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.
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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