Assignment 1,computer networks-317

Assignment 1

1. Assignment-1
Topic Name : Illustrate the basic concept of Computer networks and
Distributed systems, Goals of networking, General approaches of
communication within a network, Network classification, Uses and network
software.
Course Title:Computer Networks Theory
Course Code: CSE-317


Submitted To
Pranab Bandhu Nath
Senior Lecturer
Department Of CSE
City University
Submitted By
Khondoker Sadia
Id:1834902542
Semester:8
th

Batch:49
th

2. COMPUTER NETWORK
A network is a set of devices (often referred to as nodes) connected by communication links.
A node can be a computer, printer, or any other device capable of sending and/or receiving data
generated by other nodes on the network
Computer network as an interconnected collection of autonomous computers. Two computers
are said to be interconnected if they are capable of exchanging information. Central to this
definition is the fact that the computers are autonomous. This means that no computer on the
network can start, stop, or control another.

DISTRIBUTED SYSTEM
A distributed system, also known as distributed computing, is a system with multiple
components located on different machines that communicate and coordinate actions.A
distributed system is a collection of independent computers. But the main difference with
computer network is that, in a distributed system, the whole collection of computers appears to
its users as a single coherent system. A well-known example of distributed system if World
Wide Web.

GOALS OF NETWORKING
A network must be able to meet a certain number of criteria. The most important of
these are performance, reliability, and security.

• Performance: Performance can be measured by the amount of time required for a message
to travel from one device to another or the elapsed time between an inquiry and a response.
The performance of a network depends on a number of factors, including the number of
users,the type of transmission medium, the capabilities of the connected hardware, and the
efficiency of the software.
• Reliability: A file can have copies on two or three different machines, so if one of . them
is unavailable (hardware crash), the other copies could be used. For military, banking, air
reservation and many other applications it is of great importance.
• Security: Network security issues include protecting data from unauthorized access,
protecting data from damage and development, and implementing policies and procedures
for recovery from breaches and data losses.
• Resource Sharing: The aim is to make all programs, data and peripherals available to
anyone on the network irrespective of the physical location of the resources and the user.
• Cost Factor: Personal computers have better price/performance ratio than microcomputers.
So it is better to have PC's, one per user, with data stored on one shared file server machine.
• Communication Medium: Using a network, it is possible for managers, working far apart,
to prepare financial report of the company. The changes at one end can be immediately
noticed at another and hence it speeds up co-operation among them.

3. GENERAL APPROACHES OF COMMUNICATION WITHIN A
NETWORK

There are two main approaches to networking:
• Peer-to-Peer, and
• Client-Server.


Deciding what approach to use in which situation is largely dependent on the number of
computers (or users) that will be attached to the network, and the nature of the resources to be
shared via the network.


Peer-to-Peer Networks
A Peer-to-Peer network is a workgroup where all of the connected computers (and users) are
seen as peers (equals), and there is no one computer that is used to administer or control the
network.
Peer-to-Peer networks are ideal for situations where there are no more than ten (10) computers
to be networked, few resources to share (1 printer and a few files), security is not a major issue,
and cost is very important.
However, Peer-to-Peer networks are not scalable - they are limited to fewer than ten (10)
computers, and if your network grows you would have to change your networking approach.


Client-Server Networks
In a server based network (Client-Server networks), one or more computers act as a server and
other computers are connected to this (these) server(s). The server is used to control access to
the network and to administer its resources to the clients (users), and the clients connect to the
server to access its resources.
Server based networks offer centralised control of the network and its resources - one username
(and password) can be used to decide who gets access to what; and flexibility and scalability -
you can have servers for different purposes (file servers, data servers, print servers), and from
one to several hundred clients.
However, these types of networks can be very expensive to set up and maintain - there are high
costs for equipment (specialised servers), licensing fees (associated with the server operating
system), and a full time network administrator.

4. ELEMENTARY TERMINOLOGY OF NETWORKS
Whenever we talk about a network it includes the hardware and the software that make up the
network. Now let us have a look at some typical hardware components of network.

1. Nodes (Workstations)
The term nodes refer to the computers that are attached to a network and are seeking to share
the resources of the network. Of course, if there were no nodes (also called workstations), there
would be no network at all. A computer becomes a workstation of a network as soon as it is
attached to a network.

