The main task of the transport layer is to ensure functional and secure end-to-end data transfer within a network. To do this, the OSI transport layer takes the data from the session layer (ie the fifth level) and then transfers it to the network layer (ie the third level). If necessary, the transport layer can also break data down into smaller units or bundle it into larger packetsso as to facilitate their transport.
It is possible to make these transfers with or without connection. The transport layer can use one network connection, use one connection for multiple connections, or split a transport connection across different network connections. However, it still works transparently.
Other transport layer functions include establishing and removing connections, as well as monitoring them. For a transfer with connection, the sender receives a confirmation once the data transfer is complete. The machine at the origin of the sending of the data therefore knows that all the units concerned have indeed been transferred as planned. In the absence of confirmation, a new transfer attempt is automatically initiated. Thus, the transport layer does not take into account the supports used at the level of the first three layers.
