ANSWER:

Applications that persistently listen on a port handle connection-management of the higher level protocol. The two separate connections over the same port will be handled by the same instance of an application. Two connections, one application, one listening socket. The application is responsible for maintaining application connection state, and managing the TCP connection events (open/close) for the Operating system.

New connections are established at the operating system layer, and once established are passed on to the application listening on that port. When a connection is closed, it can be closed by the OS (generally, unexpected termination for some reason) or the application (normal shutdown), and the application has to handle all cases.

by sysadmin1138 from http://serverfault.com/questions/383932