Adding this sentence would kill one interesting use case: For example, AVP and AVPF can work in the same session in a mixed operation (while AVO anf SAVP cannot). For mixed operation to be possible, however, these tools MUST use the same transport addresses.So you are speaking in favor of port overloading?
No.
Am I misunderstanding you?
Yes.
What I am worried about is RFCs allowing port overloading, and others saying it's illegal.
Please distinguish between: 1) the same transport address being indicated in otherwise explicitly grouped media session (grouped using some fid + whathaveyou attribute) 2) the same port number being used to infer grouping. These two things are fundamentally different. What I am saying is that there are legitimate use cases for 1) while all of us agree that we do not want 2). One reason for confusion appears to be one example in RFC 4585 from which I would not want to try and infer 1) but some people might be able to even though it states that you should do explicit grouping (but cannot list it in the example as the respective attribute does not yet exist). The other reason for confusion is RFC 3388 which wants to prevent people from using multiple m= lines to specify alternate codecs but phrases this in a way that you could construe as "do not use the same transport address for two m= lines". And we have RFC 4566 which states that two m= lines with the same transport address do not imply grouping and that their semantics is undefined -- obviously until you define something meaningful. This is where I think we are. All we need to do is to define a proper grouping. Joerg