Transport Protocols

There are two general types of transport protocols:

• A connectionless protocol treats each datagram as independent from all others. Each datagram must contain all the information required for its delivery.

  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.

• A connection-oriented protocol requires that hosts establish a logical connection with each other before communication can take place. This connection is sometimes called a virtual circuit, although the actual data flow uses a packet-switching network. A connection-oriented exchange includes three phases:
  1. Start the connection.
  2. Transfer data.
  3. End the connection.

  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 re-sends the missing or damaged 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.