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Lesson 5 The transport layer of the TCP-IP Protocol
Objective Responsibilities of transport layer of TCP/IP protocol

Transport Layer of the TCP/IP Protocol

Question: What are the responsibilities of the transport layer of the TCP/IP protocol?
The transport layer handles the problem of directing information between processes, rather than just between machines.
For example, a single machine may be involved in many network transactions at the same time, including FTP[1] sessions, telnet sessions, and World Wide Web (HTTP)[2] sessions.
The transport layer ensures that traffic intended for the FTP service reaches the process responsible for that service, separately from traffic intended for the HTTP and other services. The two transport-layer protocols in TCP/IP networking are called the User Datagram Protocol (UDP)[3] and the Transmission Control Protocol (TCP).

The TCP transport-layer protocol adds reliability to the process-level addressing capabilities it shares with UDP. TCP can create a reliable connection on top of the underlying unreliable network and link-layer protocols.
This connection is necessary because the link and network layers make no guarantees regarding delivery of information, nor do they arrange to acknowledge receipt of information. By some sophisticated software techniques, TCP overcomes the underlying unreliability of the lower-level protocols.

[1] File Transfer Protocol (FTP) : Protocol used to transfer data over a network.
[2] Hypertext Transfer Protocol (HTTP) : Hypertext Transport Protocol defines how messages are formatted and transmitted over the Web and how Web browsers should respond to those messages.
[3] User Datagram Protocol: A connectionless datagram service in the Transport layer used by applications that typically transmit small quantities of data.