This is not quite right. When you look at our ASIC's, every four ports on the 32 port card has 2.5Gb/s bandwidth, in each direction. For the purposed of this discussion I will talk about one direction, multiply by two for up and down bandwidth to get total bandwidth. First thing is that when frames enter the switch port we strip off the 8/10B encoding. The math looks like this 4/250MB/sec equals 62.5MB/s then multiply 1.2(to account for 8/10B encoding) x 62.5 to get 75MB/s. 250MB/s divided by 75MB/s gets you to 3.3 oversubscription. There are some additional steps we take to get from 3.3 to 3.2 but they are still confidential at this point.
