🚀 go-pugleaf

   I have gotten flamed for saying that the Presentatio Layer can be (more
or less) null in an OSI-compliant implementation. The main argument seemed to
involve "having" to do ASN.1/BER encoding/decoding and prepending Presentation
and Session headers onto each datagram at run time.
   Now somebody is seriously confused, so I'll toss this to the net and see
who can set everyone straight....
   My understanding of ASN.1/BER is that it is a means for describing Abstract
Objects (such as the english word "Hello") in a universally-understood manner.
So if I am sending bits to somebody who is expecting a BER encoding of the
ASN.1 description of the sequence of characters "Hello", she will first expect
a sequence of octets that say "here's an english-language character [tag and
type] and it is an H..." and then some more that say "Okay, here's another one,
and it's an e..." and so forth. No matter if I'm running on a PDP-6 and she
has a CDC 6600. We agree to use BER to encode/decode and everything is cool.
   However, if we have agreed in advance to use ASCII, I can just send the
5 ASCII octets 'H', 'e', 'l', 'l' and 'o'. Can't I? If I don't need ASN.1/
BER I don't see that the OSI standards force me to use it.
   Furthermore, this nonsense about "having to do the encoding at runtime" is
laughable. That's like saying I have to calculate TCP checksums on data at
the same time I send it, rather than when I store it to disk if I want. The
messages in the X protocol are already known and can be encoded at compile-
time.
   Of course, the BER decoding still needs to take place, but since the 
protocol in question (X) has well-known messages, I can do table-driven
decoding at minimal additional overhead.
   And I also got flamed for failing to realize that even if the Presentation
Layer/Sesseion Layers do nothing, P/S headers need to be prepended to the
datagram. Aren't the headers going to be "dull" (in the sense of not costing
much to calculate) with a protocol layer that isn't doing anything? Again, it
seems like most of the information ought to be calculable in advance so as not
to slow down operation of the protocol.
   I think I'm not completely wrong -- and I never like being made a fool of
by other people over the Net. So I'll make a fool out of myself and say
that I think these arguments are specious and that X can live in Layer 7
quite happily and a non-brain-dead OSI protocol implementation (if such a
thing were to be brought into existence) would not make it unhappy and
bored up there....

-Johnny The-OSI-Reference-Model-has-nothing-to-do-with-Implementation
(#include <stddisclaimer.h>)