The Life-Cycle of TCP/IP Connections
In the process of opening and closing, a TCP connection progresses through a series of states, as illustrated below.
An HTTP connection is a type of TCP/IP connection. It follows the TCP/IP life-cycle.
A connection opens with a pair of SYNchronization messages. It closes with a pair of FINish messages. The messages are in pairs because they go one in each direction. This is the so-called “handshake” between two TCP/IP stacks.
Note that each state name is associated with a code number, “1 closed” for example. That code is the value used by an SNMP MIB (simple network management protocol, management information base).