Re: [codec] #16: Multicast?
"Raymond (Juin-Hwey) Chen" <rchen@broadcom.com> Tue, 18 May 2010 02:36 UTC
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From: "Raymond (Juin-Hwey) Chen" <rchen@broadcom.com>
To: Koen Vos <koen.vos@skype.net>
Date: Mon, 17 May 2010 19:32:44 -0700
Thread-Topic: [codec] #16: Multicast?
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Cc: "codec@ietf.org" <codec@ietf.org>
Subject: Re: [codec] #16: Multicast?
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Hi Koen, I agree with Roman that this 1X versus 3X debate has reached a point that it is almost irrelevant. What's really relevant now is the question of whether the IETF codec should have a low-delay mode with a codec frame size of 5 to 10 ms, and for that question you previously wrote on May 6: > Anyway, I think we're all aligned here: ultra-low delay is > important and has been part of the requirements from day one. Has > anyone disagreed? After this email of yours, I have not seen anyone explicitly disagreed. In fact, of the 6 intended applications listed in the WG charter, draft-ietf-codec-requirements-00 lists 2 of them having < 10 ms codec delay as a requirement and 3 of them having < 10 ms codec delay as "desirable" or "highly desirable". It seems to me that the consensus in the WG is that we need a low-delay mode with a 5 to 10 ms codec frame size to address delay-sensitive applications, and we need another higher-delay mode with perhaps a 20 ms frame size to get higher bit-rate efficiency for applications that are less sensitive to delay. If we agree with that (and I thought you already agreed on May 6), then whether the frame size multiplier is 1X or 3X doesn't really matter and shouldn't affect the codec requirements or the direction of the codec design. With that said, I don't want you to think I impolitely ignored your comments in your email below, so I will respond to them in-line. (For those who are not interested, please ignore the rest of this email.) You wrote: > Quoting "Raymond (Juin-Hwey) Chen": >> I didn't come up with this 3*(codec frame size) delay number for IP >> phones myself. A very senior technical lead in Broadcom's IP phone >> chips group told me that > Still: > - You've presented no satisfactory explanation for your theory [Raymond]: I already explained and analyzed it in my previous emails. The codec-dependent delay = (codec frame size) + (codec look-ahead) + (codec filtering delay) + (processing delay to encode and decode one frame) + (transmission delay to send one frame of compressed bit- stream) + (multi-tasking delay due to processor not immediately available to start encoding and decoding operations as soon as one frame of input audio samples or received bit-stream is ready) + (possibly miscellaneous other delays) Although the processing delay is short (but not zero) for a PC having 2 ~ 3 GHz CPU, for IP phones the clock speed of the processor is much lower, resulting in significantly higher processing delay than in a PC. Also, the multi-tasking delay can be quite significant, and it is dependent on the codec frame size in IP phones. All these delay components here and there can easily add up to 3X codec frame size. If you have a copy of the 1995 Elsevier book "Speech Coding and Synthesis" edited by W.B. Kleijn and K.K. Paliwal, please go read Section 2 and see Fig. 1 of my chapter 6 on low-delay coding of speech. It should help you understand what I have been saying. Unfortunately due to copyright restrictions, I cannot scan those pages and attach with this email. > - Nor any verifiable empirical evidence [Raymond]: The one-way delay measurement was done at the lab of Broadcom's IP phone chip group. I don't know how I can make that "verifiable" to you. > - It comes from an anonymous source [Raymond]: I didn't just say that I heard it from someone who worked at some (unnamed) company; I specifically said this info came from Broadcom's IP phone group. Is that not sufficient? > - It has changed over time (going from 5x to 3x) [Raymond]: I admit that this was my mistake due to a misunderstanding of what that senior technical lead I mentioned above told me. Initially he said the real-world one-way delay was about 5X codec frame size. I thought he meant codec-dependent delay; that's why I initially used 5X. Later he clarified to me that when he said 5X, he included codec-independent delay, and the codec-dependent delay component was really 3X, so I corrected myself to 3X. > - It goes against accepted wisdom [Raymond]: No, the commonly accepted wisdom back in late 1980s and early 1990s (when several dozen low-delay speech coding papers were published) was 3X codec frame size, although some might have used 2X as the best-case scenario. Since then the CPU of PCs has increased in speed by more than 30X (in early 1990s a popular CPU was the 90 MHz Pentium) and the network speed also increased a lot, so I can believe you that PC-based softphones could potentially reach below 2X as you said, but IP phone processors are much slower than the CPUs of PCs, making it harder to get below 2X. In any case, 1X was never the commonly accepted wisdom, since it is theoretically impossible. > So I'd say the burden of proof is on you. [Raymond]: Broadcom currently ships more than half of the world's IP phone chips, and Broadcom's IP phone group has also measured the one- way codec-dependent delay carefully in the lab with carefully chosen signals, equipment, and methodology, so I don't see why Broadcom's measurement is any less valid than Cullen's, to the point that the burden of proof is on us. I don't believe Broadcom's IP phone implementation is particularly bad in delay compared with others, either (otherwise we are unlikely to be the market leader). In any case, I didn't say that I believe Cullen's results must be wrong. I was just surprised at the discrepancy of the measurement results from these two different sources and would like to find out why and possibly reconcile the seemingly contradictory results. That's why I asked Cullen to share more details about his measurements. Raymond
