What is the clock frequency inside 10Gb and 100Gb Ethernet cards?

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http://serverfault.com – As I understand, a 10Gb Ethernet card is capable over putting 10Gb every second on (say) a fibre optics cable. Now naively, for this to happen in hardware, one will need a 10GHz clock running the network card. It's possible to half that frequency by clocking on both edges, but 5GHz is still awefully high for transistors to support. For 100Gb Ethernet, 50GHz seems completely unreasonable. What is the clock frequency of clocks running (say) a 10Gb Ethernet card? Are there tricks to used to cut down this frequency from the "naive" 10GHz frequency? (HowTos)