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

[Alan Clark <[e-mail]>]

Hi Roni

That is correct.

With regard to the choice of reference point - this would typically be the
first packet however could also be based on a running average of the delay.
A jitter buffer does need to deal with timing drift, which could cause a
gradual empty or fill of the buffer, and also with delay
increases/reductions due to route changes - this can be addressed either by
detecting the condition and resetting the reference point or by using the
running average delay value.

Best Regards

Alan 


On 1/16/13 4:15 PM, "Roni Even" <[e-mail]> wrote:

> Hi Alan,
> If you insert the received packet at 40 ms and you are currently start
> reading from 0 you are delaying by 40 ms and 40 ms is the nominal delay.  So
> it does not matter what is the jitter buffer size, you are expecting to render
> or decode a packet if it arrives between 0 or 40 ms compared to the first
> packet. I assume for fixed buffer this will not change but for adaptive buffer
> the nominal delay may change.
> I agree on the last sentence of your explanation, the question is how you
> define the on-time insertion point or expected time. I believe you  are saying
> it is based on the first packet that arrives.
> Roni
>  
> 
> From: Alan Clark [mailto:[e-mail]]
> Sent: 16 January, 2013 6:29 PM
> To: Roni Even; Dan (Dan); 'Kevin Gross'; Qin Wu
> Cc: 'xrblock'
> Subject: Re: [xrblock] Fw: I-D Action: draft-ietf-xrblock-rtcp-xr-jb-02.txt
>  
> Hi Roni
> 
> Nominal delay is the delay that is applied to a packet that arrives at its
> expected time (i.e. 0 jitter) - and corresponds to the late window of the
> jitter buffer
> 
> Jitter buffer size can be ambiguous as the term is sometimes used to mean the
> late window and sometimes the overall buffer size.
> 
> For example.
> 
> A jitter buffer is configured to have 200ms of overall buffer space. Initially
> packets are inserted into this at the 40ms point and hence incur 40ms of delay
> as they propagate to the 0ms ³read² point. If all the packets arrive with zero
> jitter they would all incur 40ms of delay within the buffer.
> 
> If a packet arrives 10ms later than expected then it is written to the buffer
> at the (40-10)ms point however if a packet arrives more than 40ms late then it
> is discarded.
> 
> If a packet arrives 50ms earlier than expected it is written to the (40+50)ms
> point and would wait 90ms before being played out.
> 
> With an adaptive jitter buffer, If the jitter level is high and packets are
> being discarded then the insertion point for on-time packets could be moved to
> say 100ms. This results in the delay for on-time/ zero jitter packets being
> 100ms but would reduce the discard rate
> 
> So the nominal delay is the time difference/ buffer size difference between
> the on-time insertion point and the point at which packets are read out and
> decoded.
> 
> Regards
> 
> Alan
> 
> 
> On 1/16/13 10:01 AM, "Roni Even" <[e-mail]> wrote:
> Hi Alan,
> I am not sure what applies a nominal delay means. Is the first packet defines
> the start of the jitter buffer and nominal delay is the size of the fixed
> jitter buffer.  
> When saying that the jitter buffer may increase or reduce is this for the
> adaptive jitter buffer?
>  
> Roni
>  
> 
> From: [e-mail] [mailto:[e-mail]] On Behalf Of
> Alan Clark
> Sent: 16 January, 2013 2:18 PM
> To: Dan (Dan); Kevin Gross; Qin Wu
> Cc: xrblock
> Subject: Re: [xrblock] Fw: I-D Action: draft-ietf-xrblock-rtcp-xr-jb-02.txt
> 
> 
> A typical jitter buffer uses the first packet received as its timing
> reference, and applies a nominal delay to that before playing out.  During
> later operation, the jitter buffer may increase or reduce the nominal delay or
> may pick a new reference packet. This nominal delay represents the ³late
> window² - so if a packet arrives more than ³nominal delay ms² after its
> expected time then it will be discarded.
> 
> ³On time² - in this case - refers to the expected arrival time of the packet
> when calculated with reference to the first or a later selected reference
> packet.
> 
> Jitter buffer implementations don¹t necessary do this mathematically however
> this is a generalized description that models the behavior of most jitter
> buffers used for VoIP and Videoconferencing.
> 
> Playout buffers used in video streaming applications operate quite
