

rWX11sNcGvusjU22NzXiuE+379Oddr3enq6SMGAAFY0RRe7fACNAus22RS5wTATQk) id 1FJKcW-0000Fz-2r
	for [email-masked]; Tue, 14 Mar 2006 20:16:12 -0500
Date: Tue, 14 Mar 2006 20:15:50 -0500
To: "ext Magnus Westerlund" <[email-masked]>
From: Nikolai Leung <[email-masked]>
Subject: Re: [AVT] draft-hdesineni-avt-avpf-ccm-pd-extn-00.txt
Cc: [email-masked], [email-masked], [email-masked]

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Hi Magnus,

One of the problems with the usual method of having only the receiver 
adjust its de-jitter buffer and play out times based on the arrival of 
traffic is that,

1.  In wireless systems like HSDPA/HRPD where a single down/forward link 
channel is shared among all the users in the cell and assigned by the 
scheduler to users based on their individual down/forward link quality, the 
E2E delays of packets can vary significantly at different locations in a 
cell and under different loading conditions (i.e., # users in the 
cell).  It is important to note that the variation in E2E (down/forward 
link) delays at different locations is the result of changes in the link 
throughput because of variations in the radio link quality.  The 
instantaneous data rate assigned to a user is based on what can be 
supported by the radio link at that location.  As this changes, so does the 
delivery time for packets of a particular size.

In the attached slide the dashed lines show the distribution of average E2E 
delays for packet-switched video telephony users being served in 57 cells 
by a HSDPA/HRPD-type of scheduler in each cell.  Note that in the 
simulations there are a significant # of users who experience an E2E delay 
of over 600ms.  The number of users seeing longer delays gets worse as the 
loading in the cells increases (i.e., going from 8 to 12 users/cell).

2.  To accommodate for these variations, a receiver can use a very deep 
(long) de-jitter buffer to accommodate for this significant variation in 
E2E delays.  However this produces a long static E2E delay as a static 
de-jitter buffer will have to accommodate for the longest E2E delay the 
receiver expects to receive.  In the cases we are seeing, the longest E2E 
delay can exceed what is acceptable for conversational services.

3.  The receiver can also do adawOD3cS7ptpd
sgAptive de-jitter buffering and adapt its 
play out times based on the arrival times of packets.  While this allows 
the receiver to adapt to shorter E2E conditions when in good link quality 
(closer to the base station) or lightly loaded cells, it still suffers from 
the problem that as the user moves further away from the base station or 
more users enter the cell the user will experience unacceptably long delays 
for conversational services.  Again this can be seen in the attached figure.

PDAR Message

The PDAR message allows terminals to still perform de-jitter buffer/play 
out time management based on packet arrivals.  But it also introduces a 
procedure to tell the sender the status of arrivals at the receiver.  We 
are establishing a control loop between the sender and receiver that allows 
the receiver to better control the play out times of the media (and not 
simply react to what it receives from the sender).

For example, as packets are starting to arrive delayed (i.e. closer to 
their play out times at the receiver) the receiver can start to delay its 
play out times and also indicate to the sender that packets are arriving 
later (and by how much) than the receiver requires.

I think there might be some confusion about the PDAR since we called it a 
"Request."  It does not request that packets be sent earlier by the sender 
since as you point out this is usually not possible.  It is an indication 
to the sender that the receiver is not receiving its packets at the desired 
time for play out (and by how much).  The sender is to interpret this 
indication to mean that the link rate may be too slow and/or congestion 
from cell loading too heavy to support the current rate it is transmitting 
at.

In summary, the PDAR is an indication of the receiver's play out situation 
as it is affected by the
+ link speed/quality
+ congestion
+ sender's packet sizes/sending rate

The sender can use the PDAR to adjust its output rate (essentially decrease 
its frame/packet sizes) to get its transmission through the slower link 
more quickly and address the play out situation at the receiver.  We think 
this is a good control-loop feedback variable since it is directly linked 
to the play out times of the receiver, and thus directly controls the 
quality rendered to the user.

