[rtcweb] RTCWEB Data Channel: Usage of PPID for protocol multiplexing

[Christer Holmberg <[e-mail]>]

Hi,

This is related to the e-mail Paul sent yesterday (Data Channel question: correlating streams with channels).

Section 5 of draft-ietf-rtcweb-data-channel-06 says:

"Each SCTP user message contains a so called Payload Protocol
                Identifier (PPID) that is passed to SCTP by its upper layer and sent
                to its peer.  This value can be used to multiplex multiple protocols
                over a single SCTP association.  The sender provides for each
                protocol a specific PPID and the receiver can demultiplex the
                messages based on the received PPID."

Now, when I look at the IANA registration page for PPID values, most seem to be associated with specific protocols.

However, if I e.g. use PPID values 51-54 (as rtcweb applications will do) they don't say anything about the protocol. They refer to an encoding format, and multiple protocols may have the same format.

I would assume that the SCTP stream id would have to be used to multiplex protocols.

Regards,

Christer