Re: [xrblock] Fw: I-D Action: draft-ietf-xrblock-rtcp-xr-jb-02.txt

[Qin Wu <[e-mail]>]

----- Original Message ----- 
From: "Glen Zorn" <[e-mail]>
To: "Kevin Gross" <[e-mail]>
Cc: "Qin Wu" <[e-mail]>; <[e-mail]>; <[e-mail]>
Sent: Sunday, December 23, 2012 4:06 PM
Subject: Re: [xrblock] Fw: I-D Action: draft-ietf-xrblock-rtcp-xr-jb-02.txt


> On 12/22/2012 05:19 AM, Kevin Gross wrote:
> 
>> Section 3.2
> >
> > Jitter Buffer Configuration I think the two reporting options are
> > potentially over simplification of how these systems can work. An
> > adaptive receiver has to adapt to maximum latency and to delay
> > variation. The former is accomplish by adjusting the playout delay,
> > the latter by reallocating buffer space. I suggest we might want to
> > report these behaviors separately, for example: 00 - fixed jitter
> > buffer and delay 10 - adaptive playout delay 01 - adaptive buffer
> > size 11 - adaptive delay and size
> >
> >
> > [Qin]:Sounds good to me.
> 
> RFC 3611 allows reporting the following jitter buffer configuration 
> parameters in the VoIP Metrics Report Block:
> 
>    jitter buffer adaptive (JBA): 2 bits
>          Adaptive (11) / non-adaptive (10) / reserved (01)/ unknown
>          (00).  When the jitter buffer is adaptive, then its size is
>          being dynamically adjusted to deal with varying levels of
>          jitter.  When non-adaptive, the jitter buffer size is
>          maintained at a fixed level.  When either adaptive or non-
>          adaptive modes are specified, then the jitter buffer size
>          parameters below MUST be specified.
> 
>    jitter buffer rate (JB rate): 4 bits
>          J = adjustment rate (0-15).  This represents the implementation
>          specific adjustment rate of a jitter buffer in adaptive mode.
>          This parameter is defined in terms of the approximate time
>          taken to fully adjust to a step change in peak to peak jitter
>          from 30 ms to 100 ms such that:
> 
>          adjustment time = 2 * J * frame size (ms)
> 
>          This parameter is intended only to provide a guide to the
>          degree of "aggressiveness" of an adaptive jitter buffer and may
>          be estimated.  A value of 0 indicates that the adjustment time
>          is unknown for this implementation.
> 
> Kevin's suggested text seems to cover the first two values of the 
> "jitter buffer adaptive" field more than adequately but "unknown" seems 
> to be MIA.  
>Is it not possible that the type of jitter buffer might be 
> unknown? 

[Qin]: Good question. It looks we need to get alignment beween JB draft and RFC3611 for this.
Kevin, would you like to clarify why you classify the adaptive one further into three?

> Is the "jitter buffer rate" field useless?  If not, why is an 
> equivalent not included in the new draft?  It seems like if the plan is 
> to have these new report blocks replace the old ones, they should at 
> least contain the same data...

[Qin]: JB draft focus on reporting How jitter buffers are capable of automatically adjusting to changes in delay
rather than changs in rate. That is say jb metrics are measured in millisecond while jitter buffer rate is measured
in unit from 0 to 15.
Also jitter buffer rate is more like configuration parameter that is only applied to adaptive jitter buffer and doesn't 
look to me a mandotary feature that need to be supported for the implementation.

>>
> > [KG] I've seen recent discussion from others that leads me to wonder
> > whether they're going to be OK with it. I hope this proposal can get
> > a more thorough review before being included in the draft.
> >
> >
> > Block length Is requirement to discard reports with unexpected length
> > common practice with these reports? The alternative is to allow
> > reports to be revised to increased size with appended data. Original
> > implementations then ignore anything beyond the original size. It's a
> > little more flexible but maybe we don't want to go there. I've
> > checked RFC 3611 and don't see any guidance on this. It would be nice
> > to specify consistent behavior around this for all reports.
> >
> >
> > [Qin]:Yes. I have fixed this with adding the following sentence to
> > say: "
> >
> > The block MUST be discarded if the block length is
> >
> > set to a different value.
> >
> > "
> >
> >
> > [KG] I did not claim there was anything broken in the draft so I am
> > confused that you claim to have fixed it. If your "Yes" reply was in
> > response to "Is requirement to discard reports with unexpected length
> > common practice with these reports?" it would be helpful to point out
> > a draft or two on which you've modeled this behavior.
> >
> >
> > Jitter buffer nominal delay Needs to specify reference points for
> > reported delay: From receipt to playout? From RTP timestamp to
> > playout?
> >
> >
> > [Qin]:One reference point is the packet that arrives exact on time.
> >
> >
> > We need a definition for the "exactly on time". Exactly on time
> > according to whom and with respect to what? The other reference point
> > is playout time. This also needs to be defined. Playout of first byte
> > in the payload?
> 
> I'm still waiting for someone to define "nominal" in this context (hint: 
> this
> 
>    jitter buffer nominal delay (JB nominal): 16 bits
>          This is the current nominal jitter buffer delay in
>          milliseconds, which corresponds to the nominal jitter buffer
>          delay for packets that arrive exactly on time.  This parameter
>          MUST be provided for both fixed and adaptive jitter buffer
>          implementations.
> 
> does not contain a definition ;-)

[Qin]: As I clarified to Kevin, implementation specific time window will tell us
what the exactly on time means. the jitter buffer can be considered as a time
 window with one side (the early side) aligned with the recent minimum delay
 and the other side (the late side) representing the maximum permissible delay
 before a packet would be discarded.

So nominal just means packets arrive within the time wondow and can be 
successully played out.