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COMMUNICATIONS AND NETWORKS

What is data communication?

This refers to one computer transferring data, instructions and information to another
computer or some other computers. The basic model for data communication consists of:

(a) A sending device that initiates an instruction to transmit data, instruction or

information e.g computer A which sends signals to another computer B.
(b) A communications device that converts data, instructions or information from the
sending device into signals that can be carried by a communications channel e.g.
Modem which converts digital signals into analog signals.
(c) A communications channel or a path over which signals are sent e.g. a standard
telephone line along which the analog signals are sent.
(d) A communications device that receives the signals from the communications channel
and converts them into a form understood by the receiving device e.g. Modem B, which
converts the analog signals back into digital signals.
(e) A receiving device i.e. computer B that accepts the signals from computer A.
(f) Communications software which consists of programs that manage transmission of data,
instruction and information between computers.

Uses of data communications

 Voice mail
 Fax
 E-mail
 BBS
 Instant messaging
 Chart rooms
 Newsgroups
 Internet telephony
 Video conferencing
 Groupware
 Telecommunicating
 Global positioning system

COMMUNICATION DEVICES

These are devices that enable two or more computers to exchange items such as data,
instructions and information with each other. The primary function of a communication
device (e.g a modem) is to convert or format signals so that they become suitable for the
communications channel or a receiving device.
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 Common types of communications devices are;
1. Dial-up modems
2. ISDN and DSL modems
3. Cable Modems
4. Network Interface cards
5. Multiplexer

1. DIAL-UP MODEMS. A modem is a communications device that converts between

analog and digital
signals. The word modem is derived from a combination of words Modulation and
Demodulation
Modulation is to convert digital signals into analog signals
Demodulation is to convert analog signals into digital signals.
A modem connected to a sending computer converts the computers digital signals into analog
signals (i.e. modulation) which can travel over a communications channel e.g. a telephone line.

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 Another modem at the receiving end converts the analog signals back into digital signals (i.e.
demodulation) that can be understood by the receiving computer.

A modem can be external or internal.

External Modem is a standalone device that attaches to a serial port on a computer with
a cable to a telephone outlet with a standard telephone cord.

Internal Modem is an expansion card that can be inserted into an expansion slot on a
computers motherboard; and the modem then attaches to a telephone outlet with a standard
telephone cord.

Most personal computers modems transmit data between 28.8kbps and 56kbps

Most modems today are also fax modems because they send computer prepared documents
as faxes and also receive faxes.

2. ISDN and DSL Modems

ISDN (Integrated Services Digital Network) is a set of standards for digital transmission
of data over a standard telephone line. With ISDN, the same telephone line that could normally
carry only one signal can now carry three or more signals at once using a technique called
Multiplexing.

ISDN requires that both ends of the connection have an ISDN modem. ISDN lines also require
a special ISDN telephone for voice communications.

Advantages of ISDN lines

- Provides faster transfer rates that dial-up
Modems.
- Faster web page downloads and clearer video
conferencing. - Produce very clear voice
conversations.

DSL (Digital Subscribe Lines) provides high speed connections to the internet over a regular
copper telephone line. The user must have a special network card or DSL modem to connect
to digital subscriber line. It is much easier to install and can provide much faster data
transfer rates than ISDN.

ADSL (Asymmetric Digital Subscriber line) is a type of DSL that supports faster transfer
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 rates when receiving data (i.e. downstream rate) than when sending data (i.e. upstream).
ASDL is ideal for internet access because most users download more information from
the internet than they upload.

3. CABLE MODEMS.

A cable modem sends and receives data over the cable television (CATV) network. Cable
modems can transmit data at speeds (500kbps to 2mbps) much faster than dial-up
modems or ISDN. It can also be integrated with a set-to-box to provide faster viewing of
multi-media websites.

4. NETWORK INTERFACE CARDS

A network interface card (NIC) or LAN adapter is an expansion card that enable a
computer or device to connect to a network. The Ethernet card is the most common type
of network card. The transfer rate on Ethernet network can be 10mbps, 100mbps or
1,000mbps.

Fig: Network interface card.

DEVICES USED TO INTERCONNECT NETWORKS

5. MULIPLEXER. A Multiplexer is a communication device that combines two or more

input signals from various devices into a single stream of data and then transmits over a single
transmission medium.

N.B
Transmission Media consists of materials or techniques capable of carrying one or more
signals. Transmission media can be physical or wireless.

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 (a) Physical transmission media use wire, cable and other physical materials to send
communication signals.
(b) Wireless transmission media send communication signals through air or space
using radio, microwave and infrared signals.

A multiplexer increases the efficiency of communications and reduces the need for and the
cost of using separate transmission media. Both the sending end and receiving ends
need a multiplexer for data transmission to occur. At the sending end, a multiplexer
combines separate data transmission into a single data stream and then compress the data
and sends it over a communications channel. At the receiving end , the multiplexer
separates the single stream of data into its original parts.

6. AHUB. A hub is also called a concentrator or multi-station access unit. It is a

device that provides a central point for cables in a network. It allows devices to be
connected to a server.

