The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Transport Layer Protocols            9  Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)

Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) 1 2 3 TCP/IP Transport Layer Protocol (TCP and UDP) Addressing: Ports and Sockets

The Solution: Two Very Different Transport Protocols

Fixing this problem was simple: let the network layer (IP) take care of basic data movement on the internetwork, and define two protocols at the transport layer. One would provide a rich set of services for those applications that need that functionality, with the understanding that some overhead was required to accomplish it. The other would be simple, providing little in the way of classic layer-four functions, but it would be fast and easy to use. Thus, the result of two TCP/IP transport-layer protocols:

• Transmission Control Protocol (TCP): A full-featured, connection-oriented, reliable transport protocol for TCP/IP applications. TCP provides transport-layer addressing to allow multiple software applications to simultaneously use a single IP address. It allows a pair of devices to establish a virtual connection and then pass data bidirectionally. Transmissions are managed using a special sliding window system, with unacknowledged transmissions detected and automatically retransmitted. Additional functionality allows the flow of data between devices to be managed, and special circumstances to be addressed.
  
  
• User Datagram Protocol (UDP): A very simple transport protocol that provides transport-layer addressing like TCP, but little else. UDP is barely more than a “wrapper” protocol that provides a way for applications to access the Internet Protocol. No connection is established, transmissions are unreliable, and data can be lost.

By means of analogy, TCP is a fully-loaded luxury performance sedan with a chauffeur and a satellite tracking/navigation system. It provides lots of frills and comfort, and good performance. It virtually guarantees you will get where you need to go without any problems, and any concerns that do arise can be corrected. In contrast, UDP is a stripped-down race car. Its goal is simplicity and speed, speed, speed; everything else is secondary. You will probably get where you need to go, but hey, race cars can be finicky to keep operating.

Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) 1 2 3 TCP/IP Transport Layer Protocol (TCP and UDP) Addressing: Ports and Sockets