Normally, the transport layer creates individual connection for each session. If high throughput is required, the transport layer may establish multiple network connections, dividing the data among individual connection thereby improving the through put.
To reduce cost the transport layer may also multiplex several transport connections on to the network connection. However, multiple connections or multiplexing must not be seen by the session layer.
The transport layer may also determines the type of service given to the user of the network. Error free point-to-point connection is the most popular transport layer service where messages or bytes are delivered in order in which they were sent. Another kind of transport service is the transportation of isolated messages with no guarantee of delivery. The transport layer is a true end layer between source to destination.