PADLIPSKY@A.ISI.EDU.UUCP (12/24/86)
Depending on just what he meant by it, there are some potentially intriguing implications lurking in Marshall Rose's statement the other day that the "FTAM" Draft International Standard doesn't even use "the same underlying services" as its (presumed) predecessor Draft Proposal did. This should be clarified, since if it turns out to mean either that the principles of Layering have suddenly been altered (after all, if they were both at/for the same L, one wouldn't think the underlying services _could_ differ, by definition--unless the trick is that they decided to go to/from "connectionless"), or that the DP was somehow aimed at/for the "wrong" L originally, it really ought to cost ISO a fair amount of credibility. Maybe Marshall was just speaking more casually than I'd assumed he was, though. Whatever the explanation, I think we should all get to hear it. On a probably less significant plane, I also wonder, not having noticed an expansion of "FTAM" anywhere in the message, whether the "AM" means "Access Method." (The "FT" is presumably clear from context.) If so, is this literally or merely figuratively in the IBM "OS" (and successors) sense of the term? If literally, is the problem with the DIS and the DP perhaps that Access Methods don't really correspond cleanly to Layers and it was a change of the arbitrary designation from (I'd imagine, but not bet) 7 to 6 that altered the "underlying services"? -------
mrose@NRTC-GREMLIN.ARPA.UUCP (12/27/86)
I always speak casually, but your inference was correct: the DP
FTAM was written at a time when the Presentation Layer was not
solid enough to use. It consisted of some encoding mechanisms and
an abstract syntax methodology, but did not contain the "usual"
network-style primitives (e.g., OPEN, CLOSE, TRANSFER). So, the
"sanctioned" interpretation was:
- in FTAM you had the presentation encoding mechanisms
- presentation was NULL
- session did all the work
The fact that the DIS uses presentation is not a fundamental change
in thinking--it merely reflects the fact that the presentation
specification can now be used. For those of you familiar with the
1984 CCITT recommendations on Message Handling Systems, the
situation is identical (X.409 is used to encode/decode, X.215 is
used to move bits).
FTAM is File Transfer, Access, and Management.
/mtrPADLIPSKY@A.ISI.EDU.UUCP (12/30/86)
In response to your message sent Fri, 26 Dec 86 21:00:25 -0800 I'd feel myself to have been remiss if I didn't observe that the explanation of why the FTAM DIS is inconsistent with the FTAM DP exposes at least a fundamental flaw in ISO's committee structure and arguably one (or more) in the "Reference Model" itself, but on reflection I'd feel I was wasting everybody's time if I bothered to spell it out in any detail--it ought to be nearly obvious anyway. Suffice it to say that it's probably impossible to do Top-down and Bottom-up simultaneously, especially if two (or more) teams are involved, each thinking itself to be in charge. (I will take another I Told You So on my old "It's Layer [sic] 5-7" line, though, and it might not be too pushy to insist on one for the Slogan that begins "The more Layers, the more committees.") rueful cheers, map -------