COMPUTERNETWORKS
[CSE303]
LECTURE NOTES
DIPLOMA –III SEM(JUT)
(2025-2026)
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
GOVERNMENT POLYTECHNIC COLLEGE RANCHI
II Year Diploma .CSE–III S
1
,Data Communication:
When we communicate, we are sharing information. This sharing can
be local or remote. Between individuals, local communication usually occurs face to face,
while
remote communication takes place over distance.
Components:
A data communications system has five components.
1. Message:-The message is the information (data) to be communicated. Popular forms of
information include text, numbers, pictures, audio, and video.
2. Sender :-The sender is the device that sends the data message. It can be a computer,
workstation, telephone handset, video camera, and so on.
3. Receiver:- The receiver is the device that receives the message. It can be a computer,
workstation, telephone handset, television, and so on.
4. Transmission medium:- The transmission medium is the physical path by which a
message
travels from sender to receiver. Some examples of transmission media include twisted-pair
wire,
coaxial cable, fiber-optic cable, and radio waves
5. Protocol:-. A protocol is a set of rules that govern data communications. It represents an
agreement between the communicating devices. Without a protocol, two devices may be
connected but not communicating, just as a person speaking French cannot be understood by
a
person who speaks only Japanese.
Data Flow:-
Communication between two devices can be simplex, half-duplex, or full-duplex as shown in
Figure
2
, Simplex:-In simplex mode, the communication is unidirectional, as on a one-way
street. Only oneof the two devices on a link can transmit; the other can only receive
(see Figure a). Keyboards and traditional monitors are examples of simplex devices.
The keyboard can only introduce input; the monitor can only accept output. The
simplex mode can use the entire capacity of the channel to send data in one direction.
Half-Duplex:- In half-duplex mode, each station can both transmit and receive, but
not at the same time. When one device is sending, the other can only receive, and vice
versa The half-duplex mode is like a one-lane road with traffic allowed in both
directions. When cars are traveling in one direction, cars going the other way must
wait. In a half-duplex transmission, the entire capacity of a channel is taken over by
whichever of the two devices is transmitting at the time. Walkie-talkies and CB
(citizens band) radios are both half-duplex systems. The half-duplex mode is used in
cases where there is no need for communication in both directions at the same time;
the entire capacity of the channel can be utilized for each direction.
Full-Duplex:- In full-duplex mode, both stations can transmit and receive
3
, simultaneously. It is used when communication in both directions is required all the
time. The capacity of the channel, however, must be divided between the two
directions. Here, signals going in one direction share the capacity of the link with
signals going in another direction, this sharing can occur in two ways:
Either the link must contain two physically separate transmission paths, one for
sending and the other for receiving.
Or the capacity is divided between signals traveling in both directions.
What is Computer Network :
A computer network is a group or system of two or more interconnected
computing devices, such as computers, smartphones, printers, and servers.
The goal is to allow these devices to communicate and share resources like data,
applications, and hardware.
Connections can be made through wired connections (like Ethernet or fiber
optic cables) or wireless technologies (like Wi-Fi).
Example:
Local Area Network (LAN): In an office, a LAN connects all computers,
printers, and a file server to a central router.
4
[CSE303]
LECTURE NOTES
DIPLOMA –III SEM(JUT)
(2025-2026)
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
GOVERNMENT POLYTECHNIC COLLEGE RANCHI
II Year Diploma .CSE–III S
1
,Data Communication:
When we communicate, we are sharing information. This sharing can
be local or remote. Between individuals, local communication usually occurs face to face,
while
remote communication takes place over distance.
Components:
A data communications system has five components.
1. Message:-The message is the information (data) to be communicated. Popular forms of
information include text, numbers, pictures, audio, and video.
2. Sender :-The sender is the device that sends the data message. It can be a computer,
workstation, telephone handset, video camera, and so on.
3. Receiver:- The receiver is the device that receives the message. It can be a computer,
workstation, telephone handset, television, and so on.
4. Transmission medium:- The transmission medium is the physical path by which a
message
travels from sender to receiver. Some examples of transmission media include twisted-pair
wire,
coaxial cable, fiber-optic cable, and radio waves
5. Protocol:-. A protocol is a set of rules that govern data communications. It represents an
agreement between the communicating devices. Without a protocol, two devices may be
connected but not communicating, just as a person speaking French cannot be understood by
a
person who speaks only Japanese.
Data Flow:-
Communication between two devices can be simplex, half-duplex, or full-duplex as shown in
Figure
2
, Simplex:-In simplex mode, the communication is unidirectional, as on a one-way
street. Only oneof the two devices on a link can transmit; the other can only receive
(see Figure a). Keyboards and traditional monitors are examples of simplex devices.
The keyboard can only introduce input; the monitor can only accept output. The
simplex mode can use the entire capacity of the channel to send data in one direction.
Half-Duplex:- In half-duplex mode, each station can both transmit and receive, but
not at the same time. When one device is sending, the other can only receive, and vice
versa The half-duplex mode is like a one-lane road with traffic allowed in both
directions. When cars are traveling in one direction, cars going the other way must
wait. In a half-duplex transmission, the entire capacity of a channel is taken over by
whichever of the two devices is transmitting at the time. Walkie-talkies and CB
(citizens band) radios are both half-duplex systems. The half-duplex mode is used in
cases where there is no need for communication in both directions at the same time;
the entire capacity of the channel can be utilized for each direction.
Full-Duplex:- In full-duplex mode, both stations can transmit and receive
3
, simultaneously. It is used when communication in both directions is required all the
time. The capacity of the channel, however, must be divided between the two
directions. Here, signals going in one direction share the capacity of the link with
signals going in another direction, this sharing can occur in two ways:
Either the link must contain two physically separate transmission paths, one for
sending and the other for receiving.
Or the capacity is divided between signals traveling in both directions.
What is Computer Network :
A computer network is a group or system of two or more interconnected
computing devices, such as computers, smartphones, printers, and servers.
The goal is to allow these devices to communicate and share resources like data,
applications, and hardware.
Connections can be made through wired connections (like Ethernet or fiber
optic cables) or wireless technologies (like Wi-Fi).
Example:
Local Area Network (LAN): In an office, a LAN connects all computers,
printers, and a file server to a central router.
4
