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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 that it may vary under various circumstances, I read that too, but that is the most general case ? What would be a plain answer to the question Which layer takes care of flow control ?

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2 Answers 2

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This is how I learnt it in the ISO-OSI model:

  • Physical layer is not responsible for flow control in general.
  • Data link layer may provide flow control "on the wire".
  • Network layer provides flow control between routers by ICMP. The end terminals usually do not use the network layer barely. IP does not provide flow control.
  • Transport layer, more specifically TCP provides flow control by a backtracking algorithm while UDP does not. TCP has various flow and congestion avoiding protocols, such as TCP Vegas.

As I get it: when routers have flow control problems, it is handled in the network layer, when end points have this problem, it's handled in the transport layer.

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Flow control is generally implemented on two layers Datalink Layer (Layer 2) and Transport Layer (Layer 4).

Webopedia Link

Wikipedia Link

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