--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/include/twjit.h	Fri Jul 05 18:50:48 2024 +0000
@@ -0,0 +1,135 @@
+/*
+ * Themyscira Wireless jitter buffer implementation: definition of
+ * structures and API functions.
+ */
+
+#pragma once
+
+#include <stdint.h>
+#include <stdbool.h>
+
+#include <osmocom/core/linuxlist.h>
+#include <osmocom/core/timer.h>
+
+/*
+ * twjit configuration tunings, usually set via vty.
+ */
+struct twrtp_jibuf_config {
+	/* buffer depth: starting minimum and high watermark */
+	uint16_t bd_start;
+	uint16_t bd_hiwat;
+	/* interval for thinning of too-deep standing queue */
+	uint16_t thinning_int;
+	/* guard against time traveler RTP packets */
+	uint16_t max_future_sec;
+	/* min and max time delta in starting state, 0 means not set */
+	uint16_t start_min_delta;
+	uint16_t start_max_delta;
+};
+
+/*
+ * Stats collected during the lifetime of a twjit instance.
+ */
+struct twrtp_jibuf_stats {
+	/* normal operation */
+	uint32_t delivered_pkt;
+	uint32_t delivered_bytes;
+	uint32_t handovers;
+	/* undesirable, but not totally unexpected */
+	uint32_t too_old;
+	uint32_t underruns;
+	uint32_t output_gaps;
+	uint32_t thinning_drops;
+	/* unusual error events */
+	uint32_t bad_packets;
+	uint32_t duplicate_ts;
+	/* independent analysis of Rx packet stream */
+	uint32_t ssrc_changes;
+	uint32_t seq_skips;
+	uint32_t seq_backwards;
+	uint32_t seq_repeats;
+	uint32_t intentional_gaps;
+	uint32_t ts_resets;
+};
+
+/*
+ * Each twjit instance has two sub-buffers; each subbuf is a queue of
+ * received RTP packets that have the same SSRC and whose timestamps
+ * increment in the expected cadence, with each ts delta being an
+ * integral multiple of the samples-per-quantum constant.
+ */
+struct twrtp_jibuf_sub {
+	uint32_t ssrc;
+	uint32_t head_ts;
+	struct llist_head queue;
+	uint32_t depth;
+	/* last packet arrival time, used only in starting state */
+	struct timeval last_arrival;
+	uint32_t delta_ms;
+	/* thinning mechanism */
+	uint16_t drop_int_count;
+	/* running config for this subbuf */
+	struct twrtp_jibuf_config conf;
+};
+
+/*
+ * Each twjit instance is in one of 4 fundamental states at any moment,
+ * as enumerated here.
+ */
+enum twrtp_jibuf_state {
+	TWJIT_STATE_EMPTY,
+	TWJIT_STATE_HUNT,
+	TWJIT_STATE_FLOWING,
+	TWJIT_STATE_HANDOVER,
+};
+
+/* Main structure for one instance of twjit */
+struct twrtp_jibuf_inst {
+	/* pointer to config structure given to twrtp_jibuf_create(),
+	 * memory must remain valid, but content can change at any time. */
+	struct twrtp_jibuf_config *ext_config;
+	/* count of RTP timestamp units per quantum */
+	uint32_t ts_quantum;
+	/* quanta per second, used to scale max_future_sec */
+	uint32_t quanta_per_sec;
+	/* operational state */
+	enum twrtp_jibuf_state state;
+	struct twrtp_jibuf_sub sb[2];
+	uint8_t read_sb;	/* 0 or 1 */
+	uint8_t write_sb;	/* ditto */
+	/* Rx packet stream analysis */
+	uint32_t last_ssrc;
+	uint32_t last_ts;
