TCP is typically used by applications that require guaranteed delivery. It is a sliding window protocol that provides handling for both timeouts and retransmissions.

TCP establishes a full duplex virtual connection between two endpoints. Each endpoint is defined by an IP address and a TCP port number and is implemented as a finite state machine.

The byte stream is transfered in segments. The window size determines the number of bytes of data that can be sent before an acknowledgement from the receiver is necessary.

Transmission Control Protocol (TCP) is a connection-oriented, reliable delivery byte-stream transport layer communication protocol, currently documented in IETF RFC 793 . It does the task of the transport layer in the simplified OSI model of computer networks.

In the Internet protocol suite, TCP is the intermediate layer between the Internet Protocol below it, and an application above it. Applications most often need reliable pipe-like connections to each other, whereas the Internet Protocol does not provide such streams, but rather only unreliable packets.

Applications send streams of 8-bit bytes to TCP for delivery through the network, and TCP divides the byte stream into appropriately sized segments (usually delineated by the maximum transmission unit (MTU) size of the data link layer of the network the computer is attached to). TCP then passes the resulting packets to the Internet Protocol, for delivery through an internet to the TCP module of the entity at the other end. TCP checks to make sure that no packets are lost by giving each byte a sequence number, which is also used to make sure that the data is delivered to the entity at the other end in the correct order. The TCP module at the far end sends back an acknowledgement for bytes which have been successfully received; a timer at the sending TCP will cause a timeout if an acknowledgement is not received within a reasonable round trip time, and the (presumably lost) data will then be re-transmitted. The TCP checks that no bytes are damaged by using a checksum; one is computed at the sender for each block of data before it is sent, and checked at the receiver.