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Transport layer is the third layer in the TCP/IP reference model.

Description

• Responsible for host-to-host message delivery along with flow control, congestion control and error recovery.
• The core protocols of transport layer are Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).
• Either one of them protocol is selected, depending upon the type of communication application software needed.
• In TCP packets are called as segments, while in UDP it is called as datagrams.
• TCP - is a connection-oriented, reliable and stateful protocol.
• Connection-oriented - Establishes a logical connection between sender and receiver before sending any data packets.
• Reliable - Receiver sends acknowledgement of received packet to the sender.
• Stateful - Both sender and receiver keeps track of the state of communication session.
• Responsible for establishment and termination of the TCP connection, ordering of sequence number and acknowledgement number, flow control and error recovery of lost and damaged packets.
• Has high overhead.
• UDP - is a connectionless, unreliable and stateless datagram protocol.
• Connectionless - Establishing a connection between sender and receiver is not required.
• Unreliable - No acknowledgement of received packet.
• Stateless - Doesn't keep track of the state, works on timeout criteria.
• Used in application like streaming media (video, audio), where reliability, error recovery and flow control is not important.
• Has less overhead.
• New protocols Datagram Congestion Control Protocol (DCCP), Stream Control Transmission Protocol (SCTP) etc are used.
• Network devices used : Router, Gateway.