7. A REPATER. This is a device that accepts a signal from a transmission medium,

amplifies it and retransmits it over a medium. As signals travel over a long distance, it
undergoes a reduction in strength, an occurrence called Attenuation.

Repeaters are used in both copper wire cables carrying electrical signals and in fibre
optics carrying light. Repeaters are also used extensively in broadcasting, where they are
known as translators or booster.

8. BRIDGE. A bridge is a device that connects two LANS using the same protocol,
such as the Ethernet. Bridges are uses to connect similar networks over a wide area
communication links.

Advantages of bridges
- They are self-configuring.
- Primitive bridges are often inexpensive.
- LANs interconnected are separate and physical constraints such as
number of stations, repeaters and segment length don’t apply
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 Disadvantages of bridges
- Bridges are more expensive than repeaters.
- Bridging of different MAC protocols introduces errors.
- Do not limit the scope of broadcasts.
- Because bridges do more than repeaters by viewing MAC address, the
extra processing makes them slower than repeaters.

9. GATEWAY. A gateway is a
combination of hardware and software that connects networks that use different
protocols.

10. ROUTER. A router is an intelligent communication device that sends 9routes)

communication traffic to the appropriate network using the fastest available path.

Fig: A bridge

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 11. SWITCH. A switch is used to store address of every device down each cable
connected to it. By delivering each message only to the connected device it was intended for,
a network switch conserves network bandwidth and offers generally better performance
than a hub. It is more intelligent.

COMMUNICATIONS PROTOCOL
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 A communications protocol is a set of rules and procedures for exchanging information among
computers on a network. Protocols define how communications channel is established, how
information is transmitted and how errors are detected and corrected.

Different kinds of computers can communicate with each other using the same protocol. Two
widely used protocols for LANs are Ethernet and Token ring. The TCP/IP is a set of protocols
widely used on the Internet.

Ethernet is a LAN protocol that allows personal computers to contend for access to the
network. Ethernet was the first industry standard LAN protocol developed by Xerox in 1976.

Advantages of Ethernet
- It is relatively in expensive and easy to maintain and install. Sometimes it is more
efficient and economical to use a bridge to connect two separate LANs instead of creating one
large LAN that combines the two separate LANs.

COMMUNICATIONS CHANNELS

A Communications channel is the communications path between two devices. It is composed

of one or more transmission media

The width of the communications channel is called The Bandwidth. The higher the
bandwidth, the more data and information the channel can transmit.

For analog signals, bandwidth is expressed in hertz (Hz) or cycles per second. Foe digital
signals, bandwidth is expressed in bits per second (bps)

FACTORS AFFECTING TRANSMISSION RATE OF A NETWORK

(a) Transfer rate. Is the speed of transmitting data and information. Transfer rates
are usually expressed in bits per second (bps), kilobytes per second (kbps) or
megabytes per second (mbps). The transfer rate of a transmission medium depends on
the mediums bandwidth and its speed. The following contributes to the transfer rate of
a network.

(i) Network topology. Since data travels in both directions in a bus network, if data
collides, then it as to be sent again, and slow the network down. On the other hand, start
networks have fewer collisions and usually run faster

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 (ii) Capacity of hardware. Hubs, switches and network interface cards have their own
maximum speeds.

(iii) The server. Amount of Ram and the speed of the hard disk.

(iv) Location of software and files. Storing software on the workstation hard disks
reduce network traffic and speed up performance.

Transfer rates of various connection lines to the Internet

Types of lines Transfer rates

Dial up Up to 56kbps
ISDN Up to 128kbps
ADSL 128kbps to 9mbps
Cable TV
T1 1.544mbps
T3 44mbps
ATM 155mbps to 622mbps

(a) A dial up Line. This is a temporary connection that uses one or more analog telephone
lines for communication. Using a dial-up line to transmit data is similar to using the
telephone to make a call.

Advantages of dial-up lines

- It cost no more than making a regular telephone call.
- Computers at any two locations can establish a connection using modems
and the telephone network.
Disadvantages
-The user cannot control the quality of the connection because switching the telep
company’s switching office randomly selects the line for connection.

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 (b) ISDN (Integrated services Digital Network) is a set of standards for digital
transmission of data over standard copper telephone lines. It requires both ends of the
connection to have an ISDN Modem.

(c) DSL (Digital subscriber lines) provides high speed connections to the internet over a
regular copper telephone line

(d) ADSL (Asymmetric Digital Subscriber line) is a type of DSL that supports faster
transfer rates when receiving data (i.e. downstream rate) than when sending data
(i.e. upstream rate)

(e) Cable TV network also provides high speed internet connections from users equipped
with cable modem.

(f) A T-carrier line is a digital line that carries multiple signals over a single communication
line using the multiplexing technique. T1 line can carry 24 separate signals at a
transfer rate of 64kbps each for a transmission rate of 24mbps. A t3 can carry 672
individual signals at a transmission rate of 43mbps. The internet backbone also use
T-3 lines

Advantages
 T-carrier lines provide very fast transfer rates.

Disadvantages
 T-carrier lines are so expensive that only medium to large companies can afford the
investment.

(g) ATM (Asynchronous Transfer mode). This is a dedicated connection switching

technology that organizes digital data into 53 bytes’ cell units and transmits them over
a physical medium using digital signal technology.

