Introduction to Computer Networks: - The basic concept of Computer networks, Goals of networking.

1. Note-1
Introduction to Computer
Networks: -
Basic concept of Computer networks, Goals of networking.
Course Title: Computer Networks Theory
Course Code: CSE 317
Submitted To
Pranab Bandhu Nath
Senior Lecturer, Department Of
CSE City University, Dhaka
Submitted By
Md. Alif Khan Rifat
ID: 1834902518
BSc in CSE (Day)
Batch: 49th

2. Origins of computer networks:
The concept of networking has been around for a long time but in the case of computer networks
Initially, the network was mainframe-based. The first introduction of a computer network was in
1958 which was known as ASGA (Semi-Automatic Ground Environment), It was used to connect
government computers to various radar stations in the United States and Canada. Later, In the
1970s, researchers at the Massachusetts Institute of Technology (MIT) developed the Compatible
Time-Sharing System, or CTSS, on IBM mainframe computers. This allows multiple users to
perform multiple tasks at the same time. And the dial-up modem is added so that the user can
connect to it by dialing. Then came the first commercial dial-up service on a commercial basis in
1974. It was used on the American Airlines network. We know that the network of the '60 and '70
centuries was mainframe-based. Then came Ethernet, Robert-Markoff, a student at Herbert
University, drew attention to the first Ethernet in his Ph.D. thesis. After that, the network of
experimental Ethernet was formed. Then, in the 1980s, the United States Department of Defense
launched a project called Arpa, with the aim of maintaining direct communication from one
military base to another during the war. ARPANET is an advanced research project agency
network used in the US military. Then in 1971 ARPANET was expanded and its main use was to
exchange emails or electronic messages. ARPANET continued to grow in the eighties. Then in
1979, ARPANET was divided into two parts. One is the Internet, the Internet we use today, was
established in 1979, and the other is DARPANET, which was opened to the American Army.
Computer network:
In short, we say a computer network is an interconnection between two or more computer
systems with the aim of sharing information. The link between the devices in the network could
either be wired or wireless.
In other words, a computer network is a group of computers that use a set of common
communication protocols over digital interconnections for the purpose of sharing resources
located on or provided by the network nodes. The interconnections between nodes are formed
from a broad spectrum of telecommunication network technologies, based on physically wired,
optical, and wireless radio-frequency methods that may be arranged in a variety of network
topologies.
Computer networks today vary from being just a simple ad hoc to a wide enterprise connection
that involves more than one network. There are different kinds of computer networks and the
most prevalent ones today include;
LAN:
Local Area Network This is a network that exists between computers confined in a single
location. e.g. The connection between a home/office computer and a printer is the simplest of
LAN you can find today.
MAN:
Metropolitan Area Network involves the interconnection of computers that are located in two
different cities. The link between these computers is usually called a VPN tunnel (Virtual Private
Network) because it's added security features like encryption of the data which is transmitted
along the communication channel.

3. WAN:
Wide Area Network is a network that connects computer systems to the global Internet. This is
the network that has actually revolutionized the world and it has influenced the way we
communicate today.
Goals of Computer Networks:
Goals of Computer Networks, mainly to make communication easier. The following are some
important goals of computer networks:
Resource sharing:
This is the main aim of a computer network. It means to make all program's peripherals and data
available to anyone computer on the network to all other computers in the network without regard
to the physical locations of them. Thus users at large distances can share the resources or can see
data of a computer in the same way that a local user uses them. Another aspect of resource
sharing is load sharing. That is if required, a job can be performed using various computers in the
network by portioning it which reduces time consumption and load both for a particular
computer.
Improve Performance:
Another closely related goal is to increase the performance of the system. The performance of a
computer can be improved by adding one or more processors
to it as the workload on it grows. For example, if the system is full instead of replacing it buy a
larger one at large expansive it is better to add more processors to it at less cost and less
disruption to the user.
High reliability:
A second goal is to provide high reliability by having alternative sources of supply. For example,
all files could be replicated on two or three machines, so if one of them is Unavailable, the other
copies could be available.
Cost Reduction:
Another goal of networking is the reduction of cost. Resource sharing automatically reduces cost
and hence money can be saved.
Scalability or Communication Medium:
Computer networks provide a powerful communication medium. A file that was
updated/modified on a network can be seen by the other users on the network immediately.
Security:
Security is the main characteristic of a Computer network where you can take necessary steps for
protecting your data from unauthorized access.

