That is the Session layer in action. Not only does it initiate the communication, it lays down the rules for the communication, maintains the communication, and is responsible for ending it in an orderly manner. Think of it as a mediator between your computer and the end system you are communicating with. Once again the Session layer encapsulates the data from above and sends it down to the layer below it, the Transport Layer. Transport Two of the major functions of the Transport layer are error detection and flow control.
Error detection is just what it sounds like.
However, that isn't necessarily the same thing as error correction. Depending on the situation the Transport layer may or may not provide for any error correction. In some cases, it will pass on the message that an error was detected and one of the upper layers of the model will take care of the correction. Flow control is essentially a valve that either opens or closes to allow or restrict the flow of data, depending on the situation. The sender and receiver agree to how much the window should be open initially.