The solid lines in the attached figure show the results of feeding back 
this packet delay information to the senders of point-to-point packet 
switched video telephony calls.  The senders adjust their transmitted video 
frame sizes (video QP values) based on this delay information and are able 
to adapt well to the variations in link and loading conditions.  Most of 
the E2E delays are centered around 150ms as opposed to the dashed lines 
where E2E delays peak around 620ms and can range up to 1000ms.

What are the other congestion indicators that you were thinking of?

Regards,

-Nik

At 04:24 AM 3/14/2006, ext Magnus Westerlund wrote:
>Hi Nikolai,
>
>I have looked at this draft an do question the usability of having the 
>receiver request that delivery is done earlier. Lets look how things 
>usually are done and why.
>
>In a conversational case, i.e. minimal delay is the target, the sender 
>encodes, packetize and transmit as soon as it can, while avoiding 
>congestion. The packet-based (normally best-effort) network transports the 
>packet from the sender to one or more receivers. The receivers uses a 
>jitter-buffer to cope with the variation of the time it takes from 
>sampling until removal from the buffer.
>
>In those cases you have multiple receivers not doing a receiver side 
>adaptation to the jitter and delivery delay seems really problematic. 
>Where a receiver can adopt to its individual situation, a sender need to 
>take all receivers into account.
>
>Even in a single receiver use case, the request for adjusting the packet 
>delay may be impossible to react to. If a receiver request the sender to 
>send the packets earlier so that they arrive in time, that means that the 
>sender is capable of moving the transmission to earlier. In many casTHIzKyeg7HiOJOLlV/tFjQKbL04UPPEyPkd3WBwPD0Nx2WeuFTBYzNWqO8EJPqzyRPuduwrra
uHNENlhKN4LqhkfH0Ze it 
>is already running a minimal delay setup from sampling until transmission. 
>Thus the receiver is not capable of moving the schedule earlier.
>
>I also think it is important to consider where is the delay between the 
>transmitter and receiver coming from? I think we can break it up into 
>static delay that can't vary, like the propagation delay through the 
>medium. However the static delay is not really guaranteed to not change in 
>an IP network. If you have a route change for your traffic then your delay 
>may change. Then there is the varying delay, caused by for example buffer 
>levels in the routers. In the case of mobile radio networks it may also be 
>caused by radio link layer retransmission or the HSDPA scheduler. So we do 
>have several effects in play, some which is congestion dependent.
>
>As I see it requesting changes in the delay is not really productive. The 
>thing the sender do have partial control over is the congestion situation. 
>Thus it seems primarily be of interest to combat congestion. For that I 
>think there is better indicators than a request to adjust the delay.
>
>So can you please explain why PDAR is a good mechanism?
>
>
>Cheers
>
>Magnus Westerlund
>
>Multimedia Technologies, Ericsson Research EAB/TVA/A
>----------------------------------------------------------------------
>Ericsson AB                | Phone +46 8 4048287
>Torshamsgatan 23           | Fax   +46 8 7575550
>S-164 80 Stockholm, Sweden | mailto: [email-masked]
>
>_______________________________________________
>Audio/Video Transport Working Group
>[email-masked]
>https://www1.ietf.org/mailman/listinfo/avt

--=====================_7160536==.ALT
Content-Type: text/html; charset="us-ascii"

