NCP
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... Network Control Program (NCP). In most HOSTs, the NCP will be a part
of the executive, so that processes will use system calls to
communicate with it. The primary function ...
... of the executive, so that processes will use system calls to
communicate with it. The primary function of the NCP is to establish
connections, break connections ...
... NCP in one HOST must communicate
with a NCP in another HOST. To this end, a particular link between
...
... link. Messages
received over the control link are always interpreted by the NCP as a
sequence of one or more control commands. As an example, one of the
kinds of control commands is used to assign a link ...
... sockets and 128 receive sockets. A process may request from the
local NCP the use of any one of the sockets with the same user
number; the request is granted if the socket ...
... Here we sketch the mechanisms of establishing, switching and breaking
a connection. As noted above, the NCP interacts with user processes
via system calls and with other NCPs via control commands. We
...
... connection. As noted above, the NCP interacts with user processes
via system calls and with other NCPs via control commands. We
therefore begin with a partial description of system calls and
control commands.
...
... socket>.
The NCP concatenates <AEN 1> and <AEN 2> each with the user
number of the process and the HOST number to form 40-bit ...
... sockets. It then sends a Request for Connection (RFC)
control command to the distant NCP. When the distant NCP
responds positively, the connection ...
... Connection (RFC)
control command to the distant NCP. When the distant NCP
responds positively, the connection is established and the
...
... responds positively, the connection is established and the
process is unblocked. If the distant NCP responds
negatively, the local NCP unblocks the requesting process,
...
... process is unblocked. If the distant NCP responds
negatively, the local NCP unblocks the requesting process,
but informs it that the system call has failed.
...
...
where <port> and <AEN 1> are as above. The NCP retains the ports
and <AEN 1> and blocks the process. When an RFC control
...
... socket. To accept the call, the process issues the Accept
system call. The NCP then sends back an RFC control
command.
...
... UTAH) needs waiting RFNM's before all other messages. At another
site (e.g., SRI), the NCP could benefit by receiving messages for the
user who is next to be run.
...