TRANSFER RATE
This is the speed of transmitting data and information usually expressed in bits per
second (bps) and kilobytes per second (kbps) or megabits per second (mbps)

N.B
(a) BASEBAND TRANSMISSION. This transmits only one signal at a time.
(b) BROADBAND TRANSMISSION. This can transmit multiple signals
simultaneously. They transmit signals at a much faster speed. Two widespread
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 applications of broadband transmission are; -Digital subscriber lines
-Cable television networks.
(c) SIMPLEX TRANSMISSION. In simplex transmission, data flow in one direction from
the sending device to the receiving device. It is used only when the sending device does
not require a response from the receiving device. Examples include:
 Security systems
 Fire alarms
 Temperature sensors that contain a sensor Printing systems, pagers.

(d) HALF DUPLEX TRANSMISSION. In half duplex transmission, data can flow in either
direction, from the sending device to the receiving device and back but only in one
direction at a time. Examples include:
 Fax machines
 Radio calls
 Credit card verification systems.
 Automatic teller machines

FULL DUPLEX TRANSMISSION. In full duplex transmission, data can flow in both
directions at the same time. A regular telephone line supports full duplex
transmission so that both parties can talk at the same time. It is used for most
interactive computer applications and for computer-to-computer data transmission
i.e. a regular telephone line.

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 A NETWORK

A network is a collection computers and devices connected together via communication

devices and media. Communication devices enable two or more computers to exchange
items such as data, instructions and information with each other.

The primary function of a communication device (e.g. a modem) is to convert signals so

that they become suitable for the communications channel or a receiving device.

A network can relatively small or extensively large.

A LOCAL AREA NETWORK (LAN)

This is a network that connects computers in a limited geographical area such as a

school computer laboratory, an office or a group of closely positioned buildings.

Each computer or a device on the network is called a node. The nodes are connected to the
LAN via cables.

A wireless LAN is a local area network that uses no physical wires but wireless media
such as radio waves.
A network operating system is the system software that organizes and coordinates the
activities of a LAN.

KINDS OF A LAN
Two kinds of LAN are peer to peer and client/server network.

(a) PEER-TO-PEER NETWORK

- Each computer on a peer-to-peer network can share hardware, data or
information located on any other computer on the network.
- Each computers stores files on its own storage devices.
- Each computer on the network contains both the network operating
system and application software.
- A peer-to-peer network is a simple, inexpensive network that generally
connects less than 10 computers together.

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 - Ideal for home and small business.

Fig: Illustration of a peer-to-peer network

Advantages of peer-to-peer network

- Less expensive to implement.
- Does not require additional specialized network
administration software. - Does not require a dedicated
network administrator.
Disadvantages
- Does not scale well to large networks and administration becomes
unmanageable. - Each user must be trained to perform administrative
tasks.
- Less secure.
- All machines sharing resources negatively impact the performance.

(b) CLIENT/SERVER NETWORK

A client/server network has one or more computers acting as a server while the
other computers (i.e clients) on the network can request services from the server.

A client/server network typically provides an efficient means to connect 10 or more

computers together.

Most client/server networks have a network administrator who is in charge of the

network.

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 Fig: Illustration of Client server network

Advantages of client/server
network - Provides for better security.
- Easier to administer when the network is large because administration is
centralized. - All data can be backed up on one central location.

Disadvantages
- Requires expensive specialized network administrative and operational
software.
- Requires expensive, more powerful hardware from the server machine.
- Requires a professional administrator.
- Has a single point of failure, User data is un available if the server is
down.

A WIDE AREA NETWORK (WAN)

This is a network that covers a large geographical area such as one that connects the
district offices of an enterprise across the country or across several countries in the world.
WANS are designed to:
- Operate over a large geographical area
- Allow access over a serial interfaces operating at a slow speed.
- Provide full time and part-time connectivity.
- Connect devices separated over wide, even global areas.

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 world‟s largest WA.N

ADVANTAGES OF USING A NETWORT INTERNET

(a) Facilitates communication because people can communicate efficiently and easily
via e-mail, instant messaging, chat rooms, telephony and video conferencing.
(b) Reduce costs by sharing hardware (e.g. a printer) and software (e.g. using a
network version or site license of a program).
(c) Sharing data and information stored on other computers on the network. (d)Allow
tight control over who has access to what data.

DISADAVANTAGES OF USING A NETWORK

(a) The hardware, software and expertise required to set up a network can be
expensive.
(b) Networks are vulnerable security problems.
(c) If the server fails to work, the complete network may also fail to work.

COMPONENTS OF A LAN
Local area networks are made up of several standard components.

(a) Connecting or cabling system. LANs do not use a telephone network, instead they use
some other cabling or connection system either wired or wireless. Wired connection
may be twisted pair wiring, coaxial or fibre optic cable. Wired connection may be
infrared or radio wave transmission. Wireless network are

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 especially useful if computers are portable and moved often. However, they are
subject to interference.