2. Network Interface Card(NIC)
NIC mainly provide the physical interface between computer and cabling.NIC prepares data,
sends the data, and controls the flow of data. It can also receive and translate the data into bytes
for the CPU to understand.
• NIC is a hardware component that is mainly used to connect one computer with another
on a Network.
• The main role of NIC is to move the serial signals on the network cables or media into
parallel data streams inside the PCs.
• Transfer rate supported by NIC is 10Mb/s,100 Mb/s ,1000 Mb/s.
• Two or more NIC’s are used in the server in order to split the load.
• The main job of NIC is controlling access to the media.
• NIC can be wired or wireless. In wired NIC, there are cables and connectors that act as
a medium to transfer data. While in the wireless card, the connection is generally made
using an antenna that uses radio-wave technology

3. Hub
Hubs are those devices that are used to link several computers together. Hubs repeat one signal
that comes in on one port and then copies it to other ports.
• A network hub is basically a centralized distribution point for all the data transmission
in a network.
• Hub is a passive device.
• The hub receives the data and then rebroadcasts the data to other computers that are
connected to it. Hub mainly does not know the destination of a received data packet.
Thus it is required to send copies of data packets to all the hub connections.
• Also, Hubs consumes more bandwidth on the network and thus limits the amount of
communication.
• One disadvantage of using hubs is that they do not have the intelligence to find out the
best path for the data packets which then leads to inefficiencies and wastage.

4. Switch
Switch mainly resembles a Hub. It is a layer-2 device and it is used for the intelligent
forwarding of messages. By intelligent we mean the decision-making ability of the switch. As

5. hub works in the way by sending data to all ports on the device, whereas the switch sends the
data to only that port that is connected with the destination device.
• The switch is a network component and is mainly used to connect the segments of the
network.
• The switch is more intelligent than the network hub.
• Mainly Switches are capable of inspecting the data packets as soon as they are received,
then determine the source and destination of that packet, and then forward it
appropriately.
• Switch differs from the hub as it also contains ports of different speeds.
• Before forwarding the data to the ports switch performs the error checking and this
feature makes the switch efficient.
• As the switch delivers the message to the connected device it was intended for, thus it
conserves the bandwidth of the network and offers better performance than the hub.
• The most important feature of the switch is that it supports unicast(one to one),
multicast(one to many), and broadcast(one to all) communications.
• The switch makes use of MAC address in order to send data packets to the selected
destination ports.

5. Repeater
The repeater is a Physical layer device. As the name suggests, the repeater is mainly used to
regenerate the signal over the same network and it mainly regenerates before the signal gets
corrupted or weak.
They are incorporated into the networks in order to extend the coverage area. Repeaters can
connect signals by making the use of diffrent types of cables.
• Repeaters are cost-effective.
• Repeaters are very easy o install, and after their installation, they can easily extend the
coverage area of the network.
• But there is a problem with repeaters and it is they cannot those networks that are not
of the same type.
• Repeaters do not help to reduce the traffic in the network.

6. Router
The router is a network component that is mainly used to send or receive data on the computer
network. The process of forwarding data packets from the source to the destination is referred
to as Routing.
• The router is a Network Layer(i.e Layer 3) device.
• The main responsibilities of the router are receiving data packets, analyzing them, and
then forwarding the data packets among the connected computer networks.
• Whenever any data packet arrives, then first of all the router inspects the destination
address and then consults with its routing tables in order to decide the optimal route and
then transfers the packet along this route towards the destination.
• Routers are mainly used to provide protection against broadcast storms.
• Routers are expensive than a hub, switches, repeaters, and bridges.

6. • Routers can also connect different networks together and thus data packets can also be
sent from one network to another network.
• Routers are used in both LAN as well as in WAN(wide area network).
• Routers share data with each other in order to prepare and refresh the routing tables.
.
7. Modem
The modem is basically a hardware component that mainly allows a computer or any other
device like a router, switch to connect to the Internet. A modem is basically a shorthand form
of Modulator-Demodulator. One of the most important functions of the modem is to convert
analog signals into digital signals and vice versa. Also, this device is a combination of two
devices: modulator and demodulator. The modulator mainly converts the digital data into
analog data at the time when the data is being sent by the computer. The demodulator basically
converts the analog data signals into digital data at the time when it is being received by the
computer.

8. Server
A computer that facilitates "the sharing of data" software" and hardware - resources (e.g.
"printers" modems etc,) on the network" is termed as a server. On small networks, sometimes,
all the shareable stuff (like files, data, software etc.) is stored on the server. A network can have
more than one server also. Each server has a unique name on the network and all users of
network identify the server by its unique name. Servers can be of two types: nondedicated and
dedicated servers.
Non-dedicated Servers:. On small networks, a workstation that can double up as a server, is
known as non-dedicated server since it is not completely dedicated to the cause of serving.
Such servers can facilitate the resource-sharing among workstations on a proportionately
smaller scale. Since one computer works as a workstation as well as a server, it is .slower and
requires. more memory. The (small) networks using such a server are known as peer-to-peer
networks.
Dedicated Servers:. On bigger network installations, there is a computer reserved for server's
job and its only job is to help workstations access data, software and hardware resources. It
does not double-up as a workstation and such a server is known as dedicated server.
9. Bridge
It is another important component of the computer network. The bridge is also a layer-2( that
is data link layer device). A bridge is mainly used to connect two or more local area networks
together. These are mainly used as they help in the fast transferring of the data.
But these are not versatile like routers.
Thus Bridge can mainly transfer the data between different protocols (i.e. a Token Ring and
Ethernet network) and operates at the data link layer or level 2 of the OSI (Open Systems
Interconnection) networking reference model as told above.
Bridges are further divided into two:
• Local bridge These are ordinary bridges.
• Remote bridges These are mainly used to connect networks that are at a distance from
each other. Generally Wide Area Network is provided between two bridges

