II. Environment

We assume that the host will have a time-sharing operating system in which the CPU is shared by processes.

We envision that each process is tagged with a user number. There may be more than one process with the same user number; if so, they should all be cooperating with respect to using the network.

We envision that each process contains a set of ports which are unique to the process. These ports are used for input to or output from the process, from or to files, devices, or other processes.

We also envision that a process is not put to sleep (i.e., blocked or dismissed) when it attempts to LISTEN or CONNECT. Instead it is informed when some action is complete. Of course, a process may dismiss itself so that it wakes up only on some external event.

To engage in network activity, a process attaches a local socket to one of its ports. Sockets are identified by user number, host and AEN; a socket is local to a process if the user numbers of the two match and they are in the same host. Thus, a process need only specify an AEN when it is referring to a local socket.

Each port has a status which is modified by system calls and concurrent events outside the process (e.g., a 'close connection' command from a foreign host). The process may look at a port's status as any time (via the STATUS system call).

We assume a one-to-one correspondence between ports and sockets.