> On Feb 23, 2026, at 9:18 AM, Paul Koning via cctalk <[email protected]>
> wrote:
>
> Correct.
>
> The layer and component names in DECnet are different from those in other
> protocols, OSI as well as TCP/IP. Phase IV tried to move somewhat towards
> OSI terminology and of course Phase V completed that move, but Phase III and
> before are different. So we have NSP which OSI calls "transport" and ARPAnet
> calls TCP (and before that NCP, I think). And Phase III speaks of the
> "transport" layer which OSI calls the network layer and ARPAnet calls IP.
>
> Another somewhat confusing thing is that in some cases DECnet has
> conventional names for the client, the server, and the protocol, all
> separate. So we see NFS/FAL/DAP, NCP/NML/NICE, TLK/LSN/<something>.
>
> NCP as a standardized element, with its protocol NICE, arrived in Phase III.
> I was somewhat surprised to find a predecessor of both the program and the
> protocol in Phase II for TOPS-20, since as far as I remember there isn't
> anything like it in the Phase II version of DECnet/E, nor have I ever seen a
> protocol spec for the Phase II version of NICE. Reverse engineering it from
> the sources explains the odd message numbering in (phase III) NICE, though:
> the numbering starts at 15 because the numbers below that were used (mostly
> for similar functions but with quite different encoding) in the Phase II
> version of the protocol.
More: in Phase IV we recognized the naming conflict between existing DECnet
layers and OSI. Rather than go directly to OSI names, that was judged to be
confusing because the two most important layers have roughly the same names but
reversed: transport = network layer, and NSP (network services protocol) =
transport layer. So instead Phase IV was given new names for those layers that
are descriptive and were not in use for any other purpose at the name:
"routing" and ECL ("end communication layer").
paul
