<div dir="ltr">for all practical purposes, the operation of the IMPs had little to do with the design of TCP except for the fact that TCP did not assume one message at a time regime that was part of the 1822 IMP/Host interface specification.<div><br></div><div>v</div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Sep 17, 2015 at 6:35 PM, Bradley Fidler <span dir="ltr"><<a href="mailto:fidler@ucla.edu" target="_blank">fidler@ucla.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div><div style="font-size:small;font-family:arial"><div dir="ltr"><div style="font-family:arial,sans-serif;font-size:13px">Are there other historical questions that might be answered using the IMP Guys' article (<a href="http://walden-family.com/bbn/imp-code.pdf" target="_blank">http://walden-family.com/bbn/imp-code.pdf</a>) and method as a starting-point? Maybe with an expanded version of the IMP program simulation, if someone were interested?</div><div style="font-family:arial,sans-serif;font-size:13px"><br></div><div style="font-family:arial,sans-serif;font-size:13px">For example, if we knew less about the IMP software -- if what Dave wrote below wasn't widely known -- then the simulation might have been a great way to test the impact of line speeds and thus how different ideas contributed to the initial design.</div><div style="font-family:arial,sans-serif;font-size:13px"><br></div><div style="font-family:arial,sans-serif;font-size:13px">As another example, consider the impact of congestion on the routing algorithm. The improvements to the algorithm over time are documented in BBN reports, and in part through this documentation we also know that some of these problems were discovered as a consequence of increasing traffic and (if I recall correctly) node count. It would be great to be able to model the response of given versions of the routing algorithm to increased traffic and network size. It would require a lot of assumptions, to be sure, but there is a bit published on the distribution of hop counts, packet size, etc. of which someone could make use. More speculatively, I also wonder if there's enough complaining about congestion on extant listserv archives from the 1980s to combine it with network maps in order to generate some findings on how much traffic might have been common at the time -- and then some even more speculative (but better than nothing!) findings on user counts based on estimates of traffic per user. Perhaps we already have good congestion figures in the NIC archive at CHM, though, or somewhere else... In any case, this is just one off-the-cuff example. Can anyone think of others?</div><div style="font-family:arial,sans-serif;font-size:13px"><br></div><div style="font-family:arial,sans-serif;font-size:13px">This isn't to fetishize the ARPANET, but to point out one possible way to learn more about the interplay of these or other factors in the histories of networking. One advantage of modeling ARPANET things is that the findings could apply in part to the many networks that were largely ARPANET clones.</div><div style="font-family:arial,sans-serif;font-size:13px"><br></div><div style="font-family:arial,sans-serif;font-size:13px">Brad</div><div style="font-family:arial,sans-serif;font-size:13px"><br></div><div style="font-family:arial,sans-serif;font-size:13px"><br></div></div></div></div>
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<br><div class="gmail_quote">On 17 September 2015 at 14:23, <span dir="ltr"><<a href="mailto:dave.walden.family@gmail.com" target="_blank">dave.walden.family@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">As Bob Armstrong knows, the IMP code (from 1973 or there abouts) that Bob simulated was highly tuned for the actual line speeds of the net. Maybe the code knew about something less than 56KBS (I'd have to study the listing). Also the IMP knew of a maximum of 5 inter-IMP modem interfaces, and I don't think it ever used more than 4 and I think option for the 5th doesn't work (at least in the simulated version, and likely in the real code). Thus simulating lots of low speed lines might require modifying the IMP assembly code.<br>
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Sent from my iPad<br>
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On Sep 17, 2015, at 4:14 PM, Jacob Goense <<a href="mailto:dugo@xs4all.nl" target="_blank">dugo@xs4all.nl</a>> wrote:<br>
<br>
> On 2015-09-17 19:11, <a href="mailto:jnc@mercury.lcs.mit.edu" target="_blank">jnc@mercury.lcs.mit.edu</a> wrote:<br>
>> I suspect the only way to say with any certainty how well a network<br>
>> built out<br>
>> of lots of slow lines, as opposed to a few fast ones, would have worked<br>
>> is a<br>
>> comprehensive simulation. Which is not likely to happen, of course! ;-)<br>
><br>
> Well, there is an ARPAnet IMP in simh now. According to Bob Armstrong..<br>
><br>
> "The hooks are in there to allow simh to support the IMP side of the<br>
> 1822 host interface, and the next step would be to recover the OS for<br>
> an ARPAnet era host and then extend the corresponding simulator to talk<br>
> to the IMP simulation."<br>
><br>
><br>
><br>
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