Sliding window protocol
Preconception of what is Sliding window protocol
There is a fixed sender window size. This size determines the number of frames (data link layer's protocol data unit) to be sent simultaneously before receiving an ACK. Window size must be greater than 1. Otherwise, it would reduce to stop and wait protocol.
सुनिश्चितः इति ।
The word निश्चितः indicates that the number of frames is fixed while transmission. However, it is not an absolute number that is fixed. It may vary in different contexts. सु उपसर्गः is added to indicate this "depending upon context". सुनिश्चितः means well defined according to situation.