[ih] Fwd: Internet at Sea

[Craig Partridge]

As I recall it was called the Defense Simulation INternet (DSIN) or
something close and was carefully engineered to have enough capacity to
link the various simulators.  It made heavy use of UDP.

Couple of quick comments (some of my college classmates were the core of
the initial implementation team, but I was not on the team, so some details
may be not quite right) about the networking aspects.

Both network bandwidth and the number of messages was at a premium and the
team figured this out quite quickly.  They were working initially with the
1983-vintage Internet, with no working congestion control and where
effective Ethernet speed was about 1Mbps due to network adapter limitations
and Unix kernel limitations.

They had, initially, an n*n comms pattern, every "thing" in the simulated
space was tracking what every other "thing" was doing to ensure everyone
had a faithful representation of the world.  Each node drove its own
graphics displays (and there were multiple per tank).  You didn't have to
get too many tanks, plus shells and other moving things, and the network
saturated if you sent out an update on every action.

So what they did was develop predictive algorithms for each item.  For
instance, if a tank was speeding along, the algorithm predicted it would
continue along its current path and the tank only sent an update when it
deviated from the predicted path.  Each node was, therefore, calculating
what it thought each item in the space was doing and looking for occasional
updates.  This sharply reduced network traffic and made performance quite
good -- and this is the core of the simulation protocols that were
developed in the late 1980s and early 1990s.

There were some early hiccoughs.  There's an art to figuring out how often
to update and soldiers (who were getting to play the world's best video
game in high end tank simulators) were quick to figure out glitches and
take advantage.  As I recall, one trick was to drive your tank at maximum
speed (something like 60 mph) crosswise in front of your opponent's tank
with your gun pointing ahead -- so they think you're an unsuspecting target
but also have to line up a shot on a fast moving object.   Then, just
before you estimate your opponent has got their shot ready, you stomp on
the brakes and turn your turret towards them and fire.  What the opponent
would see is your tank magically jump backwards and shoot at them.

Side story: as I understand the politics of simulation, the SIMNET project
had a number of challenges getting the various contractors to play nicely.
I think BBN finally ended up buying the specialized graphics display
company to reduce friction.  But what made SIMNET a big success was the
NATO Tank Competition.  The US Army historically did poorly -- someone (the
SIMNET PM?), in a stroke of marketing genius, had SIMNET code the tank
course into the simulator and let the Army team practice on it.  The US won
the competition....

Craig



On Tue, Oct 7, 2025 at 1:26 PM Jack Haverty via Internet-history <
internet-history at elists.isoc.org> wrote:

