that contains N computers, every computer is connected by using communication cables.
A total number of N x ( N-1 ) cables are required (Fig. 8). When N increases, the number of cables
will then increase at a rapid rate. For example, when N = 100, the total number of cable is 100 x 99
= 9900! Therefore, many computer networks use special design in order to save the number of
cables used.
The design of network nowadays can be divided into three types: star network, ring network
and bus network. In a computer network, the devices (e.g. the computer, the printer and the scanner,
etc.) are connected to the communication cables and are called terminals.
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Fig. 8 Simple network
Computer Network Technology
Fig. 9 Star network
(a) Star network
If one central computer is used to connect all the terminals in the network, this structure is
called a star network (Fig. 9). In a star network, the communication between terminals must be
transferred and processed by the central computer. For example, terminal 1 wants to send a
message to terminal 2 that it must first send the message to the central computer for processing, and
then re-transfer to terminal 2.
A star network can be used to provide central database for every client. For example, the
network system in the stock exchange companies provides the stock brokers with the stock
exchange database, and to allow them carry out their trade. Since a star network is completely
controlled by a central computer, it has a very high efficiency. For example, the central computer in
a stock exchange company can control the time to start and stop the trade in order to avoid
confusion.
In a star network, every client computer can join or disconnect from the network at any time.
This does not affect the operation of the network. Similarly, if any one of the client computers is
not functioning, the network is still operative. However, the network does not work when the server
is out of order. Therefore, a backup system of the main server and data storage devices is usually
engaged in the star network, so that they can substitute that server which is out of order to avoid
prolonged out of service.
(b) Ring network
If all the terminals in a network are connected to form a ring, this kind of structure is called a
ring network (Fig. 10). In a ring network, terminals can communicate with each other directly. For
example: terminal 1 can transfer information to terminal 2 in a certain direction at a very high speed.
There is no central computer to
control the communication in a ring
network, so the connection method and
configuration are easier and is suitable for
smaller network. For example, several
computers in an organization can be
connected by a ring network to form a
area network. However, if there is a fault
point of the network, then the whole
will be affected.
Fig. 10 Ring network
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(c) Bus network
If all the computers in a network are connected to a central bus, this kind of structure is called
a bus network (Fig. 11). In a bus network, terminals can communicate with each other directly, for
example, terminal 1 can send messages to terminal 2 rapidly along the central bus.
No central computer is required to
control the communication in a bus
network, so terminals can be added or
removed from the network at any time
without affecting the overall functioning
of the network. Similarly, error in one
terminal will not affect the whole network.
The bus network allows users to share
devices and communicate with each other
easily, and it is cheap and easily installed.
Yet the transmission speed of messages
will be lower.
Fig. 11 Bus network
4 Commonly used network components
Computers require certain components to connect a network. These components are called
network components, for example, network interface cards, modems, hubs and routers, etc.
(a) Network interface card
A network interface card is usually called a network card (Fig. 12). It plugs onto the slot on
the circuit board of a computer. Then it is connected to the network using communication cable, to
enable the computer to sends and receive message on the network. When the computer is
transmitting signals, it sends the data to the network card. The network card temporarily stores and
processes the data, and adds the necessary transmission information (e.g. title, IP address, error
prevention information, etc.). It then converts the data to digital signals and transmits along the
cable. When the network card of another computer receives the signal, the procedure is reversed to
convert the signals into computer data.
Fig. 12 Network interface card
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(b) Modem
Fig. 13 The use of modem
If the computer uses a telephone line for communication, like connecting to the internet, a
modem is required. This is because the computer uses digital signals to transmit data, while the
telephone line can only transmit analogue signals. The main functions of a modem are modulation
and demodulation. Modulation is the conversion from digital signals which are transmitted by the
computer to analogue signals which can be transmitted along the telephone lines. Demodulation is
the conversion from analogue signals transmitted by the telephone line to digital signals receivable
by the computer. Using a modem, two computers can then communicate through the telephone line
(Fig. 13). The transmission speed of the modem used nowadays is commonly at 56 kbps (Fig. 14a).
However, many computer users now use broadband connection (Fig.14b) which has a higher
transmission speed.
Fig. 14 (a) 56k bps modem
(b) Broadband modem
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The transmission speed of broadband is faster than that of modem by 30 fold, which
is about 1.5M or 187.5 KB/s. However, the speed of broadband transmission may be
influenced by the following factors:

Whether the server which contains the web pages has the restriction on the speed of
access and the bandwidth;

Whether it is in the busy or non-busy period; and

The internal and external bandwidths of the broadband internet service provider
(ISP).
