Re: Protocol Definition

Joe Touch <touch@isi.edu> Mon, 18 June 2012 22:44 UTC

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Date: Mon, 18 Jun 2012 15:44:25 -0700
From: Joe Touch <touch@isi.edu>
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To: Alessandro Vesely <vesely@tana.it>
Subject: Re: Protocol Definition
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On 6/18/2012 3:30 AM, Alessandro Vesely wrote:
...
> I noticed no disagreement between "method" and "mechanism", at the
> time.  In retrospect, those two terms might seem to allude to a
> different depth of semantic explanations.  Rereading that thread, I
> find that the same ambiguity holds for algorithm descriptions:  one
> can give a full description (or coding) of, say, sqrt, without
> actually saying that the square of the result will match its argument
> up to some rounding error.  The specification does not have to relate
> the underlying mathematical abstraction.

This is the difference between a behavioral description and a procedural 
description.

Behavioral treats a system as a "black box", and defines the system as a 
function and how it transforms its input into its output.

Procedural specifies the particular steps taken inside the box.

Procedural is more specific than behavioral:

	behavioral = any of a number of ways of calculating SQRT
	procedural = one specific algorithm for calculating SQRT

Semantics is a completely different thing - the assignment of "meaning" 
to symbols. Neither procedural nor behavioral descriptions need to 
include semantic descriptions.

> Protocol specifications, especially when dealing with policies, do not
> have to describe the exact meaning of the relevant tokens.  To do that
> would often look like mandating a state or a reaction, neither of
> which is needed to ensure interoperability.

In a protocol, state transitions and response messages are specified. 
Protocols are typically described procedurally, FWIW.

> In fact, the protocol
> just has to ensure that a policy can be transmitted correctly.  Many
> would rather leave a policy token underspecified than get involved in
> its details.

This is like claiming that a protocol is just "bits on the wire", and it 
is not accurate.

> In that respect, a protocol is not a complete method.  The "upper
> layer", where policies and politics are dealt with, seems to be too
> fuzzy to be specified.  I think this limitation is consistent with the
> etymological meaning of the term, that refers to forms of conduct that
> don't betray intentions.  Is that right?

Conduct, intention, and semantics refer to human interpretations of 
events. Unless a human is part of your protocol stack, they're not relevant.

I agree with AB - these issues aren't relevant to IETF descriptions of 
protocols.

Joe