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Dave Reed sent me the following comments via PM, I think it may be
helpful for the discussion, particularly his remark on the
asymptotic behaviour, so I forward this to the list (with explicit
permission of DPR).<br>
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<th align="RIGHT" nowrap="nowrap" valign="BASELINE">Betreff:
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<td>Re: [e2e] Why do we need congestion control?</td>
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<th align="RIGHT" nowrap="nowrap" valign="BASELINE">Datum: </th>
<td>Tue, 2 Apr 2013 18:59:46 -0400 (EDT)</td>
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<th align="RIGHT" nowrap="nowrap" valign="BASELINE">Von: </th>
<td><a class="moz-txt-link-abbreviated" href="mailto:dpreed@reed.com">dpreed@reed.com</a></td>
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<th align="RIGHT" nowrap="nowrap" valign="BASELINE">An: </th>
<td>Detlef Bosau <a class="moz-txt-link-rfc2396E" href="mailto:detlef.bosau@web.de"><detlef.bosau@web.de></a></td>
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<th align="RIGHT" nowrap="nowrap" valign="BASELINE">Kopie
(CC): </th>
<td><a class="moz-txt-link-abbreviated" href="mailto:end2end-interest@postel.org">end2end-interest@postel.org</a></td>
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<p style="margin:0;padding:0;">"Erasure codes" is not a proper
term for this. Which creates lots of confusion on the list,
and that will get worse. Erasure codes correct erasures, but
that is not the key attribute of fountain codes. You need
"ratelessness".</p>
<p style="margin:0;padding:0;">Â </p>
<p style="margin:0;padding:0;">The correct technical term is
"rateless erasure codes". That is, codes that correct
erasures but are not dependent on a particular "error rate".Â
A "rateless erasure code" has the property that the goodput
over the long term on *any* erasure channel is asymptotically
equal to the total number of symbols actually delivered (or
symbols sent minus symbols erased).  An erasure channel is an
information theoretic "channel" where the loss process causes
erasure of zero or more symbols in the stream, but all symbols
actually delivered to the destination are correct.</p>
<p style="margin:0;padding:0;">Â </p>
<p style="margin:0;padding:0;">Fountain codes are one example of
a rateless erasure code. If you look up "rateless erasure
code" on Google, you can learn all about them.</p>
<p style="margin:0;padding:0;">Â </p>
<p style="margin:0;padding:0;">Feel free to forward this
clarification to e2e, since I cannot post there.</p>
<p style="margin:0;padding:0;">Â </p>
<p style="margin:0;padding:0;">PS: rateless erasure codes do not
obviate the need for congestion signalling within a network.</p>
Â
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