4. Network security is not merely interested in the surveillance of the computer systems at each
point of the interaction chain; having said that, it aims to guarantee that the whole system is
secure. Network security necessitates protecting the usability, stability, honesty, and security of
networks and also data.
Application of Computer Network:
Network application: - Some of the network applications in different fields are the following.
o . Business Applications
o . Information services
o . Teleconferencing
o . Mobile Users
o . Communication Medium
o . e-commerce
o . Home Applications
o . Electronic commerce
o . E-mail etc.
Network Hardware & Software:
There are three components of Computer Network
o Hardware Equipment
o Software
o Cables and Connectors
Hardware Equipment:
Networking hardware, also known as network equipment or computer networking devices, are electronic
devices that are required for communication and interaction between devices on a computer network.
Specifically, they mediate data transmission in a computer network. Units that are the last receiver or
generate data are called hosts, end systems, or data terminal equipment. These hardware components
include Hub, Switch, NIC (network interface card), modem, router, Server, Client, Peers, Transmission,
Bridge, Gateway, Repeaters.
HUB:
A hub is a network device that connects computers to each other. It works on the data link layer
of the OSI Model. The hub does not store any addresses on any device. When data from a device
comes to the hub, the hub transmits that data through all its ports without seeing any of it.
There are two types of network hubs mainly: active and passive. A third designation, intelligent
hubs, is synonymous with a switch.

5. Active: Active hubs repeat and strengthen incoming transmissions. They are also sometimes
referred to as repeaters.
Passive: Passive hubs simply serve as a point of connectivity, without any additional capabilities.
Advantages-
• The price is low.
• Can connect different mediums.
Disadvantage-
• Network traffic increases.
• There is a possibility of interruption in data exchange.
• Data filtering is not possible.
Switch:
A switch is a network device that connects the network's servers, workstations, and various
peripheral devices. The difference between a switch and a hub is that the switch sends data from
the sender end to a specific port on the receiving computer. The switch has a MAC table where
the MAC addresses of all the devices connected to the switch are stored.

6. Advantages-
• There is no problem in exchanging data.
• Broadcasts can be controlled using a virtual LAN.
Disadvantages-
• The price is higher than the hub.
• Data cannot be filtered.
• The configuration is relatively complex.
Router:
Router - In a word, the process of sending data from one network to another is called routing.
And the device used for routing is the router. We have to talk a little more to make sense. It is an
intelligent Internet network connectivity device that facilitates data exchange between two or
more networks. Based on the data source and destination, the router chooses the easy, secure and
short distance path for data transfer. It works on three types of networks LAN, MAN, and WAN.
Advantages of the router-
• Reduces problems with data transmission.
• Data filtering is possible.
• Can connect different types of networks such as Ethernet, tokens, rings, etc.
Disadvantages of the router-
• Routers cost more.
• The router cannot be connected without the same protocol network.
• The configuration is relatively complex.

7. Modem:
A modem is a network device that transmits computer information to another computer via a
telephone line. The word modem stands for Modulator and Demodulator. The modulator's job is
to convert digital signal to analog signal and the Demodulator's job is to convert analog signal to
digital signal.
Repeater:
The signal gradually weakens after passing a certain distance during the flow of data signal
through the network media. Then this signal has to be amplified or strengthened to reach the
destination. The repeater is the device used to amplify the signal.

8. Bridges:
Bridges form a large network by connecting multiple networks. It's a lot like a switch or a hub.
The difference is that the hub or switch connects different nodes of the same network while the
bridge connects more than one small network.
Gateways:
Gateways are used to connect different types of networks. Devices like hubs, switches, routers,
etc. do not facilitate protocol translation, but they do facilitate gateways. It works on protocol
translation when connected to different networks. Gateways can be divided into several parts
according to the type of work. One of them is Address Gateway, Protocol Gateway, Application
Gateway, etc.
Server:
A server is a computer that provides data to other computers. It may serve data to systems on a
local area network (LAN) or a wide area network (WAN) over the Internet. Many types of

