<div dir="ltr"><div class="gmail_extra"><br><div class="gmail_quote">On Sat, May 25, 2013 at 4:34 PM, Lachlan Andrew <span dir="ltr"><<a href="mailto:lachlan.andrew@gmail.com" target="_blank">lachlan.andrew@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="overflow:hidden">I've always wondered why<br>
switched ethernet (which does the ISO layer-3 tasks of addressing,<br>
routing over multiple point-to-point links and buffering) is called a<br>
"link layer" by the internet community...<br></div></blockquote></div><br>It's called "feature creep". Ethernet 2.0 (predates 802.*) was clearly a link layer. IEEE keeps adding stuff. Many Internet purists complained. We now are paying for doing nearly everything twice: once in silicon by way of the IEEE and once in the Internet proper. As far as the internet is concerned, the extra complexity in the lower layer is mostly a waste.</div>
<div class="gmail_extra"><br></div><div class="gmail_extra">However there are a couple of really important exceptions: there is a multiplicative scale increase from doing both routing and switching. Today a single router with dozens of interfaces connected to switching fabrics can have hundreds or thousands of peers. This is in part how the Internet itself beats Moore's law. (The switches typically use MPLS)</div>
<div class="gmail_extra"><br></div><div class="gmail_extra">Otherwise there would be some key router components that need to beat Moore's law squared: router buffer memory size needs to scale with the data rate, router FIB memory needs to scale with routing table size, and access time for both also needs to scale with data rate. We at least partially ease the scale pressure on these components by increasing the Internet branchiness rather than path lengths.</div>
<div class="gmail_extra"><br></div><div class="gmail_extra">As for link layer flow control, it doesn't work. You can buy it today in many technologies, but if you turn it on, you will rediscover head-of-line blocking and global resource contention. e.g. If you have one overloaded exit, the cascaded backlogs at each stage through the fabric guarantee congestion and/or resource starvation everywhere, even if the rest of the fabric is otherwise lightly loaded.</div>
<div class="gmail_extra"><br></div><div class="gmail_extra"><div><div dir="ltr"><div>Thanks,</div>--MM--<br>The best way to predict the future is to create it. - Alan Kay<br><br>Privacy matters! We know from recent events that people are using our services to speak in defiance of unjust governments. We treat privacy and security as matters of life and death, because for some users, they are.</div>
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