<html>
<head>
<meta content="text/html; charset=UTF-8" http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
<div class="moz-cite-prefix">Am 13.02.2013 21:39, schrieb Joe Touch:<br>
</div>
<blockquote cite="mid:511BFA0E.9090303@isi.edu" type="cite">
<br>
FWIW, bufferbloat examples I've seen tend to focus on *upload* out
of the home. As you note, download isn't the issue as much.
<br>
<br>
Try this:
<br>
    - upload a video to youtube (or anywhere)
<br>
    - ping somewhere else
<br>
</blockquote>
<br>
Now, what will happen? The TCP socket will fully utilize the
outgoing interface's buffer. And the ICMP packet has to enqueue
itself at the end of the queue.<br>
<br>
However, this is not a problem of too much buffering. This is a
scheduling problem. Actually, VJCC extends TCP's self<i>_clocking_ </i>into
a self<i>_scheduling_</i>.<br>
<br>
As far as this works at all, it will achieve some kind of
"statistically similar throughput" for greedy sources and long term
flows.<br>
<br>
However, from the perspective of the ICMP echo request, the whole
issue appears as some kind of head of line blocking. (With numerous
heads...)<br>
<blockquote cite="mid:511BFA0E.9090303@isi.edu" type="cite">
<br>
That can happen within a single machine (that was the first case I
heard about, and as anticipated the issue was in-kernel buffering)
or between two machines (if the home router has too much buffering
and too little brains to do proportional sharing).
<br>
<br>
</blockquote>
<br>
Absolutely. However, this is no issue. What you describe is an IP
stack that "works as designed".<br>
<br>
<blockquote cite="mid:511BFA0E.9090303@isi.edu" type="cite">Less
buffering - either in the OS or the router - sometimes helps
reduce delay because the greedy application backs off (due to
losses), is scheduled to transmit less often (when on the same
machine), or simply loses more packets.
<br>
</blockquote>
<br>
I don't think that the described effect is a buffering issue. The
problem is that we intertwined<br>
- congestion control<br>
- ressource sharing<br>
- scheduling <br>
<br>
into one complex algorithm - and now, we wonder why the whole thing
works as designed.<br>
<br>
And BTW, the congavoid paper only talks about TCP. I don't remember
that Van Jacobson or Michael Karels talked about "ping fairness" in
this paper.... ;-)<br>
<br>
<br>
<br>
<br>
<pre class="moz-signature" cols="72">--
------------------------------------------------------------------
Detlef Bosau
GalileistraÃe 30
70565 Stuttgart Tel.: +49 711 5208031
mobile: +49 172 6819937
skype: detlef.bosau
ICQ: 566129673
<a class="moz-txt-link-abbreviated" href="mailto:detlef.bosau@web.de">detlef.bosau@web.de</a> <a class="moz-txt-link-freetext" href="http://www.detlef-bosau.de">http://www.detlef-bosau.de</a>
------------------------------------------------------------------
The nonsense that passes for knowledge around wireless networking,
even taught by "professors of networking" is appalling. It's the
blind leading the blind. (D.P. Reed, 2012/12/25)
------------------------------------------------------------------
</pre>
</body>
</html>