On Oct 9, 2015, at 11:01 AM, Paul Koning <[email protected]> wrote:
> >> On Oct 9, 2015, at 9:38 AM, Johnny Billquist <[email protected]> wrote: >> >>>> ... >>> Phase II use NSP v3.1 so that’s probably another indication that it’s a >>> Phase I product. >> >> John, maybe you can clear some things up for me. >> Looking at the Wikipedia article about DECnet, it claims that phase I was >> simply between two nodes. No larger than that. And in addition was RSX-11 >> only. And it was 1974. > > It wouldn't be at all surprising if the information about Phase I were > inaccurate given its undocumented status. > I tend to agree with Paul here. I’m also pretty sure that it was RSX-11D only as well. The systems I used were moved into a newly built machine room sometime around Aug-Sep 1976 and the was when we installed DECnet. As to the limit of two nodes I have no direct knowledge but in mid-1977, Volvo were using a DV-11 in their Phase I network. An 8-line multiplexor which took up 9 backplane slots would seem to be overkill for a 2 node network. >> Phase II says multiple implementations on different systems, and a max of 32 >> nodes. Also supposedly added task-to-task programming interfaces. And >> supposedly 1975. >> >> Phase I definitely had task-to-task interfaces along with TLK/LSN and file transfer (PLE seems to ring a bell as the NFT equivalent). The timeframe here seems to be off. I moved to the US in Jan 1977 to be the project leader for DECnet-11D/IAS. The original plan called for a 9-month development cycle but it ended up more like 18+ months, so mid-1978 would be more accurate. >> Now, looking at the DECNET/8 documentation, there is some discrepancy here. >> DECNET/8 supports up to 127 nodes. It only have point-to-point links, but it >> clearly have some idea of dealing with several hops to reach the >> destination. It also obviously have task-to-task programming interfaces, >> which looks very similar to what I know from phase IV. >> >> Now, I'm happy to believe that Wikipedia is just plain wrong, but it would >> be interesting to hear if you can provide any more details to what phase I >> and phase II differed on, and where DECNET/8 would fit based on that. > > I looked at the document you sent. While it has some hints about the > protocol in chapter 6, it doesn't come close to telling us what's necessary > to build a compatible implementation. DDCMP might be compatible; the bits of > packet layout given on page 6-4 seem to match those of the later DDCMP specs. > > NSP, on the other hand, clearly is not compatible. Again, there are only > hints of packet layouts -- only some of those are shown and their semantics > not described. It has an optional routing header just as Phase II does, but > encoded differently. And the message type field (MSGFLG, first byte of the > NSP message header proper) looks somewhat like that of later versions of NSP > but the encoding is substantially different. The Connect message looks > vaguely like a later Connect Initiate, but the details are quite different. > Based on what little I can see, the statement in the Phase II spec that Phase > I was incompatible (implying "it's not feasible for a Phase II node to > interoperate with a Phase I node") is indeed accurate. > > The normal case of Phase II was that it allowed communication only between > adjacent nodes. A given node could have multiple interfaces, presumably > connected to different neighbors, and it would use the destination address of > a packet to choose the correct interface on which to communicate. The same > would, I assume, apply to Phase I. > > Phase II had an optional routing header for something called "intercept" > operation. The DECnet/8 document describes the same sort of thing though the > encoding is different. I can't tell if DECnet/8 could actually supply > routing headers; it does say clearly that it would not act on them. > Similarly, most Phase II implementations didn't handle routing headers either > (would neither generate nor accept them). The Phase II spec is not all that > clear on how they are supposed to be generated or used, in fact. I vaguely > remember that TOPS-10 (or -20?) used them, with the front end processor > acting as the forwarding node and the main CPU as endpoint. So communication > would be two hops: PDP-10 to front end to other node. While theoretically > there might be more hops, in practice that didn't happen. For one thing, > Phase II NSP doesn't appreciate lost packets. > > In Phase III all that changed, with a real routing protocol, clearly > documented routing operation, and an NSP that would do retransmission to > handle lost datagrams. > > paul > > _______________________________________________ > Simh mailing list > [email protected] > http://mailman.trailing-edge.com/mailman/listinfo/simh _______________________________________________ Simh mailing list [email protected] http://mailman.trailing-edge.com/mailman/listinfo/simh
