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Re: Stats proposal, updated

From: Stefan Hakansson LK <stefan.lk.hakansson@ericsson.com>
Date: Fri, 20 Jul 2012 15:00:05 +0200
Message-ID: <50095655.7030409@ericsson.com>
To: public-webrtc@w3.org
On 07/20/2012 12:49 PM, Harald Alvestrand wrote:
> On 07/02/2012 05:56 PM, Stefan Hakansson LK wrote:
>> 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
>> views?
>
> Yes, I ignored that, since specific stats aren't defined in the proposal
> yet.
> I was kind of assuming that the local/remote IP address of the interface
> in use was available as a "statistic", which gives the same result (I
> think).

Yes, perhaps that is all what is needed.
>
>>
>>>>
>>>> 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).
> Only if they're the same app, or have standardized another interface for
> that purpose. We already have RTCP.
>
>>
>>>
>>>> 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 app.
>>
>> 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.
> Then let's remove "removeStream" altogether, and have the streams
> remain, but in the Closed state.
That is one way to do it. Would it enable freeing up resource? I'm 
thinking about a situation where audio and video is streamed to a remote 
peer, and the data connection is used as well. If the sender/sending app 
determines that audio or video will not be used for a while, resources 
like codecs should be released (but the data connection should remain) 
to other (web and native) apps.

>
>>
>>>
>>>> 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 Friday, 20 July 2012 13:00:36 UTC

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