Is the channel utilization rate of the select repeat protocol high?
Compared with the stop-and-wait protocol and the fallback N-frame protocol, the selective repeat protocol has an improved channel utilization. The stop-and-wait protocol would stop sending a packet every time it was sent and wait for the other party's confirmation. After receiving the confirmation, it would send the next packet. The channel utilization rate of this method was very low, and the channel utilization rate would be even lower if there was a time-out re-transmission. In the backward N frame protocol, an error could lead to subsequent correct retransmissions, which was a huge waste of communication resources. The selective replay protocol prevented the repeated transmission of data frames that had already arrived at the receiver. The basic idea was that if a frame was wrong, the subsequent frames would be stored in the receiver's buffer first, and the sender would be required to re-transmit the wrong frame, which would be sent to the host in the correct order along with the other frames that were originally in the buffer. This further improved the channel utilization, but at the cost of increasing the buffer space. " Choose " was equally exciting. Everyone was welcome to read it!
How to calculate the channel utilization rate of the selected replay protocol?
Let the transmission delay + the round-trip delay + the reception delay be the transmission period of one frame, and the continuous period is the ARQ. The channel utilization rate of (including the selection of the re-transmission protocol) is more than that of the stop-and-wait protocol by (n)(window size). The channel utilization rate of the stop-and-wait protocol is (<<<frac><br>><<br>></>>)(where <<br> is the transmission delay,<<<Ta>> is the reception delay, and <<<br> is the round-trip delay). Therefore, the calculation formula for the channel utilization rate of the chosen replay protocol <<br> is <<frac>{n <times><>></>><). At the same time, the number of bits in the frame sequence number is set to <<k>>, and the transmission window of the <<PR>> protocol is usually <<<leq2 ^{k}-1>>. In the case where both <<T>> and <<T>> are determined, the larger the <<N>>, the greater the channel utilization. "Choose" was equally exciting. Everyone was welcome to read it!
Channel utilization of backward n-frame protocol
The N-frame Backoff (GGN) protocol allows the sender to send multiple data frames in succession to improve channel utilization. In the stop-and-wait protocol, the sender could only send one frame at a time, and the channel utilization rate was low. However, GGN adopted the sliding window method, and the sender maintained a set of sending windows, which could send multiple data frames at a time. The calculation of channel utilization is related to many factors, such as data transmission rate, one-way transmission delay, data frame length, etc. Suppose the data transmission rate is R (bit per second), the one-way transmission delay is T (s), and the data frame length is L (bit). In an ideal situation, the sender can continue to send data frames without considering errors and retransmissions during transmission. At this time, the channel utilization can be approximately expressed as: <U>=<frac{L}>{(2T +<frac{L}{R})R}>. In the GGN protocol, the larger the transmission window, the more data frames allowed to be transmitted, and the higher the channel utilization rate. However, the transmission window could not be infinitely large. When using n bits to code, the maximum transmission window is <<2> n>-<1>. However, if there was an error and the transmission needed to be repeated, the GGN protocol's transmission mechanism would affect the channel utilization. Since GGN uses a cumulative acknowledgment method, the sender will move the sending window forward after receiving the acknowledgment. If the sender does not receive the acknowledgment or receives a negative acknowledgment (NAC), it needs to retreat N frames and resend all the sent frames after the acknowledgment frame. When an error occurs, the frame that has been transmitted correctly will also be retransmitted, thus reducing the channel utilization to a certain extent. "Choose" was equally exciting. Everyone was welcome to read it!
