Sliding window protocol
The term sliding window ( to German as " to verschiebendes window " ) refers to the data flow control in computer networks a window that allows a sender to transfer a certain amount of data before an acknowledgment is expected back.
Network protocols that are based on sliding windows, sliding window protocols or sliding window protocols are called. The term is especially significant for data packets.
Operation
The sliding window method aims at optimum utilization of the capacity of the line and the receiver, ie as possible to send as many data packets ( data frames). In this case, the maximum amount present in the transmission data represents the delay -bandwidth product, which can be sent without waiting for the first acknowledgment.
The sliding window method, the transmitter performs continuously a list of consecutive sequence numbers, corresponding to the number of frames that it may transmit. Once a data packet is successfully delivered to the recipient, this it sends an acknowledgment, also referred to as ACK signal back, which causes the transmitter to transmit another frame. However, if the sender does not receive ACK within the timeout period, it will attempt to transmit the frame again. Under the condition that the delay -bandwidth product is already achieved, but no new frame can be transferred, that is, there is a jam in the pipe. The transmission window shifts with each incoming acknowledgment by the confirmed frame dropping out of the window and a new frame to be transmitted is added to the window. The window always contains only unconfirmed frames. In the event that frames are lost during transmission, the sender must keep all data packets in its memory, so that they can be retransmitted.
Analogous to the transmitter and the receiver window manages a sliding window. However, both windows may not necessarily have the same size, since it can vary by sending and receiving frames over time. The size of the send window is determined by the maximum indicated by the beneficiary as well as the network load. Each confirmation of a successfully transmitted frame contains a value that indicates, for what amount of further data packets, the receiver still has free capacity.
Unlike the stop-and -wait algorithm
In stop- and-wait algorithm that is an ARQ protocol, as well as the sliding window method, the transmitter waits after the transmission of a frame for an acknowledgment before transmitting the next frame. If within the waiting period no acknowledgment, the sender transmits the frame again. In contrast to this algorithm, the only one authorized transmitter a pending frame to the connecting line and is thus inefficient, the sliding-window algorithm may transmit several frames simultaneously. A sliding window algorithm is just a special type of stop-and -wait algorithm. Both work the same way, if the size of the send window is set to 1 frame at the sliding window algorithm.
Tasks
The sliding-window algorithm has in the field of computer networking the following tasks:
The sliding-window protocol is used by the Transmission Control Protocol ( TCP) to transmit data as efficiently as possible. And the Point-to- Point Protocol (PPP), the sliding window method is applied.
Example of use
As an example of the application of the method herein the use of a sliding window will be described in a radar device:
In some radars is generated with this method of analog target bursts a digital target signal. Are written in a memory in the radar plot extractor assembly designated as a number of burst periods all known echo signals. Then, the signals of the pulse periods, starting from the first range cell are compared. Achieved the echo signal in each pulse period ( ie, in the memory: all parallel storage groups considered ) a certain threshold, then the position of the sliding window represents the coordinates of the object to be located.