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!
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!
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!
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!
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!
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!
Choose the method of retransmitting the protocol
In the field of network communications, the following are some common ways to choose a replay protocol: ** 1. Based on the transmission control protocol, select a repeat transmission ** 1. ** About confirmation mechanism ** - In the case of a protocol, the receiver would send an acknowledgment (ACK) after receiving the data packet. The sender waits for an acknowledgment after sending the data packet. If it is not received within the specified time, it will be considered as a lost data packet and will trigger a replay. For SACK, it was a type of extension to the protocol. The receiver uses SACK to inform the sender which packets have been successfully received and which need to be retransmitted. In this way, the sender could know more accurately which data packets needed to be retransmitted and avoid unnecessary full retransmissions. 2. ** Relating to the conditions for triggering the replay ** - ** Retransmission over time **: After the sender sends the data packet, start the retransmission timer and wait for the receiver's acknowledgment. If the timer expired and the message was still not received, it would be considered that the data packet was lost and a time-out re-transmission was triggered. However, for the selective replay protocol, it could more accurately determine the parts that needed to be retransmitted in this case. For example, in a complex network situation where some packets were delayed but not lost, SACK could distinguish between received and unreceived packets, unlike normal retransmissions where all packets could be retransmitted. - ** Fast Retransmission **: When the receiver receives three Duplicate IPs with the same serial number, the sender will think that the corresponding data packet is lost and immediately re-transmit it. The selective repeat protocol can be combined with the fast repeat. After the fast repeat is triggered, the data packet can be retransmitted more accurately according to the SACK information, thus improving the efficiency of the repeat. - ** Congession-triggered Retransmission **: When the sender discovers network congestion, a retransmission may be triggered. In this case, the selection of the re-transmission protocol could determine which packets needed to be re-transmitted according to the information such as the sender's window size adjusted by the congestion control algorithm and SACK, so that network resources could be more effectively used for re-transmission in a congested situation. 3. ** About the sliding window mechanism ** - The sliding window mechanism was used by the protocol to achieve flow control and congestion control. The sender's window size determines the number of packets that can be sent. When the receiver returned an acknowledgment, the sender's window slid. The sliding window could be operated more flexibly when the replay protocol was selected. For example, according to the Sack information, the part of the window that has been confirmed to be received can be marked more accurately. The data packets that have not been confirmed but have been received by the Sack do not need to be retransmitted. The window can slide and adjust according to this accurate information, thereby improving the efficiency of data transmission. ** Two, selective re-transmission in a wireless communication system (like the situation in NR1)** 1. ** Regarding hybrid automatic repeat request ** - In a wireless communication system, although forward error correction (FEC) is used, such as ldmp code error correction in NR, an error data unit may still be received. HARQ relies on a combination of error-correcting codes and retransmissions of the error data units. In this case, the selection of the re-transmission may be based on the characteristics and requirements of the three protocol layers that provide the re-transmission function in the MR, namely, the MC, the SCI, and the PDCP. For example, the MC layer may pay more attention to the data packet re-transmission strategy related to the medium access, the DLC layer may focus on the re-transmission logic related to the radio link control, and the PDCP layer may determine the re-transmission content from the perspective of the packet data convergence protocol. Through this multi-layer selective replay structure, a balance could be made between speed and reliability. The replay operation could be determined based on the feedback of the status report. "Choose" was equally exciting. Everyone was welcome to read it!
Choose which layer the replay protocol is on
The selective replay protocol was a transport layer protocol. It was a specific example of automatic repeat request (ARQ), which could be used for message unit transmission and confirmation. It was designed to deal with problems such as packet loss, wrong packet, and disorder during network transmission to ensure reliable data transmission. In this protocol, the sending process continuously sends a number of frames according to a window of a specified size, and the receiving process continues to receive and confirm frames after an error occurs. Different from the Fallback N-frame protocol (GGN), it sets up a single acknowledgment, increases the receiving window, and designs a receive buffer to buffer the frames that arrive out of order. This allows only the wrong frames to be retransmitted, thereby improving transmission performance. "Choose" was equally exciting. Everyone was welcome to read it!
Choose the size of the window for the replay protocol.
For the selective replay protocol, the window size is <= 2^(m - 1). When n bits are used to number the frames, in order to prevent the old and new receive windows from overlapping after the receiver moves the window forward, the maximum size of the transmit window does not exceed the range of the sequence number, that is, WT <2n-1. When the transmit window takes the maximum value, it is found to be the same as the transmit window and 2n-1 (in most cases, the transmit window is equal to the receive window and 2n-1, because this is the most efficient). If the value of the transmit window is greater than 2n-1, it may cause the new and old receive windows to overlap. "Choose" was equally exciting. Everyone was welcome to read it!
Choose which layer to set the replay protocol on
The selection of the replay protocol was set at the transport layer. Transmission layer protocol such as the Transmission Control protocol (TCM) used a packet replay strategy to deal with problems in network transmission to ensure reliable data transmission. Choosing a replay protocol was a way to achieve reliable transmission. It used a specific mechanism to ensure that only the wrong frames were retransmitted during the data transmission process to improve transmission efficiency. These operations were within the scope of the transmission layer. "Choose" was equally exciting. Everyone was welcome to read it!