What does the transport layer in telecommunications focus on?

The transport layer in telecommunications primarily focuses on ensuring reliable data transfer and managing flow control between communicating systems. This layer is responsible for establishing, maintaining, and terminating connections, as well as ensuring that data segments are delivered accurately and in the correct sequence. It implements error recovery protocols and manages congestion control to maintain optimum performance while data is being transmitted.

The concepts of reliability and flow control are essential because they help prevent data loss and ensure that data is sent and received in a synchronized manner. For example, protocols like TCP (Transmission Control Protocol) operate at the transport layer and provide mechanisms for these functions, making it possible for applications to communicate effectively over complex networks.

The other options address functions that belong to different layers of the network model. Routing and forwarding pertain to the network layer, data encryption and security are typically handled at the application layer or through specific security protocols, and signal modulation and demodulation are associated with the physical layer where actual transmission occurs.