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Community Member

Can someone explain the math behind the 3.2:1 oversubscription on the 2Gb, 32 port cards?

4 REPLIES
Gold

Re: Oversubscription on 32 port blades

I'm also very curious to find out the math behind 3.2:1

Cisco Employee

Re: Oversubscription on 32 port blades

On the 9032, there is 8 port groups of 4 ports each with a total sustained rate of up to 400MB/sec each direction on each port group. Because of the 8B/10B encoding this works out to be 3.2GB/sec. This means 3.2G of fibre channel frames can be handled at any given moment.

Community Member

Re: Oversubscription on 32 port blades

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.

Community Member

Re: Oversubscription on 32 port blades

Can you post the same info for the new 4G blades?

Thanks!

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