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

[Peter Thatcher <[e-mail]>]

The PPID isn't exposed to the application.  It's just used to
distinguish text/binary/control.    If an application uses different
data channels with different protocols, it should use the SID to
distinguish between them, not the PPID.  In fact, even if it wanted to
use the PPID, it wouldn't be able to.

On Wed, Feb 5, 2014 at 3:23 AM, Christer Holmberg
<[e-mail]> wrote:
> 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
>
>
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