(b) Microcomputers with interface cards. Two or more computers are required along
with network interface cards. A network card which is inserted into expansion slot
in a micro-computer enable the computer to send a nd receive messages on the LAN.
Now days, newer computers come with network cards already embedded in the
motherboard.
(c) Network operating systems. The network operating system software manages the
activity of the network. Depending on the type of a network, the operating system may
be stored on a file server or on each microcomputer on the network. Examples of
network operating systems include:
– Novell’s NetWare
– Windows NT etc.

(d) Other shared devices. Printers fax machine, scanners, storage devices and peripherals
may be added to the network as necessary and shared by all users.

(e) Bridges and gateways. A LAN many stand-alone but it may also connect to other
networks either similar or different in technology. Hardware and software devices are
used as interfaces to make these connections.

A Bridge is an interface that enables similar networks to communicate.

A gateway is an interface that enables dissimilar networks to communicate such as a
LAN with a WAN.

NETWORK TOPOLOGY

A network topology is the configuration or physical arrangement of the devices in a

communications network. The commonly used network topologies are;
• Bus
• Ring
• Star

(a) BUS TOPOLOGY. This is a network that consists of a single central cable that connects
all computers and devices together. The physical cable that connects the computers
and other devices is known as the bus or the backbone. Data, instructions and
information in a bus can be transmitted in both directions.

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 Fig: Illustration of a bus topology

Advantages of a bus network - Inexpensive and easy to install.

- Computers and devices can be attached and detached any
point on the bus without disturbing the rest of the network.
- Failure one device usually does not affect the rest of the bus
network. - Requires less cable length.
Disadvantages
- If the bus fails to work itself, the complete network remains inoperative.
- If many computers are attached, the amount of data flowing along the
cable increases, data collision occur and the network slows down

(b) RING TOPOLOGY. This consists of a cable forming a closed ring or loop, with all
the computers and devices in a network.
Data transmitted on a ring network travels from device to device around the entire
ring in one direction only. If a device on a ring network fails, all devices before the
failed device are unaffected but those after the failed device cannot function.

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 Advantages of ring topology
- Can span a larger distance than a bus.
- No collision occurs (one direction only) so that the speed of data is high.
Disadvantages of ring topology
- If the cable fails, the whole network goes down.
- More difficult to install and troubleshoot the ring.
- Because all stations are wired together, to add a station, you must shut
down the network temporarily.

(c) STAR TOPOLOGY. Star networks are one of the most common computer networks.
In this all computers and devices connect to a central computer thus forming a star. The
central computer that provides a connection point for devices in the network is called
the HUB or Switch.

Advantages of a Star network - Easy to install and maintain.

- Computers and devices can be added to or removed from the network with
little or no disruption to the network.
- It is reliable because each device connects directly to the hub. If one
device fails, only that device is affected
- Good performance. Data packets are sent quickly as they do not have to
travel through any unnecessary nodes.

Disadvantages of a star network

- If a hub fails, the entire network is inoperable.
- Lots of cable required so the installation cost is
expensive. - If the central computer fails, the
entire network fails.

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 Networks can use a combination of these topologies. Hybrid networks are a combination
of star, ring and bus networks. They include:

• Extended star topology

• Hierarchical Topology
• Mesh topology

For example, a small college campus might use a bus network to connect buildings and
star and ring network with in certain buildings.

N.B
FDDI (Fibre Distributed data Interface) is a newer and higher speed network capable of
transmitting 100megabits per second. A FDDI network uses fibre optic cable with an
adaptation or ring topology. The FDDI network is being used for such high speed-tech
purpose as electronic imaging, high-resolution graphics and digital video.

Considerations When Choosing a Topology:

• Money. A linear bus network may be the least expensive way to install a
network; you do not have to purchase concentrators.
• Length of cable needed. The linear bus network uses shorter lengths of
cable.
• Future growth. With a star topology, expanding a network is easily done by
adding another concentrator.
• Cable type. The most common cable in schools is unshielded twisted pair,
which is most often used with star topologies.

FACTORS AFFECTING DATA TRANSMISSION

(a) Transmission rate; higher frequency, wider bandwidth, more data.

Higher frequency, wider bandwidth, more data. The amount of data that can be
transmitted on a channel depends on the wave frequency-cycle of waves per second.
Frequency is expressed in hertz. As mentioned earlier, bandwidth is the difference
between highest and lowest frequencies. Data may be sent not just on one frequency
but on several frequencies within a particular bandwidth. The more frequencies it has,
the more data that can be send through that channel.

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 (b) Line configuration: Point to point and multipoint. There are two ways of connecting
communication lines;
Point to point directly connects the sending and receiving devices such as a
terminal with a central computer. This arrangement is appropriate for private line
whose sole purpose is to keep data secure while transmitting it from one device to
another.

A multipoint line is a single line that interconnects several communication devices

to one computer. Often a multipoint line, only one communication device, such as a
terminal, can transmit at any given time.

(c) Serial and parallel transmission. Data is transmitted in two ways; serially and in
parallel.
In serial data transmission, bits are transmitted sequentially, one after another.
Serial transmission in the way most data flows over a twisted-pair telephone line. It
is found in communication lines, Modems and mice.
In parallel data transmission, bits are transmitted through separate lines
simultaneously. The arrangement resembles cars moving in separate lanes at the
same speed on a multilane freeway. Parallel lines move faster than serial lines do
e.g to transmit data from a computer’s CPU to a printer.

