18 Jan
2018
18 Jan
'18
11:34 a.m.
On Thu, Jan 18, 2018 at 10:27 AM, Noel Chiappa via cctalk <
cctalk at classiccmp.org> wrote:
And an "end-of-packet" bit.
From: Grant
Taylor
The ARPANET supported several different kinds of interfaces between the
IMPs
(the switching nodes in the ARPANET) and hosts, but the 'usual' one was
either 'Local Host' (LH) or 'Distant Host' (DH) which were _basically_
identical except at the very lowest level - LH was TTL, and DH was
differential pair.
Those interfaces were a custom bit-serial thing with a handshake (with
"there's-your-bit", "ready-for-next-bit" lines, etc); see BBN
Report #1822:
http://www.bitsavers.org/pdf/bbn/imp/BBN1822_Jan1976.pdf
So the "ARPANET interface" in the host is a piece of custom hardware (some
were DMA; I also used one which was interrupt per byte) which went on the
host, which talked 1822 (as it was called), of either the DH or LH physical
form.
The IMP emulator emulates the DH/LH interface with UDP packets. I wired up
the dps8/m emulator to the IMP emulator, but I don't have the ARPAnet stack
for Multics, so it's just packets.
-- Charles
Do the necessary emulators support the ARPANET
interface?
Dunno, but they shouldn't be too hard to add.
The real problem is going to be 'what do you hook the simulated ARPANET
interfaces up to, and how'? I know they have IMP code running in
simulators:
http://mailman.trailing-edge.com/pipermail/simh/2013-
November/007672.html
but I dunno how one would hook _that_ simulation up to a simulated host
running a simulated ARPANET interface.