Statement so given those abstractions that ft and is nothing more than layers for the control plane just like we have layers for the day to play its wares from a control point we start with a bunch of which disconnected by some wires we then build the network operating system remember this is just software running on servers but the servers talk to all the switches they do so using this forty model Open Flow like they use the information they get from the switches to build with 70-347  global network you that is they know that apology and then you build the control program on top of that apology in that control program could be routing it can be access control can be whatever you want and I call this way years because you have a very clean separation of concerns the control program have no other job then to express the operators goals like if they want to do connectivity if they wanted to isolation that for the control program is concerned with its implemented on top this global network few the control program doesn't care where that you came from doesn't care how you found out it just said you give me the view of figure out what I'm supposed and I'll computers forwarding state that every switch should have network operating system sits there and it says I will talk to the switches and I will compute the global .

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