UNIT TWO

COMPUTER NETWORK
2.1 Definition of Network
• A network is a connection of two or more computers that are
linked together in order to share resources (such as printers,
files and disks) or allow electronic
communications.
 Using Bluetooth application in your mobile phone to share
files is an example of a network. Sometimes, the
 Internet is called the largest global network with multiple
computers and other network devices, which are all,
connected.
• For example laptop, tablet, mobile phone and the television
are connected to the central network device.
• The central network device is, in turn, connected with a
global network through an internet service provider (ISP)
company such as Ethiotelecom.
2.2 Fundamental Elements of Network
• Networks are comprised of four basic elements: hardware,
network software, protocols and connection medium.
• The backbone of any is the hardware that runs it. network
hardware includes end devices and intermediary devices.
• Network software is also a foundational element for any
network. This type of software helps to manage connected
end devices and services the network provides.
• Protocols are set of rules to facilitate electronic
communication across connected device.
• Transmission medium which can be wired or wireless,
caries message between end devices
 2.2.1 End Devices
• End devices, which are also called hosts, are devices used to send or
receive data over the network. The sending device is called a sender
and the receiving one is a receiver.
• Some examples of end devices are:
 ƒComputers (such as desktops, laptops, file servers and web servers
etc.)
 ƒNetwork printers
 ƒSecurity cameras
 ƒMobile handheld devices.
2.2.2 Intermediary devices
 Intermediary devices interconnect end devices.
 Intermediary devices connect the individual hosts to the network and
also can connect multiple individual networks to form an internetwork.
 Intermediary device includes network cards, routers or network
switches, wireless access point (WAP) and repeaters. Without these
hardware devices, end devices have no means of accessing a network.
 a. Network Interface Card (NIC)
 Network Interface Card (NIC) is a computer hardware component that connects a
computer to a computer network.
 NIC has a slot to plug-in a cable connection with a network.
b. Repeater
 the electronic signal they carry will become weak after traveling a long distance.
 Repeater enables a network segment to extend the coverage to reach beyond its
inherent distance limitation by refreshing or generating the weak network signal.
c. Switch
 A switch is a device that interconnects various devices such as computers, printers and
servers in a small business network
 Switch is more intelligent device than hub as it can segment a computer network into
smaller parts.
 In addition, switch forwards packets to specific destination after learning the network
topology.
 A hub is unintelligent device which broadcasts all received packets to all computers
connected to it except the sender.
 d. Router
 A router is such an intelligent device which operates in determination of
pathways for electronic messages in networks.
 A router, as its name suggests, works with routing or finding a route
through a network.
 The main objective of router is to connect dissimilar and different
networks simultaneously.
 The two switches are connected to each other through the router.
e. Wireless Access Points
 A wireless access point (WAP) is an intermediary device in a network
that connects various types of wireless communication devices with
wireless networks.
 The connectivity is made possible through Bluetooth and Wi-Fi
technologies.
•
• 2.2.3 Communication Protocol
 In networking, a protocol is a set of rules that governs data
communications.
 In order for different network hardware to interact with the
network, they should follow the same rules called protocols.
It is software that instructs network devices on how to
connect to the network and how to interact with one another.
 Internet Protocol (IP) is one of the important
communication protocols and used for addressing network
devices and forwarding data from one network to another.
• 2.2.4 Connection Media
 Without physical connections(wired or wireless), a network
cannot function.
 The connection media are the media which are used to carry
the message from sender to receiver.
 We have two types of communication medium: wired and
wireless
• We have two types of communication medium: wired and
wireless.
i. Wired medium: It is also called guided medium.
 It is a cable that connects end devices. Copper and fiber optic
cables are examples of wired medium.
 The most common copper cable used in networks today is
unshielded twisted-pair cable (UTP), which uses electric signal
to transmit message for a maximum distance of 100 meters.
 Fiber optic cable uses light to transmit signal at faster speed
and longer distance than copper cable.
ii. Wireless Medium: It is also referred to as unguided media or
unbounded transmission media.
It is used to communicate information through the air, water or
vacuum, e.g. radio Waves, micro waves, infrared waves and
satellite communications.
• 2.3 Types of Networks
• There are different types of network classified based
on the following four categories:
ƒ Network media
ƒ Size of the network or geographical coverage of
the network
ƒ Topology
ƒ Resource security and access
• 2.3.1 Types of Network Based on Connection
Medium
• Based on connection medium, computer networks are
classified into wired and wireless networks.
