• In the sliding window method, multiple frames are sent by the sender at a time before needing an acknowledge.
• Multiple frames sent by the source are acknowledged by the receiver using a single ACK frame.

## Sliding Window

• Sliding window refers to imaginary boxes that hold the frames on both sender and receiver side.
• It provides the upper limit on the number of frames that can be transmitted before requiring an acknowledgment.
• Frames may be acknowledged by receiver at any point even when a window is not full on receiver side.
• Frames may be transmitted by source even when window is not yet full on sender side.
• The windows have a specific size in which the frames are numbered modulo- n, which means they are numbered from 0 to n-l. For e.g. if n = 8, the frames are numbered 0, 1,2,3,4,5,6, 7, 0, 1,2,3,4,5,6, 7, 0, 1, ....
• The size of window is n-1. For e.g. In this case it is 7. Therefore, a maximum of n-l frames may be sent before an acknowledgment.
• When the receiver sends an ACK, it includes the number of next frame it expects to For example in order to acknowledge the group of frames ending in frame 4, the receiver sends an ACK containing the number 5. When sender sees an ACK with number 5, it comes to know that all the frames up to number 4 have been received.