res_rtp_asterisk: Fix standard deviation calculation
For some input to the standard deviation algorithm extremely large, and wrong numbers were being calculated. This patch uses a new formula for correctly calculating both the running mean and standard deviation for the given inputs. ASTERISK-29364 #close Change-Id: Ibc6e18be41c28bed3fde06d612607acc3fbd621f
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@ -384,7 +384,7 @@ struct ast_rtp {
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unsigned int txcount; /*!< How many packets have we sent? */
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unsigned int txoctetcount; /*!< How many octets have we sent? (txcount*160)*/
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unsigned int cycles; /*!< Shifted count of sequence number cycles */
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double rxjitter; /*!< Interarrival jitter at the moment in seconds */
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double rxjitter; /*!< Interarrival jitter at the moment in seconds to be reported */
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double rxtransit; /*!< Relative transit time for previous packet */
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struct ast_format *lasttxformat;
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struct ast_format *lastrxformat;
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@ -511,34 +511,36 @@ struct ast_rtcp {
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unsigned int reported_jitter; /*!< The contents of their last jitter entry in the RR */
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unsigned int reported_lost; /*!< Reported lost packets in their RR */
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double reported_maxjitter;
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double reported_minjitter;
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double reported_normdev_jitter;
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double reported_stdev_jitter;
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unsigned int reported_jitter_count;
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double reported_maxjitter; /*!< Maximum reported interarrival jitter */
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double reported_minjitter; /*!< Minimum reported interarrival jitter */
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double reported_normdev_jitter; /*!< Mean of reported interarrival jitter */
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double reported_stdev_jitter; /*!< Standard deviation of reported interarrival jitter */
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unsigned int reported_jitter_count; /*!< Reported interarrival jitter count */
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double reported_maxlost;
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double reported_minlost;
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double reported_normdev_lost;
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double reported_stdev_lost;
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double reported_maxlost; /*!< Maximum reported packets lost */
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double reported_minlost; /*!< Minimum reported packets lost */
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double reported_normdev_lost; /*!< Mean of reported packets lost */
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double reported_stdev_lost; /*!< Standard deviation of reported packets lost */
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unsigned int reported_lost_count; /*!< Reported packets lost count */
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double rxlost;
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double maxrxlost;
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double minrxlost;
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double normdev_rxlost;
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double stdev_rxlost;
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unsigned int rxlost_count;
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double rxlost; /*!< Calculated number of lost packets since last report */
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double maxrxlost; /*!< Maximum calculated lost number of packets between reports */
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double minrxlost; /*!< Minimum calculated lost number of packets between reports */
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double normdev_rxlost; /*!< Mean of calculated lost packets between reports */
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double stdev_rxlost; /*!< Standard deviation of calculated lost packets between reports */
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unsigned int rxlost_count; /*!< Calculated lost packets sample count */
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double maxrxjitter;
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double minrxjitter;
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double normdev_rxjitter;
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double stdev_rxjitter;
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unsigned int rxjitter_count;
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double maxrtt;
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double minrtt;
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double normdevrtt;
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double stdevrtt;
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unsigned int rtt_count;
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double maxrxjitter; /*!< Maximum of calculated interarrival jitter */
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double minrxjitter; /*!< Minimum of calculated interarrival jitter */
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double normdev_rxjitter; /*!< Mean of calculated interarrival jitter */
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double stdev_rxjitter; /*!< Standard deviation of calculated interarrival jitter */
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unsigned int rxjitter_count; /*!< Calculated interarrival jitter count */
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double maxrtt; /*!< Maximum of calculated round trip time */
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double minrtt; /*!< Minimum of calculated round trip time */
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double normdevrtt; /*!< Mean of calculated round trip time */
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double stdevrtt; /*!< Standard deviation of calculated round trip time */
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unsigned int rtt_count; /*!< Calculated round trip time count */
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/* VP8: sequence number for the RTCP FIR FCI */
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int firseq;
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@ -3317,49 +3319,32 @@ static unsigned int ast_rtcp_calc_interval(struct ast_rtp *rtp)
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return interval;
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}
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/*! \brief Calculate normal deviation */
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static double normdev_compute(double normdev, double sample, unsigned int sample_count)
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static void calc_mean_and_standard_deviation(double new_sample, double *mean, double *std_dev, unsigned int *count)
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{
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normdev = normdev * sample_count + sample;
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sample_count++;
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double delta1;
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double delta2;
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/*
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It's possible the sample_count hits the maximum value and back to 0.
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Set to 1 to prevent the divide by zero crash if the sample_count is 0.
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*/
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if (sample_count == 0) {
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sample_count = 1;
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/* First convert the standard deviation back into a sum of squares. */
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double last_sum_of_squares = (*std_dev) * (*std_dev) * (*count ?: 1);
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if (++(*count) == 0) {
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/* Avoid potential divide by zero on an overflow */
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*count = 1;
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}
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return normdev / sample_count;
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}
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static double stddev_compute(double stddev, double sample, double normdev, double normdev_curent, unsigned int sample_count)
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{
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/*
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for the formula check http://www.cs.umd.edu/~austinjp/constSD.pdf
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return sqrt( (sample_count*pow(stddev,2) + sample_count*pow((sample-normdev)/(sample_count+1),2) + pow(sample-normdev_curent,2)) / (sample_count+1));
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we can compute the sigma^2 and that way we would have to do the sqrt only 1 time at the end and would save another pow 2 compute
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optimized formula
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*/
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#define SQUARE(x) ((x) * (x))
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stddev = sample_count * stddev;
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sample_count++;
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/*
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It's possible the sample_count hits the maximum value and back to 0.
