Even through jumbo frames are not standardized, most new network equipment supports them (though generally support is disabled by default). If you IPv4 route jumbo packets to a network that doesn't support them, the router will fragment for you. Under IPv6, it is the sender's responsibility to choose an MTU that is supported by all networks between source and destination. IPv6 routers do no fragmentation.<div>
<br></div><div>Although consumer products are often dumbed down, it is not difficult to find switches with comprehensive QoS configurability. Weighted fair queuing is a popular scheme. Strict priority is a bit dangerous but useful for latency-critical applications. The IEEE has just ratified a credit-based algorithm called 802.1av. What I find is missing from all but the high-end equipment is configurability of buffering capacity and behavior. Bad buffering can burn an otherwise competent QoS implementation.</div>
<div><br></div><div>In his talks, Jim Gettys claims that these QoS features do not fix bufferbloat - they just move the problem elsewhere. I generally agree with this though I find that moving the problem elsewhere is sometimes a perfectly acceptable solution.</div>
<div><br></div><div>Kevin Gross</div><div><br><br><div class="gmail_quote">On Fri, May 13, 2011 at 2:21 PM, Dave Taht <span dir="ltr"><<a href="mailto:dave.taht@gmail.com">dave.taht@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<br><br><div class="gmail_quote">On Fri, May 13, 2011 at 2:03 PM, Kevin Gross <span dir="ltr"><<a href="mailto:kevin.gross@avanw.com" target="_blank">kevin.gross@avanw.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204, 204, 204);padding-left:1ex">
<div link="blue" vlink="purple" lang="EN-US"><div><p class="MsoNormal"><span style="font-size:11pt;color:rgb(31, 73, 125)">Do we think that bufferbloat is just a WAN problem? I work on live media applications for LANs and campus networks. I'm seeing what I think could be characterized as bufferbloat in LAN equipment. The timescales on 1 Gb Ethernet are orders of magnitude shorter and the performance problems caused are in many cases a bit different but root cause and potential solutions are, I'm hoping, very similar.</span></p>
<p class="MsoNormal"><span style="font-size:11pt;color:rgb(31, 73, 125)"> </span></p><p class="MsoNormal"><span style="font-size:11pt;color:rgb(31, 73, 125)">Keeping the frame byte size small while the frame time has shrunk maintains the overhead at the same level. Again, this has been a conscious decision not a stubborn relic. Ethernet improvements have increased bandwidth by orders of magnitude. Do we really need to increase it by a couple percentage points more by reducing overhead for large payloads?</span></p>
<p class="MsoNormal" style="text-indent:0.5in"><span style="font-size:11pt;color:rgb(31, 73, 125)"> </span></p><p class="MsoNormal"><span style="font-size:11pt;color:rgb(31, 73, 125)">The cost of that improved marginal bandwidth efficiency is a 6x increase in latency. Many applications would not notice an increase from 12 us to 72 us for a Gigabit switch hop. But on a large network it adds up, some applications are absolutely that sensitive (transaction processing, cluster computing, SANs) and (I thought I'd be preaching to the choir here) there's no way to ever recover the lost performance.</span></p>
<p class="MsoNormal"><span style="font-size:11pt;color:rgb(31, 73, 125)"> </span></p></div></div></blockquote><div><br>You are preaching to the choir here, but I note several things:<br><br>Large frame sizes on 10GigE networks to other 10GigE networks is less of a problem than 10GigE to 10Mbit networks. I would hope/expect that frame would fragment in that case.<br>
<br>Getting to where latencies are less than 10ms in the general case makes voip feasible again. I'm still at well over 300ms on bismark.<br><br>Enabling higher speed stock market trades and live music exchange over a lan would be next on my list after getting below 10ms on the local switch/wireless interface!<br>
