TCP is the most common protocol of the transport layer and its jobs includes the reliable data transfer. TCP is based upon the connection oriented protocol and also we can call it stream oriented protocol. As the connection is established we can send the bytes not the packets. TCP contains a header and type of data that is transferred is not mentioned here. The fields of the TCP format are shown in the following table.

(16) Source port Destination port Sequence Number (32) ACK No (32) HLen (4) Reserved (6) Code (6) Window (16) Checksum (16) Urgent Pointer (16) Options Padding
Payload (maximum 65535-20-20 bytes) Table 1: TCP format with fields

User Data Protocol is found in transport layer and shows connectionless characters used on internet. It is based on the single send and receive message. Remote procedure calls are the good example of the UDP. For the purpose of the broadcasting of routing tables of nearby routers with RIP and OSPF, where the connection is not needed; UDP proves to be more effective. Header of the UDP is simply four 16 bit with field source port, destination port, checksum, message length and payload. Payload can be calculated the by subtractions of both UDP header length and IP header length. UDP and TCP use the same kind of checksums and UDP with checksum zero is not a valid checksum.

TCP Handshake
To facilitate the characters of connection-oriented protocols, all the TCP connections start with a handshake into three steps.