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Re: [AVT] MPEG2-TS preamble drafts

Hi David

Please check my quick reply

BR
Frank
----- Original Message ----- From: "David R Oran" <oran at cisco.com> 
To: "Frank Xia" <xiayangsong at huawei.com>
Cc: "Ingemar Johansson S" <ingemar.s.johansson at ericsson.com>; <avt at ietf.org>
Sent: Monday, November 09, 2009 9:15 PM
Subject: Re: [AVT] MPEG2-TS preamble drafts



On Nov 10, 2009, at 12:05 PM, Frank Xia wrote:


Hi Ingemar

Thank you for the review.

BR
Frank
----- Original Message ----- From: "Ingemar Johansson S" <ingemar.s.johansson at ericsson.com 
>
To: <avt at ietf.org>
Cc: <abegen at cisco.com>; <xiayangsong at huawei.com>; <yangpeilin at huawei.com
>
Sent: Monday, November 09, 2009 8:12 PM
Subject: MPEG2-TS preamble drafts


Hi
I have tried to compare the two competing ID's on MPEG2-TS preamble. Not being an expert in this area I anyway try to get an understanding
As I see it draft-xia-avt-mpeg2ts-preamble-00.txt is a simple version of draft-begen-avt-rtp-mpeg2ts-preamble-03.txt as the former does not need a specification of a new preamble format (for simplicity I call the drafts XIA and BEGEN) The benefit XIA is that the endpoints (that understands RFC4588) does not need to be upgraded to understand a new preamble format, I cannot put any weight on this possible benefit. 

The benefit with XIA compared to BEGEN comes with some drawbacks
1) Increased transmission overhead : BEGEN compresses the preamble info into one packet while XIA needs to transmit each packet that contains the preamble. This naturally means that the overhead increases. Does anybody have some figures as regards to how much this overhead increases ?. 

Frank=> I once tried to give a calculation in my
previous email.  It is quoted below "
let's say preamble consists of 20 TSes which has 20*188*8 bits.

where do you get this? The ECM or PAT/PMT you need may be 1/2 a GOP
back in the data stream. That could be a megabit or more of useless
traffic.
Frank=>I am curious how the preamble can occupy 1/2 GOP.
Probably, you can us give a rough illustration.

Let's say it is true. Then, what is the gain after your compression?
Remember PAT/PMT only needs 2 TS in most cases.
ECM has more, but your compression can contribute little.


Assume unicast RTP burst last 3 seconds with 2M bandwith
which is 3*2M bits in total. Preamble occupies around 0.5% of total unicast." 
I may be wrong.

I would like to ask Avi a question. How many RTP packets
needs in his solution for carrying preamble?
I don't think there are big difference between the two solutions
2) Vulnerability to packetloss: XIA transmits the packets with preamble in several RFC4588 packets, which means that if one of these packets is lost the whole preamble is rendered useless. BEGEN compresses the preamble and can can possibly use this "compression gain" to transmit two identical preamble packets to cope with lossy environments. 
Frank=>This question is a variant of the above question.
In fact, each of packets in RAMS needs retransmission if one is lost.
The possibilty of  preamble packets loss have very limited impact
given the small volume of the traffic.
In addition, if I was to come up with a solution to the preamble problem I would first consider the XIA alternative then the more elaborate BEGEN alternative. I am curious to know if the authors of BEGEN originally considered the alterantive outlined in XIA and if so what the motivation was to go for the current proposal.
Unfortunately I cannot say do this or that but I hope that my questions will help to advance this in a direction that is satisfactory for all. 

/Ingemar

=================================
INGEMAR JOHANSSON  M.Sc.
Senior Research Engineer

Ericsson AB
Multimedia Technologies
Labratoriegränd 11
971 28, Luleå, Sweden
Phone +46-1071 43042
SMS/MMS +46-73 078 3289
ingemar.s.johansson at ericsson.com
www.ericsson.com
Visit http://labs.ericsson.com !
=================================
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