TCP/IP Network Model

Transport Layer
The Transport layer uses TCP and UDP.
TCP provides a reliable virtual circuit (connection-oriented) for
application processes. Connection-oriented means that a connection
must be established between systems before they can exchange data.
Furthermore, TCP uses acknowledgments between systems to ensure
data delivery.
UDP is a connectionless protocol for application processes. It is faster
than TCP for certain applications since it does not require setting up a
connection and handling acknowledgments. It is also known as a
stateless protocol because systems using UDP to exchange data have no
indication of the operational status of one another.
Figure 1-6 compares the Transport layer of the TCP/IP model to the
Transport layer of the ISO/OSI reference model.