<html>
<body>
<font size=3>Hi Magnus,<br><br>
One of the problems with the usual method of having only the receiver
adjust its de-jitter buffer and play out times based on the arrival of
traffic is that,<br><br>
1.&nbsp; In wireless systems like HSDPA/HRPD where a single down/forward
link channel is shared among all the users in the cell and assigned by
the scheduler to users based on their individual down/forward link
quality, the E2E delays of packets can vary significantly at different
locations in a cell and under different loading conditions (i.e., # users
in the cell).&nbsp; It is important to note that the variation in E2E
(down/forward link) delays at different locations is the result of
changes in the link throughput because of variations in the radio link
quality.&nbsp; The instantaneous data rate assigned to a user is based on
what can be supported by the radio link at that location.&nbsp; As this
changes, so does the delivery time for packets of a particular
size.<br><br>
In the attached slide the dashed lines show the distribution of average
E2E delays for packet-switched video telephony users being served in 57
cells by a HSDPA/HRPD-type of scheduler in each cell.&nbsp; Note that in
the simulations there are a significant # of users who experience an E2E
delay of over 600ms.&nbsp; The number of users seeing longer delays gets
worse as the loading in the cells increases (i.e., going from 8 to 12
users/cell).<br><br>
2.&nbsp; To accommodate for these variations, a receiver can use a very
deep (long) de-jitter buffer to accommodate for this significant
variation in E2E delays.&nbsp; However this produces a long static E2E
delay as a static de-jitter buffer will have to accommodate for the
longest E2E delay the receiver expects to receive.&nbsp; In the cases we
are seeing, the longest E2E delay can exceed what is acceptable for
conversational services.<br><br>
3.&nbsp; The receiver can also do adaptive de-jitter buffering and adapt
its play out times based on the arrival times of packets.&nbsp; While
this allows the receiver to adapt to shorter E2E conditions when in good
link quality (closer to the base station) or lightly loaded cells, it
still suffers from the problem that as the user moves further away from
the base station or more users enter the cell the user will experience
unacceptably long delays foICNDpYCXXSV8MEOtuJl7wTGNK7SlkVVIoZJZOeyQ4DRj+xJ4FpmeBMZXVA
BAAAAAAAAADgAAAAAAAAAJUBAAAAAAAACr conversational services.&nbsp; Again this
can be seen in the attached figure.<br><br>
PDAR Message<br><br>
The PDAR message allows terminals to still perform de-jitter buffer/play
out time management based on packet arrivals.&nbsp; But it also
introduces a procedure to tell the sender the status of arrivals at the
receiver.&nbsp; We are establishing a control loop between the sender and
receiver that allows the receiver to better control the play out times of
the media (and not simply react to what it receives from the
sender).<br><br>
For example, as packets are starting to arrive delayed (i.e. closer to
their play out times at the receiver) the receiver can start to delay its
play out times and also indicate to the sender that packets are arriving
later (and by how much) than the receiver requires.<br><br>
I think there might be some confusion about the PDAR since we called it a
&quot;Request.&quot;&nbsp; It does not request that packets be sent
earlier by the sender since as you point out this is usually not
possible.&nbsp; It is an indication to the sender that the receiver is
not receiving its packets at the desired time for play out (and by how
much).&nbsp; The sender is to interpret this indication to mean that the
link rate may be too slow and/or congestion from cell loading too heavy
to support the current rate it is transmitting at.&nbsp; <br><br>
In summary, the PDAR is an indication of the receiver's play out
situation as it is affected by the <br>
+ link speed/quality<br>
+ congestion<br>
+ sender's packet sizes/sending rate<br><br>
The sender can use the PDAR to adjust its output rate (essentially
decrease its frame/packet sizes) to get its transmission through the
slower link more quickly and address the play out situation at the
receiver.&nbsp; We think this is a good control-loop feedback variable
since it is directly linked to the play out times of the receiver, and
thus directly controls the quality rendered to the user.<br><br>
The solid lines in the attached figure show the results of feeding back
this packet delay information to the senders of point-to-point packet
switched video telephony calls.&nbsp; The senders adjust their
transmitted video frame sizes (video QP values) based on this delay
information and are able to adapt well to the variations in link and
loading conditions.&nbsp; Most of the E2E delays are centered around