> differently. Basically a received chunk of encoded video is added to the
> playout buffer - encoded video is read from the buffer. When the buffer level
> drops below a threshold then another chunk of video is requested from the
> server. There is an equivalent to ³nominal delay² as the buffer will always
> try to make sure there is at least a minimal level of video in the buffer
> before playing out - however there would not be the equivalent of an ³on time²
> packet.
> 
> Regards
> 
> Alan
> 
> 
> On 1/16/13 5:36 AM, "Dan (Dan)" <[e-mail]> wrote:
> Kevin, Qin,
>  
> Do you want to discuss this one2one, or should we organize a short conference
> call? Do other think that they can contribute to clarify the issues, or want
> to participate? 
>  
> Dan
>  
>  
>  
> 
> From: [e-mail] [mailto:[e-mail]] On Behalf Of
> Kevin Gross
> Sent: Tuesday, January 15, 2013 11:08 PM
> To: Qin Wu
> Cc: xrblock
> Subject: Re: [xrblock] Fw: I-D Action: draft-ietf-xrblock-rtcp-xr-jb-02.txt
> 
> I think we need to have a phone call to discuss this whole thing.
> 
> 
> Kevin Gross
> 
> [phone]
> 
> Media Network Consultant
> 
> AVA Networks - www.AVAnw.com <http://www.AVAnw.com>  <http://www.AVAnw.com>
> <http://www.avanw.com/> , www.X192.org <http://www.X192.org>
> <http://www.X192.org>  <http://www.X192.org>
>  
> 
> On Mon, Jan 14, 2013 at 8:27 PM, Qin Wu <[e-mail]> wrote:
> 
> Hi,Kevin:
> 
> I like to make some additioal clarification to your question.
> 
> I think the packet arrives exactly on time, is also referred to the packet
> that has nominal delay.
> 
> So we have two ways to address this.
> 
> a. It is more like implementation specific issue,e.g., rely on timing
> information in the headers of previous
> 
> packet and current packet or rely on time window to determine this. So we can
> leave this to the specific
> 
> implemenations. 
> 
> 
> 
> b. we can explain the packet that arrives exactly on time as the packet that
> has nominal delay.
> 
> The nominal delay can either be choosen as the jitter buffer delay for the
> packet with minimal delay(i.e.,
> 
> the reference packet is choosen as the packet with minmal delay) or average
> delay for all the packets that arrives
> 
> within the implementation specific time window during the measurement
> interval.
> 
> I am not sure we should details to talk about this, but If we take (b), we
> prefer to add the following sentence in the draft to say:
> 
> "Note that the reference packet is generally selected as the packet
>  with minimum delay based on the most common criterion (see Sections 1
> <http://tools.ietf.org/html/rfc6798#section-1>  and 5.1 of [RFC5481
> <http://tools.ietf.org/html/rfc5481> ]).
> 
> "
> 
> Let me know what you think about this.
> 
> 
> 
> Regards!
> 
> -Qin
> 
> ----- Original Message -----
> 
> From: Qin Wu <mailto:[e-mail]>
> 
> To: Kevin Gross <mailto:[e-mail]>
> 
> Cc: xrblock <mailto:[e-mail]>
> 
> Sent: Monday, January 14, 2013 8:46 AM
> 
> Subject: Re: [xrblock] Fw: I-D Action: draft-ietf-xrblock-rtcp-xr-jb-02.txt
> 
> 
> 
> Kevin:
> 
> As I clarified to you in the previous email, "implemention specific time
> window" described in Burst Gap drafts will be used to identify a "packet that
> arrives exactly on time".
> 
> That is to say, if the receiving packet falls within  implemention specific
> time window and can be sucessfully playout, such packet will be regarded as
> packet that arrives exactly on time.
> 
> Hope this clarifies.
> 
> 
> 
> Regards!
> 
> -Qin
> 
> ----- Original Message -----
> 
> From: Kevin Gross <mailto:[e-mail]>
> 
> To: Qin Wu <mailto:[e-mail]>
> 
> Cc: xrblock <mailto:[e-mail]>
> 
> Sent: Sunday, January 13, 2013 6:04 AM
> 
> Subject: Re: offlist//Re: [xrblock] Fw: I-D Action:
> draft-ietf-xrblock-rtcp-xr-jb-02.txt
> 
> 
> Qin, 
> 
> 
> 
> Of the jitter buffer delay metric, the draft currently says "It is calculated
> based on the difference between the receipt time and the playout time for the
> packet that arrives exactly on time."
> 
> 
> 
> My issue is that I don't know how to identify a "packet that arrives exactly
> on time".
> 
> 
> Kevin Gross
> 
> [phone] <tel:%2B1-303-447-0517>
> 
> Media Network Consultant
> 
> AVA Networks - www.AVAnw.com <http://www.AVAnw.com>  <http://www.AVAnw.com>
> <http://www.AVAnw.com> , www.X192.org <http://www.X192.org>
> <http://www.X192.org>  <http://www.X192.org>
>    
> 
> 
> 
> 
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