Re: [codec] #28: Layered bit-stream

["Christian Hoene" <[e-mail]>]

Hi,

 

I respect the requirements of gateway manufactures and I think it is important to consider them.

 

Let me explain my arguments a bit more by discussion point b.

 

*  (b) I agree with Dimity that layered codecs reduce the complexity of VOIP gateways and perhaps conference bridges.  



I see that there is an important need to reduce the computational complexity at gateways and conference bridges. Layered coding is
an easy solution that helps to reduce complexity. However, I think that there are many other ways to achieve similar complexity
reduction WITHOUT requiring layered coding. One example is a special encoder that encodes multiple streams at the same time. 

 

*  Also, with layered codec designs you get wire-speed management of channel bandwidth, so there can be a delay benefit as well as a
complexity reduction.

 

Also, a fast management of channel bandwidth can be achieved by controlling the encoder (via a feedback channel not locally)

 

Thus, I would vote for a NEED NOT or even MUST NOT because the costs of layered encoding are imposed to all users of the codec but
the benefit is only to the gateways.

 

With best regards,

 

 Christian

 

 

 

---------------------------------------------------------------

Dr.-Ing. Christian Hoene

Interactive Communication Systems (ICS), University of Tübingen 

Sand 13, 72076 Tübingen, Germany, Phone [phone] 
 <http://www.net.uni-tuebingen.de/> http://www.net.uni-tuebingen.de/

 

From: stephen botzko [mailto:[e-mail]] 
Sent: Thursday, May 06, 2010 3:41 PM
To: Christian Hoene
Cc: Dmitry Yudin; [e-mail]
Subject: Re: [codec] #28: Layered bit-stream

 

A couple of observations on this

(a) I agree with Christian that layered codecs usually need higher bitrates to achieve the same quality. Of course we do want good
quality over our desired bitrate range, and it is likely to be more difficult to achieve that with a layered codec.

(b) I agree with Dimity that layered codecs reduce the complexity of VOIP gateways and perhaps conference bridges.  Also, with
layered codec designs you get wire-speed management of channel bandwidth, so there can be a delay benefit as well as a complexity
reduction.

(c) Arguing about the relative priority of multipoint conferences vs point to point calls is pointless, because they are clearly
both MUSTS.

I am not sure if Christian is arguing that layered codecs SHALL NOT be considered, or if the requirements allow but are not biased
towards layered proposals.  If might be useful to clarify this point.

Stephen Botzko




On Thu, May 6, 2010 at 9:13 AM, Christian Hoene <[e-mail]> wrote:

Hi Dimitry,

>Hi Christian,
>
>From application point of view, the layered stream structure allows
>server manipulate channel bandwidth individually for each user with zero
>performance overhead.

I understand. Because you as an application programmer want to have an easy life, the codec designer shall develop a more
complicated codec? In addition, everybody should suffer from a higher bit rate? No, that is not fair.

> Obviously, conferencing is the most important use-case.

No, end-to-end connections are more frequent than conference calls.


>
>> a) First, this use case is a local optimization only. Thus, the must
>not be standardized.

>What do you mean exactly? "local optimization" of what?

I mean that the layered coding is only used within one computer. It is not important in-between computers. And, it is only a
performance optimization that make the conference gateway faster.

Sincerely,

 Christian



>
>> b) Second, instead of layered coding one can use other ways of
>tweaking the implementation
>> performance. For example, if you calculate a 512 FFT do get two 256
>FFTs for free.
>> I bet there are thousand other shortcuts which I am not aware of.

>How do this interrelates with scalability? Please, explain.
>
>Let's return back to the subject:
>    Shall layered coding be supported? - we think "yes", because ...
>(see my first sentence)
>    Who needs it?                      - answered
>    Can we drop this requirement?      - only if we have real good
>reasons for it. Do we have them?
>
>Best regards,
>Dmitry

>
>-----Original Message-----
>From: Christian Hoene [mailto:[e-mail]]
>Sent: Wednesday, May 05, 2010 11:02 PM
>To: Vladimir Sviridenko; [e-mail]
>Cc: Slava Borilin; Dmitry Yudin; [e-mail]
>Subject: RE: [codec] #28: Layered bit-stream
>
>Hi Vladimir,
>
>>2/ we think that VoIP and Videoconferencing systems are users of such
>>codecs.
>
>Could you please explain your position a bit?
>
>As far as I understand, layered coding helps if multiple streams having
>the sample content but different rates must be generated.
>For example, if a conferencing system stream the same audio stream to N
>users but each users has a different bandwidth. Just encode
>all layers and drop the higher layers for the low bandwidth users. This
>approach is easy and efficient and reduce the encoding
>complexity.
>
>The arguments against are simple.
>a) First, this use case is a local optimization only. Thus, the must not
>be standardized.
>b) Second, instead of layered coding one can use other ways of tweaking
>the implementation performance. For example, if you
>calculate a 512 FFT do get two 256 FFTs for free. I bet there are
>thousand other shortcuts which I am not aware of.
>
>Thus, I have the opinion that layered coding is not worth the extra
>bandwidth of 20 or more percentage. It is just good locally but
>not needed for interoperability.
>
>Yours,
>
> Christian
>
>
>
>
>
>
>>Yours,
>>Vladimir Sviridenko
>>SPIRIT
>>
>>-----Original Message-----
>>From: [e-mail] [mailto:[e-mail]] On Behalf
>>Of codec issue tracker
>>Sent: Sunday, May 02, 2010 5:10 PM
>>To: [e-mail]
>>Cc: [e-mail]
>>Subject: [codec] #28: Layered bit-stream
>>
>>#28: Layered bit-stream
>>------------------------------------+----------------------------------
>-
>>----
>> Reporter:  hoene@...                 |       Owner:
>>     Type:  defect                  |      Status:  new
>> Priority:  minor                   |   Milestone:
>>Component:  requirements            |     Version:
>> Severity:  Active WG Document      |    Keywords:
>>------------------------------------+----------------------------------
>-
>>----
>> Shall layered coding be supported?
>> Who needs it?
>> Can we drop this requirement?
>>
>>--
>>Ticket URL: <http://trac.tools.ietf.org/wg/codec/trac/ticket/28>
>>codec <http://tools.ietf.org/codec/>
>>
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