The document provides an overview of computer networking, highlighting the definition, purpose, and importance of computer networks in resource sharing, reliability, inter-process communication, and cost reduction. It details various networking protocols such as TCP, IP, HTTP, and others, explaining their functions in data transmission and communication. Additionally, the document outlines networking models like OSI and TCP/IP, as well as the applications and uses of networks in communication, resource access, and productivity enhancement.

1. Computer Network
Unit 1
Data Communication and Computer
Network

2. Introduction and necessity of
computer networking
• A computer network is a group of devices connected with
each other through a transmission medium such as wires,
cables etc.
• A computer network is a set of computers sharing resources
located on or provided by network nodes. The computers use
common communication protocols
over digital interconnections to communicate with each
other. These interconnections are made up
of telecommunication network technologies, based on
physically wired, optical, and wireless radio-frequency
methods that may be arranged in a variety of network
topologies.
• The purpose of having computer network is to send and
receive data stored in other devices over the computer
network.

3. Network goals and motivation
I. Resource Sharing-
The main goal of the computer network is Resource Sharing. It is to create all
the programs, data and hardware accessible to anyone on the network without
considering the location of resource and the user.
II. Reliability-
If there are alternate sources of supply, all files could be replicated on two or,
machines. If one of them is not available, due to hardware failure, the other
copies could be used.
III. Inter-process Communication –
Network users, located geographically apart, may converse in an interactive
session through the network.
IV. Flexible access –
Files can be accessed from any computer in the network. The project can be
begun on one computer and finished on another.
V. Cost Reduction –
Smaller Computers have much better price/performance compared to larger
ones. Mainframes are may faster one but costly as well.
VI. Communication – A file that was modified or updated on a network can be seen
by the other users on a network immediately.

4. Network Protocols
• A network protocol is an established set of rules that
determine how data is transmitted between different
devices in the same network.
• Types of protocols are explained below
• TCP
• IP
• HTTP
• HTTPS
• FTP
• SMTP
• POP
• IMAP

5. Network Protocols
1. TCP (Transmission Control Protocol):
– TCP is used to transfer the data over the internet.
It divides the data into small packets and sends it
to the destination through the network and make
sure that no packets got lost in transmission.
– The use of packets facilitates speedy transmission
since different parts of a message can be sent by
different routes and then reassembled at the
destination.
Tcp used for connection establishment between device and Ip finds
the address of system and sends their and tcp disconnect the connection

6. Network Protocols
2.IP (Internet Protocol):
– Internet Protocol (P) is the method used to route
information to the proper address. Every
computer on the internet has to have its own
unique address known as the IP address.
– Every packet sent will contain an IP address
showing where it is supposed to go.
– Note IP does not make physical connections
between computers but relies on TCP for this
function.

7. Network Protocols
3. HTTP (Hyper Text Transfer Protocol):
– HTTP is an application protocol that is used in the
address bar of the web browser before WWW. It
defines a mechanism for communication between
the browser and the web browser.
– Whenever we search anything in the address of
browser so it brings that website in front of us.
– It uses port 80.

8. Network Protocols
4. HTTPs (Hypertext Transfer Protocol over
Secure Socket Layer)
– It defines secure communication between a web
server and a web browser.
– A web page using this protocol will have https: at
the front of its URL. It uses port 443.

9. Network Protocols
5. File Transfer Protocol
– The File Transfer Protocol is a standard
communication protocol used for the transfer of
computer files from a server to a client on a
computer network.
– FTP is built on a client–server model architecture
using separate control and data connections
between the client and the server.
– It uses tcp/ip protocol to enable data transfer.

10. Network Protocols
6. Simple Mail Transfer Protocol
– SMTP is a set of communication guidelines that
allow software to transmit an electronic mail over
the internet is called Simple Mail Transfer
Protocol.
– It is a program used for sending and receiving
messages to other computer users based on e-
mail addresses.
– There are 2 more protocol with SMTP(POP and
IMAP).

