Transport Layer Protocol

The original TCP/IP protocol suit specifies two protocols for the transport layer: UDP and TCP. First we will discuss the UDP that is the simpler one then to the other TCP.A new third protocol is also design are STCP.

User Datagram Protocol (UDP):

The user datagram protocol (UDP) is also called as connectionless, unreliable transport protocol. It does not add anything to the services of IP except to process to process communication. If we say that, why would we want to use is it? There are many advantages of UDP other than disadvantages.
UDP is only use simpler transfer. If we want to send the simple message then we use UDP, if we don’t want to use reliability. To send a simple message through the UDP take less interaction to the sender and receiver then TCP or SCTP.

UDP operations:

UDP uses concepts common to transport layer. It is fixed 8-bytes header size. We will discuss it briefly.

Connectionless Services:

As discuss previously, connectionless services provided by the UDP. This means that every datagram are independent. Each datagram is free that is coming from one point and going to other point. Datagram are not numbered. Independent means to say that each datagram are not travel in same path. The datagram that coming from same destination are not related to each other. They are free for use. That’s why we say that the messages that have small content are compatible for the UDP.

Flow and Error Control:

UDP is a very simple, unreliable protocol. There is no flow control or window mechanism. This means that any error or duplication is undetected from the sender. When the receiver detects an error through checksum, it silently discards the message.

Encapsulation and Decapsulation:

To send a message from one points to other UDP Encapsulate and decapsulate the message in IP datagram.

Uses of UDP:

1.       UDP is best for a process that is require simple request-response communication with little concern   for flow and error control. It is not usually used for FTTP that needs to be send bulk of data.

2.       UDP is suitable for the process with internal flow and error control mechanism.

3.       UDP is used for transport protocol for multicasting.

4.       UDP is used for management process such as SNMP.

Transmission control protocol

The second transport layer protocol that we discuss is transmission control protocol (TCP) like UDP, is a process-to-process (program-to-program) protocol. Like UDP it is also use port number. Unlike UDP, TCP is a connection oriented protocol: it creates a virtual connection between two TCPs to send data. TCP is called a connection oriented, reliable transport protocol.

TCP Features:

TCP has several features that are briefly summarized in this section.

Numbering system:

Although the TCP software keeps track of the segments being transmitted or received, there is no field for a segment number value in the segment header, there are two fields called the sequence number and acknowledgment number. These two fields refers to the byte number and not the segment number.

Uses of TCP:

1.  It is reliable service. It uses a mechanism to check the safe and sound arrival of data     
2.  It gives us a connection oriented service.
3. There is a numbring system exist between the segments