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Set to 1 to prevent the divide by zero crash if the sample_count is 0.
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* Below is an implementation of Welford's online algorithm [1] for calculating
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* mean and variance in a single pass.
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*
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* [1] https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance
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*/
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if (sample_count == 0) {
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sample_count = 1;
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}
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return stddev +
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( sample_count * SQUARE( (sample - normdev) / sample_count ) ) +
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( SQUARE(sample - normdev_curent) / sample_count );
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delta1 = new_sample - *mean;
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*mean += (delta1 / *count);
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delta2 = new_sample - *mean;
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#undef SQUARE
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/* Now calculate the new variance, and subsequent standard deviation */
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*std_dev = sqrt((last_sum_of_squares + (delta1 * delta2)) / *count);
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}
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static int create_new_socket(const char *type, int af)
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@ -4434,7 +4419,6 @@ static void calculate_lost_packet_statistics(struct ast_rtp *rtp,
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unsigned int expected_packets;
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unsigned int expected_interval;
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unsigned int received_interval;
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double rxlost_current;
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int lost_interval;
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/* Compute statistics */
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@ -4464,6 +4448,13 @@ static void calculate_lost_packet_statistics(struct ast_rtp *rtp,
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/* Update RTCP statistics */
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rtp->rtcp->received_prior = rtp->rxcount;
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rtp->rtcp->expected_prior = expected_packets;
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/*
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* While rxlost represents the number of packets lost since the last report was sent, for
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* the calculations below it should be thought of as a single sample. Thus min/max are the
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* lowest/highest sample value seen, and the mean is the average number of packets lost
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* between each report. As such rxlost_count only needs to be incremented per report.
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*/
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if (lost_interval <= 0) {
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rtp->rtcp->rxlost = 0;
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} else {
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@ -4478,16 +4469,9 @@ static void calculate_lost_packet_statistics(struct ast_rtp *rtp,
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if (lost_interval > rtp->rtcp->maxrxlost) {
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rtp->rtcp->maxrxlost = rtp->rtcp->rxlost;
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}
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rxlost_current = normdev_compute(rtp->rtcp->normdev_rxlost,
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rtp->rtcp->rxlost,
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rtp->rtcp->rxlost_count);
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rtp->rtcp->stdev_rxlost = stddev_compute(rtp->rtcp->stdev_rxlost,
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rtp->rtcp->rxlost,
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rtp->rtcp->normdev_rxlost,
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rxlost_current,
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rtp->rtcp->rxlost_count);
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rtp->rtcp->normdev_rxlost = rxlost_current;
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rtp->rtcp->rxlost_count++;
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calc_mean_and_standard_deviation(rtp->rtcp->rxlost, &rtp->rtcp->normdev_rxlost,
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&rtp->rtcp->stdev_rxlost, &rtp->rtcp->rxlost_count);
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}
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static int ast_rtcp_generate_report(struct ast_rtp_instance *instance, unsigned char *rtcpheader,
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@ -5423,7 +5407,6 @@ static void calc_rxstamp(struct timeval *tv, struct ast_rtp *rtp, unsigned int t
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double prog;
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int rate = ast_rtp_get_rate(rtp->f.subclass.format);
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double normdev_rxjitter_current;
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if ((!rtp->rxcore.tv_sec && !rtp->rxcore.tv_usec) || mark) {
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gettimeofday(&rtp->rxcore, NULL);
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rtp->drxcore = (double) rtp->rxcore.tv_sec + (double) rtp->rxcore.tv_usec / 1000000;
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@ -5458,11 +5441,8 @@ static void calc_rxstamp(struct timeval *tv, struct ast_rtp *rtp, unsigned int t
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if (rtp->rtcp && rtp->rxjitter < rtp->rtcp->minrxjitter)
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rtp->rtcp->minrxjitter = rtp->rxjitter;
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normdev_rxjitter_current = normdev_compute(rtp->rtcp->normdev_rxjitter,rtp->rxjitter,rtp->rtcp->rxjitter_count);
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rtp->rtcp->stdev_rxjitter = stddev_compute(rtp->rtcp->stdev_rxjitter,rtp->rxjitter,rtp->rtcp->normdev_rxjitter,normdev_rxjitter_current,rtp->rtcp->rxjitter_count);
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rtp->rtcp->normdev_rxjitter = normdev_rxjitter_current;
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rtp->rtcp->rxjitter_count++;
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calc_mean_and_standard_deviation(rtp->rxjitter, &rtp->rtcp->normdev_rxjitter,
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&rtp->rtcp->stdev_rxjitter, &rtp->rtcp->rxjitter_count);
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}
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}
