23 Feb
2026
23 Feb
'26
2:26 p.m.
On Feb 23, 2026, at 9:18 AM, Paul Koning via cctalk
<cctalk(a)classiccmp.org> 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