[Asterisk-Users] ATTN: Keith

[Robert Webb]

> -----Original Message-----
> From: asterisk-users-bounces at lists.digium.com 
> [mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of 
> Andrew Kohlsmith
> Sent: Saturday, June 11, 2005 11:58 AM
> To: asterisk-users at lists.digium.com
> Subject: Re: [Asterisk-Users] ATTN: Keith
> 
> On Saturday 11 June 2005 11:35, Tracy Phillips wrote:
> > > That is *precisely* why the RFC is worded "should" -- it is 
> > > optional.  If the RFC said "must" then it is required.  RFCs are 
> > > worded very carefully as a general rule.
> 
> > I am just glad everyone doesn't have that attitude about RFCs.
> 
> I'm not sure I understand -- I'm not making this up, RFCs use 
> "must" and "should" very carefully.  The latter is a 
> guideline, and the former is a rule.  I'm trying to find the 
> link describing this but it's eluding me at the moment.
> 
> I think this is a VERY good thing; RFCs are like the laws of 
> the internet; they should not be open to interpretation since 
> they define the protocols used to interoperate.
> 
> -A.


Andrew,

  Did some looking for you. It is contained in RFC 2119, Key words for
use in RFCs to Indicate Requirement Levels.

Here is an excerpt:

Abstract

   In many standards track documents several words are used to signify
   the requirements in the specification.  These words are often
   capitalized.  This document defines these words as they should be
   interpreted in IETF documents.  Authors who follow these guidelines
   should incorporate this phrase near the beginning of their document:

      The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
      NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and
      "OPTIONAL" in this document are to be interpreted as described in
      RFC 2119.

   Note that the force of these words is modified by the requirement
   level of the document in which they are used.

1. MUST   This word, or the terms "REQUIRED" or "SHALL", mean that the
   definition is an absolute requirement of the specification.

2. MUST NOT   This phrase, or the phrase "SHALL NOT", mean that the
   definition is an absolute prohibition of the specification.

3. SHOULD   This word, or the adjective "RECOMMENDED", mean that there
   may exist valid reasons in particular circumstances to ignore a
   particular item, but the full implications must be understood and
   carefully weighed before choosing a different course.

4. SHOULD NOT   This phrase, or the phrase "NOT RECOMMENDED" mean that
   there may exist valid reasons in particular circumstances when the
   particular behavior is acceptable or even useful, but the full
   implications should be understood and the case carefully weighed
   before implementing any behavior described with this label.

5. MAY   This word, or the adjective "OPTIONAL", mean that an item is
   truly optional.  One vendor may choose to include the item because a
   particular marketplace requires it or because the vendor feels that
   it enhances the product while another vendor may omit the same item.
   An implementation which does not include a particular option MUST be
   prepared to interoperate with another implementation which does
   include the option, though perhaps with reduced functionality. In the
   same vein an implementation which does include a particular option
   MUST be prepared to interoperate with another implementation which
   does not include the option (except, of course, for the feature the
   option provides.)

6. Guidance in the use of these Imperatives

   Imperatives of the type defined in this memo must be used with care
   and sparingly.  In particular, they MUST only be used where it is
   actually required for interoperation or to limit behavior which has
   potential for causing harm (e.g., limiting retransmisssions)  For
   example, they must not be used to try to impose a particular method
   on implementors where the method is not required for
   interoperability.

So here you are absolutely correct.

Robert