The Transport layer is the fourth layer in Open System Interconnection (OSI) which works to makes client server tools a reality. Transport layer is also known as the host-host layer. It ensures that data is delivered error free in sequence with no losses or duplications. So we can say that this layer is responsible for end to end delivers of messages between the networked hosts.This layer also breaks large messages from the Session layer into smaller packets to be sent to the destination computer and reassembles packets into messages to be presented to the Network layer. To controls the reliability of a given link, it use flow control, segmentation/de-segmentation and error control.
Normally it sends an acknowledgment to the originator for messages received.In additionally transport layer protocols also provide services to manage flow control and end to end error recovery. However in transport layer some protocols are state and connection oriented. So transport layer can keep track of the segments and retransmit those that fail