This document provides an introduction to computer networks, covering the history of networks like ARPANET, goals of computer networking like resource sharing, applications like e-commerce, and network hardware and software components. It discusses the development of early networks in the 1960s-70s that led to the Internet, goals of high reliability and flexible access. The document also summarizes network hardware like network interface cards, servers, clients, and cables; software components like network operating systems and protocols; and defines common network devices like routers, bridges, hubs, and switches.

1. Class Work-1
Topic Name : Introduction To Computer Networks
( History Of Computer Networks,
ARPANET, Goals Of Computer Networks,
Application Of Computer Networks,
Network Hardware & 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:8th
Batch:49th

2. History Of Computer Networks:
❖ A network is a group of connected communicating devices such as computers and
printers. An internet is two or more networks that can communicate with each other. In
1967, at an Association for Computing Machinery (ACM) meeting, ARPA presented
its ideas for ARPANET, a small network of connected computers. By 1969, ARPANET
was a reality. In 1972, Vint Cerf and Bob Kahn, both of whom were part of the core
ARPANET group, collaborated on what they called the Internetting Projec1. Cerf and
Kahn's landmark 1973 paper outlined the protocols to achieve end-to-end delivery of
packets. This paper on Transmission Control Protocol (TCP) included concepts such
as encapsulation, the datagram, and the functions of a gateway. Shortly thereafter,
authorities made a decision to split TCP into two protocols:
Transmission Control Protocol (TCP) and Internetworking Protocol (lP).
ARPANET:
❖ ARPANET, in full Advanced Research Projects Agency Network.
• ARPANET was the network that became the basis for the Internet. Based on a
concept first published in 1967, ARPANET was developed under the direction of
the U.S. Advanced Research Projects Agency (ARPA). In 1969, the idea became a
modest reality with the interconnection of four university computers.The initial
purpose was to communicate with and share computer resources among mainly
scientific users at the connected institutions. ARPANET took advantage of the new
idea of sending information in small units called packets that could be routed on
different paths and reconstructed at their destination.
• In the 1980s, ARPANET was handed over to a separate new military network, the
Defense Data Network, and NSFNet, a network of scientific and academic
computers funded by the National Science Foundation. In 1995, NSFNet in turn
began a phased withdrawal to turn the backbone of the Internet (called vBNS) over
to a consortium of commercial backbone providers (PSINet, UUNET,ANS/AOL,
Sprint, MCI, and AGIS-Net99).
• Because ARPA's name was changed to Defense Advanced Research Projects
Agency (DARPA) in 1971, ARPANET is sometimes referred to as DARPANET.
(DARPA was changed back to ARPA in 1993 and back to DARPA again in 1996.)
The history of ARPANET and developments leading up to today's Internet can be
found in Where Wizards Stay Up Late, by Katie Hafner and Matthew Lyon.

3. Computer Networks :
❖ Networking is referred as connecting computers electronically for the purpose of
sharing information. Resources such as files, applications, printers and software are
common information shared in a networking.WAN is a network that covers wider
area than LAN and usually covers cities, countries and the whole world.
Goals Of Computer Networks:
❖ The following are some important goals of computer networks:
1. Resource Sharing –
Many organization has a substantial number of computers in operations,
which are located apart. Ex: A group of office workers can share a common
printer, fax, modem, scanner etc.
2. High Reliability –
If there are alternate sources of supply, all files could be replicated on two or
more machines. If one of them is not available, due to hardware failure, the
other copies could be used.
3. Inter-process Communication –
Network users, located geographically apart, may converse in an interactive
session through the network. In order to permit this, the network must
provide almost error-free communications.
4. Flexible access –
Files can be accessed from any computer in the network. The project can be
begun on one computer and finished on another.
Other goals include Distribution of processing functions, Centralized
management, and allocation of network resources, Compatibility of
dissimilar equipment and software, Good network performance, Scalability,
Saving money, Access to remote information, Person to person
communication etc.
5. Security –
It means protecting data from unauthorized access.

4. Application of Computer Networks:
• Business Applications .
• Communication Medium.
• e-commerce.
• Home Applications.
• Electronic commerce.
• Mobile Users.
• Social Issue.
Network Hardware & Software:
❖ There are three components of Computer Networks.
1. Hardware Equipment.
2. Software.
3. Cables and Connectors.
➢ Hardware: NIC, Server, Client, Peers, Transmission, Medium,
Router,Bridge, Hub, Switches, Gateway, Repeaters.
➢ Software: Network Operating System, Protocols Switches (TCP/IP,
OSI).
➢ Cables and Connectors: Twisted pair cable,
Coaxial cable,Fiber-optic cable.
Hardware:
1. NIC: A network interface card (NIC) is a hardware component
without which a computer cannot be connected over a network. It is a
circuit board installed in a computer that provides a dedicated

5. network connection to the computer. It is also called network
interface controller, network adapter or LAN adapter.
Purpose
• NIC allows both wired and wireless communications.
• NIC allows communications between computers connected via local
area network (LAN) as well as communications over large-scale
network through Internet Protocol (IP).
• NIC is both a physical layer and a data link layer device, i.e. it provides
the necessary hardware circuitry so that the physical layer processes
and some data link layer processes can run on it.
Types of NIC Cards
NIC cards are of two types –
Internal Network Cards:
In internal networks cards, motherboard has a slot for the network card where
it can be inserted. It requires network cables to provide network access.
Internal network cards are of two types. The first type uses Peripheral
Component Interconnect (PCI) connection, while the second type uses
Industry Standard Architecture (ISA).

