Describe the responsibilities of the OSI Model's Transport layer.

The Transport layer of the OSI Model is responsible for the end-to-end delivery of data between source and destination hosts. Its main responsibilities include:

1. Segmentation and Reassembly: The Transport layer breaks down the data received from the upper layers into smaller segments or packets for efficient transmission over the network. It also reassembles these segments at the receiving end.

2. Connection Establishment and Termination: The Transport layer establishes a logical connection between the source and destination hosts before data transmission. It ensures that both ends are ready to send and receive data. Once the communication is complete, it terminates the connection.

3. Reliability and Error Control: The Transport layer ensures reliable delivery of data by implementing error detection and correction mechanisms. It checks for errors in the received data and requests retransmission if necessary. It also provides flow control to prevent overwhelming the receiving host.

4. Flow Control: The Transport layer manages the flow of data between the sender and receiver to avoid congestion and prevent data loss. It regulates the rate at which data is sent, ensuring that the receiving host can handle the incoming data.

5. Multiplexing and Demultiplexing: The Transport layer allows multiple applications or processes to use the network simultaneously. It assigns unique identifiers, known as port numbers, to each application or process. This enables the Transport layer to multiplex multiple data streams into a single network connection and demultiplex them at the receiving end.

6. Quality of Service (QoS): The Transport layer can prioritize certain types of traffic over others based on their QoS requirements. It ensures that critical data, such as real-time audio or video, receives higher priority and is delivered with minimal delay or loss.

Overall, the Transport layer plays a crucial role in ensuring reliable and efficient communication between hosts by providing end-to-end data delivery, error control, flow control, multiplexing, and QoS management.