Computer Networks

Document created by: Engr. Md. Tareq Hossain – tareq@uoda.edu.bd Page 1 of 8
Title: Computer Networks
Code: CSE-304, Batch – 41
Lecture – 02, Date: 17 January 2018
Providing Resources in a Network
Networks come in all sizes. They can range from
simple networks consisting of two computers to
networks connecting millions of devices.
Simple networks installed in homes enable sharing of
resources, such as printers, documents, pictures and
music between a few local computers.
Home office networks and small office networks are
often set up by individuals that work from a home or
remote office and need to connect to a corporate
network or other centralized resources. Additionally,
many self-employed entrepreneurs use home office
and small office networks to advertise and sell
products, order supplies and communicate with customers. Communication over a network is usually more
efficient and less expensive than traditional forms of communication, such as regular mail or long distance
phone calls.
In businesses and large organizations, networks can be used on an even broader scale to allow employees to
provide consolidation, storage, and access to information on network servers. Networks also allow for rapid
communication such as email, instant messaging, and collaboration among employees. In addition to internal
organizational benefits, many organizations use their networks to provide products and services to
customers through their connection to the Internet.
The Internet is the largest network in existence. In fact, the term Internet means a ‘network of networks’.
The Internet is literally a collection of interconnected private and public networks, such as the ones described
above. Businesses, small office networks, and even home networks usually provide a shared connection to
the Internet.
It is incredible how quickly the Internet has become an integral part of our daily routines.
All computers connected to a network that
participate directly in network communication are
classified as hosts or end devices. Hosts can send and
receive messages on the network. In modern
networks, end devices can act as a client, a server, or
both. The software installed on the computer
determines which role the computer plays.
Servers are hosts that have software installed that
enable them to provide information, like email or
web pages, to other hosts on the network. Each
service requires separate server software. For
example, a host requires web server software in order to provide web services to the network.

Clients are computer hosts that have software installed that enable them to request and display the
information obtained from the server. An example of client software is a web browser, like Internet Explorer.
A computer with server software can provide services
simultaneously to one or many clients.
Additionally, a single computer can run multiple types of
server software. In a home or small business, it may be
necessary for one computer to act as a file server, a web
server, and an email server.
A single computer can also run multiple types of client
software. There must be client software for every
service required. With multiple clients installed, a host
can connect to multiple servers at the same time. For
example, a user can check email and view a web page
while instant messaging and listening to Internet radio.
Client and server software usually runs on separate computers, but it is also possible for one computer to
carry out both roles at the same time. In small businesses and homes, many computers function as the
servers and clients on the network. This type of network is called a peer-to-peer network.
The simplest peer-to-peer
network consists of two directly
connected computers using a
wired or wireless connection.
Multiple PCs can also be
connected to create a larger
peer-to-peer network but this
requires a network device, such
as a hub, to interconnect the
computers.
The main disadvantage of a
peer-to-peer environment is
that the performance of a host
can be slowed down if it is
acting as both a client and a
server at the same time.
In larger businesses, due to the
potential for high amounts of
network traffic, it is often necessary to have dedicated servers to support the number of service requests.

Components of a Network
The path that a message takes from source to destination can be as simple as a single cable connecting one
computer to another or as complex as a network that literally spans the globe. This network infrastructure is
the platform that supports the network. It provides the stable and reliable channel over which our
communications can occur.
The network infrastructure contains three categories of network components:
 Devices
 Media
 Services
Devices and media are the physical elements, or hardware, of the network. Hardware is often the visible
components of the network platform such as a laptop, PC, switch, router, wireless access point, or the
cabling used to connect the devices. Occasionally, some components may not be so visible. In the case of
wireless media, messages are transmitted through the air using invisible radio frequency or infrared waves.
Network components are used to provide services
and processes. These are the communication
programs, called software, that run on the
networked devices. A network service provides
information in response to a request. Services
include many of the common network applications
people use every day, like email hosting services
and web hosting services. Processes provide the
functionality that directs and moves the messages
through the network. Processes are less obvious to
us but are critical to the operation of networks.