6. External Network Cards:
In desktops and laptops that do not have an internal NIC, external NICs are
used. External network cards are of two types: Wireless and USB based.
Wireless network card needs to be inserted into the motherboard, however no
network cable is required to connect to the network. They are useful while
traveling or accessing a wireless signal.
2. Server: A server is a computer or system that provides resources,
data, services, or programs to other computers, known as clients, over
a network. In theory, whenever computers share resources with client
machines they are considered servers. There are many types of
servers, including web servers, mail servers, and virtual servers.
Types of servers
There are many types of servers that all perform different functions. Many
networks contain one or more of the common server types:

7. i File servers.
ii Print server.
iii Application servers.
iv DNS servers.
v Mail servers.
vi Web servers.
vii Database servers.
viii Computer hardware servers.
ix Virtual servers.
x Cloud servers etc.
3. Client: A client is a piece of computer hardware or software that
accesses a service made available by a server as part of the client-
server model of computer networks. The server is often (but not
always) on another computer system, in which case the client accesses
the service by way of a network.It is a computer that connects to and
uses the resources of a remote computer, or server. Many corporate
networks comprise a client computer for each employee, each of which
connects to the corporate server.
4. Peers: 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.
5. Transmission: Transmission media is a communication channel that
carries the information from the sender to the receiver. Data
is transmitted through the electromagnetic signals. The main
functionality of the transmission media is to carry the information in
the form of bits through LAN(Local AreaNetwork).
6. Medium: Communication medium refers to the physical channel
through which data is sent and received. Data is sent in the form of
voltage levels which make up the digital signal. ... The speed of data

8. transmission or data rate depends upon the type of medium being used
in the network.
7. Router:A router receives and sends data on computer
networks. Routers are sometimes confused with network hubs,
modems, or network switches. However, routers can combine the
functions of these components, and connect with these devices, to
improve Internet access or help create business networks.
8. Bridge:A bridge in a computer network is one kind of network device,
used to separate a network into sections. Every section in the network
represents a collision domain that has separate bandwidth. So that
network performance can be improved using a bridge. In the OSI
model, a bridge works at layer-2 namely the data link layer. The main
function of this is to examine the incoming traffic and examine
whether to filter it or forward it.
bridge-modem
Working principle of a bridge: The working principle of a bridge is, it
blocks or forwards the data depending on the destination MAC address and
this address is written into every data frame.

9. Bridge-in- computer-network
In a computer network, a bridge separates a LAN into different segments like
segment1 & segment2, etc and the MAC address of all the PCs can be stored
into the table. For instance, PC1 transmits the data to PC2, where the data will
transmit to the bridge first. So the bridge reads the MAC address & decides
whether to transmit the data to segment1 or segment2. Therefore, the PC2 is
accessible in segment1, which means the bridge transmits the data in
segment1 only & eliminates all the connected PCs in segment2. In this way,
the bridge reduces traffic in a computer network.
9. 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.

10. 10. 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 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.
11. Gateway: A gateway is a network node that forms a passage
between two networks operating with different transmission
protocols. The most common type of gateways, the network gateway
operates at layer 3, i.e. network layer of the OSI (open systems
interconnection) model. However, depending upon the functionality,
a gateway can operate at any of the seven layers of OSI model. It acts
as the entry – exit point for a network since all traffic that flows
across the networks should pass through the gateway. Only the
internal traffic between the nodes of a LAN does not pass through the
gateway.

11. 12. Repeaters: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.
Software:
i. Network Operating System: Network Operating System is a
computer operating system that facilitates to connect and
communicate various autonomous computers over a network.
An Autonomous computer is an independent computer that has
its own local memory, hardware, and O.S. It is self capable to
perform operations and processing for a single user.

12. ii. Protocols switches:Protocol switching can be used to upgrade
network protocols or fix minor bugs at run-time without having
to restart applications Security.
• Communication protocols include basic data communication tools
like TCP/IP and HTTP.
• A network switch is a device that operates at the Data Link layer
of the OSI model—Layer 2.
Cables and Connectors:
i. Twisted pair cable: One of the earliest guided transmission
media is twisted pair cables. A twisted pair cable comprises of
two separate insulated copper wires, which are twisted together
and run in parallel. The copper wires are typically 1mm in
diameter. One of the wires is used totransmit data and the other
is the ground reference.
ii. Coaxial cable : Coaxial cable, or coax is a type of electrical
cable consisting of an inner conductor surrounded by a
concentric conducting shield, with the two separated by a
dielectric; many coaxial cables also have a protective outer
sheath or jacket.

13. Types of Coaxial Cables
There are two types of coaxial cables:
iii. Fiber-optic cable: Fiber optic cable is a high-speed data
transmission medium. It contains tiny glass or plastic filaments
that carry light beams. ... The receiving end of a fiber
optic transmission translates the light pulses into binary values,
which can be read by a computer.