diff --git a/daemon/media_socket.c b/daemon/media_socket.c
index e54c3cf73..42242a1e9 100644
--- a/daemon/media_socket.c
+++ b/daemon/media_socket.c
@@ -1232,6 +1232,8 @@ loop_ok:
 	if (media->protocol && media->protocol->rtp && !rtcp && !rtp_payload(&rtp_h, NULL, s)) {
 		i = (rtp_h->m_pt & 0x7f);
 
+		// XXX two hash table lookups for each packet, not ideal
+		// XXX limit size of hash tables
 		rtp_s = g_hash_table_lookup(stream->rtp_stats, &i);
 		if (!rtp_s) {
 			ilog(LOG_WARNING | LOG_FLAG_LIMIT,
@@ -1243,6 +1245,9 @@ loop_ok:
 		else {
 			atomic64_inc(&rtp_s->packets);
 			atomic64_add(&rtp_s->bytes, s->len);
+
+			struct ssrc_entry *se = get_ssrc(ntohl(rtp_h->ssrc), call->ssrc_hash);
+			se->payload_type = i;
 		}
 	}
 
diff --git a/daemon/rtcp.c b/daemon/rtcp.c
index 243595163..da0c377d9 100644
--- a/daemon/rtcp.c
+++ b/daemon/rtcp.c
@@ -227,6 +227,7 @@ struct rtcp_chain_element {
 struct rtcp_process_ctx {
 	// input
 	struct call *call;
+	struct call_media *media;
 	const struct timeval *received;
 
 	// handler vars
@@ -616,6 +617,7 @@ static int __rtcp_parse(GQueue *q, const str *_s, struct stream_fd *sfd, const e
 	rtcp_handler_func func;
 	str s = *_s;
 	struct call *c = sfd->call;
+	struct call_media *m = sfd->stream->media;
 	struct rtcp_process_ctx log_ctx_s,
 				*log_ctx;
 	unsigned int len;
@@ -624,6 +626,7 @@ static int __rtcp_parse(GQueue *q, const str *_s, struct stream_fd *sfd, const e
 
 	ZERO(log_ctx_s);
 	log_ctx_s.call = c;
+	log_ctx_s.media = m;
 	log_ctx_s.received = tv;
 
 	log_ctx = &log_ctx_s;
@@ -1162,10 +1165,10 @@ static void logging_destroy(struct rtcp_process_ctx *ctx) {
 
 
 static void mos_sr(struct rtcp_process_ctx *ctx, const struct sender_report_packet *sr) {
-	ssrc_sender_report(ctx->call, &ctx->scratch.sr, ctx->received);
+	ssrc_sender_report(ctx->media, &ctx->scratch.sr, ctx->received);
 }
 static void mos_rr(struct rtcp_process_ctx *ctx, const struct report_block *rr) {
-	ssrc_receiver_report(ctx->call, &ctx->scratch.rr, ctx->received);
+	ssrc_receiver_report(ctx->media, &ctx->scratch.rr, ctx->received);
 }
 
 
diff --git a/daemon/ssrc.c b/daemon/ssrc.c
index 4a7cc4be3..82f84ecdb 100644
--- a/daemon/ssrc.c
+++ b/daemon/ssrc.c
@@ -2,6 +2,7 @@
 #include <glib.h>
 #include "aux.h"
 #include "call.h"
+#include "rtplib.h"
 
 
 
@@ -10,6 +11,7 @@ static struct ssrc_entry *create_ssrc_entry(u_int32_t ssrc) {
 	ent = g_slice_alloc0(sizeof(struct ssrc_entry));
 	ent->ssrc = ssrc;
 	mutex_init(&ent->lock);
+	ent->payload_type = -1;
 	return ent;
 }
 static void add_ssrc_entry(struct ssrc_entry *ent, struct ssrc_hash *ht) {
@@ -19,12 +21,30 @@ static void free_sender_report(void *p) {
 	struct ssrc_sender_report_item *i = p;
 	g_slice_free1(sizeof(*i), i);
 }
+static void free_stats_block(void *p) {
+	struct ssrc_stats_block *ssb = p;
+	g_slice_free1(sizeof(*ssb), ssb);
+}
 static void free_ssrc_entry(void *p) {
 	struct ssrc_entry *e = p;
 	g_queue_clear_full(&e->sender_reports, free_sender_report);
+	g_queue_clear_full(&e->stats_blocks, free_stats_block);
 	g_slice_free1(sizeof(*e), e);
 }
 
