[ih] inter IMP hackery [was Recently restored and a small ARPANET was run using simulated IMP hardware, ]

[Alex McKenzie]

 Geoff,
I'm having second thoughts about the reliability of my memory.  I withdraw my comment about the two mag tape TIPs being at Tinker and McClellan.  I think I've mixed up two stories.  I'll do a bit more checking to see if I can find where the 2 mag tape TIPs were actually installed.
Sorry,Alex

    On Monday, September 7, 2020, 11:01:20 AM EDT, Alex McKenzie via Internet-history <internet-history at elists.isoc.org> wrote:  
 
  Geoff,
There were two mag tape TIPs, at Tinker and McClellan Air Force Bases.  The motivation was to allow the Air Force to experiment with using the ARPAnet to replace whatever method they were using to exchange large amounts of data.  I think the test was successful and Tinker and McClellan then decided to attach Hosts to the TIPs to continue operational use of the net to do their data exchanges.  Steve Crocker was involved in helping the Air Force people design the Host software to use the ARPAnet, which led to an amusing story which Steve has recounted several times (it crashed the network, and one of the BBN people decided it was deliberate).  As I recall the test was run in the summer of 1972 and shortly after that the mag tape hardware and software stopped being supported by BBN.
Cheers,Alex

    On Sunday, September 6, 2020, 9:05:33 PM EDT, the keyboard of geoff goodfellow via Internet-history <internet-history at elists.isoc.org> wrote:  
 
 Dave (or Bernie), can you provide any elucidation on the ARPANET MTIPs (the
TIPs that had a magnetic tape unit attached to them)?

yours truly kinda recalls there were perhaps two of them... one being at
GWC?

why were they created and to whom did they send their data?

geoff

On Sun, Sep 6, 2020 at 2:50 PM dave walden via Internet-history <
internet-history at elists.isoc.org> wrote:

> I can describe the genesis.  The IMP code was originally for one host
> computer and several inter-IMP modems (that was what our contract
> specified), and I coded the IMP/Host and Host/IMP code for that in
> parallel with Bernie coding the DDT, etc. Then some host site wanted a
> second host on its IMP -- I think maybe UCLA for its IBM 360.  ARPA
> called us and asked if the IMP could handle more than one Host.  Our
> hardware guys said the Honeywell computer could support (if I remember
> correctly) up to seven interfaces which could be up to four Host
> interfaces or up to four inter-IMP modem interfaces.  We looked at the
> IMP/Host and Host/IMP code and it seemed fairly easy to make it
> reentrant, so we told ARPANET "yes".  Once the IMP would know how to
> handle multiple Hosts and given there was a bit in the header words
> between IMPs and Host to say "real" Host or "fake" Host, the
> possibilities were fairly clear.  I implemented the reentrant IMP-host
> and host-IMP code, and Bernie changed the routines he had written or was
> writing:
> - TTY in/out
> - DDT in/out
> - parameter change packets into the IMP and trace packets out of the IMP
> - into the IMP to be discarded and statistics packets out of the IMP
> For the regular reports from IMPs to the Network Monitoring Center, a
> bit of code in the IMP could send packets to a real host; I don't
> remember which of the fake Hosts they looked like they were coming from
> -- stats maybe.
>
> On 9/6/2020 7:30 PM, Bernie Cosell via Internet-history wrote:
> > Early on as we were coding the IMP stuff the question arose as to what
> to do
> > about the TTY [and how the hell were we to debug the damn thing].  We did
> > several things in this regard.  First I wrote a simple DDT [about as
> powerful as
> > the test-word switches on our PDP-1 :o)] but it allowed us to poke
> around in the
> > dead hulk of the code of a stopped system to see what went wrong and
> also put
> > patches in.  I believe it was originally a stand alone - the imp would
> crash or hit a
> > diagnostic trap and they we could run the DDT and look at buffers and
> counters
> > and pointers and such and generally try to figure out what happened.
> When the
> > IMP was running solidly enough [which actually happened pretty early on
> in its
> > development],  I can't remember the genesis of the underlying idea,
> but  we
> > thought we could route the DDT *over* the net to other IMPs and poke at
> *then*.
> > I came up with a scheme that Will [I think] thought was way too
> complicated:
> >
> >
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-- 
Geoff.Goodfellow at iconia.com
living as The Truth is True
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