bssgp: Use measured leak rate for flow control

The leak rate sent to the SGSN does not reflect the current CS level,
lost frames, and control message overhead. So the SGSN cannot do
proper queue control under non-optimal conditions.

This commit computes the leak rate for the last flow control interval
by computing the maximum theoretical leak rate and basically
substracting control blocks, nacked blocks, and reduced block sizes
due to CS downgrade. By using this approach, the value will by more
stable on low load, where the value will tend to be near the value
derived from the configuration. On full load the transmitted value is
completely derived from the measurements.

Note that the MS default values are no adapted to the adapted BVC
leak rate, since a single MS which has a lower link quality would
otherwise be reducing the rate of another MS with good radio
conditions, which would not make much sense if they did not share any
PDCH.

Sponsored-by: On-Waves ehf

1 files changed, 31 insertions, 5 deletions

diff --git a/src/tbf_dl.cpp b/src/tbf_dl.cpp
index aabe8e3e..64fbef4e 100644
--- a/src/tbf_dl.cpp
+++ b/src/tbf_dl.cpp
@@ -712,7 +712,8 @@ static uint16_t bitnum_to_bsn(int bitnum, uint16_t ssn, uint16_t mod_sns)
 	return (ssn - 1 - bitnum) & mod_sns;
 }
 
-int gprs_rlcmac_dl_tbf::analyse_errors(char *show_rbb, uint8_t ssn)
+int gprs_rlcmac_dl_tbf::analyse_errors(char *show_rbb, uint8_t ssn,
+	ana_result *res)
 {
 	gprs_rlc_data *rlc_data;
 	uint16_t lost = 0, received = 0, skipped = 0;
@@ -720,9 +721,13 @@ int gprs_rlcmac_dl_tbf::analyse_errors(char *show_rbb, uint8_t ssn)
 	memset(info, '.', sizeof(info));
 	info[64] = 0;
 	uint16_t bsn = 0;
+	unsigned received_bytes = 0, lost_bytes = 0;
+	unsigned received_packets = 0, lost_packets = 0;
 
 	/* SSN - 1 is in range V(A)..V(S)-1 */
 	for (int bitpos = 0; bitpos < m_window.ws(); bitpos++) {
+		bool is_received = show_rbb[m_window.ws() - 1 - bitpos] == 'R';
+
 		bsn = bitnum_to_bsn(bitpos, ssn, m_window.mod_sns());
 
 		if (bsn == ((m_window.v_a() - 1) & m_window.mod_sns())) {
@@ -736,6 +741,17 @@ int gprs_rlcmac_dl_tbf::analyse_errors(char *show_rbb, uint8_t ssn)
 			continue;
 		}
 
+		/* Get general statistics */
+		if (is_received && !m_window.m_v_b.is_acked(bsn)) {
+			received_packets += 1;
+			received_bytes += rlc_data->len;
+		} else if (!is_received && !m_window.m_v_b.is_nacked(bsn)) {
+			lost_packets += 1;
+			lost_bytes += rlc_data->len;
+		}
+
+		/* Get statistics for current CS */
+
 		if (rlc_data->cs != current_cs()) {
 			/* This block has already been encoded with a different
 			 * CS, so it doesn't help us to decide, whether the
@@ -745,7 +761,7 @@ int gprs_rlcmac_dl_tbf::analyse_errors(char *show_rbb, uint8_t ssn)
 			continue;
 		}
 
-		if (show_rbb[m_window.ws() - 1 - bitpos] == 'R') {
+		if (is_received) {
 			if (!m_window.m_v_b.is_acked(bsn)) {
 				received += 1;
 				info[bitpos] = 'R';
@@ -763,6 +779,11 @@ int gprs_rlcmac_dl_tbf::analyse_errors(char *show_rbb, uint8_t ssn)
 		name(), m_window.v_a(), m_window.v_s(), lost, received,
 		skipped, bsn, info);
 
+	res->received_packets = received_packets;
+	res->lost_packets = lost_packets;
+	res->received_bytes = received_bytes;
+	res->lost_bytes = lost_bytes;
+
 	if (lost + received <= 1)
 		return -1;
 
@@ -778,6 +799,7 @@ int gprs_rlcmac_dl_tbf::update_window(const uint8_t ssn, const uint8_t *rbb)
 	char show_v_b[RLC_MAX_SNS + 1];
 	const uint16_t mod_sns = m_window.mod_sns();
 	int error_rate;
+	struct ana_result ana_res;
 
 	Decoding::extract_rbb(rbb, show_rbb);
 	/* show received array in debug (bit 64..1) */
@@ -800,10 +822,10 @@ int gprs_rlcmac_dl_tbf::update_window(const uint8_t ssn, const uint8_t *rbb)
 		return 1; /* indicate to free TBF */
 	}
 
-	if (bts_data()->cs_adj_enabled && ms()) {
-		error_rate = analyse_errors(show_rbb, ssn);
+	error_rate = analyse_errors(show_rbb, ssn, &ana_res);
+
+	if (bts_data()->cs_adj_enabled && ms())
 		ms()->update_error_rate(this, error_rate);
-	}
 
 	m_window.update(bts, show_rbb, ssn,
 			&lost, &received);
@@ -811,6 +833,10 @@ int gprs_rlcmac_dl_tbf::update_window(const uint8_t ssn, const uint8_t *rbb)
 	/* report lost and received packets */
 	gprs_rlcmac_received_lost(this, received, lost);
 
+	/* Used to measure the leak rate */
+	gprs_bssgp_update_bytes_received(ana_res.received_bytes,
+		ana_res.received_packets + ana_res.lost_packets);
+
 	/* raise V(A), if possible */
 	m_window.raise(m_window.move_window());