Interpretation of continuous ARQ protocol

The continuous ARQ protocol has many characteristics. It is a connection protocol between the receiving and receiving parties. From its English and Chinese translations, We can roughly understand the basic concepts of this agreement. Continuous ARQ protocol: Automatic repeat request (auto repeat request), which uses the receiver to request the sender to re-transmit the erroneous data packets to recover the erroneous packets. It is one of the methods used in communication to handle errors caused by channels; another method is channel error code ｡

Traditional automatic retransmission requests are divided into three types: stop-and-wait ARQ, go-back-n (go-back-n) ARQ, and selective repeat) ARQ ｡

The latter two protocols are the combination of Sliding Window Technology and request re-transmission technology. Since the window size is large enough, the frame can flow continuously on the line, so it is also called the continuous ARQ protocol ｡

The difference between the three lies in the different processing mechanisms for erroneous data packets. In the stop equation ARQ, after the data packet is sent, the sender waits for the receiver's status report. If the status report message is successfully sent, send subsequent data packets. Otherwise, the packets are re-transmitted ｡

Stop equation ARQ. The size of the sending and receiving windows is 1. After each frame is sent, the sender must stop and wait for confirmation from the receiver, the method requires the minimum buffer storage space, but the channel efficiency is low ｡

In ARQ with n frames rolled back, when the sender receives the status report of the receiver indicating that the packet has an error, the sender will re-transmit the n Packets in the past, the receiving window is equal to 1 ｡

The sender can send message frames consecutively. However, if an error occurs on a frame, the sender must resend the frame and the next n frames. This method improves the channel utilization, however, the more frames that have been sent to be confirmed, the more frames that may have to be returned and resend ｡

In the selective retransmission ARQ, when the sender receives the status report from the receiver indicating that the packet has an error, the sender only sends the packet with an error. Select the retransmission protocol, both the sending and receiving windows are greater than 1. The sender only retransmits frames with errors and caches the frames sent after the error frames, this reduces the overhead for re-transmission of the correct frames after an error frame ｡

In the three consecutive ARQ protocols, complexity increases and efficiency increases. In addition to the traditional ARQ, there are also Hybrid ARQ (Hybrid-ARQ). In the Hybrid ARQ, after the datagram is transmitted to the receiver, even if an error occurs, the receiver instructs the sender to re-send part or all of the error message, and merges the message information received again with the message information received last time to restore the message information ｡

In modern wireless communication, ARQ is mainly used in the wireless link layer ｡

For example, the optional retransmission of ARQ and Hybrid ARQ are used in WCDMA and CDMA 2000 wireless communications ｡

Advantage: relatively simple. disadvantage: the communication channel utilization is not high, that is, the channel is far from being filled by data bits ｡