7. Some Bridge protocols are spanning tree protocol, source routing protocol, and source routing
transparent protocol.




CLASSIFICATION OF NETWORK

Communication Networks can be of following 5 types:
1. Local Area Network (LAN)
2. Metropolitan Area Network (MAN)
3. Wide Area Network (WAN)
4. Wireless
5. Inter Network (Internet)
1. Local Area Network (LAN)
LANs are used widely as it is easy to design and to troubleshoot. Personal computers and workstations
are connected to each other through LANs. We can use different types of topologies through LAN,
these are Star, Ring, Bus, Tree etc. LAN can be a simple network like connecting two computers, to
share files and network among each other while it can also be as complex as interconnecting an entire
building. LAN networks are also widely used to share resources like printers, shared hard-drive etc
Characteristics of LAN
• LAN's are private networks, not subject to tariffs or other regulatory controls.
• LAN's operate at relatively high speed when compared to the typical WAN.
• There are different types of Media Access Control methods in a LAN, the prominent ones
are Ethernet, Token ring.
• It connects computers in a single building, block or campus, i.e. they work in a restricted
geographical area.

Applications of LAN
• One of the computer in a network can become a server serving all the remaining computers
called clients. Software can be stored on the server and it can be used by the remaining
clients.
• Connecting Locally all the workstations in a building to let them communicate with each
other locally without any internet access.
• Sharing common resources like printers etc are some common applications of LAN.

Advantages of LAN
• Resource Sharing: Computer resources like printers, modems, DVD-ROM drives and
hard disks can be shared with the help of local area networks. This reduces cost and
hardware purchases.
• Software Applications Sharing: It is cheaper to use same software over network instead
of purchasing separate licensed software for each client a network.

8. • Easy and Cheap Communication: Data and messages can easily be transferred over
networked computers.
• Centralized Data: The data of all network users can be saved on hard disk of the server
computer. This will help users to use any workstation in a network to access their data.
Because data is not stored on workstations locally.
• Data Security: Since, data is stored on server computer centrally, it will be easy to manage
data at only one place and the data will be more secure too.
• Internet Sharing: Local Area Network provides the facility to share a single internet
connection among all the LAN users. In Net Cafes, single internet connection sharing
system keeps the internet expenses cheaper.

Disadvantages of LAN
• High Setup Cost: Although the LAN will save cost over time due to shared computer
resources, but the initial setup costs of installing Local Area Networks is high.
• Privacy Violations: The LAN administrator has the rights to check personal data files of
each and every LAN user. Moreover he can check the internet history and computer use
history of the LAN user.
• Data Security Threat: Unauthorised users can access important data of an organization if
centralized data repository is not secured properly by the LAN administrator.
• LAN Maintenance Job: Local Area Network requires a LAN Administrator because, there
are problems of software installations or hardware failures or cable disturbances in Local
Area Network. A LAN Administrator is needed at this full time job.
• Covers Limited Area: Local Area Network covers a small area like one office, one
building or a group of nearby buildings.


2. Metropolitan Area Network (MAN)
It was developed in 1980s.It is basically a bigger version of LAN. It is also called MAN and
uses the similar technology as LAN. It is designed to extend over the entire city. It can be
means to connecting a number of LANs into a larger network or it can be a single cable. It is
mainly hold and operated by single private company or a public company.

Characteristics of MAN
• It generally covers towns and cities (50 km)
• Communication medium used for MAN are optical fibers, cables etc.
• Data rates adequate for distributed computing applications.

Advantages of MAN
• Extremely efficient and provide fast communication via high-speed carriers, such as
fibre optic cables.
• It provides a good back bone for large network and provides greater access to WANs.
• The dual bus used in MAN helps the transmission of data in both directions
simultaneously.

9. • A MAN usually encompasses several blocks of a city or an entire city.

Disadvantages of MAN
• More cable required for a MAN connection from one place to another.
• It is difficult to make the system secure from hackers and industrial espionage(spying)
graphical regions.

3. Wide Area Network (WAN)
It is also called WAN. WAN can be private or it can be public leased network. It is used for
the network that covers large distance such as cover states of a country. It is not easy to design
and maintain. Communication medium used by WAN are PSTN or Satellite links. WAN
operates on low data rates.

