[CentOS] Check my math please
warren at etr-usa.com
Thu Nov 6 20:32:32 UTC 2008
Sean Carolan wrote:
> For a back-of-the napkin calculation can we not assume that data equal
> to the entire size of the file will be streamed to the client during
You can if you're using some of the fudge factors others have mentioned
here. The headers for IP + UDP + RTP take at least 3.5% of the
bandwidth for a network using a PMTU of 1500 bytes. If the smallest MTU
between your system and the receiver is smaller, the percentage goes up.
And, the percentage goes up anyway because those numbers only talk
about the minimum overhead. RTP headers are flexible, as are most
higher-level protocols, like TCP.
We're also ignoring any other traffic on the link. With RTP, for
instance, there are usually RTCP and RTSP channels as well. Without
these parallel data channels, the stream doesn't work.
You also have to account for retries and buffering. If your network
link is exactly as big as it has to be for the ideal case, you will
still have problems because the time it takes to deal with lost or
damaged packets comes out of your bit rate budget. There's a limit to
the effectiveness of prebuffering.
10% total overhead isn't unreasonable.
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