Subject: [AVT] Mulplexing the datas with FLEXMUX + TCRTP

From: [email-masked]
Date: Wed, 6 Feb 2002 05:08:19 EST

Hello,

I'm a french engineer studient and I'm doing a paper about MPEG-4 and the 
multimedia. While I was preparing my paper, I've discovered that using 
FLEXMUX + TCRTP could be more interesting that using FLEXMUX alone or TCRTP 
alone.

With FLEXMUX or TRCTP, I can send less packets on the network by multiplexing 
theim. In both case I can choose the number of packets I want to multiplex.

According to the MPEG-4 standard, I use the synchronization layer. If I only 
use FLEXMUX, I can choose the number of SL-PDU packets I want to to multiplex 
and also witch one will be in the multiplexed packet. I can choose to insert 
SL-PDU A and not SL-PDU B in the multiplexed solution...But whatever I do, I 
will always have a 40 bytes header for each paquets due to the [IP/UDP/RTP] 
encapsulation. For reducing the overheads, I can increase the size of the 
payload by inserting more SL-PDU packets, but in case of lost, it could be a 
big problem for the receiver.

If I only use TCRTP, I can multiplex a number of [IP/UDP/RTP] packets. But I 
can't witch SL-PDU packets will be multiplexed. With the CRTP compression 
algorithm, I will reduce the 40 bytes header of the [IP/UDP/RTP] packet to 2 
bytes. Whatever the size of my TCRTP packet is, I will always have a 24 bytes 
header (20 bytes for the IP header + 1 bytes for the TYPE + 1 byte for the 
LEN + 2 bytes for the [IP/UDP/RTP] compression of each packets). For reducing 
the overheads, I have increase the size of the payloads by multiplexing more 
[IP/UDP/RTP] packets. But in case of lost, I will have the same problem as 
using FLEXMUX alone because in both case, I have used the synchronization 
layer. At egal size of payload, we have less overhead with TCRTP than with 
FLEXMUX.

If I use FLEXMUX + TCRTP : with FLEXMUX I control the number of SL-PDU 
packets multiplexed and also witch packet will be multiplexed. Then, with 
CRTP, I reduce the [IP/UDP/RTP] header of each paquets multiplexed before. 
Finally, the overhead will always be more reduced. For some algorithm, like 
AAC, multiplexing 5 packets give me a 2,3 per cent overhead… witch is very 
few. In that case, I think that we don't really need to use TCRTP. So, using 
TCRTP depend on a certain value of overhead, calculated just before choosing 
to use it or not.

I would like to know your opinion about my method and if it could be 
interresting for the community to continue to write a paper about that.

I'm waiting for your anwsers.
Best regards,

Yannick DAMBIELLE
PS: I apologize for my poor english.

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