Choose to resend arq and continue arq
The continuous ARQ protocol meant that the sender maintained a sending window of a certain size. All packets within the sending window could be sent out continuously without waiting for the other party's confirmation. Every time the sender received a confirmation, the sending window would slide forward by one packet. The receiver usually uses the method of accumulating acknowledgement. It is not necessary to send acknowledgement to the received packets one by one, but to send acknowledgement to the last packet that arrives in order, indicating that all the packets up to this packet have been received correctly. Its advantage was that it was easy to implement, and even if it was confirmed to be lost, it did not need to be retransmitted. Its disadvantage was that it could not reflect to the sender the information of all the packets that the receiver had received correctly. When the quality of the communication line was not good, it would have a negative impact. For example, there might be a Go-back- N phenomenon, that is, it needed to go back and retransmit the N packets that had been sent. The selective repeat ARQ protocol is an improved ARQ protocol. In this protocol, the sender also maintained a transmission window, but when the receiver found that a packet was lost, the sender only needed to re-transmit the lost packet, and did not need to re-transmit the packet that had been correctly received. This is different from the continuous ARQ protocol where all packets after a packet are retransmitted if the packet is lost. The ARQ protocol could improve the channel utilization and reduce unnecessary retransmissions, but it was relatively complicated to implement, and more control information was needed to determine which packets needed to be retransmitted. " Choose " was equally exciting. Everyone was welcome to read it!
Choose to resend the arq protocol
The selective repeat ARQ protocol is a type of automatic repeat request (ARQ). In this protocol, the sending process continuously sends a number of frames according to a window of a specified size. Even if a frame is lost during the transmission, it will continue to send. The receiving process continues to receive and acknowledge frames after an error, which is different from Go-back- N ARQ. If a certain frame was wrong, the correct frame sent later could not be submitted to the network layer immediately, but was instead stored by the receiver. At the same time, the sender was required to only resend the wrong frame. Once the retransmitted frame was received, it would be submitted to the network layer together with the original stored frame in the correct order. Its basic features include only retransmitting data frames with errors or timer overtimes; the frames sent by the sender need to be distinguished by different numbers; the sender needs to have a large sending buffer to retain the possible retransmitted frames; the receiver also has a large buffer to temporarily store the data frames with the serial number after the error frame in the receiving window. In the selective repeat (PR) protocol (belonging to the category of the selective repeat ARQ protocol), the receiver can receive and confirm non-consecutive data packets, and the sender only needs to repeat the unconfirmed data packets, thus improving the efficiency of data transmission. The main goal of this protocol was to improve the reliability and efficiency of data transmission. Compared with the Fallback N protocol, it reduced the overhead of retransmitting the correct frame after the error frame. In the Fallback N protocol, if a packet was lost in the window, even if all the other packets in the window had been received by the receiver, the sender still needed to retransmit all the packets in the window. In modern wireless communications, ARQ was mainly used in the wireless link layer. For example, in the wireless communications of the wdm and cdma2000, the selective repeat ARQ protocol was used. "Choose" was equally exciting. Everyone was welcome to read it!
ARQ and GGN
The ARQ protocol (Automatic Repeat-reQuest) was an error correction protocol in the data link layer. There were stop-and-wait ARQ and continuous ARQ. The stop-wait ARQ protocol sends a message at a time, and sends the next message after confirmation. The sending window and the receiving window are both 1, so it requires a small buffer but is inefficient. The continuous ARQ protocol, which was known as the backward n-frame GGN and the selective repeat ARQ, was a combination of sliding window and request for repeat. It could continuously send a number of information frames without waiting for the previous frame to be confirmed, which greatly improved the transmission efficiency. However, the sender needed to set up a repeat table to store the frames to be confirmed. After receiving the confirmation frame, the frame would be deleted from the repeat table, which required more storage space. The GGN protocol (Go-Back- N) was also known as the sliding window protocol. In this protocol, the sender is allowed to send multiple packets without waiting for acknowledgment, but the number of unacknowledged packets in the pipeline cannot exceed a certain maximum number N. The sender must respond to three types of events: a call from the upper layer, an acknowledgment, and a time out event. The confirmation of the packet with the sequence number n is done in a cumulative confirmation manner, indicating that the receiver has correctly received all the packets before and including the sequence number n. If there is a time out, the sender will resend all the packets that have been sent but not acknowledged. "Choose" was equally exciting. Everyone was welcome to read it!
