The TCP Protocol

TCP works on top of IP, and adds reliability, and a 'virtual stream' notion to what IP provides.

TCP uses port numbers in order to allow the establishment of up to 32767 simultaneous connections between each two machines on an internetwork. Thus, a TCP connection would be identified by two IP addresses and two port numbers, e.g. 198.70.1.7:80 - 207.91.14.5:3024

TCP's reliability is limited - if there is too much packet loss, it the connection will work very slow. It also cannot guarantee that packets are not corrupted, due to a rather simplistic CRC (Cyclic Redundancy Checksum) algorithm.