[AVTCORE] Need feedback on RFC5285bis (RTP header extensions) comments

[Roni Even <[e-mail]>]

Hi,
Paul made a very thorough SDP review and had some comments on which I am looking for feedback.


1.       In section 7 "If an extension is marked as "sendonly" and the answerer desires to  receive it, the extension MUST be marked as "recvonly" in the SDP answer.  An answerer that has no desire to receive the extension or does not understand the extension SHOULD remove it from the SDP  answer." . Is there a reason for the "SHOULD" here or should we change it to "MUST" or maybe if not removed to  respond with "inactive"  or "sendonly" if want to send and and not receive?



2.       In this case if the offer is refused by removing the extmap line, can the ID be re-used?



3.        In section 7 "Local identifiers in the valid range inclusive in an offer or answer MUST NOT be used more than once per media section (including the session-level section).  A session update MAY change the direction qualifiers of extensions under use.  A session update MAY add or remove extension(s).  Identifiers values in the valid range MUST NOT be altered (remapped)." Paul asked what is the scope over which identifiers must not be altered. His thought was only for the current RTP session so when a call is transferred (one party is still in the call) they may be altered. Any thoughts?



4.       Is it valid to use IDs in the (unusable) range in answers? (I guess that would give the offerer info that it could use in a future offer.). I am not sure what was meant here. Is it an answer to an offer with an ID in the valid range? Or is it about keeping an alternative from the offer with the unusable space and not remove it? I assume that the answer cannot add extensions to the ones in the offer, will need a new offer for that.



5.       May values from the (unused) range that are used in offers (or answers) be reused differently in subsequent offers?



6.       Would the following be valid? (Only the directionality differs.)



     OFFER:

     a=extmap:4096/sendonly http://example.com/082005/ext.htm#opt1

     a=extmap:4096/recvonly http://example.com/082005/ext.htm#opt1



7.       Is it allowed to use the "alternatives" mechanism with only a single alternative? This would be a way to avoid "wasting" an ID value until you know if your peer supports the option. I see this usage in an example, but it is not mentioned in text. If this is an intended usage then it would be good to provide some further explanation.





Thanks

Roni Even

As the document editor.