Apart from the service quality of the broadband internet service provider, the
transmission speed of broadband may also be determined by other factors, such as the
operating systems, browsers and the peripheral devices of the computers of the users.
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(c) Hub
A hub (Fig. 15) is a basic network component. It is mainly used to connect computers in a
network to form a local area network. A hub can be viewed as a middle-way. It uses
communication cable to connect the input and output ports of several computers of several
networks. A hub can be used to:
(i)
connect more than ten computers to from a local area network.
(ii) connect with other hubs to form a star network which can connect more than 100 computers
together.
A passive hub will simply transmit the received data to the destination. On the contrary, an
active hub will amplify and re-process the data, and then transmit the processed data to the
destination. This can avoid the data becoming less accurate due to distant transfer. There are
different types of hubs. They can have different transmission speeds and different numbers of input
and output ports.
Fig. 15 Hub
(d) Router
The major functions of a router are partition of a large network or connecting local area
network to a wide area network. These wide area networks are the components of the internet. It
can be used to connect two networks with different transmission protocols. In the internet, different
networks are connected by routers (Fig. 16). When a router on a certain network receives data
transmitted by a computer, it will store the data temporarily. Then the router will choose a suitable
transmission path according to the address of destination stated by the data. After that, the data will
be transmitted to the router of the next network. In such a way, the data will be transferred
continuously along routers until it reaches the designated network and computer.
Fig. 16 Routers in the internet
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5 Internet
The first network system was the air security system SAGE established in the United States in
1950 – 1960. There were 23 computer networks in this system. Every network used a central
computer to connect the radars, air security systems and different places. In 1964, SABRE which
was a flight ticket booking system was established. It was the first commercial computer network
that adopted many technique of the SAGE system.
In 1969, a trial wide area network APPANET was established in the U.S.A. to prevent the
computer systems from being turned down by nuclear attack. It started to employ the technology of
TCP/IP to connect computers. This formed the basis of the internet. In 1986, the National Science
Foundation of United States used this technology to connect five super computer centres in the
United States at that time. A new network called NSFNET was formed. This network then
connected to other universities and research centres in other regions of the United States afterward.
A bigger network was formed. The primary function of this network was to enable the researchers
to communicate and exchange information rapidly.
Since the network communications grows quickly, an organization formed by an university
and private company was established in 1987, in order to handle the internet. After certain period
of time, networks in other countries, including North American and European public commercial
computers were also connected to NSFNET, an internet which crossed countries started to form
(Fig. 17). The internet does not belong to any individual organisation. The Internet Engineering
Task Force sets the related regulations of the Internet, and then the regulations were enforced by
different regions.
Fig. 17 Illustration of Internet
The internet is formed by several thousands of small local area networks, and the management
and maintenance of each small local area network are carried out by the creator of the network. In
computer communication, in order to provide bi-directional information exchange quickly, the
length of each information is limited because information which is too long will cause long waiting
for the reply of the message. Therefore, the designers of the network limit the maximum length of
message in each transmission. Messages that are too long will be divided into several packets.
Each packet contains a group of data, including a set of data (e.g. title of the address of the
destination) in the header information and a piece of shorter message. Each packet will be
transmitted individually in the network along the router, until it reaches the destination.
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Original message
Packet 1
Packet 2
Packet 3
Packet 4
Header Message1
Header Message2
Header Message3
Header Message4
息
Fig. 18 Illustration of packets
4
In order to allow the users to use the internet conveniently, some of the internet users and
software companies create browsers, search engines and communication software, etc. Many of
these are distributed by the internet service provider free of charge, so this can make the internet
popular in every corner of the world within such a short period of time. The internet is the biggest
information system in the world. Its advantage is to enable clients to share messages and resources.
Users can download different information from the internet, like application programs, documents,
pictures, music, movies, information of personal bank accounts and individual taxation information,
etc. Since the internet is growing continuously, many internet companies are set up rapidly all over
the world. Thus, the application of the internet will continue to develop.
6 Electronic communication facilities
Modern communication network can give large area coverage. For example, telephone in
Hong Kong can connect not only Hong Kong island, Kowloon, New Territories and outlying islands
using cables, but also many major cities in the world using electronic communication facilities.
Traditional communication cables use copper wires to transmit electronic signals. For example,
twisted pair (Fig. 19) formed by two copper wires twisted together. The price is low and it is easier
to install.