ARQ protocol works
The ARQ protocol (Automatic Repeat Request) is one of the error correction protocol in the data link layer of the OSI model. It mainly includes the stop-equation ARQ protocol and the continuous ARQ protocol (including the ARQ protocol with N frames back and the selective repeat ARQ protocol). Their working process is as follows: ** 1. Stop equation ARQ protocol working process ** 1. ** From ** - First, the network layer data was packaged into a data frame, and then the data frame was sent to the data link layer's transmission buffer. Then, the data frame in the transmission buffer was sent out, and a timer was set for the packet at the same time. After that, he entered a waiting state. - There were only two types of frame numbers (serial numbers): 0 and 1. The sender sends a packet with a sequence number of 0 or 1. - If the receiver receives an acknowledgment signal, the next frame will be sent (sequence number alternated), and if the receiver receives a negative acknowledgment signal, the frame will be retransmitted. 2. ** Receiving party ** - Waiting for the data frame sent by the sender to be placed into the receive buffer of the data link layer. - If the data frame is correct, the data frame will be unpacked, the grouped data will be handed over to the network layer, and then an acknowledgment frame will be sent back to the sender, indicating that the data frame has been received correctly; if the data frame is wrong, it will not be processed (waiting for the sender to resend). ** 2. Working process of the continuous ARQ protocol ** **(1) Working process of ARQ protocol with N frames backoff ** 1. ** From ** - The sender could send several frames in a row without waiting for the other party's reply. - If the sender receives a positive response from the receiver after sending a frame, it can continue to send. If it receives a negative response to a previous frame, it will resend all the subsequent frames starting from that frame. - The frames sent by the sender needed to be differentiated by different numbers, and there had to be a large buffer to keep the frames that could be retransmitted. 2. ** Receiving party ** - It could only be received in sequence, which meant that it could only receive one frame. **(2) Operating process of the ARQ protocol ** 1. ** From ** - A certain size of the transmission window is maintained, and the frames within the transmission window can be continuously sent out. The sender would slide the sending window forward by one packet each time it received a confirmation. - When the receiver receives a negative acknowledgment for a frame, only the wrong frame is retransmitted, instead of retransmitting all the subsequent frames like the ARQ protocol that backs up N frames. 2. ** Receiving party ** - It could receive frames that arrived out of order and buffer the correctly received frames. After all the frames arrived in order, they would be submitted to the network layer together. The size of the sending and receiving windows of the sender and receiver has a certain limit. "Choose" was equally exciting. Everyone was welcome to read it!
Automatic repeat request arq
Automatic Repeat Request (ARQ) is one of the error correction protocol in the data link layer and transmission layer of the OSI model. It used confirmation and time-out mechanisms to achieve reliable information transmission on the basis of unreliable services. If the sender does not receive an acknowledgment frame after a period of time, it will usually resend. ARQ includes the stop-and-wait ARQ protocol and the continuous ARQ protocol: - Stop and Wait ARQ protocol: Stop sending after sending a packet and wait for the other party to confirm (reply with an ACK). If no acknowledgment is received after the time limit, the transmission will be considered a failure and the next packet will be sent again until the acknowledgment is received. In the case of no error, the sender sends a packet, the receiver receives and replies with an acknowledgment within a specified time, and the sender sends the next packet. In the case of an error (overtime re-transmission), as long as the acknowledgment is not received within the specified time, the previously sent packet will be re-transmitted. If the receiver receives a duplicate packet, it will discard the packet but send an acknowledgment at the same time. The advantage of this protocol was its simplicity, but the disadvantage was its low channel utilization and long waiting time. - Continuous ARQ protocol: The sender maintains a sending window, and the packets within the sending window can be sent continuously without waiting for the other party's confirmation. The receiver usually uses a cumulative acknowledgment to send an acknowledgment to the last packet that arrives in order, indicating that all the packets to this packet position have been received correctly. In addition, there were also hybrid automatic repeat request (HARQ) and other related concepts that had different applications in the field of communication technology. "Choose" was equally exciting. Everyone was welcome to read it!
arq protocol sending window maximum
In the ARQ protocol, the maximum transmission window is related to the type of the protocol. 1. ** Stop and Wait ARQ protocol **: After sending a frame, the sending station must wait for an acknowledgment signal. After receiving an acknowledgment signal, it will continue to send the next frame. There is no mention of the maximum value of the sending window size. 2. ** Repeat ARQ protocol **: It is a combination of sliding window technology and automatic repeat request technology. The maximum sending window is 2^(n - 1)(considering the possible loss of the ACK, it will be repeated after a time limit). 3. ** Continuous ARQ protocol (includes two types of protocol: - For the backward N-frame protocol, 1 <transmission window <= 2n- 1. - For the selective replay protocol, the transmit window is <= 2^(n - 1), and when the transmit window is the maximum, the receive window = transmit window = 2n - 1. "Choose" was equally exciting. Everyone was welcome to read it!