- [codec] #16: Multicast? codec issue tracker
- Re: [codec] #16: Multicast? Colin Perkins
- Re: [codec] #16: Multicast? Christian Hoene
- Re: [codec] #16: Multicast? Marshall Eubanks
- Re: [codec] #16: Multicast? stephen botzko
- Re: [codec] #16: Multicast? Colin Perkins
- Re: [codec] #16: Multicast? Colin Perkins
- Re: [codec] #16: Multicast? stephen botzko
- Re: [codec] #16: Multicast? Christian Hoene
- Re: [codec] #16: Multicast? stephen botzko
- Re: [codec] #16: Multicast? Marshall Eubanks
- Re: [codec] #16: Multicast? Christian Hoene
- Re: [codec] #16: Multicast? stephen botzko
- Re: [codec] #16: Multicast? Christian Hoene
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Jean-Marc Valin
- Re: [codec] #16: Multicast? Koen Vos
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Mikael Abrahamsson
- Re: [codec] #16: Multicast? Jean-Marc Valin
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Koen Vos
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? stephen botzko
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Koen Vos
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Mikael Abrahamsson
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Mikael Abrahamsson
- Re: [codec] #16: Multicast? (Bluetooth) Koen Vos
- Re: [codec] #16: Multicast? Koen Vos
- Re: [codec] #16: Multicast? stephen botzko
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Koen Vos
- Re: [codec] #16: Multicast? (Bluetooth) Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? (Bluetooth) stephen botzko
- Re: [codec] #16: Multicast? Christian Hoene
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Christian Hoene
- Re: [codec] #16: Multicast? Christian Hoene
- Re: [codec] #16: Multicast? (USB) Roni Even
- Re: [codec] #16: Multicast? codec issue tracker
- Re: [codec] #16: Multicast? stephen botzko
- Re: [codec] #16: Multicast? Cullen Jennings
- Re: [codec] #16: Multicast? Mikael Abrahamsson
- Re: [codec] #16: Multicast? Koen Vos
- Re: [codec] #16: Multicast? (Bluetooth) Koen Vos
- Re: [codec] #16: Multicast? stephen botzko
- Re: [codec] #16: Multicast? Christian Hoene
- Re: [codec] #19: How large is the frame size depe… Christian Hoene
- Re: [codec] #19: How large is the frame size depe… stephen botzko
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #19: How large is the frame size depe… Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? (Bluetooth) Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? stephen botzko
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? stephen botzko
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Koen Vos
- Re: [codec] #16: Multicast? Christian Hoene
- Re: [codec] #16: Multicast? Gregory Maxwell
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Koen Vos
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Koen Vos
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Koen Vos
- Re: [codec] #16: Multicast? Koen Vos
- Re: [codec] #16: Multicast? Benjamin M. Schwartz
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] Thresholds and delay. stephen botzko
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Kevin P. Fleming
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Jean-Marc Valin
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Jean-Marc Valin
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Christian Hoene
- Re: [codec] #16: Multicast? Koen Vos
- Re: [codec] #16: Multicast? Christian Hoene
- Re: [codec] #16: Multicast? Ben Schwartz
- Re: [codec] #16: Multicast? Marshall Eubanks
- Re: [codec] #16: Multicast? Brian Rosen
- Re: [codec] #16: Multicast? Christian Hoene
- Re: [codec] #16: Multicast? Jean-Marc Valin
- Re: [codec] Thresholds and delay. Ben Schwartz
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] Thresholds and delay. stephen botzko
- Re: [codec] #16: Multicast? Christian Hoene
- Re: [codec] Thresholds and delay. Ben Schwartz
- Re: [codec] #20: Computational complexity? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] Thresholds and delay. jari.hagqvist
- Re: [codec] Thresholds and delay. stephen botzko
- Re: [codec] Thresholds and delay. Ben Schwartz
- Re: [codec] Thresholds and delay. Marshall Eubanks
- Re: [codec] #16: Multicast? Cullen Jennings
- Re: [codec] Thresholds and delay. Michael Knappe
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Koen Vos
- Re: [codec] #16: Delay factor: algorithmic delay … Christian Hoene
- Re: [codec] #16: Delay factor: algorithmic delay … Mikael Abrahamsson
- Re: [codec] #16: Delay factor: algorithmic delay … Roman Shpount
- Re: [codec] #16: Delay factor: algorithmic delay … stephen botzko
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Cullen Jennings
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Koen Vos
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Koen Vos
- Re: [codec] #16: Multicast? Christian Hoene
- Re: [codec] #16: Multicast? Jean-Marc Valin
- Re: [codec] #16: Multicast? Herve Taddei
- Re: [codec] #16: Multicast? Christian Hoene
- Re: [codec] #16: Multicast? Jean-Marc Valin
- Re: [codec] #16: Multicast? Sandy (Alexander) MacInnis
- Re: [codec] #16: Multicast? Christian Hoene
- Re: [codec] #16: Multicast? Raymond (Juin-Hwey) Chen
- Re: [codec] #16: Multicast? Roman Shpount
- Re: [codec] Suggested summary... Herve Taddei
- Re: [codec] #16: Multicast? Herve Taddei
- Re: [codec] #16: Multicast? Cullen Jennings
- [codec] Suggested summary... Christian Hoene
- Re: [codec] Suggested summary... stephen botzko
- Re: [codec] Suggested summary... Herve Taddei
- Re: [codec] Suggested summary... Christian Hoene
- Re: [codec] Suggested summary... Michael Knappe
- Re: [codec] Suggested summary... stephen botzko
- Re: [codec] Suggested summary... Christian Hoene
- Re: [codec] Suggested summary... Christian Hoene
- Re: [codec] Suggested summary... stephen botzko
- Re: [codec] Suggested summary... Raymond (Juin-Hwey) Chen
- Re: [codec] Suggested summary... Christian Hoene
- Re: [codec] Suggested summary... Herve Taddei
- Re: [codec] Suggested summary... Raymond (Juin-Hwey) Chen