Transport Layer TCP/IP

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Introduction

The Transport Layer in the TCP/IP model is vital for ensuring the reliable delivery of data between applications running on different hosts.
TCP provides a robust, connection-oriented service that guarantees the delivery and order of data, while UDP offers a lightweight, connectionless service for applications where speed and efficiency are more critical than reliability. Together, TCP and UDP enable a wide range of internet services, from web browsing and email to real-time gaming and video streaming.
It is also called the host-to-host layer.

The Transport Layer in the TCP/IP model is responsible for providing reliable data transfer, error checking, and flow control between two devices or hosts on a network.

It is responsible for end-to-end data delivery/integrity.
It sits above the Internet Layer and below the Application Layer, ensuring that data is delivered to the correct application on the destination device in a reliable manner.
The transport layer identifies the data/segments through the Socket address (combination of port number & I.P. address).

The primary functions of the Transport Layer are:-

End-to-end communication:
- It provides direct communication between two systems or devices over a network.
Segmentation and reassembly:
- The Transport Layer breaks large data into smaller segments at the sender, and the receiver reassembles them into the original data.
Error detection and correction:
- It ensures that data is transferred without errors, and retransmits segments if necessary.
- Both TCP and UDP include checksums to verify that data has not been corrupted during transmission.
- TCP also uses sequence numbers and acknowledgments to ensure error correction.
Flow control:
- It manages the rate of data transmission to prevent overwhelming the receiver.
- TCP uses a windowing mechanism for flow control.
Multiplexing and Demultiplexing:
- It uses port numbers to identify different applications or services running on a device, allowing multiple applications to share the network.
Connection Establishment and Termination (TCP only):
- TCP uses the three-way handshake to establish a reliable connection and a similar process to close it gracefully.