• Wired Network
 Wired networks, also called Ethernet networks, are the most
common type of local area network (LAN) technology.
 A wired network is simply a collection of two or more
computers, printers, and other devices linked by Ethernet
cables.
Figure 2.9 Wired
network
• Wireless Network
• Wireless networks have no physical connection with
the wired network; instead they get connected
through the wireless access point (WAP).
• Wireless network allows for devices to be shared
without networking cable which increases mobility.
• The backbone of wireless network is always a wired
network.
• 2.3.2 Types of Networks Based on Size
• Computer networks can be characterized by their
sizes.
• The number of devices connected in the network
and the geographical coverage of the network is
called the size of the network
• Some of the network types based on size are:
 ƒ Personal area network or PAN
 ƒ Local area network or LAN
 ƒ Metropolitan area network or MAN
 ƒ Wide area network or WAN
 Personal Area Network (PAN)
• A personal area network (PAN) ƒ is the
smallest area network which can be made using
Bluetooth network.
• A personal area network (PAN) is a computer
network organized around an individual person
within a single building. If there is no wireless
network, this connection must be done with
cables.
 Local Area Network (LAN )
• Local Area Network (LAN )is larger than PAN and
smaller than MAN in number of computers and
geographical coverage.
• Local Area Network (LAN) is generally an
organizational or a privately owned network within a
single office, building or campus covering a distance
of a few kilometers.
• The main reason for designing a LAN is to share
resources such as storage spaces, printers, programs
and data. It also enables the exchange of information.
 Metropolitan Area Network
• Metropolitan Area Network (MAN) convers
area of a city and can contain multiple LANs.
ƒ
 Wide Area Network (WAN )
• A wide area network (WAN) occupies a very
large area such as an entire country or the
entire world.
• A WAN can contain multiple smaller networks
such as LANs or MANs. The Internet is the
best-known example of a public WAN.
 2.3.3 Types of Network Based on
Topologies
• Network topology defines how various
computers or electronic devices represented as
nodes are connected to one another in the
network.
• Network topology is the physical arrangement of
devices on a network and can be bus, star, ring
and mesh topologies.
• A bus topology is a cheap network where
computers are connected to a common
backbone cable. There is a long cable called
bus.
 b. Mesh Topology
• In a mesh topology, every computer in a network
is connected to each other independently.
• Mesh topology needs more cable and more ports
on the computer.
 c. Star Topology
• In star topology, all computers are connected
separately to a central device, which can be a
switch.
• A failure of the central device results in a failure
of the entire network.
 d. Ring Topology
• ƒ Ring topology looks like finger ring that
connects devices in such a way that each device
is connected to other two adjacent devices.
Failure of one node in ring topology network will
affect the whole network.
 2.3.4 Types of Network Based on
Resource Security and Access
Based on security and access, network can be either client-
server or peer-to-peer network.
• ‘ƒ Peer-to-peer and client-server networks are based on
resource access and sharing. ƒ
• In peer-to-peer network, resources are distributed among
peers and each peer can be a server and client at the same
time.
• In a Peer-to-Peer network, each machine (computer) is
known as peer and can participate in the sharing of files
or resources.
• A peer-to-peer network is also called workgroup
 Advantages of peer-to-peer network
• ƒ Server is not required. ƒ
• All computers are equal in the network. ƒ
• No additional cost is needed for dedicated-
machine.
 Disadvantages of peer-to-peer network
• Provides share level security, i.e. it applies a
trust-based security. ƒ
• Can work in small environments only
• ƒ In client server, resources to be shared over
the network are administered centrally and
there is a dedicated server which provides
resources called servers and there is also a
dedicated client which requests a resource from
the server.
• A client-server network involves multiple
clients or workstations, connecting to at least
one central server.
 2.4 Advantages and Disadvantages of
Network
 ƒ Network is advantageous in
• increasing communication speed,
• sharing data, s
• haring hardware,
• sharing software and getting entertainment.
• ƒ Network also disadvantageous in security
concerns and incurring cost for setting up and
administration of network, hardware, software
and the like.
• ƒVirus and malware
• Vulnerabilities
• Complex
• ƒ Cost
• Social media effect on youth and adults
• Computer network can be used to exchange
data and information, and to share resources
such as hardware (e.g. storage spaces) and
software.
• A virus can travel over the network and can
affect our file on the computer.