11. Network Protocols
7. Post Office Protocol
– POP is a message access protocol that extracts
and retrieves email from a remote mail server for
access by the host machine. POP is an application
layer protocol in the OSI model that provides end
users the ability to fetch and receive email.
– POP send mail from sender to receiver and have
no backup

12. Network Protocols
8.IMAP(internet mail access protocol)
– Internet Message Access Protocol (IMAP) is a better version of POP.
– By using IMAP the main advantage is user can retrieve our deleted
email from the server.
9. User Datagram Protocol
– (UDP) is a communications protocol that is primarily used to establish
low-latency and loss-tolerating connections between applications on
the internet.
– It is connection less and unreliable protocol.
– It transfer data without establishing connection.
– It transfer data in a short distance.
– Use ip service to send data.
– UDP speeds up transmissions by enabling the transfer of data before
an agreement is provided by the receiving party.

13. Network Protocols
10. TELNET
– Telnet is an application protocol used on the Internet or local area
network to provide a bidirectional interactive text-oriented
communication facility using a virtual terminal connection. User
data is interspersed in-band with Telnet control information in an
8-bit byte oriented data connection over the Transmission Control
Protocol(TCP).
11. DHCP
– DHCP is a network management protocol used to dynamically
assign an IP address to many devices/node on a network so they
can communicate using IP(Internet Protocol).
– DHCP is also used to configure the proper subnet mask, default
gateway, and DNS server information on the device. It uses port
68.

14. Networking Model
• The two most important network models are
the Open Systems Interconnection Reference
(OSI) and the Internet Model.
• OSI Model
– The OSI Model (Open Systems Interconnection
Model) is a conceptual framework used to
describe the functions of a networking system.

15. Networking Model

16. OSI Layer
a. Application Layer
This layer is responsible for providing an interface to the
application user. It provides protocols that allow software
to send and receive information and present meaningful
data to users. A few examples of application layer
protocols are the (HTTP), (FTP), (POP), (SMTP).
b. Presentation Layer
The presentation layer prepares data for the application
layer.
c. Session layer
The session layer creates communication channels, called
sessions, between devices.

17. OSI Layer
d. Transport Layer
– The transport layer takes data transferred in the session
layer and breaks it into “segments” on the transmitting
end. It is responsible for reassembling the segments on the
receiving end, turning it back into data that can be used by
the session layer.
e. Network Layer
– The network layer has two main functions. One is breaking
up segments into network packets, and reassembling the
packets on the receiving end. The other is routing packets
by discovering the best path across a physical network. The
network layer uses network addresses (typically Internet
Protocol addresses) to route packets to a destination node.

18. OSI Layer
f. Data Link Layer
– The data link layer establishes and terminates a
connection between two physically-connected
nodes on a network. It breaks up packets into
frames and sends them from source to
destination.
g. Physical Layer
– The physical layer is responsible for the physical
cable or wireless connection between network
nodes.

19. OSI Layer

20. Networking Model

21. Internet Model
• Application Layer
• Transport Layer
• Internet Layer
• Link Layer

22. Internet Model
• The four layers in the TCP/IP protocol suite are −
• Network Access Layer −It is the lowest layer that is concerned with
the physical transmission of data. TCP/IP does not specifically define
any protocol here but supports all the standard protocols.
• Internet Layer −It defines the protocols for logical transmission of
data over the network. The main protocol in this layer is Internet
Protocol (IP) and it is supported by the protocols ICMP, IGMP, RARP,
and ARP.
• Transport Layer − It is responsible for error-free end-to-end delivery
of data. The protocols defined here are Transmission Control
Protocol (TCP) and User Datagram Protocol (UDP).
• Application Layer − This is the topmost layer and defines the
interface of host programs with the transport layer services. This
layer includes all high-level protocols like Telnet, DNS, HTTP, FTP,
SMTP, etc.

23. Application and use of networks
1. Communication
It is used for sending and receiving a message from one and
other through network by using electronic mail.
2. Accessing Resources
Networks allow computers to share and access resources with
other computing devices connected to it.
3. Centralization of data
Data can be stored on one server instead of several devices. For
example, on a small home network, all the data can be
centralized by using a server. By doing this, anyone with access
to the network can work with the data stored on the central
server without needing to connect several external hard drives
or flash drives to a computer.

24. Application and use of networks
5. Transfer of files
One way in which data and information can be shared on a network
is by sharing files. By sharing files, you allow users connected to the
same network (whether that is a local network or the internet) to
gain access to specific files.
6. Increase Productivity
The use of networks allow most people to work and study more
productively.
7. Entertainment
Access to the internet provides access to an almost unlimited
amount of entertainment. Examples include: games , multimedia, books,
movies.