[ih] ruggedized Honeywell 516 ARPANET IMP cabinet top lifting hooks (Was: The IMP Lights story (Was: Nit-picking an origin story))

[Jack Haverty]

I heard similar claims about the ARPANET's survivability.

IIRC, the IMPs themselves were militarized, but could still be 
obliterated in a "hostile battlefield".  But the ARPANET itself would 
continue to function, with the remaining undamaged IMPs still operating 
and providing host-host communications - even if enough nodes had been 
destroyed to render the network into several fragments.   The reasoning 
was that, unlike other network designs of the era, there was no central 
locus of control in the ARPANET.

In other network designs, there was a control center located at some 
node, which handled setting routes, establishing and closing 
connections, et al.  So if that node was destroyed, all nodes would 
become unable to communicate, even if they were undamaged.   IIRC, IBM 
networks of that era had that characteristic.

IMPs had a NOC, but it wasn't involved in minute-by-minute control 
operations.   Each IMP was self-contained and able to interact with 
whatever other IMPs and circuits it could contact after events like 
circuit failures or disappearance of other IMPs.  IMPs didn't need a NOC 
to open/close connections and pass traffic between hosts.

IMPs themselves wouldn't survive a "nuclear event", or likely even a 
non-nuclear one.   But the remaining IMPs would continue to operate the 
ARPANET even if it was split up into several pieces.   IMPs wouldn't 
survive, but the network would.

The Internet followed a similar design principle, with no centralized 
control - although we thought about it when TCPV2 was being transformed 
into TCP/IPV4, as a possible approach to providing functionality such as 
"policy-based routing".

Jack

PS - The "Pluribus IMP" was a later design, using a highly redundant 
multiprocessor computer architecture that could survive multiple 
failures, although not a bomb.  Probably.  It was used in some "clones" 
of ARPANET within the government.  I once heard a rumor about when one 
such IMP was decommissioned.  The technicians decided to see how robust 
the hardware really was.  So they "decommissioned" a node, while it was 
running, using an M16 rifle.  It took way more shots than they expected 
before the IMP finally stopped working. Apocryphal story?  Maybe.  I 
wasn't there to watch.   More info about Pluribus IMP at 
https://apps.dtic.mil/sti/html/tr/ADA151312/index.html

PPS - re the massive hooks on the original IMPs:  IMPs were built using 
commercially available computers from Honeywell.  I always assumed that 
the militarized model had hooks (and other features such as those 
massive connectors) because it was a requirement for DoD procurements, 
and Honeywell computers were probably used in the military for other 
purposes than IMPs.  Hooks were probably required for use in moving 
equipment on/off naval vessels with cranes, securing equipment when used 
in places while in motion (ships, jeeps, planes...) and other such needs 
in military installations.


On 8/25/25 08:24, Dave Crocker via Internet-history wrote:
> On 8/25/2025 6:00 AM, Steve Crocker via Internet-history wrote:
>> There was no requirement or expectation that the IMPs would survive a
>> nuclear event.
>
>
> Again, as a mere passenger on the packet-switching technical 
> development train, trying to learn what I could, I don't recall ever 
> hearing nuclear survival as a goal, but I do remember repeatedly 
> hearing something like "survive hostile battlefield conditions".
>
> When reciting this to others, such as doing TCP/IP presentations, I 
> noted that this turned out to include average commercial operating 
> environments...
>
> Also, my understanding is that a precise example of hostile 
> battlefield conditions was not tested until the first Iraq War, and 
> then it was Iraq's network (using Ciscos?) that did indeed survive...
>
> d/
>

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