CS3591 – Computer Networks Unit-1
UNIT I - INTRODUCTION AND APPLICATION LAYER
Data Communication - Networks – Network Types – Protocol Layering – TCP/IP Protocol
suite –OSI Model – Introduction to Sockets - Application Layer protocols: HTTP – FTP –
Email protocols(SMTP - POP3 - IMAP - MIME) – DNS – SNMP
INTRODUCTION TO NETWORKS
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 or
receiving data generated by other nodes on the network.
When we communicate, we are sharing information. This sharing can be local or
remote.
CHARACTERISTICS OF A NETWORK
The effectiveness of a network depends on three characteristics.
1. Delivery: The system must deliver data to the correct destination.
2. Accuracy: The system must deliver data accurately.
3. Timeliness: The system must deliver data in a timely manner.
CRITERIA NECESSARY FOR AN EFFECTIVE AND EFFICIENT
NETWORK
A network must be able to meet a certain number of criteria. The most important of
these are performance, reliability, and security.
Factors that affect the Factors that affect the Factors that affect the
Performance of a network: Reliability of a network: Security of a network:
1. Number of users 1. Efficiency of software. 1.Protecting data from
2. Type of transmission 2. Frequency of failure unauthorized access and
medium 3.Recovery time of a viruses.
3. Capabilities of the network after a failure
connected hardware
1
,CS3591 – Computer Networks Unit-1
COMPONENTS INVOLVED IN A NETWORK PROCESS
The five components are:
1. Message - It is the information to be communicated. Popular forms of
information include text, pictures, audio, video etc.
2. Sender - It is the device which sends the data messages. It can be a computer,
workstation, telephone handset etc.
3. Receiver - It is the device which receives the data messages. It can be a
computer, workstation, telephone handset etc.
4. Transmission Medium - It is the physical path by which a message travels from
sender to receiver. Some examples include twisted-pair wire, coaxial cable,
radiowaves etc.
5. Protocol - It is a set of rules that governs the data communications. It represents
an agreement between the communicating devices. Without a protocol, two
devices may be connected but not communicating.
KEY ELEMENTS OF PROTOCOL
Syntax: Refers to the structure or format of the data, meaning the order in which
they are presented.
Semantics: Refers to the meaning of each section of bits.
Timing: Refers to two characteristics. (1). When data should be sent and (2). How
fast they can be sent.
TRANSMISSION MODES
o The way in which data is transmitted from one device to another device is known
as transmission mode.
o The transmission mode is also known as the communication mode.
o Each communication channel has a direction associated with it, and transmission
media provide the direction. Therefore, the transmission mode is also known as a
directional mode.
o The transmission mode is defined in the physical layer.
2
,CS3591 – Computer Networks Unit-1
Types of Transmission mode
The Transmission mode is divided into three categories:
o Simplex Mode
o Half-duplex Mode
o Full-duplex mode (Duplex Mode)
SIMPLEX MODE
o In Simplex mode, the communication is unidirectional, i.e., the data flow in one
direction.
o A device can only send the data but cannot receive it or it can receive the data but
cannot send the data.
o This transmission mode is not very popular as mainly communications require the
two-way exchange of data. The simplex mode is used in the business field as in
sales that do not require any corresponding reply.
o The radio station is a simplex channel as it transmits the signal to the listeners but
never allows them to transmit back.
o Keyboard and Monitor are the examples of the simplex mode as a keyboard can
only accept the data from the user and monitor can only be used to display the
data on the screen.
o The main advantage of the simplex mode is that the full capacity of the
communication channel can be utilized during transmission.
Advantage of Simplex mode:
o In simplex mode, the station can utilize the entire bandwidth of the
communication channel, so that more data can be transmitted at a time.
Disadvantage of Simplex mode:
o Communication is unidirectional, so it has no inter-communication between
devices.
3
, CS3591 – Computer Networks Unit-1
HALF-DUPLEX MODE
o In a Half-duplex channel, direction can be reversed, i.e., the station can transmit
and receive the data as well.
o Messages flow in both the directions, but not at the same time.
o The entire bandwidth of the communication channel is utilized in one direction at
a time.
o In half-duplex mode, it is possible to perform the error detection, and if any error
occurs, then the receiver requests the sender to retransmit the data.
o A Walkie-talkie is an example of the Half-duplex mode.
o In Walkie-talkie, one party speaks, and another party listens. After a pause, the
other speaks and first party listens. Speaking simultaneously will create the
distorted sound which cannot be understood.
Advantage of Half-duplex mode:
o In half-duplex mode, both the devices can send and receive the data and also can
utilize the entire bandwidth of the communication channel during the
transmission of data.
Disadvantage of Half-Duplex mode:
o In half-duplex mode, when one device is sending the data, then another has to
wait, this causes the delay in sending the data at the right time.
FULL-DUPLEX MODE
o In Full duplex mode, the communication is bi-directional, i.e., the data flow in
both the directions.
o Both the stations can send and receive the message simultaneously.
o Full-duplex mode has two simplex channels. One channel has traffic moving in
one direction, and another channel has traffic flowing in the opposite direction.
o The Full-duplex mode is the fastest mode of communication between devices.
o The most common example of the full-duplex mode is a Telephone network.
When two people are communicating with each other by a telephone line, both
can talk and listen at the same time.