+	uint16_t last_seq;
+	bool got_first_packet;
+	/* stats over lifetime of this instance */
+	struct twrtp_jibuf_stats stats;
+};
+
+/* twjit module API functions */
+
+struct twrtp_jibuf_inst *twrtp_jibuf_create(void *ctx, uint16_t quantum_ms,
+					    uint32_t quantum_ts_inc,
+					    struct twrtp_jibuf_config *config);
+
+void twrtp_jibuf_destroy(struct twrtp_jibuf_inst *twjit);
+
+struct msgb;
+
+/* RTP input, takes ownership of msgb */
+void twrtp_jibuf_input(struct twrtp_jibuf_inst *twjit, struct msgb *msg);
+
+/* output function, to be called by TDM/GSM/etc fixed-timing side */
+struct msgb *twrtp_jibuf_output(struct twrtp_jibuf_inst *twjit);
+
+/* vty configuration functions */
+
+void twrtp_jibuf_init_defaults(struct twrtp_jibuf_config *config);
+
+void twrtp_jibuf_vty_init(int twjit_node);
+
+struct vty;
+
+int twrtp_jibuf_config_write(struct vty *vty,
+			     const struct twrtp_jibuf_config *conf,
+			     const char *name, const char *prefix);

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Makefile	Fri Jul 05 18:50:48 2024 +0000
@@ -0,0 +1,15 @@
+OBJS=	twjit.o
+LIB=	libtwrtp.a
+
+include ../config.defs
+
+CPPFLAGS=${OSMO_INCLUDE} -I../build-inc
+
+all:	${LIB}
+
+${LIB}:	${OBJS}
+	ar rcu $@ ${OBJS}
+	ranlib $@
+
+clean:
+	rm -f *.[oa] errs

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/twjit.c	Fri Jul 05 18:50:48 2024 +0000
@@ -0,0 +1,393 @@
+/*
+ * Themyscira Wireless jitter buffer implementation: code body.
+ */
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <string.h>
+#include <arpa/inet.h>	/* for network byte order functions */
+
+#include <osmocom/core/linuxlist.h>
+#include <osmocom/core/msgb.h>
+#include <osmocom/core/talloc.h>
+#include <osmocom/core/timer.h>
+#include <osmocom/core/utils.h>
+
+/* FIXME: this libosmo-netif dependency needs to be removed */
+#include <osmocom/netif/rtp.h>
+
+#include <themwi/rtp/twjit.h>
+
+void twrtp_jibuf_init_defaults(struct twrtp_jibuf_config *config)
+{
+	memset(config, 0, sizeof(struct twrtp_jibuf_config));
+	config->bd_start = 2;	/* smallest allowed */
+	config->bd_hiwat = 3;	/* Nstart+1 is practically-useful minimum */
+	config->thinning_int = 17;	/* prime number, usually 340 ms */
+	config->max_future_sec = 10;	/* 10 s is a long time for voice */
+}
+
+/* create and destroy functions */
+
+struct twrtp_jibuf_inst *
+twrtp_jibuf_create(void *ctx, uint16_t quantum_ms, uint32_t quantum_ts_inc,
+		   struct twrtp_jibuf_config *config)
+{
+	struct twrtp_jibuf_inst *twjit;
+
+	twjit = talloc_zero(ctx, struct twrtp_jibuf_inst);
+	if (!twjit)
+		return NULL;
+
+	twjit->ext_config = config;
+	twjit->ts_quantum = quantum_ts_inc;
+	twjit->quanta_per_sec = 1000 / quantum_ms;
+	twjit->state = TWJIT_STATE_EMPTY;
+	INIT_LLIST_HEAD(&twjit->sb[0].queue);
+	INIT_LLIST_HEAD(&twjit->sb[1].queue);
+
+	return twjit;
+}
+
+void twrtp_jibuf_destroy(struct twrtp_jibuf_inst *twjit)
+{
+	msgb_queue_free(&twjit->sb[0].queue);
