Hi Paul,

I had been following that discussion on DECnet/8, although pretty silently as I don't have much useful information to add. It is interesting to understand the impetus for the enhancements to the protocol.

Also of interest is this talk about the origins of RSTS-11. Where was this and was it recorded (posted to YouTube, etc.)?

Regards, Tim.

On Tue, 27 Jun 2023 at 08:22, Paul Koning <paulkoning@comcast.net> wrote:
Since there has been a bunch of work done to revive what is supposedly a DECnet Phase I implementation (DECnet/8 for RTS/8) I realized I could perhaps get some more information going back that far.  Some months ago Nathan Brookwood (formerly known as Nathan Teichholz) gave a talk about the beginning of RSTS-11, and in that he mentioned as an aside that he subsequently served as program manager for the initial development of DECnet.

So I asked him if DECnet/8 sounded familiar and if he could tell me anything further about that time.  His reply:

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I was responsible for coordinating all the versions of DECnet for the initial "Phase I" releases, but developers in each operating system were responsible for the implementations. Each group was building from the definitions of DDCMP and NSP that were extant in the 1973-75 period. There was also a testing and communications protocol called "NICE" (don't ask me what that stood for) and a file transfer utility.

The Phase I versions did not include routing, and when the developers tried to add routing capabilities to those first versions, they discovered that there was a need to make significant changes to NSP that would preclude backwards compatibility with the Phase I versions. The implementation of DDCMP survived intact, since physical link protocols are below the routing protocols level.
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That ties into the statement in the Phase III General Description document which says that Phase I nodes can't coexist with later versions in the same network, and it also matches what the DECnet/8 manual makes quite clear in its chapter discussing the protocol details: Phase I NSP is conceptually pretty similar to Phase II NSP, but the packets are 100% incompatible.  So the "significant changes" Nathan mentioned are what happened in DECnet Phase II -- which modifies NSP to include sequence numbers and ACKs and in the process also changes lots of other details in the protocol encoding.  That still wasn't quite enough, and Phase III filled in some missing details in an upward compatible fashion (the Connect Ack and Retransmitted Connect Initiate message, as well as timeout and retransmit algorithms).

        paul

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