4
UNIT I - INTRODUCTION AND APPLICATION LAYER
Data Communication - Networks – Network Types – Protocol Layering – TCP/IP Protocol
suite –OSI Model – Introduction to Sockets - Application Layer protocols: HTTP – FTP –
Email protocols(SMTP - POP3 - IMAP - MIME) – DNS – SNMP
INTRODUCTION TO NETWORKS
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 or
receiving data generated by other nodes on the network.
When we communicate, we are sharing information. This sharing can be local or
remote.
CHARACTERISTICS OF A NETWORK
The effectiveness of a network depends on three characteristics.
1. Delivery: The system must deliver data to the correct destination.
2. Accuracy: The system must deliver data accurately.
3. Timeliness: The system must deliver data in a timely manner.
CRITERIA NECESSARY FOR AN EFFECTIVE AND EFFICIENT
NETWORK
A network must be able to meet a certain number of criteria. The most important of
these are performance, reliability, and security.
Factors that affect the Factors that affect the Factors that affect the
Performance of a network: Reliability of a network: Security of a network:
1. Number of users 1. Efficiency of software. 1.Protecting data from
2. Type of transmission 2. Frequency of failure unauthorized access and
medium 3.Recovery time of a viruses.
3. Capabilities of the network after a failure
connected hardware
1
,CS3591 – Computer Networks Unit-1
COMPONENTS INVOLVED IN A NETWORK PROCESS
The five components are:
1. Message - It is the information to be communicated. Popular forms of
information include text, pictures, audio, video etc.
2. Sender - It is the device which sends the data messages. It can be a computer,
workstation, telephone handset etc.
3. Receiver - It is the device which receives the data messages. It can be a
computer, workstation, telephone handset etc.
4. Transmission Medium - It is the physical path by which a message travels from
sender to receiver. Some examples include twisted-pair wire, coaxial cable,
radiowaves etc.
5. Protocol - It is a set of rules that governs the data communications. It represents
an agreement between the communicating devices. Without a protocol, two
devices may be connected but not communicating.
KEY ELEMENTS OF PROTOCOL
Syntax: Refers to the structure or format of the data, meaning the order in which
they are presented.
Semantics: Refers to the meaning of each section of bits.
Timing: Refers to two characteristics. (1). When data should be sent and (2). How
fast they can be sent.
TRANSMISSION MODES
o The way in which data is transmitted from one device to another device is known
as transmission mode.
o The transmission mode is also known as the communication mode.
o Each communication channel has a direction associated with it, and transmission
media provide the direction. Therefore, the transmission mode is also known as a
directional mode.
o The transmission mode is defined in the physical layer.
2
,CS3591 – Computer Networks Unit-1
Types of Transmission mode
The Transmission mode is divided into three categories:
o Simplex Mode
o Half-duplex Mode
o Full-duplex mode (Duplex Mode)
SIMPLEX MODE
o In Simplex mode, the communication is unidirectional, i.e., the data flow in one
direction.
o A device can only send the data but cannot receive it or it can receive the data but
cannot send the data.
o This transmission mode is not very popular as mainly communications require the
two-way exchange of data. The simplex mode is used in the business field as in
sales that do not require any corresponding reply.
o The radio station is a simplex channel as it transmits the signal to the listeners but
never allows them to transmit back.
o Keyboard and Monitor are the examples of the simplex mode as a keyboard can
only accept the data from the user and monitor can only be used to display the
data on the screen.
o The main advantage of the simplex mode is that the full capacity of the
communication channel can be utilized during transmission.
Advantage of Simplex mode:
o In simplex mode, the station can utilize the entire bandwidth of the
communication channel, so that more data can be transmitted at a time.
Disadvantage of Simplex mode:
o Communication is unidirectional, so it has no inter-communication between
devices.
3
, CS3591 – Computer Networks Unit-1
HALF-DUPLEX MODE
o In a Half-duplex channel, direction can be reversed, i.e., the station can transmit
and receive the data as well.
o Messages flow in both the directions, but not at the same time.
o The entire bandwidth of the communication channel is utilized in one direction at
a time.
o In half-duplex mode, it is possible to perform the error detection, and if any error
occurs, then the receiver requests the sender to retransmit the data.
o A Walkie-talkie is an example of the Half-duplex mode.
o In Walkie-talkie, one party speaks, and another party listens. After a pause, the
other speaks and first party listens. Speaking simultaneously will create the
distorted sound which cannot be understood.
Advantage of Half-duplex mode:
o In half-duplex mode, both the devices can send and receive the data and also can
utilize the entire bandwidth of the communication channel during the
transmission of data.
Disadvantage of Half-Duplex mode:
o In half-duplex mode, when one device is sending the data, then another has to
wait, this causes the delay in sending the data at the right time.
FULL-DUPLEX MODE
o In Full duplex mode, the communication is bi-directional, i.e., the data flow in
both the directions.
o Both the stations can send and receive the message simultaneously.
o Full-duplex mode has two simplex channels. One channel has traffic moving in
one direction, and another channel has traffic flowing in the opposite direction.
o The Full-duplex mode is the fastest mode of communication between devices.
o The most common example of the full-duplex mode is a Telephone network.
When two people are communicating with each other by a telephone line, both
can talk and listen at the same time.
4