Fig. 19 Twisted pair
However, copper wires have many disadvantages and limitations e.g. easily influenced by
external magnetic field, lower transmission speed, larger volume, higher cost when connecting
places that are farther apart, etc. Therefore, some of the communication network will use coaxial
cables, optical fibres, microwave and satellite, etc.
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(a) Coaxial cable
Communication cables usually connect computers to other electrical appliances, but the
magnetic field built inside of such electrical appliance may produce interference on the
communication cables. Coaxial cables are not easily interfered by magnetic field. The quality of
the transmitted messages is better and of higher transmission capacity. There is one or more copper
wires, which are wrapped by insulated sheath at the centre of the cable. The outside of the copper
wire is wrapped by nets of metallic wires. This can prevent the copper wires in the center of the
cable from interference. Coaxial cables can be used in local area network. It can also be laid
underground or undersea.
Fig. 20 Coaxial cable
(b) Optical fibre cable
Optical fibres are made up of tiny and transparent plastic fibres (Fig. 21a). Light can be
transmitted from one end to the other inside a bent optical fibre. This is because light undergoes
total internal reflection continuously inside the optical fibres (Fig. 21b). When using optical fibres
to transmit signals, electrical signal is first converted into light signal. Then the light signal can be
transmitted to distant places via optical fibres. When the light signals are received by the
instrument, they are then converted back to electrical signals which are required by telephone or
other electrical appliances. When compared with traditional copper wires, optical fibres will not be
interfered by external magnetic field. They have high transmission speed, and lighter, cheaper and
can transmit various kinds of signals. The data transmission capacity of optical fibres is 1500 times
that of copper cables. Thus, in communication engineering, optical fibres start to replace traditional
copper wires. For example, Hong Kong International Airport, iTV, etc. use optical fibre.
Fig. 21 (a) Optical fibre cable
(b) The phenomenon of total internal reflection
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(c) Microwave
Microwave is a kind of electromagnetic wave. The frequency of microwave ranges from 1
GHz –300 GHz, and sometimes it is treated as a kind of wireless radio wave. When using microwave
for transmitting signals, the electrical signals are first converted to microwave, and then the
microwave is transferred from the transmitter to the remote receiver (Fig. 22) at a straight line at the
speed of light. Since microwave transmission is easily hindered by external objects, the transmitter is
usually set up at places of high altitude. Microwave transmission is also easily influenced by the
distance of transmission. Transmission at long distance will weaken the microwave signal, so usually
repeaters are added along the paths. However, bad weather conditions will sometimes interfere the
microwave signal. Television stations in Hong Kong also use microwave to transmit news or
television programs.
Fig. 22 Microwave receiver
Fig. 23 Satellite
d) Satellite
Since microwave can travel through the atmosphere, satellites are used as microwave
transmission stations. When using satellites to transmit signals, electrical signals are first converted
into microwave signals. And then the transmitters on the ground transmit the signal to the satellite
in the space (Fig. 23). Satellite modulates and amplifies the received signals. It then transmits the
signals to many receivers in different regions at the same time. Satellites can transmit a large
amount of signals without being affected by the external environments. Therefore, many countries
and national organization will use satellite for communication and broadcasting e.g. Asian Satellite
II. However, satellite and transceiver not only require large setup cost and advanced technology,
but also the high cost of using rockets to carry the satellite.
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7 The applications of electronic communication
(a) Fixed network telephone
Telephone allows users at two or more places to communicate by sound. Telephones must first
be connected by telephone lines. The receiver of the telephone will convert the speaker’s voice into
electrical signals by magnetic field effect. The electrical signals are then transmitted to the receiver
of the telephone at the other end. Then the electrical signals will be converted back to sound by the
magnetic effect formed by electrical currents. Since the transmission speed of telephone signals is
very high, the transmission takes a very short time. Telephone users can communicate interactively.
Early telephones were directed by telephone receptionists. The users sent out signals
indicating that they wanted to speak. Then the telephone receptionist would connect the call. For
example, A used the telephone to call B, then the two telephones were connected together via the
connection network. A signal was sent to telephone B at the other end. Then the users of the two
telephones could then talk to each other (Fig. 24a). After the conversation, the telephone
receptionist separated the two telephone lines, so that other users could use the telephones.
