Sliding Window

(n.) Also referred to as windowing, a method of flow control for transferring data over networks. TCP sends data across a network in packets and requires the receiving device to send an acknowledgement, or ACK, when it successfully has received the packet, which signals the sending device that another packet can be sent. Window size is the number of data packets that can be sent without waiting for an ACK. With the sliding window method, the receiving device can send a single acknowledgement message for multiple packets of data sent in one window. Within that acknowledgement message is information about the receiving device s buffer size, which tells the sending device to increase or decrease the number of packets in the next transmission (this is where the “sliding” in the name comes in). If the application reading the data processes the packets at a slower rate than the sending device is transmitting them, it will tell the sending device to decrease the number of packets or temporarily cease transmission altogether, in order to free up room in the buffer; if the receiving application can process the packets faster than the sending device is transmitting them, it will tell the sending device to increase the number of packets in the next window as the application s buffer can handle more data.