[opendtv] Re: tolerance Latency , Jitters & packet loss issues for MPEG-2 TS over IP netwo

  • From: "Kon Wilms" <kon@xxxxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx, opendtv@xxxxxxxxxxxxx
  • Date: Sat, 26 Feb 2005 13:05:54 -0500

> Packet loss is evil - any lost paclets show up either as lost video or
> audio.  You can add FEC, but some SIP STBs are not going to have the
> processing power to do FEC in software and there aren't any IP STBs
> with hardware FEC support.  Some MPEG-4 system do really long time
> jitter buffers and retry on lost multicast packets.

FEC on IP is rather pointless unless you want to start modifying the IP stack 
drivers. The 
packets get ditched at the TCP or UDP decode layer if the checksum doesn't 
compute, so they 
aren't even present for the error correcting decoder to attempt to repair them. 
The desired 
mode for IP is to do plain ECC using large blocks - so you can recover complete 
packets. For 
this you need vandermonde matrix based ECC, LDPC ECC, or similar. 

As for jitter, it is/can be a problem for IP networks. We've had to do jitter 
analysis on IP 
streams (MPEG2 over UDP, RTSP, etc.) many a time, even when using large decoder 
buffers. 
Can you name a manufacturer that doesn't make use of a SmartBits or similar 
testing system 
when testing IP video servers and receivers?

BTW Ethereal has a rather nice jitter analysis module with some graphing 
functions, and its 
free.

> Your middleware vendor better have the answer to all of the questions
> or you picked the wrong vendor...

Indeed. I have a feeling OpenDTV is the middleware consultant. And Integrator. 
I'd just like to 
know what project this is that everyone keeps working on for free - there must 
be something 
someone knows that I don't. :-)

Cheers
Kon

 
 
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