W3C home > Mailing lists > Public > public-webrtc@w3.org > July 2012

Re: Stats proposal, updated

From: Stefan Hakansson LK <stefan.lk.hakansson@ericsson.com>
Date: Mon, 2 Jul 2012 17:56:23 +0200
Message-ID: <4FF1C4A7.7000303@ericsson.com>
To: public-webrtc@w3.org
On 06/28/2012 11:53 AM, Harald Alvestrand wrote:
> I'm on holiday, but wanted to respond to this briefly....
> On 06/25/2012 09:22 AM, Stefan Hakansson LK wrote:
>> On 06/21/2012 02:24 PM, Harald Alvestrand wrote:
>>> As usual, apologies for the formatting, and errors in the WebIDL is a
>>> certainty, not a possibility.
>>> I've tried to insert the level of indirection that allows us to return a
>>> set of objects for (say) a media stream with FEC that uses multiple
>>> SSRCs rather than just a single object.
>> I think the proposed stats to track look like a good start, but I
>> think that an additional one that could be of interest is the actual
>> interface/network used. The app gets to know (sort of) what interfaces
>> that are available since the candidates are handled by the app. But
>> knowing what interface that was in actual use could be very helpful.

I got no comment on th above part (which was the most important!). Any 

>> Regarding the API, an alternative approach could be to tie this more
>> to the tracks of the MediaStreams, e.g. add something to the
>> MediaStreamTrack interface:
>>      void getInfo(Function handler);
>> The info delivered would depend on the source of the track. For tracks
>> in local (i.e. generated locally and not delivered by a
>> PeerConnection) MediaStreams, the info would be things like sampling
>> rate, channels (mono, 5.1) for audio; resolution and frame rate for
>> video. If the MediaStream has traveled over a PeerConnection, the info
>> listed in your document (packets received/lost, ssrc, codec, ) would
>> be appended.
>> This would associate the stats to a MediaStreamTrack, getting rid of
>> referencing problems (when MediaStreams are added or removed) if the
>> local/remoteStreams is used. In addition, if the corresponding info is
>> requested for data channels, it could easily be added to those.
>> One drawback is that only the receiving app would get the stats
>> associated with the PeerConnection transport.
> I think this is a fatal flaw - it means that the sender can't tell if
> the recipient is suffering packet loss, for instance. Given that the
> information is already delivered to the sender node by means of RTCP, it
> seems strange not to give access to it locally. I don't see a reason to
> accept this drawback.

The sender's app could see if the receiver's app send the info over (e.g 
using the data channel).

>> But as said, the main receiver of stats is the service provider, and
>> reporting per MediaStreamTrack allows the service provider to
>> correlate stats (perhaps using the MediaStream label). And in most
>> cases it is the same application in both ends, and the receiving end
>> could share the stats with the sending end (perhaps using the data
>> channel) if desired.
> This won't work in the case where the app is written to communicate with
> something that is not itself (such as a media gateway). I don't see a
> reason to accept this limitation.

That depends on what ways the media GW has a way to communicate with the 

Anyway, I certainly has nothing against exposing stats to the sender app 
as well, but I think we should do something about the API in that case. 
I don't like the idea that "removeStream" would create empty entries in 
the local/remoteStream arrays.

>> If there are different apps used, they could still agree on stats
>> exchange (just as they would have to agree on a bunch of other things
>> to get things working) if desired.
>> Stefan
>>> Comments welcome!
>>>                        Harald
Received on Monday, 2 July 2012 15:56:48 UTC

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