On 12. okt. 2013, at 23:00, Bernard Aboba <[email protected]> wrote:
> [BA] A few points: > > a. No B-frames in interactive uses, as others have said. > b. With SVC, you can apply FEC or RTX only to the base layer. So if there > is loss in the base, you can recover. Loss in enhancement layers may be > "lived with" by dropping down to base frame rate/resolution/quality. So not > essential to apply FEC, RTX (or QoS) to enhancement layers, especially since > if there is high loss in enhancement layers a logical response is to stop > sending them (duh). I see. Well, should we perhaps really suggest a "lower-priority-than-other-packets-in-the-same-5-tuple" DSCP then? Cheers, Michael > > > > Michael said: > > > I'll begin by apologizing for asking what I'm quite sure is a terribly > > stupid question to many of you. > > > > The question is: > > > > It has long been known that media data can have different levels of > > importance. Simply put, if packet #1 from a single source contains parts of > > a video's I-Frame and packet #2 contains only parts of B-Frames, and both > > end up in the same queue, controlled by an AQM (for instance), it would be > > better for the video stream if packet #2 would be dropped rather than > > packet #1. > > > > There is nothing new with this story; it's not hard to find research papers > > that document various variations of this theme, showing benefits in video > > quality. > > > > My question is, why is none of this happening? > > > > Is it because DSCP values are typically associated with sources, and hence, > > marking packet #2 as "less" important would put the source at the risk of > > having its packets less important than not only its own other packets, but > > anybody else's? But there is equipment that does per-connection stuff, and > > such things could probably better be done near the edges, where the > > bottleneck typically is... so if that's the whole issue, we could define > > DSCP values that mean relative importance *within the same five-tuple > > only*. Surely that has been thought about and probably proposed by folks > > before, so what happened? Why isn't it done? > > > > Or is it because per-five-tuple-functionality in the network is regarded as > > being too costly, and not encouraged, and hence not standardized? > > > > I'm just trying to understand the reasons for this particular long-standing > > difference between research an reality. > > > > Cheers, > > Michael > >