Characteristics of WAN
• It generally covers large distances(states, countries, continents).
• Communication medium used are satellite, public telephone networks which are
connected by routers.

Advantages of WAN
• Covers a large geographical area so long distance business can connect on the one
network.
• Shares software and resources with connecting workstations.
• Messages can be sent very quickly to anyone else on the network. These messages can
have picture, sounds or data included with them(called attachments).
• Expensive things(such as printers or phone lines to the internet) can be shared by all
the computers on the network without having to buy a different peripheral for each
computer.
• Everyone on the network can use the same data. This avoids problems where some
users may have older information than others.

Disadvantages of WAN
• Need a good firewall to restrict outsiders from entering and disrupting the network.
• Setting up a network can be an expensive, slow and complicated. The bigger the
network the more expensive it is.
• Once set up, maintaining a network is a full-time job which requires network
supervisors and technicians to be employed.
• Security is a real issue when many different people have the ability to use information
from other computers. Protection against hackers and viruses adds more complexity
and expense.

10. 4. Wireless Network
Digital wireless communication is not a new idea. Earlier, Morse code was used to implement
wireless networks. Modern digital wireless systems have better performance, but the basic idea
is the same.
Wireless Networks can be divided into three main categories:
a) System interconnection
b) Wireless LANs
c) Wireless WANs

System Interconnection
System interconnection is all about interconnecting the components of a computer using short-
range radio. Some companies got together to design a short-range wireless network called
Bluetooth to connect various components such as monitor, keyboard, mouse and printer, to the
main unit, without wires. Bluetooth also allows digital cameras, headsets, scanners and other
devices to connect to a computer by merely being brought within range.
In simplest form, system interconnection networks use the master-slave concept. The system
unit is normally the master, talking to the mouse, keyboard, etc. as slaves.

Wireless LANs
These are the systems in which every computer has a radio modem and antenna with which
it can communicate with other systems. Wireless LANs are becoming increasingly common in
small offices and homes, where installing Ethernet is considered too much trouble. There is a
standard for wireless LANs called IEEE 802.11, which most systems implement and which is
becoming very widespread.

Wireless WANs
The radio network used for cellular telephones is an example of a low-bandwidth wireless
WAN. This system has already gone through three generations.
• The first generation was analog and for voice only.
• The second generation was digital and for voice only.
• The third generation is digital and is for both voice and data.


5. Inter Network
Inter Network or Internet is a combination of two or more networks. Inter network can be
formed by joining two or more individual networks by means of various devices such as
routers, gateways and bridges.

11. APPLICATIONS & USES OF NETWORKS
In the short time they have been around, data communication networks have become an
indispensable part of business, industry, and entertainment. Some of the network applications
in different fields are the following:
• Marketing and sales. Computer networks are used extensively in both marketing and sales
organizations. Marketing professionals use them to collect, exchange, and analyze data relating
to customer needs and product development cycles. Sales applications include teleshopping,
which uses order entry computers or telephones connected to an order-processing network, and
on-line reservation services for hotels, airlines, and so on.
• Financial services. Today's financial services are totally dependent on computer networks.
Applications include credit history searches, foreign exchange and investment services, and
electronic funds transfer (EFT), which allows a user, to transfer money without going into a
bank (an automated teller machine is a kind of electronic funds transfer; automatic paycheck
deposit is
another).
• Manufacturing. Computer networks are used today in, many aspects of manufacturing,
including the manufacturing process itself. Two applications that use networks to provide
essential services are computer-assisted design (CAD) and computer-assisted manufacturing
(CAM), both of which allow multiple users to work on a project simultaneously.
• Electronic messaging: Probably the most widely used network application is electronic mail
(e-mail).
• Directory services: Directory services allow lists of files to be stored in a central location to
speed worldwide search operations.
• Information services: Network information services include bulletin boards and data banks.
A World Wide Web site offering the technical specifications for a new product is an
information service.
• Electronic data interchange (EDI): EDI allows business information (including documents
such as purchase orders and invoices) to be transferred without using paper.
• Teleconferencing: Teleconferencing allows conferences to occur without the participants
being in the same place. Applications include simple text conferencing (where participants
communicate through their keyboards and computer monitors). voice conferencing (where
participants at a number of locations communicate simultaneously over the phone) and video
conferencing (where participants can see as well as talk to one another).
• Cellular telephone: In the past two parties wishing to use the services of the telephone
company had to be linked by a fixed physical connection. Today's cellular networks make it
possible to maintain wireless phone connections even while traveling over large distances.
• Cable television: Future services provided by cable television networks may include video
on request, as well as the same information, financial, and communications services currently
provided by the telephone companies and computer networks.

12. References
1. Forouzan, Behrouz A. “Data Communications and Networking”
2. Kumar, Sh. Dharmender. “Computer Network”
3. https://www.studytonight.com/computer-networks.