9. servers exist, including web servers, mail servers, and file servers. Each type runs software
specific to the purpose of the server.
Peers:
Peers on the same level or providing the same function. In networking, a peer is a node that
provides the same functionality as another. For example, two desktop PCs in a network are peers.
A desktop PC and a server are not peers as they perform different operations. The desktop PC
may query the server for business data, but the server does not query the PC for the same data.
Clients:
Businesses have clients and servers have clients. In both instances, there exists a one-to-many
relationship. Just like a business may have several clients, a server can communicate with
multiple clients. In computer networking, this is called the client-server model. A client is any
device that communicates with a server. It may be a desktop computer, laptop, smartphone, or
any other network-compatible device.

10. Transmission:
Data transmission is the process of sending digital or analog data over a communication medium
to one or more computing, network, communication or electronic devices. It enables the transfer
and communication of devices in a point-to-point, point-to multipoint and multipoint-to-
multipoint environment.
Medium:
A medium is a third-party or element through which a message is communicated. This seems to
apply to information technology as well as to seances. In information technology, a medium can
be: 1. A physical transmission medium such as optical fiber 2. A presentation medium (and thus
the terms multimedia and advertising media)
NIC:
NIC stands for Network Interface Card. A network interface card is used to connect a computer to
a network. This card is also called a LAN card or network adapter card.

11. Software
Any software that interacts, increases, and facilitates the functions of a computer network is called
network software. There are two basic types of networking, the first type allows two computers to share,
send and receive data files via the network while the second type of networking allows shared access
liberty to all the users and systems that are part of the network.
Networking Operating System:
Network Operating Systems is typically installed in the server and facilitate workstations in a
network to share files, database, applications, printers, etc.
Protocol Suite:
A protocol is a rule or guideline followed by each computer for data communication. A protocol
suite is a set of related protocols that are laid down for computer networks. The two popular
protocol suites are − a. OSI Model (Open System Interconnections) b. TCP / IP
Model
Types of Computer Network Cables, And Connectors:
Computer network cables have a variety of types and can be selected according to the needs, network
conditions, protocols and network topologies used. There are 3 kinds of network cable you can use to
build a network, among others:
Coaxial Type
Types of network cables are commonly used to build networks with Bus Topology and Ring
Topology, in the use of Coaxial cable using BNC and T connector connectors when used to build
Bus topology. Coaxial cable consists of copper wire coated by insulator, conductor and then on
the outside of Coaxial cable network wrapped using PVC material.
Nowadays Coaxial network cable type has been abandoned, this is because this cable has limited
range in delivering data packet, besides this network cable is considered less flexible in its use.
Reduced networks that use Bus and Ring topology also cause the abandonment of this type of
network cable in building a computer network.

12. Network Cable Type Twisted Pair:
This type of network cable has a pairing form and each pair is mutually coated forming a spiral.
In general, the Twisted Pair network cable is the most widely used, it is because of the number of
network technicians who are choosing to build a computer network with a star topology model, as
well as many networked devices that support Twisted Pair network cables.
Twisted Pair cable market has three types that can be selected by the user according to the needs
of the UTP Cable (Unshielded Twisted Pair), FTP (Foiled Twisted Pair) and STP (Shielded
Twisted Pair). While the commonly used connector for this type of cable uses the RJ 45
connector. Of these three types of Twisted Pair cable is the most widely used UTP cable, this is
because the price of this cable is quite cheap compared to other Twisted Pair cable types.
Fiber Optic Network Cable
This type of network cable consists of a collection of fiber fibers that are considered more flexible
than Twisted Pair cables. While the connectors used in this type of cable include Fiber Connector,
Subscriber Connector, Straight Tip, Bionic, LC, D4, SMA and E200. Initially this type of
network cable is only used for the purposes - the specific purpose of one example to build a
backbone network on a network of large companies. However, as the development of Optical
Fiber is also used for the purposes of network construction in general.
This type of network cable is considered capable to transmit data with high density, in addition
fiber optics are also rated resistant to radio waves so it is rated as the best type of network cable
between the two types of network cables. However, to build a computer network using Fiber
Optic cable, required a fairly large funds, because the price and installation costs are quite
expensive.

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