A timer needs to be set after each frame is sent before waiting an ACK for that frame. The length of time it takes for a timer take to be expired depends on only when the first outstanding frames has expires first.
Some do take 5 min., 10 minutes, or even 48 hours while others depends on what the sender has set.
A sender is one that is not entitled to hold a timer for each frame. It has to hold a single timer.
When a the timer expires, the sender can then resends all the frames whose ACK has not been seen or received yet. The sender often starts the timer at the time it is sending the first frame , and because of that, it is only when the timer for the first set frames expires before the sender can resend any other outstanding frames.
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