CS3591-COMPUTER NETWORKS-UNIT-1
CS3591-COMPUTER NETWORKS
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
DATA COMMUNICATION
Data communications are the exchange of data between two devices via some form of transmission medium
such as a wire cable. For data communications to occur, the communicating devices must be part of a
communication system made up of a combination of hardware (physical equipment) and software (programs).
The effectiveness of a data communications system depends on four fundamental characteristics: delivery,
accuracy, timeliness, and jitter.
1. Delivery. The system must deliver data to the correct destination. Data must be received by the intended
device or user and only by that device or user.
2. Accuracy. The system must deliver the data accurately. Data that have been altered in transmission and left
uncorrected are unusable.
3. Timeliness. The system must deliver data in a timely manner. Data delivered late are useless. In the case of
video and audio, timely delivery means delivering data as
they are produced, in the same order that they are produced, and without significant delay. This kind of
delivery is called real-time transmission.
4. Jitter. Jitter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio
or video packets. For example, let us assume that video packets are sent every 30 ms. If some of the packets
arrive with 30-ms delay and others with 40-ms delay, an uneven quality in the video is the result.
Components
A data communications system has five components.
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, CS3591-COMPUTER NETWORKS-UNIT-1
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.
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
o 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
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, 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.
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.
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, CS3591-COMPUTER NETWORKS-UNIT-1
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.
Advantage of Full-duplex mode:
o Both the stations can send and receive the data at the same time.
Disadvantage of Full-duplex mode:
o If there is no dedicated path exists between the devices, then the capacity of the communication channel is divided into
two parts.
1.
2.
III YEAR/V SEM
Page 4
CS3591-COMPUTER NETWORKS
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
DATA COMMUNICATION
Data communications are the exchange of data between two devices via some form of transmission medium
such as a wire cable. For data communications to occur, the communicating devices must be part of a
communication system made up of a combination of hardware (physical equipment) and software (programs).
The effectiveness of a data communications system depends on four fundamental characteristics: delivery,
accuracy, timeliness, and jitter.
1. Delivery. The system must deliver data to the correct destination. Data must be received by the intended
device or user and only by that device or user.
2. Accuracy. The system must deliver the data accurately. Data that have been altered in transmission and left
uncorrected are unusable.
3. Timeliness. The system must deliver data in a timely manner. Data delivered late are useless. In the case of
video and audio, timely delivery means delivering data as
they are produced, in the same order that they are produced, and without significant delay. This kind of
delivery is called real-time transmission.
4. Jitter. Jitter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio
or video packets. For example, let us assume that video packets are sent every 30 ms. If some of the packets
arrive with 30-ms delay and others with 40-ms delay, an uneven quality in the video is the result.
Components
A data communications system has five components.
III YEAR/V SEM
Page 1
, CS3591-COMPUTER NETWORKS-UNIT-1
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.
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
o 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
III YEAR/V SEM
Page 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.
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.
III YEAR/V SEM
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, CS3591-COMPUTER NETWORKS-UNIT-1
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.
Advantage of Full-duplex mode:
o Both the stations can send and receive the data at the same time.
Disadvantage of Full-duplex mode:
o If there is no dedicated path exists between the devices, then the capacity of the communication channel is divided into
two parts.
1.
2.
III YEAR/V SEM
Page 4
