Subject: [MMUSIC] SDP Syntax vs. RFC 3108

From: Tom Taylor <[email-masked]>
Date: Tue, 22 Jul 2003 20:51:09 -0400

I took the action last week to compare RFC 3108 syntax against sdp-new, to see if 
any action was necessary to realign them.

RFC 3108 documents the SDP conventions for ATM.  It defines a lot of attributes, 
which should not be a problem for syntax.  However, it also modifies the c= and m= 
lines.  The c= line is not a problem; the m= line has a different grammar from SDP-new.

m= line:
========

SDP-new syntax:
media-field =         "m=" media SP port ["/" integer]
                             SP proto 1*(SP fmt) CRLF

       media =               token

       port =                1*DIGIT

       proto  =              token "/" token
                             / token

       fmt =                 token

RFC 3108 syntax (most complicated form):

m=<media> <virtualConnectionId> <transport#1> <format list#1>
          <transport#2> <format list#2> ... <transport#M> <format list#M>

media presents no problems -- same as in basic SDP.

virtualConnectionId can have several forms, matching the patterns
          token
          token "/" token
          token "/" token "/" token
          token "/" token "/" token "/" token

        To fit this, you would need to substitute
          token *("/" token))
        for the existing sub-rule
          port ["/" integer]

transport always matches
          token "/" token

        <format list> matches 1*(SP fmt)

The problem lies in the repetition.  You would need to change
          SP proto 1*(SP fmt)
to
        1*(SP proto 1*(SP fmt))

So the complete m= line to accommodate RFC 3108 becomes

  media-field =         "m=" media SP token *("/" token))
                             1*(SP proto 1*(SP fmt)) CRLF

Tom Taylor

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