12.6 Clearing a Virtual Circuit

The close system call is used to discontinue use of a socket and all of the resources held by the socket, as follows:

int s, error;
 error = close(s);

The close call closes the virtual circuit associated with a socket and frees the resources used by the socket. More specifically, close will send a Clear Request packet and then wait for a Clear Confirmation packet if the socket has an active virtual circuit associated with it. An active virtual circuit is one that is either connected, or is in the early stages of connection (that is, Call Request has been sent, but Call Connected has not been received). In this case, if a Clear Confirmation packet is not received after the amount of time specified in the link configuration file, the socket will be closed and close will return. If the socket does not have an active virtual circuit associated with it, close will return immediately.