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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)                 9  TCP/IP Transmission Control Protocol (TCP)                      9  TCP Overview, Functions and Characteristics

TCP Overview, Functions and Characteristics 1 2 3 TCP Functions: What TCP Does

Overview of TCP Characteristics and Operation

TCP is a full-featured transport layer protocol that provides all the functions needed by a typical application for the reliable transportation of data across an arbitrary internetwork. It provides transport-layer addressing for application processes in the form of TCP ports, and allows these ports to be used in establishing connections between machines. Once connections have been created, data can be passed bidirectionally between two devices. Applications can send data to TCP as a simple stream of bytes, and TCP takes care of packaging and sending the data as segments that are packaged into IP datagrams. The receiving device's TCP implementation reverses the process, passing up to the application the stream of data originally sent.

TCP includes an extensive set of mechanisms to ensure that data gets from source to destination reliably, consistently and in a timely fashion. The key to its operation in this regard is the sliding window acknowledgement system, which allows each device to keep track of which bytes of data have been sent and to confirm receipt of data received from the other device in the connection. Unacknowledged data is eventually retransmitted automatically, and the parameters of the system can be adjusted to the needs of the devices and the connection. This same system also provides buffering and flow control capabilities between devices, to handle uneven data delivery rates and other problems.

The inclusion of so many capabilities in TCP maximizes the likelihood that just about any application requiring connection-oriented reliable data delivery will be satisfied by the protocol. This is a primary goal of TCP, as it means that higher-layer applications don't individually have to provide these common functions. TCP is the most widely used TCP/IP transport protocol, employed by the majority of conventional message-passing applications.

TCP Overview, Functions and Characteristics 1 2 3 TCP Functions: What TCP Does