Fig. 24 (a) Telephones were directed
by receptionists
(b) Automatic direct network system
As telephone communication became more and more popular, the number of telephones
increased rapidly. It was impossible to use telephone receptionists to direct telephone calls for such
a large amount of telephone usage. Telephone companies started to use automatic direct network
system (Fig. 24b). Nowadays, every telephone user gets a unique telephone number made up of
digits. When a telephone number is dialled, the telephone will send out a corresponding signal to
the directing system. Then the telephone with the number dialled is connected automatically. With
technological development, telephone network starts to use optical fibres to replace traditional
telephone lines which are made up of copper. Many new telephone services start to emerge. For
example, satellite telephones, indoor wireless telephones and telephone message boxes, etc. When
compared to the mobile telephones, traditional telephone network uses fixed electric circuit network.
They are called fixed network telephones.
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(b) Mobile telephone
Mobile telephones use wireless radio waves to transmit information and data (Fig. 2 5a).
Modern mobile telephone system is divided into two types which are analogue and digital.
They use different wireless frequency and transmission format to transmit signals. Analogue
system includes: AMPS, NMTS, TACS, and NAMTS. Digital system includes: GSM, D-AMPS,
CDMA, PDC. The commonly used system in Hong Kong nowadays are GSM and CDMA, etc.
The operating principle of mobile telephone is to divide the district into several smaller regions,
like the cells of a honeycomb, so it is also called honeycomb mobile phones. Telephone network
providers set up wireless transceivers in every region. The wireless signals sent out by the mobile
phone will be received by the nearest receiver, and information of the data and the sound are then
transmitted. Telephone users can then use the mobile phones for communication.
Telephone users can use telephone in every region. But when a telephone is moved from one
region to another region. The telephone network must move the circuit from one region to another
region automatically, otherwise the communication will be terminated. Since most of the telephone
users are concentrated in the urban region, the telephone network provider will establish more
wireless electrical signal transceivers in shopping malls and building of crowded areas in order to
handle the frequent communication.
Fig. 25 (a) Mobile telephone
(b) Wireless radio signal transceiver
(c) Electronic mail
Electronic mail is usually called email for short. Computer users can use electronic mail to
send letter, information and data through the internet. Before using electronic mail, all users must
first register for an email address. For example, [email protected]. The words ctphk.com after @
mean the name of the server. The word info before the word @ means the name of the user in that
computer. Nowadays, many internet service providers will provide free email addresses for
computer users.
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中華科技出版社有限公司
Chinese Technical Press Ltd
陳大文 編輯
Chan Tai Man Editor
1902-1903 New Tech Plaza 34 Tai Yau Street
San Po Kong Kowloon
E-mail : [email protected]
Fig. 26 (a) Software of e-mail
(b) E-mail address on the name card
(d) Office network
Modern offices often use computers. They have local area network to share hardwares, share
or exchange files. Many local area networks use Ethernet (Fig. 27). Ethernet is the most successful
local area network system. It uses coaxial cables to connect several computers to form a bus
network. To send out message, the computer will first detect if there is message transmitting on the
bus. If there is no message on the bus, the computer will send out the message and monitor the bus
to make sure that there will not be any crash of the messages. If there is a crash, the computer will
terminate the transmission of the message. This method can increase the efficiency of the bus
transmission.
Fig. 27 Ethernet
Since the price of coaxial cable is higher, the newly developed Ethernet will use cheaper
traditional copper wire (telephone line) to transmit signals. Computers can be connected to a hub to
form a star network. Under such circumstances, the computer can use the original procedure of
information transmission, but the hub will handle the case of signal crash.
(e) Video conferencing
Video conferencing means the computer users carry out conference with distant users in the form
of sound and images by transmitted electric circuits (e.g. telephone line, the internet, optical fibre
cable, microwave and satellite, etc.) and video imaging devices (e.g. video camera and loudspeaker).
The techniques of video conferencing not only can be applied to commercial communication
and interviews, but also can be used for demonstration of surgical operation, online university
course, etc. Since the participants of a conference must communicate interactively, each participant
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of the video conferencing must be equipped with video imaging devices and communication
network. Besides, the network must be able to transmit electrical signals at a very high speed, so
that there will not be obvious time delay during the communication.
Fig. 28 Illustration of the video conferencing
8 The future of the technology of telecommunication
With the social and economical development, the requirements of different instruments
become higher. Although early vacuum tube radios could give clear sound, the size was big, so
people replaced them by tiny transistor radios. Similarly, technology of electrical communication
also develops at a high speed. New technologies and products are emerged continuously.
(a) The third generation of mobile phone system (3G)
When mobile phones and the internet both develop rapidly, many researchers start to use
mobile phones to read internet homepage and sending/receiving email. Such technology is called
Wireless Application Protocol (WAP). WAP sets the regulations on how to get and send
information using different wireless communication network through the internet. As long as the
mobile phones can support WAP, they can be used to share and use the resources of the internet
through wireless communication network. Such mobile phones are called WAP phones. In the
format of WAP, the language of setting the word and image is Wireless Markup Language (WML).
