/*
* A timeout has occurred.
* Return -1 if it's time to give up, else return 0.
*/
int rtt_timeout(struct rtt_info *ptr) {
/* double rto with min max clamps */
ptr->rtt_rto = rtt_minmax(ptr->rtt_rto << 1);
if (++ptr->rtt_nrexmt > RTT_MAXNREXMT)
return(-1); /* time to give up for this packet */
return(0);
}
/* include rtt_timeout */
int
rtt_timeout(struct rtt_info *ptr)
{
ptr->rtt_rto = rtt_minmax(ptr->rtt_rto * 2); /* next RTO */
if (++ptr->rtt_nrexmt > RTT_MAXNREXMT)
return(-1); /* time to give up for this packet */
return(0);
}
void rtt_init(struct rtt_info *ptr) {
ptr->rtt_base = 0;
ptr->rtt_rtt = 0;
ptr->rtt_srtt = 0;
ptr->rtt_rttvar = 2000000; /* initially 2 seconds */
/* first RTO at (srtt>>3 + rttvar) = 2 seconds */
ptr->rtt_rto = rtt_minmax(RTT_RTOCALC(ptr));
ptr->rtt_nrexmt = 0;
}
void rtt_init(struct rtt_info *ptr)
{
struct timeval tv;
gettimeofday(&tv, NULL);
ptr->rtt_base = tv.tv_sec; // # sec since 1/1/1970 at start
ptr->rtt_rtt = 0;
ptr->rtt_srtt = 0;
ptr->rtt_rttvar = 0.75;
ptr->rtt_rto = rtt_minmax(RTT_RTOCALC(ptr));
// first RTO at (srtt * (4 * rttvar)) = 3 seconds
}
void
rtt_init(struct rtt_info *ptr)
{
struct timeval tv;
Gettimeofday(&tv, NULL);
ptr->rtt_base = tv.tv_sec; /* # sec since 1/1/1970 at start */
ptr->rtt_rtt = 0;
ptr->rtt_srtt = 0;
ptr->rtt_rttvar = 6;
ptr->rtt_rto = rtt_minmax(RTT_RTOCALC(ptr));
/* first RTO at ((srtt + (4 * rttvar)) / 8) = 3 seconds */
}
// 更新RTT估算因子并计算新的RTO
void rtt_stop(struct rtt_info *ptr, uint32_t ms)
{
double delta;
ptr->rtt_rtt = ms / 1000.0; // measured RTT in seconds
// update our estimators of RTT and mean deviation of RTT.
// see Jacobson's SIGCOMM '88 paper, Appendix A, for the details.
// we use floating poing here for simplicity.
delta = ptr->rtt_rtt - ptr->rtt_srtt;
if (delta < 0.0) {
delta = -delta; // |delta|
}
ptr->rtt_rttvar += (delta - ptr->rtt_rttvar) / 4; // h = 1/4
ptr->rtt_rto = rtt_minmax(RTT_RTOCALC(ptr));
}
/* 收到新应答之后，更新RTT估算因子并计算新的RTO */
void rtt_stop(struct rtt_info *ptr, uint32_t ms)
{
double delta;
ptr->rtt_rtt = ms / 1000.0; /*measured RTT in seconds */
//Update our estimators of RTT and mean deviation of RTT.
delta = ptr->rtt_rtt - ptr->rtt_srtt;
ptr->rtt_srtt += delta / 8; /* g = 1/8 */
if (delta < 0.0)
delta = -delta; /* |delta| */
ptr->rtt_rttvar += (delta - ptr->rtt_rttvar) / 4; /* h = 1/4 */
ptr->rtt_rto = rtt_minmax(RTT_RTOCALC(ptr));
}
/* include rtt_stop */
void rtt_stop(struct rtt_info* ptr, uint32_t ms)
{
double delta;
ptr->rtt_rtt = ms / 1000.0; /* measured RTT in seconds */
/*
* Update our estimators of RTT and mean deviation of RTT.
* See Jacobson's SIGCOMM '88 paper, Appendix A, for the details.
* We use floating point here for simplicity.
*/
delta = ptr->rtt_rtt - ptr->rtt_srtt;
ptr->rtt_srtt += delta / 8; /* g = 1/8 */
if (delta < 0.0) delta = -delta; /* |delta| */
ptr->rtt_rttvar += (delta - ptr->rtt_rttvar) / 4; /* h = 1/4 */
ptr->rtt_rto = rtt_minmax(RTT_RTOCALC(ptr));
}
/*
* A response was received.
* Stop the timer and update the appropriate values in the structure
* based on this packet's RTT. We calculate the RTT, then update the
* estimators of the RTT and its mean deviation.
* This function should be called right after turning off the
* timer with alarm(0), or right after a timeout occurs.
*/
void rtt_stop(struct rtt_info *ptr) {
/* Retransmission ambiguity problem: solved */
if(ptr->rtt_nrexmt > 0) {
return;
}
/* Update most recent measured RTT in usec */
ptr->rtt_rtt = rtt_ts(ptr);
/*
* Jacobson‐Karels Algorithm
* Update our estimators of RTT and mean deviation of RTT.
* See Jacobson's SIGCOMM '88 paper, Appendix A, for the details.
*/
ptr->rtt_rtt -= ptr->rtt_srtt >> 3;
ptr->rtt_srtt += ptr->rtt_rtt;
if(ptr->rtt_rtt < 0) {
ptr->rtt_rtt = -ptr->rtt_rtt;
}
ptr->rtt_rtt -= ptr->rtt_rttvar >> 2;
ptr->rtt_rttvar += ptr->rtt_rtt;
ptr->rtt_rto = rtt_minmax(RTT_RTOCALC(ptr));
}