(d) Direction of transmission flows; Simplex, half duplex and full duplex
In simplex, data can travel in only one direction e.g traditional TV antenna. There is
no return signal.

In half duplex, data travels in both directions but only in one direction at a time. It
is seen with police and marine radios in which both parties must take turns talking.
It is also a common transmission method with computers.

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 In full duplex, data is transmitted back and forth at the same time. An example is
two people on a telephone talking and listening simultaneously. Full duplex is used
frequently between computers in communication system.

(e) Transmission mode; asynchronous versus synchronous

(f)Packet switching: getting more data on the network.

A packet is fixed-length block of data for transmission. The packet also contains
instructions about destination of the packet. Packet switching is a technique for
dividing electronic messages into packets for transmission over a network to their
destination through the most expedient route. The benefit of packet switching is
that it can handle high volume of traffic in a network. It also allows more users to share
a network.

(g)Protocols; the rules of data communication

A protocol or a communication protocol is a set of conventions governing the exchange
of data between hardware and or software components in a communications network.
The protocol in your communications software will specify how receiving devices will
acknowledge sending devices a matter called handshaking. Protocols will also specify
the type of electrical connections used, the timing of message exchange, error-detection
technique and so on.

COMMUNICATIONS PROTOCOL

A Communications protocol is a set of rules and procedures for exchanging information

among computers on a network.

Protocols define how the communication channel is established, how information is

transmitted and how errors are detected and corrected. The width of the communications
channel is called Bandwidth. The higher the bandwidth, the more data and information
the channel can transmit.

Different kinds of computers can communicate with each other using the same protocol.

N.B: Without protocols, communication wouldn’t have been possible

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 PROTOCOLS USED IN COMMUNICATION

(a) TCP (Transmission control Protocol). TCP manages the transmission of data by
breaking it into packets. It then provides routing information for sending the packets
along the fastest available path to the recipient’s computer and then reassembles the
data at the receiving end.

(b) Ethernet. Ethernet is a LAN that allows computers to contend for access to the network.
It uses a coaxial cable that carries radio frequency signals between computers at a rate
of 10megabytes per second.

(c) Token ring. Token ring is a computer LAN arbitration scheme in which conflicts
inn transmission of messages are avoided by granting of tokens, which give permission
to send data to other computers.

(d) IP (Internet Protocol). Internet protocol is a method by which data is transmitted from
one computer to another over the internet. It employs the use of a four-part numerical
address which every computer has to send information e.g 326.478.570.888

(e) HTTP (Hyper Text Transfer Protocol). HTTP is used for information exchange on the
World Wide Web (WWW). It defines how messages are requested, formatted and
transmitted over the Internet and what actions an HTTP server (browser) should
take response on various messages.

(f) FTP (File transfer protocol). File transfer protocol is a communication protocol that
sends data and files and folders over the Internet.

(g) TELNET. Telnet provides a fairly general bi-directional 8 bit oriented communication
facility. Its primary goal is to allow a standard method of interfacing terminal devices
to each other.

(h) IPX (Inter-network Packet Exchange). IPX is a networking protocol that

interconnects networks that
use Novell’s network clients and servers.

(i) SPX (Sequenced Packet Exchange). SPX is the protocol for handling packet
sequencing in Novell Netware network. It prepares the sequence of packets that the
message is divided into and manages the reassembling or received packets.

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 (j) ATM (Asynchronous Transfer Mode). ATM is a dedicated connection switching
technology that organizes digital data into 53 bytes’ cell units and transmits them over
a physical medium using digital signal technology.

NETWORK OPERATING SYSTEMS

A Network operating system is the system software that organizes and coordinates the
activities on a local area network.

Tasks performed by a Network Operating system - Administration of system

users.
- System maintenance tasks such as back up.
- File management tasks.
- Prioritizing print jobs on the network.
- Monitoring security on network resources.

Operating systems that supports the Network

Operating system Requires separate OS Network type

IBM OS/2 Wrap - Client/server
Linux - Client/server
Microsoft Windows NT, - Peer-to-peer /
98,ME Client/server
Novell Netware Dos Client/server
Sparta Com LAN Tastic Any Pc OS Peer-to-peer
Sun Solaris - Client/server
Unix - Client/server

COMMUNICATIONS SOFTWARE
This consists of programs that help to establish a connection to another computer or network,
and manage the transmission of data, instruction and information between computers and
other devices.
Communication software usually includes one or more of the following features.
(a) Dialing feature that allows a user to store, review, select and dial telephone
numbers to connect to another computer.
(b) File transfer feature that allows a user to store, review, select and dial telephone
numbers to connect to another computer.
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 (c) Terminal emulation feature that allows a personal computer to act as a specific type
of terminal so that the user can connect to and access data and resources on a mini
computer or mainframe.
(d) Internet access feature that allows a user to use the computer to connect to the
internet to send e-mail, participate in chat rooms, visit world wide web sites and so on.
Software related to communications include:
 E-mail
 Web browser
 Chat room software
 News recorder
 Instant messenger
 Groupware
 Video conferencing software
(a) E-mail or electronic mail is the transmission of messages via a computer network
such as a local area network or the Internet. The message can be simple text or can
include an attachment such as a word processing document, a graphical image, an
audio clip or a video clip. E-mail software creates, sends, receives, forwards, stores,
prints and deletes e-mail addresses.

