Pause Frame
When two device started to talking to each other, And the device is full (reaches High watermark threshold, Rx Queue Buffer is full, it will start Tail dropping.
In order to prevent the Rx Queue Buffer to stop tail dropping, Switch 2 needs to send the pause frame.
As a result, Switch 1 will stop sending the packets.
Note: When sending the pause frame, switch 1 will pause entirely for that specified duration in the pause frame