[e2e] Technology marches forward at the expense of the net?

David P. Reed dpreed at reed.com
Fri Dec 14 13:04:26 PST 2001

At 11:15 AM 12/14/2001 -0500, Tarik Alj wrote:
>- Would it be possible to evaluate in what proportion, on the average, a
>packet that gets through will contribute to the final file?

This isn't an FEC, exactly. There's an analogy here, though. The reason is 
that the recipient stops listening as soon as they have enough to 
reconstruct the file.  Every received packet contributes to the final file 
essentially 100%.

>- In other words how much bandwidth is wasted by applying FEC at such a high

 From the recipient's point of view, essentially none.  However packets 
that get part of the way to the destination consume "bandwidth" (using that 
term is incorrect here, because we aren't talking about bandwidth, but 
bitrate).  So if few packets get all the way from source to destination, 
there can be heavy overhead before the bottleneck point or error sources, 
which increases as the source transmission rate gets much larger than the 
destination reception rate.

>- what about sequences of small file transfers, such as web pages?

This approach doesn't help at all with independent request of small files 
like web pages or transaction RPCs.  And hurts more as the web page size 
gets smaller, because if RTT*(sending rate) is large, the sender will send 
a lot of redundant packets after the recipient has received the whole web 
page, but it can't stop sending until it knows that the recipient has 
received the whole file.

- David
WWW Page: http://www.reed.com/dpr.html

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