Channel utilization calculation of backward n frame protocol
1. ** sender's angle ** - Let the time to send a frame be <T_f>, the transmission delay be <T_p>, and the size of the sending window be <W>. - In the stop-and-wait protocol (transmit window <<W = 1>>), the channel utilization rate <U>=<frac>{T_f}{T_f +2T_p}>. - For the backward frame protocol (GGN), the sender can send a continuous number of frames. The total time it takes for the sender to send the W frames is W, and the total time from the start of the transmission to the time it receives the first acknowledgment frame (assuming it is received correctly) is W. - Therefore, the channel utilization rate is <U>=<frac>{WTf>}{WTf +2Tp>}. 2. ** Receiving angle ** - The receiver used the cumulative confirmation method. - Assuming that the sender sent a number of frames, the receiver will discard all the frames after the number of frames. - The sender needs to re-transmit all the frames starting from the <k> th frame, which will affect the channel utilization. In the ideal case (error-free transmission), the channel utilization rate is calculated as before. In the case of errors, the channel utilization rate will be reduced due to retransmissions. The specific degree of reduction depends on the frequency and location of errors. 3. ** Overall consideration ** - The channel utilization is also related to the number of digits in the frame number, because the transmit window size, W, has a maximum limit, W'leqslant2 ^n- 1. When W is close to this maximum value, the channel utilization rate can be improved without error, but it also increases the risk of frame number confusion (like the example of the 2-bit number mentioned earlier). Once the error is retransmitted, the channel utilization rate will be greatly affected. "Choose" was equally exciting. Everyone was welcome to read it!
Is the select replay protocol a sliding window protocol?
Yes, the selective replay protocol was based on the sliding window flow control technology. It was a sliding window protocol. " Choose " was equally exciting. Everyone was welcome to read it!
Channel utilization rate, back off n frames, acknowledgement piggybacking
Channel utilization refers to the ratio of the time needed by the sender to send valid data in the entire transmission cycle. In the Go-Back- N ARQ protocol, there were many factors to consider when calculating the channel utilization. The ARQ protocol with N frames back was a continuous automatic repeat request protocol. Under this protocol, the sender could send multiple data frames in a row, and the receiver would acknowledge each received frame. if that receive party detected an error in a certain frame, the receive party would discard the frame and all the subsequent frames, and notify the sender party to re-transmit the error frame and the subsequent frames. When calculating the channel utilization, factors such as the size of the transmission window, frame length, transmission rate, and transmission delay should be considered. Suppose the transmission window size is N, the frame length is L, the transmission rate is R, and the transmission delay is t (the two-way transmission delay is 2t). In an ideal situation, if there were no frame errors and the channel was always available for transmission, the channel utilization rate could be close to 100%. However, in reality, due to factors such as transmission delay and frame error retransmissions, the utilization rate would be reduced. The "confirmation piggybacking" meant that during the data transmission process, the receiver could piggyback the confirmation information of the forward data frame in the data frame transmitted in the reverse direction. This can reduce the overhead of sending a confirmation frame alone, thereby improving the channel utilization to a certain extent. For example, when the receiver has data to send back to the sender, the data frame can contain the confirmation information of the previously received frame. In this way, there is no need to specifically send a confirmation frame, which saves channel resources and improves channel utilization. "Choose" was equally exciting. Everyone was welcome to read it!
Backward n frame protocol and selective repeat protocol
Go-back- N (GGN): - In the stop-and-wait protocol, the sender can only send one frame at a time, and the channel utilization rate is low. However, the backward N-frame protocol uses a sliding window method, and the sender maintains a set of sending windows, and can send multiple data frames at a time. The receiver uses the method of cumulative confirmation, and the sender moves the sending window forward after receiving the confirmation. When there was a problem (such as frame loss or long delay), the sender used the method of retreating N frames to re-transmit. The timer here was used to recover data frames or confirm the loss of frames, similar to the timer in the pause protocol. Choosing the Repeat protocol: - Different from the N-frame backward protocol, when the receiver receives an out-of-order frame, it will not discard all subsequent frames like the N-frame backward protocol. Instead, it will buffer the correctly received out-of-order frame. When the sender found that a frame was lost, it only retransmitted the lost frame, instead of retransmitting the subsequent N frames from the lost frame like the backward N frames protocol. This could avoid unnecessary data retransmissions and improve transmission efficiency, especially in a poor network environment with a high packet loss rate. Both of these two types of protocol were designed to deal with the loss of frames and the disorder of order during data transmission to improve the reliability and efficiency of data transmission. However, the specific ways in which they dealt with the problem were different. "Choose" was equally exciting. Everyone was welcome to read it!
