One bit sliding window protocol is also called Stop-And-Wait protocols. In this protocol, the sender sends out one frame, waits for acknowledgment before sending next frame, thus the name Stop-And-Wait.
Problem with Stop-And-Wait protocol is that it is very inefficient. At any one moment, only in frame is in transition. The sender will have to wait at least one round trip time before sending next. The waiting can be long for a slow network such as satellite link.
This protocol uses Stop-And-Wait, since the sender transmits a frame and waits for its acknowledgment before sending the next one. One of the two data link layers goes first. The starting machine fetches the first packet from its network layer, builds a frame from it and sends it. When this (or any ) frame arrives, the receiving data link layer checks to see if it is a duplicate. If the frame is the one expected, it is passed to the network layer and the receiver's window is slid up. The acknowledgement field contains the number of the last frame received without error. If this number agrees with the sequence number of the frame the sender is trying to send, the sender knows it is done with the frame stored in buffer and can fetch the next packet from its network layer. If the sequence number disagrees, it must continue trying to send the same frame. Whenever a frame is received, a frame is also sent back.
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