(b) Web browser allows users to access and view web pages on the Internet. Most web
browsers allow the use of other internet services such as e-mail and chat rooms. Two
popular web browsers are Microsoft Internet explorer and Netscape navigator.

(c) A chat room is a location on an internet server that permits users to chat with each other
by typing lines of text on the computer. Some chat rooms support video and video chats.

(d) A newsgroup also called a discussion is an on line area where users conduct written
discussions about a particular subject. To participate in a discussion, a user sends a
message to the newsgroups and other users in the newsgroup read and reply the
message. A news reader program is required to participate in a newsgroup, and most
web browsers include a newsreader.

(e) Instant messaging is a real time communication service that notifies a user when one or
more people are on line and then allows the user to exchange messages of files with
them.

(f) Groupware is a software application that helps groups of people work together and share
information over a network.

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 (g) A Videoconference is a meeting between two or more geographically separated people
who use a network or the Internet to transmit audio and video data. A
videoconference conducted over the Internet using web browsers and web servers to
deliver the service is called a Web Conference.

THE TELEPHONE NETWORK

The public switched telephone network (PSTN) is the worldwide telephone system that
handles voice-oriented telephone calls. The telephone network is originally built to handle
voice communications. However, it is also an integral part of the computer communication
today.

Data, instructions and information can be sent over the telephone network using dial-up lines
or dedicated lines.

A dial-up line is a temporary connection that uses one or more analog telephone lines for
communications. Using a dial-up line to transmit data is similar to using a telephone to make
a call.
Advantages of a dial-up line
- It costs no more than making a regular telephone call.
- Computers at any two locations can establish a connection using modems
and the telephone network.
Disadvantages
-The user cannot control the quality of the connection because the telephone
company’s switching office randomly selects the line for connection.

A dedicated line is a permanent connection between two communication

devices. Advantages
-The quality and consistency of the connection is better than a dial-up line
because dedicated lines provide a constant connection.

A leased line is dedicated line leased from a telephone or communications service company.
Popular types of dedicated lines are;
• ISDN lines
• Digital Subscriber Lines
• Cable TV lines
• T-carrier lines
• ATM

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 Advantages of a telephone
- Immediate contact is available.
- Tone of voice helps communications
Disadvantages of a telephone
- It may take a long time to get someone on the phone.
- A call is successful only when the person to contact
is present.
- Time zone problems between different countries.

USES OF DATA COMMUNICATION

Uses of data communication include;

1. VOICE MAIL. Voice mail functions like answering machine and allows a caller to leave
a voice message, which is stored in a voice mailbox for the called party. A called party
can listen to the message, add comments to the message and reply or forward a message to
another voice mailbox in the mail system.

2. FAX. A facsimile (fax) machine is a device that transmits and receives documents
over telephone lines. Documents sent or received with a fax machine are known as Faxes.
Fax capability can also be added to the computer using a fax modem.

3. E-MAIL. E-mail or electronic mail is the transmission of messages via a computer

network such as a local area network or the Internet. E-mail software creates, sends, receives,
forwards, stores, prints and deletes email

Popular E-mail software

 Microsoft outlook express
 Endora

An e-mail address. This is a combination of a user name and a domain name that
identifies one specific user who sends or receives e-mail.

A user name or User ID. Is a unique combination of characters that identifies one specific
user e.g for the email address katumbarich@yahoo.com katumbarich is a user name, and
yahoo.com is the domain name.

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 Most e-mail programs allow users to create an address book which contains a list of
names and e-mail addresses. Most ISP’s provide their users with mail box which stores their
e-mails on a special server called a mail server.

When an e-mail arrives at the recipient’s mail server, the e-mail transfer to a POP or
POP3 server until the recipient retrieves it with his or her e-mail software.
A domain name: (e.g. www.nkpublishinghouse.com) is the text version of an IP address
e.g. (216.200.47.93). The components of a domain name are also separated by periods.

Every domain name contains a top level domain (TLD) abbreviation that identifies the
type of organization that is associated with the domain.

TLD Abbreviations Type of Domain

com Commercial business and
organizations,
companies
org Non-profit organization
net Network providers
edu Educational institutions
gov Government agencies
mil Military organisations

The Internet Corporation for assigned names and Numbers (ICANN) is responsible for
assigning and controlling TLDs
For international websites outside the United States, the domain name also includes the
country code.

Country code Country name

hk Hong Kong
cn China
tw Taiwan
uk United Kingdom
au Australia
jp Japan
ug Uganda
ke Kenya
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 The Domain name system (DNS) is the system on the internet that stores the domain names
and their corresponding IP addresses.

The DNS server translates the domain name into its associated IP address, so that data
can route to the correct computer.

TERMS IN RELATION TO E-MAIL

(a) Subject: The name of the e-mail message.