It is a language similar to HTML.
However, it is not so convenient to use WAP phones nowadays. In order to make it easier to
carry and use, mobile phones become usually small in size. Therefore there are limitations on the
memory storage and size of the screen. There is a limitation on the size of the homepage that can
be read from the internet too. Usually 1.4 kB is the maximum. If the information of a homepage is
too large, partition is necessary. Besides, the transmission speed of the mobiles phones is usually
rather low. For example, the transmission speed of GSM is 9.6 kbps. Compared with usual modem
with 56 kbps, it is much slower.
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In order to increase the transmission speed of wireless transmission, researchers are now
enthusiastically developing the third generation of mobile phone system (3G). This system uses
remote wireless to transmit information on the internet at a speed of 2Mbps. It is about 200 times
faster than the current transmission. It can transmit words, sounds, pictures, photos and videos, etc.
at a very high speed. Therefore, when the technique of 3G is completely utilized, consumers not
only can use the mobile phone to connect the internet continuously, but also enjoy various kinds of
internet service. For example, online bank account, newspapers and television, etc.
(b) Household local area network
With the increasing popularity of personal computers and the internet, Hong Kong starts to
change to an intellectual society. So every member of a family is likely to have a personal computer.
For example, parents may use the computer to work at home, read online newspaper, send and
receive emails and handle online bank account. Children attending schools may use the computers
to read electronic textbooks, self learning CD, gather information from the internet, send and
receive emails, write and edit homework or report, etc. Thus, many families now have two or more
computers and require a local area network to connect every computers and peripheral devices like
a printer and a scanner, etc. together.
The local area network of a family may connect different instruments that can be installed with
IC components. In this way, we can use the computer and the internet to control various kinds of
household appliances. For example, in summer, we can use the WAP phone to switch on the airconditioner through the internet before going home. Then when we reached home, a pre-cooled
environment is available. The development of household local area network will become
increasingly popular.
(c) Short distance wireless communication protocol
If we want to install a local area network indoors, we can use wires to connect the computers,
printers and various appliances in different rooms. Re-wiring is necessary whenever a new device
is added, so it is not convenient. It is more convenient to set the network and transmit the
information if wireless wave is used for the connection.
Researchers nowadays are enthusiastically developing a kind of short distance wireless
communication protocol called bluetooth. It is a kind of generally used short distance wireless
communication protocol. This technique uses frequency range of 2.45GHz (2.402 ~ 2.480 GHz)
that is suitable for sound and data communication. Also, it can connect one device to other devices
simultaneously. Bluetooth technology is suitable for connecting network transceiver, replacing
cables and building personal network.
(i) Connecting network transceiver
Bluetooth can transmit sound, voice and information instantly, so it enables all kind of mobile
devices (e.g. mobile phones) to connect to fixed communication devices (e.g. desktop computer).
The connection process is as easy as pluging and unpluging a socket.
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(ii) Replacing cables
Bluetooth use wireless radio wave to link up various devices. The linkage is immediate and
continuous, and it will not be influenced by ground surface and external objects. Wireless electrical
wave can cover about 30 m, and amplifiers can be used to extend the area coverage to 100m.
Therefore, bluetooth technology can establish household local area network conveniently and
connect various computer devices in different rooms.
(iii) Establishing personal temporary network
When a device that is equipped with bluetooth technology is put into an area which is also
equipped with bluetooth technology, then these two devices can build up connection quickly. Since
the bluetooth technology provides the connection method of one to one or one to many, it can
establish several micro networks which are connected to each other to form a temporary network.
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Exercise
1. Describe a computer network and its functions.
2. http://www.ctphk.com/tf-ts is an internet address. Why is the first part of the address entitled as
http? What is the function of http? Describe how to open a homepage. Illustrate with sketches
for each step.
3. What are the differences between a Local Area Network and a Wide Area Network?
4. Write down some common points in designing a network. And write down the pros and cons of
using a bus network.
5. Write down the function of each of the following network components:
(a) A network interface card
(b) A modem
(c) A hub
(d) A router
6. State the limitations in using microwave communication.
7. Describe the basic principles of using a mobile phone. How does a telephone network provider
solve the problem when a user of mobile phone walks from one district to another?
8. Why is it inconvenient for one to use WAP phone nowadays?
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