Re: [MMUSIC] [Technical Errata Reported] RFC4566 (5595)

[[e-mail] (Dale R. Worley)]

RFC Errata System <[e-mail]> writes:
> [...]  In section 5 it indicates that the SDP lines MUST appear in the
> exact order given at the top of Page 9.  The order that is shown
> indicates that the Session Attributes appear before the Time
> Description. [...]

The example is correct, but there's a subtle point about the text that
makes it vulnerable to misreading.  Viz., section 5 says:

   Some lines in each description are REQUIRED and some are OPTIONAL,
   but all MUST appear in exactly the order given here [...]

Followed by:

      Session description
         v=  (protocol version)
         o=  (originator and session identifier)
         s=  (session name)
         i=* (session information)
         u=* (URI of description)
         e=* (email address)
         p=* (phone number)
         c=* (connection information -- not required if included in
              all media)
         b=* (zero or more bandwidth information lines)
         One or more time descriptions ("t=" and "r=" lines; see below)
         z=* (time zone adjustments)
         k=* (encryption key)
         a=* (zero or more session attribute lines)
         Zero or more media descriptions

      Time description
         t=  (time the session is active)
         r=* (zero or more repeat times)

      Media description, if present
         m=  (media name and transport address)
         i=* (media title)
         c=* (connection information -- optional if included at
              session level)
         b=* (zero or more bandwidth information lines)
         k=* (encryption key)
         a=* (zero or more media attribute lines)

Look back on this and ask yourself, What is "the order given"?

It looks like the order is "session description" followed by "time
description" followed by "media descriptions, if present".  But it's
not.  "The order given" covers only the section titled "Session
description" -- "Time description" is included within it by reference in
the 10th item, and "Media description, if present" is included within it
multiply by reference in the 14th item.  (Compare with the grammar in
section 9.)

In particular, time descriptions come before session attributes.

So it would really help if this text was clarified in 4566bis.

Dale