The transport layer is the fourth layer of the OSI reference model. This layer determines how to use the network layer to provide a virtual error-free, point to point connection so that host A can send messages to host B and they will arrive un-corrupted and in the correct order. It establishes and dissolves connections between hosts. Means A communications protocol responsible for establishing a connection and ensuring that all data has arrived safely. It is defined in layer 4 of the OSI model. Often, the term transport protocol implies transport services, which includes the lower-level data link protocol that moves packets from one node to another. It is used by the session layer.