TCP/IP Note 3. Transport Layer (3) -- TCP timeout retransmission Algorithm

TCP/IP Note 3. Transport Layer (3) -- TCP timeout retransmission algorithm TCP sets a timer for each packet segment sent by TCP. As long as the retransmission time set by the timer is reached but no confirmation has been received, it is necessary to re-transmit this packet segment 1. average round-trip latency RTT round-trip latency: the time when a packet segment is sent and the time when the corresponding validation packet segment is received. The difference between the two time ranges is the average round-trip latency of the packet segment. new_RTTs = a * (old_RTTs) + (1-a) * (New RTT sample) 0 <= a <1a: (1) If a is very close to 1, it indicates that the newly calculated average round-trip latency RTT is not much changed compared with the original value, the new round-trip latency sample has little impact (the RTT value is updated slowly ). (2) If a is selected, it means that the average round-trip latency of the weighted round-trip RTT is greatly affected by the new round-trip latency sample (the RTT value is updated quickly ). (3) The typical a value is 7/82. timeout retransmission RTO (retransmission time-out) RTO = RTTs + 4 * RTTdnew_RTTd = (1-B) * old_RTTd + B * | RTTs-RTT | B :( 1) B <1 (2) Recommended Value: B = 0.25