+// returned as mos * 10 (i.e. 10 - 50 for 1.0 to 5.0)
+static void mos_calc(struct ssrc_stats_block *ssb) {
+	// as per https://www.pingman.com/kb/article/how-is-mos-calculated-in-pingplotter-pro-50.html
+	int eff_rtt = ssb->rtt / 1000 + ssb->jitter * 2 + 10;
+	double r;
+	if (eff_rtt < 160)
+		r = 93.2 - eff_rtt / 40.0;
+	else
+		r = 93.2 - (eff_rtt - 120) / 40.0;
+	r = r - (ssb->packetloss * 2.5);
+	double mos = 1.0 + (0.035) * r + (.000007) * r * (r-60) * (100-r);
+	ssb->mos = mos * 10;
+}
 
 struct ssrc_entry *find_ssrc(u_int32_t ssrc, struct ssrc_hash *ht) {
 	rwlock_lock_r(&ht->lock);
@@ -82,9 +102,10 @@ struct ssrc_ctx *get_ssrc_ctx(u_int32_t ssrc, struct ssrc_hash *ht, enum ssrc_di
 
 
 
-void ssrc_sender_report(struct call *c, const struct ssrc_sender_report *sr,
+void ssrc_sender_report(struct call_media *m, const struct ssrc_sender_report *sr,
 		const struct timeval *tv)
 {
+	struct call *c = m->call;
 	struct ssrc_entry *e;
 	struct ssrc_sender_report_item *seri;
 
@@ -102,12 +123,16 @@ void ssrc_sender_report(struct call *c, const struct ssrc_sender_report *sr,
 	mutex_lock(&e->lock);
 
 	g_queue_push_tail(&e->sender_reports, seri);
+	while (e->sender_reports.length > 10)
+		free_sender_report(g_queue_pop_head(&e->sender_reports));
 
 	mutex_unlock(&e->lock);
 }
-void ssrc_receiver_report(struct call *c, const struct ssrc_receiver_report *rr,
+void ssrc_receiver_report(struct call_media *m, const struct ssrc_receiver_report *rr,
 		const struct timeval *tv)
 {
+	struct call *c = m->call;
+
 	ilog(LOG_DEBUG, "RR from %u about %u: FL %u TL %u HSR %u J %u LSR %u DLSR %u",
 			rr->from, rr->ssrc, rr->fraction_lost, rr->packets_lost,
 			rr->high_seq_received, rr->jitter, rr->lsr, rr->dlsr);
@@ -116,18 +141,77 @@ void ssrc_receiver_report(struct call *c, const struct ssrc_receiver_report *rr,
 		return; // no delay to be known
 
