Re: [AVTCORE] Slight rewording on Selective Forwarding Middlebox
Magnus Westerlund <magnus.westerlund@ericsson.com> Wed, 01 April 2015 10:43 UTC
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Date: Wed, 01 Apr 2015 12:43:12 +0200
From: Magnus Westerlund <magnus.westerlund@ericsson.com>
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To: Bernard Aboba <bernard_aboba@hotmail.com>, "avt@ietf.org" <avt@ietf.org>
References: <55193001.9070009@ericsson.com> <55193770.3000102@ericsson.com>, <551A5EEB.3080200@ericsson.com> <BLU181-W9331685ED48AAC16F9AE4093F40@phx.gbl>
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Subject: Re: [AVTCORE] Slight rewording on Selective Forwarding Middlebox
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Hi Bernard, On 2015-03-31 18:42, Bernard Aboba wrote: > The problem is that devices using the term selective forwarding > middlebox or Selective Forwarding Unit (SFU) can operate in more than > one topology. > > For example, instead of allowing SSRCs present in the session to be > visible, some SFUs allocate their own SSRCs and thus operate more like a > mixer. Yes but let us look at the respective behaviours, the first acting as a RTP mixer that switches streams, thus selecting which of the incoming streams are forwarded in a particular outgoing stream. The other end of the spectrum is to project all incoming streams into each outgoing leg. The later is what I intended to be covered by SFM description. If the SSRC values are translated or not is less important. > > Also, a selective forwarding middlebox is not necessarily required to > have a large number of decoder instances (although many do). As an > example, an SFU utilizing the "frame marking" extension discussed in > AVTEXT at IETF 92 would presumably not require decoder instances for any > codec, and in the case of private media, would be able to decode the > payload since the keys would not be available. I agree that the SFM likely has zero decoders, the point about decoders is however present at the receiving endpoint. There are an issue in this that a SFM need to know the number of simultaneous decoder the endpoint has. > > Also, it is possible for a device to act as both an SFU and switching > mixer, so these are not orthogonal dimensions. Yes, I agree some outgoing SSRCs may be switched, while other are forwarded. But, that would fall under the composite topologies. This one actually being a really good example of such one. What I don't get out of this discussion is if anything actually need to change in the document. Cheers Magnus > > > >> Date: Tue, 31 Mar 2015 10:46:35 +0200 >> From: magnus.westerlund@ericsson.com >> To: avt@ietf.org >> Subject: Re: [AVTCORE] Slight rewording on Selective Forwarding Middlebox >> >> WG, >> >> Here is an update of the last two paragraphs taking care of some nits >> and a rewording of the very last sentence. Thanks for Dan Wing for > feedback. >> >> Note that this topology could potentially be seen as a media >> translator which include an on/off logic as part of its media >> translation. The topology has the property that all SSRCs present in >> the session are visible to an endpoint. It also has mixer aspects, >> as the streams it provides are not basically translated version, but >> instead they have conceptual property assigned to them and can be >> both turned on/off as well as being fully or partially delivered. >> Thus this topology appears to be some hybrid between the translator >> and mixer model. >> >> The differences between selective forwarding middlebox and a >> switching mixer (Section 3.6.2) are minor, and they share most >> properties. The above requirement on having a large number of >> decoding instances or requiring efficient switching of decoder >> contexts, are one point of difference. The other is how the >> identification is performed, where the Mixer uses CSRC to provide >> information on what is included in a particular RTP stream that >> represent a particular concept. Selective forwarding gets the source >> information through the SSRC, and instead uses other mechanisms to >> indicate the streams intended usage, if needed. >> >> I intended to submit an updated draft on Thursday if no objections are > made. >> >> Cheers >> >> Magnus Westerlund >> >> ---------------------------------------------------------------------- >> Services, Media and Network features, Ericsson Research EAB/TXM >> ---------------------------------------------------------------------- >> Ericsson AB | Phone +46 10 7148287 >> Färögatan 6 | Mobile +46 73 0949079 >> SE-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com >> ---------------------------------------------------------------------- >> >> _______________________________________________ >> Audio/Video Transport Core Maintenance >> avt@ietf.org >> https://www.ietf.org/mailman/listinfo/avt -- Magnus Westerlund ---------------------------------------------------------------------- Services, Media and Network features, Ericsson Research EAB/TXM ---------------------------------------------------------------------- Ericsson AB | Phone +46 10 7148287 Färögatan 6 | Mobile +46 73 0949079 SE-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com ----------------------------------------------------------------------
- [AVTCORE] Slight rewording on Selective Forwardin… Magnus Westerlund
- Re: [AVTCORE] Slight rewording on Selective Forwa… Magnus Westerlund
- Re: [AVTCORE] Slight rewording on Selective Forwa… Magnus Westerlund
- Re: [AVTCORE] Slight rewording on Selective Forwa… Bernard Aboba
- Re: [AVTCORE] Slight rewording on Selective Forwa… Roni Even
- Re: [AVTCORE] Slight rewording on Selective Forwa… David Benham (dbenham)
- Re: [AVTCORE] Slight rewording on Selective Forwa… Magnus Westerlund
- Re: [AVTCORE] Slight rewording on Selective Forwa… Magnus Westerlund