the cache protocol

GGN (N-step Backward Agreement): - The sender's theory: - The sender uses the pipeline technology to allow multiple packets to be sent without waiting for acknowledgment, but it is limited by the number of unacknowledged packets in the pipeline cannot exceed the maximum number N. When the upper layer calls the send function (rdt_send ()), the sender first checks whether the send window is full (i.e., whether there are N sent but unacknowledged packets). If the window is not full, a packet is generated and sent, and the relevant variables are updated at the same time. If the window is full, the sender can choose to return the data to the upper layer (in reality, it is more likely to buffer the data or use a synchronization mechanism. The upper layer is only allowed to call the send function when the window is full). - The receiver acknowledges the packet with the sequence number n in a cumulative 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 timer is used to detect the loss of data or acknowledgment packets), the sender will resend all the packets that have been sent but not acknowledged. - Principle of the receiver: The receiver receives the packets and uses the cumulative confirmation method to feedback the situation of the correctly received packets to the sender. PR (select the replay protocol): - The sender and receiver had their own windows. The sender sends the packet without knowing the position of the receiver's window, and the receiver receives the packet without knowing the position of the sender's window. The two windows are not synchronized. - The problem was that if the size of the sequence number space and the window size did not meet a certain condition (for example, a scenario where the size of the sequence number space was 4 and the window size was 6 would be problematic), the receiver might not be able to distinguish between different situations. For example, the receiver might mistake the retransmitted packet as a new packet and receive it incorrectly. Different from the GGN protocol, the ACK (n) and TimeOut (n) in the GGN protocol would cause a lot of resources to be retransmitted, resulting in a waste of resources. The SSR protocol was more selective in dealing with situations such as retransmissions. "Choose" was equally exciting. Everyone was welcome to read it!

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!

Both GGN (Fallback N-frame protocol) and SSR (Random Repeat protocol) were sliding window protocol under the reliable data transmission protocol in computer networks. There were the following differences between the two: 1. ** Receiving window size ** - ** GGN protocol **: Receiving window <br>(W = 1 <br>), which means that the receiver can only receive the data packets that arrive correctly in order. If an error occurs in a data packet, it will cause the subsequent packets to be discarded because they cannot be received in order by the receiver, even if these packets are not error-free and out of order. - ** PR protocol **: If the receiving window size is greater than 1, the receiver can receive packets out of order. 2. ** Confirm Method ** - ** GGN protocol **: uses cumulative acknowledgment. The receiver acknowledges the last frame of a group of frames that arrive in order, indicating that all the frames before this frame have been received. For example, if the sender sends four frames 1, 2, 3, and 4, and the receiver acknowledges frame 4, it means that the four frames 1, 2, 3, and 4 have been received. The previous frames 1, 2, and 3 are no longer separately acknowledged. - ** PR protocol **: Each packet has a separate confirmation mechanism. The receiver can confirm each correctly received packet separately, and the sender can selectively re-transmit the incorrectly received packet according to the confirmation information of the receiver. 3. ** Retransmission mechanism ** - ** GGN protocol **: When the sender receives an acknowledgment for a frame, the sending window will be moved forward. If there is a packet loss or a long delay (such as a timer exceeding), the sender needs to resend all the packets that have been sent but have not been acknowledged. For example, if the sender sends six frames, frame 1, 2, 3, 4, 5, and 6, the receiver will confirm frame 3, and the sender will think that frame 1, 2, and 3 have been sent correctly. If there is a problem later, frame 4, 5, and 6 will need to be retransmitted. - ** PR protocol **: The sender only re-sends the packet that the receiver did not receive correctly, instead of re-transmitting all the sent frames after the acknowledgment frame like the GGN protocol. 4. ** Resource utilization and wastage ** - ** GGN protocol **: Due to the method of accumulating acknowledgement and returning N frames of retransmissions, the error of one packet may lead to the retransmissions of multiple packets, even if these packets themselves are error-free. This causes a waste of resources to a certain extent, especially when the window is large and the bit error rate is high. A large number of unnecessary packets may be frequently retransmitted. - ** SP protocol **: Compared to the GGN protocol, it is more resource-saving because it only reforwards the packets that the receiver did not receive correctly, avoiding unnecessary packet retransmissions and thus improving the channel utilization. However, there were some problems with the SSR protocol. For example, the receiver and sender windows were not synchronized, which could cause errors. "Choose" was equally exciting. Everyone was welcome to read it!

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!