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

On Feb 5, 2014, at 10:09 PM, Peter Thatcher <pthatcher@google.com> wrote:

> On Wed, Feb 5, 2014 at 12:40 PM, Makaraju, Maridi Raju (Raju)
> <Raju.Makaraju@alcatel-lucent.com> wrote:
>>> 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.
>> [Raju] PPID is also used by browsers (and other webrtc implementors like native clients) to fragment user given large data into smaller fragments (via "XYZ partial", "XYZ last" PPIDs) to avoid monopolizing the SCTP link for a single data channel's data.
>> See http://tools.ietf.org/html/draft-ietf-rtcweb-data-channel-06#section-6.6 for more details.
> 
> I believe that Firefox is the browser that does that.  At the last
> IETF, I think we agreed that it's a temporary fix at best while we
> wait until this problem is solved at the SCTP layer and not above it.
> 
> I'm not aware of any native clients that use this technique, unless
> there are native clients that use Firefox's code.   Perhaps there are;
> I just don't know of any.
> 
> In any case, it's not part of the standard, and I think the plan is
> that it won't be needed long-term.
As discussed in the last IETF meeting, this PPID based fragmentation and reassembly
will be removed from the ID.

Best regards
Michael
> 
>> 
>> -Raju
>> 
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