Re: [sipcore] draft-sparks-sipcore-multiple-reasons

worley@ariadne.com Wed, 11 May 2022 02:06 UTC

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From: worley@ariadne.com
To: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Date: Tue, 10 May 2022 22:03:38 -0400
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Subject: Re: [sipcore] draft-sparks-sipcore-multiple-reasons
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Paul Kyzivat <pkyzivat@alum.mit.edu> writes:
> If an update is made to an existing protocol definition that does allow 
> multiple reasons, it could break existing implementations.

A possible "upward compatibility" mechanism is to retain the requirement
that existing protocol names still have only one value, and define a
second protocol name to carry the other values that are semantically
associated with the existing protocol name.  Thus one might have:

    Reason: SIP ;cause=200 ;text="Call completed elsewhere",
            SIP-M ;cause=200.1 ;text="Call completed by voicemail",
            SIP-M ;cause=200.1.17 ;text="Subscriber's voicemail"

Older implementations would likely discard both the SIP-M values and
process the SIP value as expected.

Dale