150ms as opposed to the dashed lines where E2E delays peak around 620ms
and can range up to 1000ms.<br><br>
What are the other congestion indicators that you were thinking
of?<br><br>
Regards,<br><br>
-Nik<br><br>
<br>
At 04:24 AM 3/14/2006, ext Magnus Westerlund wrote:<br>
<blockquote type=cite class=cite cite>Hi Nikolai,<br><br>
I have looked at this draft an do question the usability of having the
receiver request that delivery is done earlier. Lets look how things
usually are done and why.<br><br>
In a conversational case, i.e. minimal delay is the target, the sender
encodes, packetize and transmit as soon as it can, while avoiding
congestion. The packet-based (normally best-effort) network transports
the packet from the sender to one or more receivers. The receivers uses a
jitter-buffer to cope with the variation of the time it takes from
sampling until removal from the buffer.<br><br>
In those cases you have multiple receivers not doing a receiver side
adaptation to the jitter and delivery delay seems really problematic.
Where a receiver can adopt to its individual situation, a sender need to
take all receivers into account.<br><br>
Even in a single receiver use case, the request for adjusting the packet
delay may be impossible to react to. If a receiver request the sender to
send the packets earlier so that they arrive in time, that means that the
sender is capable of moving the transmission to earlier. In many case it
is already running a minimal delay setup from sampling until
transmission. Thus the receiver is not capable of moving the schedule
earlier.<br><br>
I also think it is important to consider where is the delay between the
transmitter and receiver comingAAAAAAAAAAXAAAAAAAAAHsAAAAAAAAAewAAAAAAAAB8
AAAAQAIAAAAABwAAAP//7wAAAAAA////////FAAAAAABAAD4 from? I think we can break it up into
static delay that can't vary, like the propagation delay through the
medium. However the static delay is not really guaranteed to not change
in an IP network. If you have a route change for your traffic then your
delay may change. Then there is the varying delay, caused by for example
buffer levels in the routers. In the case of mobile radio networks it may
also be caused by radio link layer retransmission or the HSDPA scheduler.
So we do have several effects in play, some which is congestion
dependent.<br><br>
As I see it requesting changes in the delay is not really productive. The
thing the sender do have partial control over is the congestion
situation. Thus it seems primarily be of interest to combat congestion.
For that I think there is better indicators than a request to adjust the
delay.<br><br>
So can you please explain why PDAR is a good mechanism?<br><br>
<br>
Cheers<br><br>
Magnus Westerlund<br><br>
Multimedia Technologies, Ericsson Research EAB/TVA/A<br>
----------------------------------------------------------------------<br>
Ericsson
AB&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
| Phone +46 8 4048287<br>
Torshamsgatan
23&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; |
Fax&nbsp;&nbsp; +46 8 7575550<br>
S-164 80 Stockholm, Sweden | mailto:
[email-masked]<br><br>
_______________________________________________<br>
Audio/Video Transport Working Group<br>
[email-masked]<br>
<a href="https://www1.ietf.org/mailman/listinfo/avt" eudora="autourl">https://www1.ietf.org/mailman/listinfo/avt</a></font></blockquote></body>
</html>

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_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt

--=====================_7160526==_--

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/93/vP/d/928vLy8vLz/vP+8/7z/vP//////vLy8vJL/vLy8////vP///7z///+8////vP//////
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////vLy8//////////////////////////////////////////////////////+8/7z///+8/7z/
vP///7z/vP+8////vP+8/7z///+8/7z/vP///7z/vP+8////vP//////////////////////////
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////////////////////////////////////////vP////////+8/////////7z/////////vP//
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/////7z/////////vP////////+8////////////////////////////////////////////////
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//////////////////////////////8A////////////////////////////////////////////
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////////////////AAAAAP8AAAAAAAAAAAAAAP8AAAD/AAD/AP8AAP8AAP//AP8A/wD//wD/AP8A
/wAA/wD//wAA/wAAAP//////////////////////////////////////////////////////////
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/wAAAAD/AP8A////AAAA////AP8A/////wD//wD/AAD//wD/AP8A//8A/wD/AP////8A//8AAP8A
AP//////////////////////////////////////////////////////////////////////////
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_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt

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