The Transport Layer is the fourth layer in the OSI (Open Systems Interconnection) model,
responsible for end-to-end communication, data segmentation, flow control, error handling,
and reliable data transfer between devices on a network.
ὒ Main Functions of the Transport Layer
The Transport Layer (Layer 4 of the OSI model) plays a crucial role in delivering data accurately,
efficiently, and reliably between applications on different devices across a network.
1. Segmentation and Reassembly
· Divides large data from the application layer into smaller, manageable segments for
transmission.
· Reassembles the segments into the correct order at the destination.
· Helps in organizing and tracking data during transmission.
2. Connection Control
· Manages the setup, maintenance, and termination of communication sessions.
· Supports:
o Connection-oriented communication (e.g., TCP) for reliable, ordered data
delivery.
o Connectionless communication (e.g., UDP) for faster, less reliable transmission.
3. Flow Control
· Regulates the amount of data sent between sender and receiver.
· Prevents the sender from overwhelming the receiver’s capacity.
· Uses mechanisms like sliding window protocol in TCP.
4. Error Control
· Detects and corrects errors that may occur during data transmission.
, · Uses checksums, acknowledgments (ACKs), and retransmissions to ensure data
integrity.
· Lost or corrupted segments are resent automatically (in TCP).
5. Multiplexing and Demultiplexing
· Allows multiple applications or services to share the network simultaneously.
· Uses port numbers to identify and direct each segment to the correct application.
o Example: Port 80 for HTTP, Port 25 for email (SMTP).
6. Reliability
· Ensures that data is delivered accurately, completely, and in the correct order.
· Key aspects of reliability include:
o Acknowledgment of received data
o Retransmission of lost data
o Proper sequencing of out-of-order packets
· Achieved mainly through TCP (Transmission Control Protocol).
· Critical for applications like emails, file transfers, or web pages where complete and
correct data is necessary.
7. Port Addressing
· Each segment includes source and destination port numbers.
· Port addressing identifies which application or service should handle the data.
· Helps route data to the correct program (e.g., web browser, email client) on the
destination device.
8. Quality of Service (QoS)
· Refers to the priority handling of different types of traffic.
· Ensures that time-sensitive data (like video calls, VoIP) is delivered with minimal delay.
responsible for end-to-end communication, data segmentation, flow control, error handling,
and reliable data transfer between devices on a network.
ὒ Main Functions of the Transport Layer
The Transport Layer (Layer 4 of the OSI model) plays a crucial role in delivering data accurately,
efficiently, and reliably between applications on different devices across a network.
1. Segmentation and Reassembly
· Divides large data from the application layer into smaller, manageable segments for
transmission.
· Reassembles the segments into the correct order at the destination.
· Helps in organizing and tracking data during transmission.
2. Connection Control
· Manages the setup, maintenance, and termination of communication sessions.
· Supports:
o Connection-oriented communication (e.g., TCP) for reliable, ordered data
delivery.
o Connectionless communication (e.g., UDP) for faster, less reliable transmission.
3. Flow Control
· Regulates the amount of data sent between sender and receiver.
· Prevents the sender from overwhelming the receiver’s capacity.
· Uses mechanisms like sliding window protocol in TCP.
4. Error Control
· Detects and corrects errors that may occur during data transmission.
, · Uses checksums, acknowledgments (ACKs), and retransmissions to ensure data
integrity.
· Lost or corrupted segments are resent automatically (in TCP).
5. Multiplexing and Demultiplexing
· Allows multiple applications or services to share the network simultaneously.
· Uses port numbers to identify and direct each segment to the correct application.
o Example: Port 80 for HTTP, Port 25 for email (SMTP).
6. Reliability
· Ensures that data is delivered accurately, completely, and in the correct order.
· Key aspects of reliability include:
o Acknowledgment of received data
o Retransmission of lost data
o Proper sequencing of out-of-order packets
· Achieved mainly through TCP (Transmission Control Protocol).
· Critical for applications like emails, file transfers, or web pages where complete and
correct data is necessary.
7. Port Addressing
· Each segment includes source and destination port numbers.
· Port addressing identifies which application or service should handle the data.
· Helps route data to the correct program (e.g., web browser, email client) on the
destination device.
8. Quality of Service (QoS)
· Refers to the priority handling of different types of traffic.
· Ensures that time-sensitive data (like video calls, VoIP) is delivered with minimal delay.