The network devices that people are most familiar with are called end devices, or hosts. These devices form
the interface between users and the underlying communication network.
Some examples of end devices are:
 Computers (work stations, laptops, file servers, web servers)
 Network printers
 VoIP phones
 TelePresence endpoint
 Security cameras
 Mobile handheld devices (such as smartphones, tablets, PDAs, and wireless debit/credit card
readers and barcode scanners)
A host device is either the source or destination of a message transmitted over the network, as shown in the
figure. In order to distinguish one host from another, each host on a network is identified by an address.
When a host initiates communication, it uses the address of the destination host to specify where the
message should be sent.
Intermediary devices interconnect end devices. These devices provide connectivity and work behind the
scenes to ensure that data flows across the network. Intermediary devices connect the individual hosts to the
network and can connect multiple individual networks to form an internetwork.
Examples of intermediary network devices are:
 Network Access (switches and wireless access points)
 Internetworking (routers)
 Security (firewalls)
The management of data as it flows through the network is also a role of the intermediary devices. These
devices use the destination host address, in conjunction with information about the network
interconnections, to determine the path that messages should take through the network.

Processes running on the intermediary network devices perform these functions:
 Regenerate and retransmit data signals
 Maintain information about what pathways exist through the network and internetwork
 Notify other devices of errors and communication failures
 Direct data along alternate pathways when there is a link failure
 Classify and direct messages according to Quality of Service (QoS) priorities
 Permit or deny the flow of data, based on security settings
Communication across a network is carried on a medium. The medium provides the channel over which the
message travels from source to destination.
Modern networks primarily use three types of
media to interconnect devices and to provide
the pathway over which data can be
transmitted. As shown in the figure, these media
are:
 Metallic wires within cables
 Glass or plastic fibers (fiber optic
cable)
 Wireless transmission
The signal encoding that must occur for the
message to be transmitted is different for each
media type. On metallic wires, the data is
encoded into electrical impulses that match
specific patterns. Fiber optic transmissions rely
on pulses of light, within either infrared or visible light ranges. In wireless transmission, patterns of
electromagnetic waves depict the various bit values.
Different types of network media have different features and benefits. Not all network media has the same
characteristics and is appropriate for the same purpose. The criteria for choosing network media are:
 The distance the media can successfully carry a signal
 The environment in which the media is to be installed
 The amount of data and the speed at which it must be transmitted
 The cost of the media and installation
When conveying complex information such as displaying all the devices and medium in a large internetwork,
it is helpful to use visual representations. A diagram provides an easy way to understand the way the devices
in a large network are connected. Such a diagram uses symbols to represent the different devices and
connections that make up a network. This type of “picture” of a network is known as a topology diagram.

Like any other language, the language of networking
uses a common set of symbols to represent the
different end devices, network devices, and media,
as shown in the figure. The ability to recognize the
logical representations of the physical networking
components is critical to being able to visualize the
organization and operation of a network.
Throughout this course and labs, you will learn both
how these devices operate and how to perform basic
configuration tasks on these devices.
In addition to these representations, specialized terminology is used when discussing how each of these
devices and media connect to each other. Important terms to remember are:
 Network Interface Card - A NIC, or LAN adapter, provides the physical connection to the network at
the PC or other host device. The media connecting the PC to the networking device plugs directly into
the NIC.
 Physical Port - A connector or outlet on a networking device where the media is connected to a host
or other networking device.
 Interface - Specialized ports on an internetworking device that connect to individual networks.
Because routers are used to interconnect networks, the ports on a router are referred to network
interfaces.
Topology diagrams are mandatory for anyone working with a network. It provides a visual map of how the
network is connected.
There are two types of topology diagrams including:
 Physical topology diagrams - Identify the physical location of intermediary devices, configured ports,
and cable installation.

 Logical topology diagrams - Identify devices, ports, and IP addressing scheme.

Specimen Questions
Q. What is the role of a computer server and a client computer?
Q. What are the components of a computer network?
Q. Name three categories of network components of the network infrastructure.
Q. What is Point to Point link? Write down advantages and disadvantages of P2P Network.
Q. Describe the SOHO Network. Write the name of encoded signals that transmit over the fiber
optic cable, copper cable and wireless media.
Q. Name of some end devices of computer networks.
Q. What is the Network Interface Card? What is its function?
Q. List the functions of process those are running on the intermediary network devices.
Q. What are the four criteria that we have to consider for choosing network media?
Q. Describe physical and logical topology with appropriate diagram.
Q. What does the intermediary devices do in computer network? Name some examples of
intermediary network devices.

Computer Networks

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