数学是一个不应该需要任何资格的词，然而，在我们的行业，我听说过Cabletron数学，思科数学，供应商数学，等等。如果需要限定符，那是因为有什么地方出错了。数学是绝对的。我不在乎是谁开始的，每个人都有自己的令人震惊的例子，没有人会完全公开自己的眼镜，每个人都试图通过创造性的“眼镜术”来隐藏自己的弱点。“我一直以来最喜欢的案例是催化剂5509所做的伟大工作。如果您还记得的话，它有三条1.2Gbps的总线，运行所有9个行卡插槽的长度。它们是一个模块，有12个GbE接口，三个总线各有一个接口和9个面板，它需要两个插槽，所以系统可以容纳4个接口。这种系统一度以54Gbps的速度销售。如何?每个分布式交换模块12Gbps, 4个= 48Gbps。三条1.2Gb总线= 3.6Gb。 Two 1GbE ports on the Supervisor III = 2Gb = 53.6Gb, round up for fun and poof = 54Gb Switch!Today I was reviewing another vendors specifications for a switch with 160Gbps per slot (they call it 320Gbps "Full Duplex") with sixteen slots. It claims a 6.2Tbps "backplane speed." If I take 16 slots @ 160Gbps per slot I get 2.56Tbps. I can understand doubling this since all fabric based backplanes are full-duplex, so that equates to 5.12Tbps. I am still missing 1.08Tbps. A friend of mine commented that the extra terabit was used by the smoke generators and mirror array. In my personal world-view I think we should stick to some terms and definitions that could make it easier for customers to figure out how well a system really performs. Take this as a strawman/draft, am open to feedback.1) Per Slot Bandwidth- single count this. If I can run 40Gb into a slot and get 40Gbps out of a slot this is a 40Gb slot. A 10Gb Ethernet is the same way, its not 20Gb because I can use it in both direction, make sense?2) Switch Fabrics- ok, get creative and feel free to double this, it seems to be common to take a 12-port 10Gb switch and claim it has a 240Gb switching capacity. This actually seems somewhat 'right' since it can move 240Gb in one second. 3) Local Switching- Don't get creative here. Most everyone's linecard does some form of local switching, but with VOQ and fabric arbitration many vendors are moving to have the forwarding decision made locally and then still move the frames across the fabric even if on the same card.4) Packets Per Second- this is an absolute, don't add up each stage. You should roughly expect 14.8Mpps per 10Gb in a wire-rate forwarding engine. 5) Backplanes- we all want to talk about how well our chassis are built and how awesome our signal/noise ratio is on our copper traces, some companies even brag about how much copper their backplane has. I can see stating what you feel the backplane capacity should be able to go to because this will help customers in knowing if that particular system 'has legs.' Be sure to list this as 'future capacity' though and don't confuse people into thinking you are shipping that today if it will take new linecards, new fabrics, and the only thing maintained is a chassis with some connectors.5) Power Draw. Give two numbers. We all need to know the worst-case 55C power draw under full load otherwise the insurance companies and UL get a little particular. But also show 50% load factor at ASHRAE published data center temperature guides. This will help with thermal and power planning./end soapboxdg