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@ -5778,7 +5758,6 @@ static int update_rtt_stats(struct ast_rtp *rtp, unsigned int lsr, unsigned int
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unsigned int rtt_lsw;
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unsigned int lsr_a;
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unsigned int rtt;
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double normdevrtt_current;
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gettimeofday(&now, NULL);
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timeval2ntp(now, &msw, &lsw);
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@ -5815,16 +5794,8 @@ static int update_rtt_stats(struct ast_rtp *rtp, unsigned int lsr, unsigned int
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rtp->rtcp->maxrtt = rtp->rtcp->rtt;
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}
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normdevrtt_current = normdev_compute(rtp->rtcp->normdevrtt,
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rtp->rtcp->rtt,
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rtp->rtcp->rtt_count);
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rtp->rtcp->stdevrtt = stddev_compute(rtp->rtcp->stdevrtt,
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rtp->rtcp->rtt,
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rtp->rtcp->normdevrtt,
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normdevrtt_current,
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rtp->rtcp->rtt_count);
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rtp->rtcp->normdevrtt = normdevrtt_current;
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rtp->rtcp->rtt_count++;
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calc_mean_and_standard_deviation(rtp->rtcp->rtt, &rtp->rtcp->normdevrtt,
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&rtp->rtcp->stdevrtt, &rtp->rtcp->rtt_count);
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return 0;
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}
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@ -5836,7 +5807,6 @@ static int update_rtt_stats(struct ast_rtp *rtp, unsigned int lsr, unsigned int
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static void update_jitter_stats(struct ast_rtp *rtp, unsigned int ia_jitter)
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{
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double reported_jitter;
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double reported_normdev_jitter_current;
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rtp->rtcp->reported_jitter = ia_jitter;
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reported_jitter = (double) rtp->rtcp->reported_jitter;
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@ -5849,9 +5819,9 @@ static void update_jitter_stats(struct ast_rtp *rtp, unsigned int ia_jitter)
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if (reported_jitter > rtp->rtcp->reported_maxjitter) {
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rtp->rtcp->reported_maxjitter = reported_jitter;
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}
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reported_normdev_jitter_current = normdev_compute(rtp->rtcp->reported_normdev_jitter, reported_jitter, rtp->rtcp->reported_jitter_count);
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rtp->rtcp->reported_stdev_jitter = stddev_compute(rtp->rtcp->reported_stdev_jitter, reported_jitter, rtp->rtcp->reported_normdev_jitter, reported_normdev_jitter_current, rtp->rtcp->reported_jitter_count);
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rtp->rtcp->reported_normdev_jitter = reported_normdev_jitter_current;
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calc_mean_and_standard_deviation(reported_jitter, &rtp->rtcp->reported_normdev_jitter,
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&rtp->rtcp->reported_stdev_jitter, &rtp->rtcp->reported_jitter_count);
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}
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/*!
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@ -5861,11 +5831,10 @@ static void update_jitter_stats(struct ast_rtp *rtp, unsigned int ia_jitter)
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static void update_lost_stats(struct ast_rtp *rtp, unsigned int lost_packets)
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{
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double reported_lost;
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double reported_normdev_lost_current;
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rtp->rtcp->reported_lost = lost_packets;
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reported_lost = (double)rtp->rtcp->reported_lost;
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if (rtp->rtcp->reported_jitter_count == 0) {
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if (rtp->rtcp->reported_lost_count == 0) {
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rtp->rtcp->reported_minlost = reported_lost;
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}
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if (reported_lost < rtp->rtcp->reported_minlost) {
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@ -5874,9 +5843,9 @@ static void update_lost_stats(struct ast_rtp *rtp, unsigned int lost_packets)
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if (reported_lost > rtp->rtcp->reported_maxlost) {
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rtp->rtcp->reported_maxlost = reported_lost;
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}
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reported_normdev_lost_current = normdev_compute(rtp->rtcp->reported_normdev_lost, reported_lost, rtp->rtcp->reported_jitter_count);
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rtp->rtcp->reported_stdev_lost = stddev_compute(rtp->rtcp->reported_stdev_lost, reported_lost, rtp->rtcp->reported_normdev_lost, reported_normdev_lost_current, rtp->rtcp->reported_jitter_count);
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rtp->rtcp->reported_normdev_lost = reported_normdev_lost_current;
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calc_mean_and_standard_deviation(reported_lost, &rtp->rtcp->reported_normdev_lost,
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&rtp->rtcp->reported_stdev_lost, &rtp->rtcp->reported_lost_count);
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}
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/*! \pre instance is locked */
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@ -6449,7 +6418,6 @@ static struct ast_frame *ast_rtcp_interpret(struct ast_rtp_instance *instance, s
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}
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update_jitter_stats(rtp, report_block->ia_jitter);
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update_lost_stats(rtp, report_block->lost_count.packets);
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rtp->rtcp->reported_jitter_count++;
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if (rtcp_debug_test_addr(addr)) {
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ast_verbose(" Fraction lost: %d\n", report_block->lost_count.fraction);
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