Continuous arq protocol and sliding window protocol
In the continuous ARQ protocol, the sender maintained a sending window of a certain size, and the packets within the window could be sent continuously without waiting for the other party's acknowledgment. The sender would slide the sending window forward by one packet every time it received an acknowledgment. The receiver usually uses the method of accumulating acknowledgement, that is, after receiving several packets, it sends an acknowledgement to the last packet that arrives in order, indicating that all the packets up to this packet have been received correctly. However, this method has shortcomings. For example, when the middle packet is lost, the sender cannot know the situation of the subsequent packets, and may need to re-transmit more packets. The sliding window protocol involves a sending window and a receiving window. The transmit window is the range of sequence numbers of the frames that have been sent but have not been acknowledged, and the receive window is the range of sequence numbers of the frames that are expected to be received. When the default window size is 1, you can operate according to the specific sending process. The sliding window protocol could improve the channel utilization and was a reliable transmission mechanism for data communication. The continuous ARQ protocol can be seen as a specific application form of the sliding window protocol under certain conditions (such as the cumulative acknowledgment method). They are all protocol mechanisms that exist to achieve effective and reliable data transmission in the network. "Choose" was equally exciting. Everyone was welcome to read it!
Which layer of protocol does arq belong to?
In modern wireless communications, ARQ was mainly used in the wireless link layer. " Choose " was equally exciting. Everyone was welcome to read it!
Rewind n steps and choose to resend
The n-step backward (GGN) and the selective repeat (PR) are two error recovery methods in computer networks. The n-step backtracking protocol (GGN) was an automatic repeat request (ARQ) protocol, also known as the sliding window protocol. In the GGN protocol, the sender can send multiple packets in a row without waiting for each packet to be acknowledged, but the number of unacknowledged packets cannot exceed the default maximum value N (window length). The sender would set a timer for the first packet in the window. If the sender received an acknowledgment from the receiver before the timer expired and there were still sent but unacknowledged packets in the window, the timer would be restarted. If all the sent packets in the window had been acknowledged, the timer would be stopped. If the sender does not receive an acknowledgment from the receiver before the timer expired, the sender will resend all the unacknowledged packets sent in the current window and restart the timer. The GGN protocol uses a cumulative confirmation method for the confirmation of the packet with the sequence number n, indicating that the receiver has correctly received all the packets before the sequence number n, including n. The purpose of choosing the Retransmission protocol (SSR) was to improve the backward n-step protocol. The error of a data packet would cause the subsequent consecutive packets to be discarded because they could not be received in order by the receiver (in fact, they did not have error codes and were out of order), causing the sender to waste communication resources by retransmitting these data packets over time. In the selective replay protocol, the size of the receiving window W was greater than 1, so that the receiver would first receive the data packets that arrived out of order without error codes and whose sequence numbers fell within the receiving window. After all the missing packets were received, they would be handed over to the upper layer. In order to achieve this, the receiver could no longer use cumulative acknowledgment, but had to confirm each correctly received data packet one by one, and the sender only retransmitted the packet with errors. "Choose" was equally exciting. Everyone was welcome to read it!
Is choosing to resend a cumulative confirmation?
Choosing to re-transmit was not a cumulative confirmation. In the selective repeat protocol, the receiver could no longer use cumulative acknowledgment, but had to confirm each correctly received data packet one by one. The purpose of this is to make the sender only re-transmit the packets with errors. Accumulated acknowledgement meant that the receiver could send back a acknowledgement packet that could acknowledge all packets up to a certain serial number, instead of sending acknowledgement packets for every serial number. For example, in the protocol, the sender sends multiple packets, and the receiver sends back a packet with a specific confirmation sequence number after successfully receiving some of the packets. The sender knows that the previous packets have been successfully sent and received, and if necessary, resends the packets starting from the confirmation sequence number. This mechanism was also applicable to other layers such as the link layer. " Choose " was equally exciting. Everyone was welcome to read it!
Three ways of automatic feedback and resend
In the satellite ATM network, the three automatic feedback retransmissions were the selective repeat protocol (SARQ), forward error control (FEC), and multi-station automatic feedback retransmissions. When dealing with the error frames in the sliding window protocol, all the correct frames after the bad frame are stored, and the sender only resends the damaged frames. Its advantage was that it only retransmitted the wrong frame, which could save the satellite link's band width and had high efficiency. Its disadvantage was that it was more complicated to implement and sensitive to memory. In the case of a high error rate, it needed to occupy a large amount of memory to store the subsequent correct frame. Due to the retransmissions, the delay would increase and change, so it was not suitable for constant bit rate (Cbr) services. Forward error control (FEC) refers to the error control method that can automatically correct a certain degree of transmission error according to the principle of coding at the transmitting end. In the satellite ATM network, the FEC mechanism can be applied to the physical layer, AAL layer, and higher layers. the FEC applied to the physical layer cannot correct cell loss, while the FEC applied to the higher layer cannot correct errors. The reference materials did not provide more information about the automatic feedback and replay of multi-station. "Choose" was equally exciting. Everyone was welcome to read it!