networking - 每个发送的 TCP 数据包是否有一个单独的重传计时器？

Question

我有一个关于 TCP 重传定时器的问题。我已经阅读了很多关于 TCP 拥塞控制的文章、博客条目和其他内容，当然我也遇到了重传计时器。
也许这是一个愚蠢的问题，但有时会提到对于每个发送的段都会启动一个计时器，而在其他地方据说会为每个发送的段重置计时器。
那么是每个发送的段有一个单独的Retransmission Timer，使得发送的段有多少个定时器，还是只有一个Retransmission Timer？

Answer 1

以下几行来自“TCPIP Illustrated, volume 1”，所以似乎只有一个定时器存在，新的取代了旧的。

Once a sending TCP has established its RTO based upon measurements of the time-varying values of effective RTT, whenever it sends a segment it ensures that a retransmission timer is set appropriately. When setting a retransmission timer, the sequence number of the so-called timed segment is recorded, and if an ACK is received in time, the retransmission timer is canceled. The next time the sender emits a packet with data in it, a new retransmission timer is set, the old one is canceled, and the new sequence number is recorded. The sending TCP therefore continuously sets and cancels one retransmission timer per connection; if no data is ever lost, no retransmission timer ever expires