Aah.... an ASN.1 firefight!
It's been a LONG time since we've had one of those, but they used to be a
regularly scheduled event on this list.
I used to have opinions on this debate - for a trip down memory lane, check
out the "canonical X.400 vs SMTP debate" on my website (sorry, typing
offline at the moment - google will find it).
One note, however:
--On 25. august 2003 15:16 -0400 Dean Anderson <dean(_at_)av8(_dot_)com> wrote:
It is certainly true that net telephony and conferencing need
extensibility - but I would suggest that the hooks for extensibility
ought to be concisely defined and placed in specific parts of the
protocol structures (such as the SDP part of today's call establishment
protocols). I see no need to burden the entire protocol representation
under a mutable layer of complexity such as ASN.1 when there is no
reason that can be articulated to require such mutability.
ASN.1 is not automatically extensible. You have to specify where the
protocol can be extended. If you don't use extensions, it should be
possible to have an ASN.1 runtime that omits the code to handle them. (One
of many possible runtime optimatizations that are possible but rarely seen
in practice, except with hand-coded encoders/decoders)
One warning to those with long memories and strong opinions:
The way one does extensibility in ASN.1 has changed greatly since the first
(1984) versions of ASN.1. Lots of the hard opinions people have here are
based on ASN.1(1984) experience, which was what SNMP originally used.
I have had people tell me that the post-1988 versions of ASN.1 are really
nice in this department, but haven't used ASN.1 seriously since
approximately 1992 (when PER was just being stabilized).
So I'm not qualified to say whether they are right or not.
Aside on complexity: The definition of ABNF, the "formal" language used to
define the SIP syntax, RFC 2234, is 14 pages long, and has been blasted by
several people as being a too complex tool for proper protocol description.
I haven't checked the pagecount of the ITU recommendations defining ASN.1
recently, but the last time I had one in hand (X.208/88), I'd estimate it
as at least 10 times that number of pages.
Harald