What does the transport layer of the OSI model ensure?

The transport layer of the OSI model is primarily responsible for ensuring that data is transferred reliably and in the correct sequence between devices in a network. This layer manages the proper segmentation of data, adds necessary headers for identification, and maintains the order of data packets, which is crucial for applications that require a guaranteed delivery process, like file transfers and streaming services. By utilizing protocols such as TCP (Transmission Control Protocol), the transport layer verifies that all data segments are received successfully and are reassembled in the right order, thus ensuring complete and accurate communication. The emphasis on reliable and sequenced delivery is essential for maintaining data integrity and supporting the capabilities of upper layers in the communication process.