The Transport Layer of OSI Model

The transport layer (Layer 4) is responsible for delivery of an entire message from an application program on the source device to a similar application program on the destination device.

The main functions of the transport layer are as follows −

• It delivers a message from a specific process of one computer to a specific process in another computer. The transport layer adds a port address to the header of the data packet.
• It divides a message into smaller segments such that each segment contains a sequence number along with the port address. It ensures that the segments arrive correctly at the receiver’s end and then reassembles them.
• It provides an error-free point-to-point channel for both connectionless and connection-oriented services.
• It isolates the upper layers, i.e., the user support layers from any changes in hardware technology in the lower layers, i.e., network support layers.
• It identifies errors like damaged packets, lost packets, and duplication of packets, and provides adequate error-correction techniques.