(b) To: carries the address of the recipient.
(c) cc: Enables copies of the E-mail message to be sent to the
third party while acknowledging other recipients.
(d) Bcc: Enables copies of the e-mail message to be sent to the third party without
acknowledging any other recipients (if present)

ADVANTAGES OF E-MAIL OVER ORDINARY MAIL

E-mail has many advantages over both ordinary mail and the telephone for example;
(a) A message can be sent anywhere in the world at the price of a call without having
to leave your desk.
(b) Speed of delivery. The message will arrive in few minutes and can be picked up
the next time recipient looks at their e-mail.
(c) Ability to send multiple recipients. The message can be sent simultaneously to a group
of people.
(d) It is easy to send a reply to an e-mail as soon as it is received using a „reply‟ button.
(e)Large files such as spread sheets and graphics can be sent as attachments.
(f) An e-mail address is universal and ordinary mail; one has to change addresses
wherever he or she is located.
(g) Assurance of whether the mail has been sent.
(h) No use of stamps.
(i) Convenient when retrieving and delivering.

3. BBS. A bulletin board system (BBS) is a computer that maintains a centralized

collection of electronic messages. The use of a BBS is declining because the Internet can
be used to access many of the same services.
4. GroupWare. This is a software application that helps groups of people work
together and share information over a network. Groupware enables members of the
workgroup to communicate, manage projects, schedule meetings and make group discussions.

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 5. Telecommunicating. Telecommunicating is a work arrangement so that employees
may work away from the standard workplace of a company, but communicate with the
office using some kinds of communication technology.

Advantages of telecommunicating
- Reduces the time and expenses from traveling to and from work.
- Allow a flexible work schedule for employees.
- Provide a convenient, comfortable work environment for disables
employees or those recovering from injuries or illness.
- Reduces air pollution caused by vehicles driven to and from work.
- Employees reduce costs due to less office space and furniture is required.
Disadvantages
- Reduces human face-to-face interaction among working staff.
- Data security may be jeopardized.
- Work has to stop if any component of the communications system fails to
work. - Leisure time at home may be replaced by work.

6. Global Positioning system. A Global positioning system (GPS) consists of one or more
earth-based receivers that accept and analyze signals sent by satellites in order to determine
the receiver’s geographical location.

Uses of GPS
- To locate a person or an object.
- Ascertain the best route between two points.
- Monitor the movement of a person or object. - Create a map.
Many cars and ships also use GPS to provide directions to a destination and weather
information.

INTERNET
The internet is a worldwide collection of networks linked together. The internet is a
largest wide area network in the world.
The internet has its roots in networking project called the ARPANET that became
functional in 1969 started by the Pentagon’s Advanced Research Agency (ARPA)

The goal of the project was to build a network that;

1. Allowed scientists at different locations to share information and work
together on military and scientific projects and
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 2. Could function even if part of the network were disabled or destroyed by a
disaster such as a nuclear attack.
The ARPANET became functional in September 1969, linking Scientific and academic
researcher in the United States.

In 1986, the National Science Foundation (NSF) connected its huge network of five
supercomputer centers called NSFnet to the ARPANET and this configuration of complex
networks and hosts became known as the Internet.

The NSFnet served as the major backbone on the internet until 1995 and then returned
its status to a research network.

Today a variety of corporations provide networks to handle the internet traffic. These
networks along with telephone companies, cable and satellite companies and the
governments, all contribute towards the internal structure of internet.

The internet remains a public cooperative and independent network. However, the World
Wide Web Consortium (W3C) is a group that overseas research and sets standards and
guidelines for many areas on the internet.

People have different reasons for connecting to the internet and most of them connect to the
internet through an Internet Service Provider.

FUNCTIONS OF THE INTERNET

(a) Communicate and collaborate. The exchange of electronic messages with business
associates and friends (sending and receiving electronic mail messages), transmit
documents and data and participate in electronic conference e.g. via yahoo messenger.

(b) Access information. With the internet, you can browse a lot of information through
website search e.g. www.google.ug. A variety of information regarding academics,
sports and entertainments is available on the internet.

(c) Downloading programs. With the use of internet, you can download various programs
and files to your personal disk from other computers elsewhere in the world.
(d) Participate in discussion. You can conduct voice transmission and join discussions
with people and friends from all over the world.

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 (e) Supply information. This involves the transfer of computer files, programs,
animations, graphics, sound, video to other computers via the internet.

(f) Find entertainments. A variety of interactive video games, short video clips, sound
and music clips are all available on the internet.

(g) Reading news and listening to broadcasts e.g. from BBC, Monitor, Bukedde among
others. (h)General information about a subject.
(i) Do research and take online courses

CONNECTING TO THE INTERNET

There are three requirements
- An access device e.g. a personal computer with a modem.
- A physical connection e.g. a telephone line.
- An internet service provider (ISP) The ISP offers options in three
categories;
 Use of a telephone line
 Use of a server
 Use of a protocol

AN INTERNET SERVICE PROVIDER

An internet service provider (ISP) is a company that supplies connections to the internet
usually for a monthly fee. Users may connect to their ISP through a LAN or through dial-
up-access. A dial-up access is a slow speed technology.