Slipping window to select the replay protocol
The sliding window selective repeat (PR) protocol was a sliding window protocol. In this protocol, the sender continuously sends a number of frames according to a window of a specified size. Even if a frame is lost in the process of sending, it will continue to send. The receiver's receiving window size was greater than 1. When an out-of-order packet was received, if the sequence number was in the receiving window, it would be first stored in the buffer and delivered to the upper layer after all the missing packets were collected. It used a selective acknowledgment method and only retransmitted the packets with errors. The sending window could only move to the right after receiving the confirmation of the leftmost sequence number, and the receiving window could only move to the right after receiving the data packet of the leftmost sequence number. Compared with the N-frame Backward (GGN) protocol, the receiver could only receive frames one by one in sequence, and the out-of-order frames were directly discarded. The cumulative acknowledgment method was used, and the sender would move the sending window forward after receiving the acknowledgment. If there was a need to re-transmit, the sender would use the N-frame Backward method to re-transmit all the sent frames after the acknowledgment frame. The selective replay protocol solved the problem of network resource waste caused by the loss of out-of-order frames in the GGN protocol. "Choose" was equally exciting. Everyone was welcome to read it!
What are the automatic repeat request protocol?
The automatic repeat request (ARQ) protocol mainly included the stop-and-wait ARQ protocol and the continuous ARQ protocol. The continuous ARQ protocol also included the N-frame backward ARQ protocol and the selective repeat ARQ protocol. The work flow of the stop-and-wait ARQ protocol was as follows: the transmitting station must wait for an acknowledgment signal after sending out a frame, and then continue to send the next frame after receiving an acknowledgment signal, and then resend the frame after receiving a negative acknowledgment signal, and must resend the frame even if no acknowledgment signal is received within a certain time interval. The continuous ARQ protocol meant that the sender maintained a sending window of a certain size, and all the 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. In the ARQ protocol that sent back N frames, after the sender sent a frame, it did not have to stop and wait for the other party's response. It could send several frames in a row. If it received a positive response from the receiver during the sending process, it could continue to send. If it received a negative response to a previous frame, all subsequent frames starting from that frame would be retransmitted. The selective repeat ARQ protocol can be used as a protocol for the transmission and acknowledgment of a message unit. When used as a protocol to transmit a message unit, the sending process continuously sends a number of frames according to a window of a specified size. Even if the frame is lost during the process, it will continue to send. The receiving process continued to receive and acknowledge frames even after the error. "Choose" was equally exciting. Everyone was welcome to read it!
What is the automatic repeat request protocol?
Automatic Repeat-reQuest (ARQ) was 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 the packet, the receiver receives and replies with an acknowledgment within a specified time, and then the sender sends it again. In the case of an error (overtime re-transmission), as long as the acknowledgment is not received after the specified time, the previously sent packet will be re-transmitted. In addition, if the receiver receives a duplicate packet, it will be discarded, but an acknowledgment will be sent. 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 three other types of ARQ, which were wait-type ARQ, N-step backward ARQ, and selective repeat ARQ. Among them, ARQ could be used as a protocol for message unit transmission and acknowledgment. The sending process would continuously send a number of frames according to a specified window size, and even if there was a frame loss during the sending process, it would continue to send. The receiving process would continue to receive and acknowledge frames after an error occurred. Most practical ARQ systems use linear block codes. Choosing the appropriate linear codes can make the undetectable error probability reach the required error index. The main advantage of ARQ was its simple error detection method, which could adjust the transmission rate according to the channel quality. Its main constraints were that it required a reliable feedback channel, would cause a long and unfixed transmission delay, and required the transmission system to control the source. It was mainly used in data transmission that did not have strict requirements for delay but had high requirements for error performance. "Choose" was equally exciting. Everyone was welcome to read it!
Which layer does the select replay protocol work on?
The selective repeat protocol was a data link layer protocol that worked in the data link layer. " Choose " was equally exciting. Everyone was welcome to read it!