A protocol is a set of rules or standards that each host must follow to allow other hosts to receive and interpret messages sent to them. There are two general types of transport protocols:
An example of such a protocol is User Datagram Protocol (UDP). UDP is a datagram-level protocol built directly on the IP layer and used for application-to-application programs on a TCP/IP host. UDP does not guarantee data delivery, and is therefore considered unreliable. Application programs that require reliable delivery of streams of data should use TCP.
An example of such a protocol is Transmission Control Protocol (TCP). TCP provides a reliable vehicle for delivering packets between hosts on an Internet. TCP breaks a stream of data into datagrams, sends each one individually using IP, and reassembles the datagrams at the destination node. If any datagrams are lost or damaged during transmission, TCP detects this and retransmits the missing datagrams. The data stream that is received is therefore a reliable copy of the original.
These types of protocols are illustrated in Figure 1 and in Figure 1.