Responsibilities of Transport Layers In TCP/IP

The Transport Layer in the TCP/IP model, which includes protocols like TCP (Transmission Control Protocol) and UDP (User Datagram Protocol), is responsible for ensuring reliable end-to-end communication between the source and destination hosts. Here are the key responsibilities of the Transport Layer in TCP/IP:

1. Segmentation and Reassembly: The Transport Layer breaks down the data received from the upper layers into smaller segments or datagrams for transmission over the network. At the receiving end, it reassembles these segments into the original data.
2. Connection Establishment and Termination: TCP, a connection-oriented protocol, establishes a connection between the sender and receiver before transmitting data and terminates the connection when the data transfer is complete. This ensures reliable and orderly data delivery.
3. Reliable Data Delivery: TCP provides mechanisms for error detection, retransmission of lost packets, and flow control to ensure that data is delivered reliably and in the correct order.
4. Flow Control: The Transport Layer implements flow control mechanisms to manage the rate of data transmission between the sender and receiver, preventing the receiver from being overwhelmed by a fast sender.
5. Multiplexing and Demultiplexing: The Transport Layer uses port numbers to multiplex and demultiplex data from different applications running on the same host. This allows multiple applications to communicate simultaneously over the network.
6. Acknowledgment: TCP uses acknowledgments to ensure that data is successfully received by the destination host. If a segment is not acknowledged within a specified timeout period, it is retransmitted.
7. Error Detection and Correction: TCP includes mechanisms for error detection using checksums to verify the integrity of the data being transmitted. If errors are detected, TCP can request retransmission of the corrupted data.
8. Connection-Oriented and Connectionless Communication: The Transport Layer supports both connection-oriented communication (TCP) and connectionless communication (UDP), providing flexibility for different types of applications.

Working of Transport Layer :

The transport layer takes services from the Application layer and provides services to the Network layer.

• At the sender’s side: The transport layer receives data (message) from the Application layer and then performs Segmentation, divides the actual message into segments, adds the source and destination’s port numbers into the header of the segment, and transfers the message to the Network layer. 
• At the receiver’s side: The transport layer receives data from the Network layer, reassembles the segmented data, reads its header, identifies the port number, and forwards the message to the appropriate port in the Application layer. 

Overall, the Transport Layer plays a crucial role in ensuring reliable, efficient, and orderly communication between network hosts in the TCP/IP protocol suite.