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

"Roni Even" <> Wed, 16 January 2013 21:19 UTC

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From: "Roni Even" <>
To: "'Alan Clark'" <>, "'Dan \(Dan\)'" <>, "'Kevin Gross'" <>, "'Qin Wu'" <>
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Date: Wed, 16 Jan 2013 23:15:58 +0200
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Subject: Re: [xrblock] Fw: I-D Action: draft-ietf-xrblock-rtcp-xr-jb-02.txt
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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.



From: Alan Clark [] 
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 "read" point. If all the packets
arrive with zero jitter they would all incur 40ms of delay within the

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



On 1/16/13 10:01 AM, "Roni Even" <> 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?

From: [] 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 "late
window" - so if a packet arrives more than "nominal delay ms" after its
expected time then it will be discarded.

"On time" - in this case - refers to the expected arrival time of the packet
when calculated with reference to the first or a later selected reference

Jitter buffer implementations don't 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 "nominal delay" 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
"on time" packet.



On 1/16/13 5:36 AM, "Dan (Dan)" <> 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? 

From: [] 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


Media Network Consultant

AVA Networks - <>  <>
, <>  <> 

On Mon, Jan 14, 2013 at 8:27 PM, Qin Wu <> wrote:


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


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

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
<>  and 5.1 of [RFC5481
<> ]).


Let me know what you think about this.



----- Original Message ----- 

From: Qin Wu <> 

To: Kevin Gross <>  

Cc: xrblock <> 

Sent: Monday, January 14, 2013 8:46 AM

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


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.



----- Original Message ----- 

From: Kevin Gross <>  

To: Qin Wu <> 

Cc: xrblock <> 

Sent: Sunday, January 13, 2013 6:04 AM

Subject: Re: offlist//Re: [xrblock] Fw: I-D Action:


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

+1-303-447-0517 <tel:%2B1-303-447-0517> 

Media Network Consultant

AVA Networks - <>  <>
, <>  <> 


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