> Answering Barbara's questions...
>
> A few years ago, someone who had worked on SIMNET told me that they had
> chosen to use a private network approach rather than running over The
> Internet which was shared with others.   I don't know any of the details
> though.
>
> My suspicion is that they built a private clone of the Internet, using
> TCP/IP routers, and circuits.  Lots of corporations were deploying
> similar private clones for use within their corporation and possibly
> some partners.
>
> For a particular project, a private "intranet" could be carefully
> managed to meet the needs for gaming, perhaps using the methodology
> learned from the ARPANET.
>
> The ARPANET had a team of analysts who looked at traffic statistics and
> trends, and designed changes to the ARPANET, e.g., to add or remove
> circuits, order higher bancwith, modify protocols, etc. That same
> philosophy could be applied to a private Internet, to maintain needed
> and consistent performance for a specific application.
>
> In addition, with all of the switches and computers involved in the
> project under the project's control, customized approaches could be
> designed and implemented.  Corporations couldn't really do that when all
> their routers came from Cisco, but a military project such as SIMNET
> could; perhaps they implemented some TOS functionality, or something
> else to address the latency requirements.  With a private system, even
> based on TCP/IP, you could do that.
>
> Coordinating with the "public" Internet, funding research on general
> solutions and implementations, and getting new mechanisms into the
> Standards Process was not needed for the project to be successful. A
> project-specific solution was sufficient.
>
> But I don't know any of the actual details about how the SIMNET
> communications worked.   So the above is just speculation.  I suspect
> the details are in reports somewhere in DTIC.
>
> /Jack
>
> On 10/7/25 10:38, Greg Skinner via Internet-history wrote:
> > forwarded for Barbara
> >
> >> ----- Forwarded Message -----
> >> From: Barbara Denny <b_a_denny at yahoo.com>
> >> To: Internet-history <internet-history at elists.isoc.org>
> >> Sent: Monday, October 6, 2025 at 10:45:00 AM PDT
> >> Subject: Re: [ih] Internet at Sea
> >>
> >> See inline comments below.
> >>
> >> On Saturday, October 4, 2025 at 03:31:27 PM PDT, Jack Haverty via
> Internet-history <internet-history at elists.isoc.org> wrote:
> >>
> >>
> >> Some better search term on discover.dtic.mil found this - the sequel to
> >> the report I just mentioned, published a year later:
> >>
> >> https://apps.dtic.mil/sti/tr/pdf/ADA239925.pdf
> >>
> >> Chapter XVI is titled "SIMNET" which has a special, but likely as yet
> >> untold, history with The Internet.
> >>
> >> Sometime in late 1982 or early 1983, ARPA asked our "Internet" group at
> >> BBN to get involved with a project that might be able to use the
> >> emerging Internet for its communications infrastructure.  That program
> >> was called SIMNET, or SIMulation NETwork, and the concept was to create
> >> a video-game type of training tool for use in combat training.  The
> >> initial use was training M-1 tank crews, but the concept included other
> >> participants, such as helicopters.  Mike Kraley and I went to a bunch of
> >> meetings to brainstorm and flesh out the ideas, as part of our ongoing
> >> work on ARPA Internet-related contracts.
> >>
> >> It became clear that for such "gaming" applications, network latency was
> >> important.  It mattered a lot.  If you fired at the enemy, you should be
> >> able to see the results immediately and consistently.  A training system
> >> had to be accurate for the things that mattered, but could cut corners
> >> to save costs for the things that didn't.
> >>
> >> Inside the Internet world, that need was one of the motivations for the
> >> introduction of the TOS field (Type Of Service) in the IP header.  Our
> >> conclusion was that the Internet would have to support at least two
> >> different types of behavior.  Possibly more since SIMNET was also
> >> envisioned to simulate radio traffic and "chatter" between the crews in
> >> the simulation, using packet voice.
> >>
> >> Datagrams associated with things like firing weapons or vocal snippets
> >> could be small, but had to get delivered quickly. Datagrams associated
> >> with things like detailed maps could be delivered at a more leisurely
> >> pace.  Terrestrial routes would be good for the former, and
> >> geosynchronous satellites appropriate for the latter.  Of course there
> >> would also need to be new appropriate routing mechanisms to make it all
> >> work as envisioned.
> >>
> >> At BBN, we wrote a proposal to start an actual SIMNET project. Shortly
> >> thereafter, in July 1983, BBN reorganized and that project was approved
> >> and the contract assigned to a part of BBN that had been doing various
> >> training systems.  So I never got to drive an M1 tank (which was an ARPA
> >> mandated requirement for everyone assigned to the project).
> >>
> >> SIMNET ended up being very successful, as detailed in that report. But
> >> the implementors discovered that the Internet, which hadn't implemented
> >> any mechanisms for TOS, couldn't provide the communications services
> >> that SIMNET needed.   They had to build their own private communications
> >> system instead.
> >>
> >>> Can you expand on your thoughts here?  I didn't really participate in
> SIMNET much but I am confused about your words here. I never heard anything
> about people deciding they needed to build their own private communications
> system instead.  Do you remember when you heard this? Or was this just a
> recommendation? Did this ever happen or did the end of the Cold War stop
> this thinking?
> >>> A little more background...
> >>   > In the fall of 1991, I was sent to Germany for demonstrations of
> packet radio (DARPA effort).   It used the LPR (Low Cost Packet Radio)
> which as far as I know was the last version of radio hardware and software
> before that program ended. BBN was also sent there to support this
> demonstration and they were tasked with the application component.  The
> demonstrations were  pretty important. The observers were at the Warrior
> Preparation Center. (FYI, The LPRs were deployed as far away as Rammstein
> Air Base. I got to ride in a real Humvee as we set up the network!). Later
> SRI got a letter from DARPA regarding this effort.  The letter said the
> success of the demonstrations resulted in the military considering using
> the lpr in support of mobile responders for Reforger '92  and made them
> feel they they could extend simulation to the battalion commander ( At some
> point I remember hearing DARPA wanted to combine both real and simulated
> elements together for training purposes).  The letter a
> >   lso said DARPA was looking forward to breaking new ground in
> warfighting simulation technology.   There was no hint of some other
> communication system.
> >>> I am also including a link to a BBN report covering simulation of the
> radio communication environment for SIMNET.  It was interesting to me
> because they chose SINCGARS for the model.  This report is dated January
> 1992 and the SRI DARPA letter is dated December 1991.
> >> https://apps.dtic.mil/sti/tr/pdf/ADA244212.pdf
> >>
> >> In retrospect, we probably didn't do enough to lay out that plan for
> >> coordinating the SIMNET and Internet evolution.  ARPA reorganized at
> >> about the same time, the ICCB became the IAB, the people involved
> >> changed, and the plan was lost.  SIMNET was successful, but TOS support
> >> in the Internet didn't happen.
> >>
> >>> BTW, if you look at the packet radio paper recently cited, there is a
> flag in the packet radio E2E header that indicates a packet speech type of
> service.  The definition of what that means for the radio is defined.  I
> would think that because of the packet speech work in the 70s, the ToS
> field in the IP header would have been used.  I haven't seen or heard about
> this so what happened?   I think there were other motivations for using
> this field in the IP header beyond SIMNET.
> >>> barbara
> >> /Jack Haverty
> >>
> >>
>
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