The Transport Layer of the OSI Model’s responsibility is to
provide end-to-end communication. There are following functions of Transport
Layer
·
Addressing
(port number)
·
Transport
(Connection-Less and Connection-Oriented)
·
Error
Correction
Addressing refer on Layer 4 as port number, suppose when you
are using an internet and you are require to do two jobs. One is browsing using
HTTP and two is download a file using FTP. Here the transport layer gives a port
number to both HTTP and FTP (80 and 20-21) and the result is that the HTTP port
80’s data is not going to mix with the FTP 20-21’s data. Their Sessions at
Layer 5 are going to handle separate and as well as at Layer 6 handle the port
80 and 20-21 differently according to the requirements and at Layer 7 port 80’s
data compare up with the HTTP on the browser and port 20-21’s data compare up
with the FTP.
Transport refer on Layer 4 as the connection-less and
connection-oriented. The two terms are use here. One is connection-less which
means when one device is sending a data to another, the sending device doesn't
going to established a connection with the reviver (no handshaking), it simple
send the data to the reviver and does not care weather it is going to reach at
the destination or not. UDP, ICMP, DNS, T FTP and IP are some of the protocols
of connection-less communication. The other term connection-oriented is
basically the opposite of the connection-less, which means its is going to
establish a connection before sending a data to the reviver (handshaking). When
the data are send, it is going to be acknowledge. By that mean
connection-oriented provide a reliable and guaranteed connection between the
devices. TCP, Frame Relay, ATM and SCTP are some of the protocols of
connection-oriented.
Error Correction is also in the function of the Layer 4. The
connection-oriented protocols are mostly used this function, because it provide
the data grantee. When the reviver revived the data the following methods it
uses for the error detection parity bit, check sum and CRC. When errors are
detected then its going to acknowledge
the sender to resend the data.