This is the fourth layer of the OSI. The transport layer accepts data from the session layer. From here it then segments this data so that it can be transported across the network. The primary responsibility of the transport layer is making sure that data is delivered free from error and in the proper sequence. In the transport layer, the user buffer is subdivided into datagrams that are network buffer sized. Consequently, flow control takes place in the transport layer. Flow control is concerned with the management of data transmission between devices. This is necessary so that more data than can be received and handled by the receiving devices is not sent by the transmitting devices.
Through multiplexing it becomes easy to transmit data from several applications onto a single physical link. Again, the transport layer establishes, maintains and terminates virtual circuits. The processes of error checking and error recovery occur in the transport layer. In error checking, various mechanisms for detecting errors are created. On the other hand, in error recover, the re transmission of data is often requested. This helps to solve any errors that may have occurred.
Certain transport protocols are used on the internet. The two main transport protocols are TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). The difference between these two transport protocols lies in their speed and reliability. Thus, the transport layer offers communication through a network between the end devices. The transport layer may provide communication that may be connection oriented or in other instances, connectionless communication, depending on the network application. For instance, the TCP is connection oriented while the UDP is regarded as connectionless.
Connections between two hosts on a network may be established by the TCP. This is done by the use of what are referred to as sockets. Sockets are often determined by the port number and the IP addresses. The main duty of the TCP is to keep track of packets delivery. Thus, it is the TCP that is also charged with the duty of knowing which packets may require resending. On the other hand, UDP provides a transmission service that is low on overheads, though no error checking is carried out. The transport layer then offers certain functions. These are the identification an application, the message receipt confirmation, the detection of errors in transmission and data flow control for the purpose of preventing overrun in the memory.
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