<br>A lot of research points to widely enabling some form of fair queuing at the servers and switches to distribute the load at sane levels. (nagle, 89) I think few gig+e vendors are doing that in hardware, and it would be good to know who is and who isn't.<br>
<br>For example, the switch I'm using on bismark has all sorts of wonderful QoS features such as fair queuing, but as best as I can tell they are not enabled, and I'm seeing buffering in the switch at well above 20ms....<br>
<br>It is astonishing that a switch chip this capable has reached the consumer marketplace...<br><br><a href="http://realtek.info/pdf/rtl8366s_8366sr_datasheet_vpre-1.4_20071022.pdf" target="_blank">http://realtek.info/pdf/rtl8366s_8366sr_datasheet_vpre-1.4_20071022.pdf</a><br>
<br>And depressing that so few of it's capabilities have software to configure them.<br></div><blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204, 204, 204);padding-left:1ex">
<div link="blue" vlink="purple" lang="EN-US"><div><p class="MsoNormal"><span style="font-size:11pt;color:rgb(31, 73, 125)">Kevin Gross</span></p><p class="MsoNormal"><span style="font-size:11pt;color:rgb(31, 73, 125)"> </span></p>
<div style="border-width:1pt medium medium;border-style:solid none none;border-color:rgb(181, 196, 223) -moz-use-text-color -moz-use-text-color;padding:3pt 0in 0in"><p class="MsoNormal"><b><span style="font-size:10pt">From:</span></b><span style="font-size:10pt"> Dave Taht [mailto:<a href="mailto:dave.taht@gmail.com" target="_blank">dave.taht@gmail.com</a>] <br>
<b>Sent:</b> Friday, May 13, 2011 8:54 AM<br><b>To:</b> <a href="mailto:rick.jones2@hp.com" target="_blank">rick.jones2@hp.com</a><br><b>Cc:</b> Kevin Gross; <a href="mailto:bloat@lists.bufferbloat.net" target="_blank">bloat@lists.bufferbloat.net</a><br>
<b>Subject:</b> Re: [Bloat] Burst Loss</span></p></div><p class="MsoNormal"> </p><p class="MsoNormal" style="margin-bottom:12pt"> </p><div><p class="MsoNormal">On Fri, May 13, 2011 at 8:35 AM, Rick Jones <<a href="mailto:rick.jones2@hp.com" target="_blank">rick.jones2@hp.com</a>> wrote:</p>
<div><p class="MsoNormal" style="margin-bottom:12pt">On Thu, 2011-05-12 at 23:00 -0600, Kevin Gross wrote:<br>> One of the principal reasons jumbo frames have not been standardized<br>> is due to latency concerns. I assume this group can appreciate the<br>
> IEEE holding ground on this.</p></div><p class="MsoNormal">Thusfar at least, bloaters are fighting to eliminate 10s of milliseconds<br>of queuing delay. I don't think this list is worrying about the tens of<br>
microseconds difference between the transmission time of a 9000 byte<br>
frame at 1 GbE vs a 1500 byte frame, or the single digit microseconds<br>difference at 10 GbE.</p><div><p class="MsoNormal" style="margin-bottom:12pt"><br>Heh. With the first iteration of the bismark project I'm trying to get to where I have less than 30ms latency under load and have far larger problems to worry about than jumbo frames. I'll be lucky to manage 1/10th that (300ms) at this point. <br>
<br>Not, incidentally that I mind the idea of jumbo frames. It seems silly to be saddled with default frame sizes that made sense in the 70s, and in an age where we will be seeing ever more packet encapsulation, reducing the header size as a ratio to data size strikes me as a very worthy goal.</p>
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<br></blockquote></div><font color="#888888"><br><br clear="all"><br>-- <br>Dave Täht<br>SKYPE: davetaht<br>US Tel: <a href="tel:1-239-829-5608" value="+12398295608" target="_blank">1-239-829-5608</a><br><a href="http://the-edge.blogspot.com" target="_blank">http://the-edge.blogspot.com</a> <br>
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