1a Control Links
1a1 Logical link 0 will be a control link between any two HOSTs on
the network
1a1a Only one control link may exist between any two HOSTs on
the network. Thus, if there are n HOSTs on the network, there
are n-1 control links from each HOST.
1a2 It will be primarily used for communication between HOSTs for
the purposes of:
1a2a Establishing user links
1a2b Breaking user links
1a2c Passing interrupts regarding the status of links and/or
programs using the links
1a2d Monitor communication
1a3 Imps in the network may automatically trace all messages sent
on link 0.
1b Primary Links
1b1 A user at a given HOST may have exactly 1 primary link to each
of the other HOSTs on the network.
1b1a The primary link must be the first link established
between a HOST user and another HOST.
1b1b Primary links are global to a user, i.e. a user program
may open a primary link, and that link remains open until it is
specifically closed.
1b1c The primary link is treated like a teletype connected over
a normal data-phone or direct line by the remote HOST, i.e. the
remote HOST considers a primary link to be a normal teletype
user.
1b1d The primary link is used for passing (user) control
information to the remote HOST, e.g. it will be used for
logging in to the remote host (using the remote hosts standard
login procedure).
1c Auxilliary Links
1c1 A user program may establish any number of auxilliary links
between itself and a user program in a connected HOST.
1c1a These links may be used for either binary or character
transmission.
1c1b Auxilliary links are local to the sub-system which
establishes them, and therefore are closed when that subsystem
is left.