FACTORS CONSIDERED WHEN CHOOSING AN INTERNET SERVICE PROVIDER

(a) Services offered. When choosing an ISP, one should ensure that the ISP supports
the services you want to access on the internet. Some ISPs do not support all
services available on the internet.

(b) Costs for internet access. It is important to ask the ISP for the detailed fee
structure. Some ISPs charge depending on the services accessed, amount of time spend
on the internet, standard fee per a given period say a month etc.… Most ISPs offer
a flat rate fee for a certain number of hours.

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 (c) Type of communication offered. This refers to the modes by which your computer
connects to the ISP for the internet access. Some ISPs offer some of the methods an not
others. Find out whether the mode of connection you are interested in is supported by
the ISP.

(d) Technical support. It is good to know how much (if nay) support you can expect from
the ISP. Find out whether it is free or charged, whether it is available on phone and
for how long. Some local ISPs send a service technician to your house when you have
a problem installing software, dialing into their systems etc.…

(e) Security. Security is very important to protect your activities on your system. I you do
not want someone to access your e-mail box, ask for the ISP how they manage security
and whether they support any kind of encryption, firewalls, virus guards etc.….

(f) Software. If you are using an online service provider, you may need special software to
access their systems. Although this software is free, you need to learn them. Some
systems don’t work well with common application packages. Check with the ISP and
find out whether your applications work.
EXAMPLES OF ISPs
- Infocom
- Utl
- Mtn
- Airtel
The internet uses an IP address system to send data to a computer at a specific
destination.

An IP (Internet Protocol) address is a number that uniquely identifies each computer or

device connected to the internet. Each IP address consists of four groups of umbers, each
separated by a period (e.g. 216.200.47.93)

The number in each group is between 255. In general, the first portion of each IP address
identifies the network and the last portion identifies the specific computer.

INTRANET
Intranet is a small version of the internet used within an organization. Intranet uses
TCP/IP protocols, supports multimedia web pages and is accessible via a web browser.
Intranet generally makes company information accessible to employees and facilitates
working in groups.

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 An intranet that extends to authorize users outside the company is called an Extranet.

To prevent an authorized access to data and information, an internet or extranet is often

protected by a Firewall. A Firewall is a general term that refers to both hardware and
software used to restrict access to data and information on a network.

A HOME NETWORK
A home network connects all computers and devices together at home or in a home office.
Common types of networks are;
- Ethernet network
- Home PLC
- Phone line network
- Home RF network

(a) Ethernet. This is a LAN protocol that allows personal computers to contend for
access to the network.

(b) A home PLC (Power line cable) This is the network that uses the same lines that
bring electricity and power into the house. The advantage is that; it requires no
additional wiring because data simply transmits through existing power lines in the
house.

(c) A phone line network. This a network that uses existing telephone lines in a house.
The phone line network does not interfere with voice and data transmissions on the
telephone lines (i.e. the ser can talk on the telephone and use the same line to
connect to the internet.

(d) A home RF (Radio frequency) network. This uses radio waves, rather than cables
to transmit data.

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 Advantages of a home network
- All computers in the house can be connected to the internet at
the same time.
- Each computer can access files and programs on the computers
in the house. - All computers can share peripherals such as
scanner or a printer.

UNDESIRBALE BEHAVIOURS INVOLVING THE INTERNET

- Spam (Containing un solicited messages) - Pirating (Illegal access to
other user’s messages) - Watching immoral websites.
- Illicit material.
- Abusive and threatening messages.
- Hacking and cracking.
- Impersonation.
THE WORLD WIDE WEB

The World Wide Web (WWW) also called the web consists of a worldwide collection of
electronic documents. Each of these documents on the web is called a Web Page.

A web page can contain text, graphics, animations, audio (i.e. multi-media elements), as
well as built-in connections called hyper links to other documents.

A HYPERLINK also called a link is a built-in connection to another related web page or
part of a web page. A link can be a word, a phrase or an image. The shape of the pointer usually
changes to a small hand with a pointing index finger when it is pointed on a link.
A HOME PAGE. Is a starting page or a table of contents for a website and normally has a
name called index.htm or index html.

A WEBSITE. This is a collection of related web pages.

(TYPES OF WEB SITES)
Affiliate
Affiliate agency
Achieve site
Attack site
Blog (web log)
Bland building site
Celebrity web site
Click to donate site

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Community site
A WEB BROWSER. This is a software program used to access and view
web pages. Examples of web browsers include;
 Internet explore
 Netscape navigator
 Mozilla fire fox
 Konquerer
 Google chrome
 Arora
 Dillo
 Lynx
 Amanya
 Kazekhase
 Netpostive
 Flock
 Avant
 Lobo
 K meleon
 Safari
 Opera
 Lunar scape
 Planet web
 QNX voyager
Today’s browsers also support push technology in which web based
content is downloaded automatically to the computer at regular
intervals or whenever the site is updated.

COMPUTER SECURITY RISKS

A computer security risk is any event or action that could cause a loss or
damage to computer hardware, software, data or information. Some
breeches to computer security are accidental, but some are planned. Some
of the more common computer security risks include;
Computer virus
An authorized access and use of computer systems.
Hardware theft and software theft. Information theft and information privacy
System failure.

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