 	struct ssrc_entry *e = get_ssrc(rr->ssrc, c->ssrc_hash);
+	struct ssrc_sender_report_item *seri;
 	mutex_lock(&e->lock);
-	// go through the list backwards until we find the SR referenced, up to 10 steps
-	int i = 0;
-	for (GList *l = e->sender_reports.tail; 
-			l && i < 10;
-			l = l->prev, i++)
-	{
-		struct ssrc_sender_report_item *seri = l->data;
+	// go through the list backwards until we find the SR referenced
+	for (GList *l = e->sender_reports.tail; l; l = l->prev) {
+		seri = l->data;
 		if (seri->ntp_middle_bits != rr->lsr)
 			continue;
-		ilog(LOG_DEBUG, "RR from %u reports delay %u from %u", rr->from, rr->dlsr, rr->ssrc);
-		break;
+		goto found;
+	}
+
+	// not found
+	goto out;
+
+found:
+	// `e` remains locked for access to `seri`
+	ilog(LOG_DEBUG, "RR from %u reports delay %u from %u", rr->from, rr->dlsr, rr->ssrc);
+	long long rtt = timeval_diff(tv, &seri->received);
+
+	mutex_unlock(&e->lock);
+
+	rtt -= (long long) rr->dlsr * 1000000LL / 65536LL;
+	ilog(LOG_DEBUG, "Calculated round-trip time for %u is %lli us", rr->ssrc, rtt);
+
+	if (rtt <= 0 || rtt > 10000000) {
+		ilog(LOG_DEBUG, "Invalid RTT - discarding");
+		goto out_nl;
 	}
+
+	e->last_rtt = rtt;
+
+	struct ssrc_entry *other_e = get_ssrc(rr->from, c->ssrc_hash);
+
+	// determine the clock rate for jitter values
+	int pt = e->payload_type;
+	if (pt < 0) {
+		pt = other_e->payload_type;
+		if (pt < 0) {
+			ilog(LOG_DEBUG, "No payload type known for RTCP RR, discarding");
+			goto out_nl;
+		}
+	}
+
+	const struct rtp_payload_type *rpt = rtp_payload_type(pt, m->rtp_payload_types);
+	if (!rpt) {
+		ilog(LOG_INFO, "Invalid RTP payload type %i, discarding RTCP RR", pt);
+		goto out_nl;
+	}
+	unsigned int jitter = rpt->clock_rate ? (rr->jitter * 1000 / rpt->clock_rate) : rr->jitter;
+	ilog(LOG_DEBUG, "Calculated jitter for %u is %u ms", rr->ssrc, jitter);
+
+	ilog(LOG_DEBUG, "Adding opposide side RTT of %u us", other_e->last_rtt);
+
+	struct ssrc_stats_block *ssb = g_slice_alloc(sizeof(*ssb));
+	*ssb = (struct ssrc_stats_block) {
+		.jitter = jitter,
+		.rtt = rtt + other_e->last_rtt,
+		.reported = *tv,
+		.packetloss = (unsigned int) rr->fraction_lost * 100 / 256,
+	};
+
+	mos_calc(ssb);
+	ilog(LOG_DEBUG, "Calculated MOS from RR for %u is %.1f", rr->from, (double) ssb->mos / 10.0);
+
+	// got a new stats block, add it to reporting ssrc
+	e = get_ssrc(rr->from, c->ssrc_hash);
+	mutex_lock(&e->lock);
+	g_queue_push_tail(&e->stats_blocks, ssb);
+	goto out;
+
+out:
 	mutex_unlock(&e->lock);
+out_nl:
+	;
 }
diff --git a/daemon/ssrc.h b/daemon/ssrc.h
index c6707fd25..0f29506ae 100644
--- a/daemon/ssrc.h
+++ b/daemon/ssrc.h
@@ -11,7 +11,9 @@
 
 
 struct call;
+struct call_media;
 struct timeval;
+struct rtp_payload_type;
 
 
 
@@ -29,13 +31,24 @@ struct ssrc_entry {
 	u_int32_t ssrc;
 	struct ssrc_ctx input_ctx,
 			output_ctx;
-	GQueue sender_reports;
+	GQueue sender_reports; // as received via RTCP
+	GQueue stats_blocks; // calculated
+	int payload_type; // to determine the clock rate for jitter calculations
+	unsigned int last_rtt; // last calculated raw rtt without rtt from opposide side
 };
 enum ssrc_dir {
 	SSRC_DIR_INPUT  = G_STRUCT_OFFSET(struct ssrc_entry, input_ctx),
 	SSRC_DIR_OUTPUT = G_STRUCT_OFFSET(struct ssrc_entry, output_ctx),
 };
 
+struct ssrc_stats_block {
+	struct timeval reported;
+	unsigned int jitter; // ms
+	unsigned int rtt; // us - combined from both sides
+	unsigned int packetloss; // percent
+	int mos; // nominal range of 10 - 50 for MOS values 1.0 to 5.0
+};
+
 struct ssrc_sender_report {
 	u_int32_t ssrc;
 	u_int32_t ntp_msw;
@@ -102,8 +115,8 @@ struct ssrc_entry *get_ssrc(u_int32_t, struct ssrc_hash * /* , int *created */);
 struct ssrc_ctx *get_ssrc_ctx(u_int32_t, struct ssrc_hash *, enum ssrc_dir); // creates new entry if not found
 
 
-void ssrc_sender_report(struct call *, const struct ssrc_sender_report *, const struct timeval *);
-void ssrc_receiver_report(struct call *, const struct ssrc_receiver_report *,
+void ssrc_sender_report(struct call_media *, const struct ssrc_sender_report *, const struct timeval *);
+void ssrc_receiver_report(struct call_media *, const struct ssrc_receiver_report *,
 		const struct timeval *);