Which layer is responsible for flow control?

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http://serverfault.com – I was reading this page at wikipedia and am confused to see that flow control is seen at three layers, Under physical layer I see the link it may define the protocol for flow control. Under network layer I see the link ...This layer uses routers and switches to manage its traffic (control flow control, error check, routing etc.) ... Under transport layer I see the line .. The transport layer controls the reliability of a given link through flow control, segmentation/desegmentation, and e... Now at which layer is the flow control generally implemented ? I can understand t (HowTos)