<div dir="ltr"><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Wed, May 21, 2014 at 12:03 PM, <span dir="ltr"><<a href="mailto:dpreed@reed.com" target="_blank">dpreed@reed.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><font face="arial"><p style="margin:0;padding:0">In reality we don't disagree on this:</p><div class="">
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<p style="margin:0;padding:0"><span style="font-family:Arial,Helvetica,Verdana,sans-serif">On Wednesday, May 21, 2014 11:19am, "Dave Taht" <<a href="mailto:dave.taht@gmail.com" target="_blank">dave.taht@gmail.com</a>> said:</span></p>
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<p style="margin:0;padding:0">> Well, I disagree somewhat. The downstream shaper we use works quite<br>> well, until we run out of cpu at 50mbits. Testing on the ubnt edgerouter<br>> has had the inbound shaper work up a little past 100mbits. So there is<br>
> no need (theoretically) to upgrade the big fat head ends if your cpe is<br>> powerful enough to do the job. It would be better if the head ends did it,<br>> of course....<br>></p>
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</div><p style="margin:0;padding:0">There is an advantage for the head-ends doing it, to the extent that each edge device has no clarity about what is happening with all the other cpe that are sharing that head-end. When there is bloat in the head-end even if all cpe's sharing an upward path are shaping themselves to the "up to" speed the provider sells, they can go into serious congestion if the head-end queues can grow to 1 second or more of sustained queueing delay. My understanding is that head-end queues have more than that. They certainly do in LTE access networks.</p>
</div></font></blockquote><div><br></div><div class="gmail_default" style="font-size:small">I have measured 200ms on a 28Mbps LTE quadrant to a single station. This was using the simplest possible test on an idle cell. Easy to see how that can grow to the second range.</div>
<div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">Similarly, Dave Taht and I took data recently that showed a large downstream buffer at the CMTS end (line card?), IIRC, it was something like .25 megabyte, using a UDP flooding tool. </div>
<div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">As always, there may be multiple different buffers lurking in these complex devices, which may only come into play when different parts of them "bottleneck", just as we found many different buffering locations inside of Linux. In fact, some of these devices include Linux boxes (though I do not know if they are on the packet forwarding path or not).</div>
<div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">Bandwidth shaping downstream of those bottlenecks can help, but only to a degree, and I believe primarily for "well behaved" long lived elephant flows. Offload engines on servers and coalescing acks in various equipment makes the degree of help, particularly for transient behavior such as opening a bunch of TCP connections simultaneously and downloading the elements of a web page I believe are likely to put large bursts of packets into these queues, causing transient poor latency. I think we'll get a bit of help out of the packet pacing code that recently went into Linux (for well behaved servers) as it deploys. Thanks to Eric Dumazet for that work! Ironically, servers get updated much more frequently than these middle boxes, as far as I can tell.</div>
<div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">Somehow we gotta get the bottlenecks in these devices (broadband & cellular) to behave better.</div><div class="gmail_default" style="font-size:small">
- Jim</div><div class="gmail_default" style="font-size:small"><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><font face="arial"><div>
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