+	msgb_queue_free(&twjit->sb[1].queue);
+	talloc_free(twjit);
+}
+
+/* RTP input to twjit */
+
+static void get_current_time(struct timeval *tp)
+{
+	struct timespec now;
+
+	osmo_clock_gettime(CLOCK_MONOTONIC, &now);
+	tp->tv_sec = now.tv_sec;
+	tp->tv_usec = now.tv_nsec / 1000;
+}
+
+static void
+init_subbuf_first_packet(struct twrtp_jibuf_inst *twjit, struct msgb *msg,
+			 uint32_t rx_ssrc, uint32_t rx_ts,
+			 const struct timeval *new_time)
+{
+	struct twrtp_jibuf_sub *sb = &twjit->sb[twjit->write_sb];
+
+	OSMO_ASSERT(llist_empty(&sb->queue));
+	OSMO_ASSERT(sb->depth == 0);
+	/* all good, proceed */
+	sb->ssrc = rx_ssrc;
+	sb->head_ts = rx_ts;
+	msgb_enqueue(&sb->queue, msg);
+	sb->depth = 1;
+	memcpy(&sb->last_arrival, &new_time, sizeof(struct timeval));
+	memcpy(&sb->conf, twjit->ext_config, sizeof(struct twrtp_jibuf_config));
+	sb->drop_int_count = 0;
+}
+
+enum input_decision {
+	INPUT_CONTINUE,
+	INPUT_TOO_OLD,
+	INPUT_RESET,
+};
+
+static enum input_decision
+check_input_for_subbuf(struct twrtp_jibuf_inst *twjit, bool starting,
+			uint32_t rx_ssrc, uint32_t rx_ts,
+			const struct timeval *new_time)
+{
+	struct twrtp_jibuf_sub *sb = &twjit->sb[twjit->write_sb];
+	struct timeval time_delta;
+	int32_t ts_delta;
+
+	if (rx_ssrc != sb->ssrc)
+		return INPUT_RESET;
+	if (starting) {
+		timersub(new_time, &sb->last_arrival, &time_delta);
+		sb->delta_ms = time_delta.tv_sec * 1000 +
+				time_delta.tv_usec / 1000;
+		memcpy(&sb->last_arrival, new_time, sizeof(struct timeval));
+	}
+	ts_delta = (int32_t)(rx_ts - sb->head_ts);
+	if (ts_delta < 0)
+		return INPUT_TOO_OLD;
+	if (ts_delta % twjit->ts_quantum)
+		return INPUT_RESET;
+	if (starting) {
+		if (sb->conf.start_max_delta &&
+		    sb->delta_ms > sb->conf.start_max_delta)
+			return INPUT_RESET;
+	} else {
+		uint32_t fwd = ts_delta / twjit->ts_quantum;
+
+		if (fwd >= sb->conf.max_future_sec * twjit->quanta_per_sec)
+			return INPUT_RESET;
+	}
+	return INPUT_CONTINUE;
+}
+
+static void toss_write_queue(struct twrtp_jibuf_inst *twjit)
+{
+	struct twrtp_jibuf_sub *sb = &twjit->sb[twjit->write_sb];
+
+	msgb_queue_free(&sb->queue);
+	sb->depth = 0;
+}
+
+static void insert_pkt_write_sb(struct twrtp_jibuf_inst *twjit,
+				struct msgb *new_msg, uint32_t rx_ts)
+{
+	struct twrtp_jibuf_sub *sb = &twjit->sb[twjit->write_sb];
+	uint32_t ts_delta = rx_ts - sb->head_ts;
+	uint32_t ins_depth = ts_delta / twjit->ts_quantum;
+	struct msgb *old_msg;
+	uint32_t old_ts_delta;
+
+	/* are we increasing total depth, and can we do simple tail append? */
+	if (ins_depth >= sb->depth) {
+		msgb_enqueue(&sb->queue, new_msg);
+		sb->depth = ins_depth + 1;
+		return;
+	}
+	/* nope - do it the hard way */
+	llist_for_each_entry(old_msg, &sb->queue, list) {
+		old_ts_delta = old_msg->cb[0] - sb->head_ts;
+		if (old_ts_delta == ts_delta) {
+			/* two packets with the same timestamp! */
+			twjit->stats.duplicate_ts++;
+			msgb_free(new_msg);
+			return;
+		}
+		if (old_ts_delta > ts_delta)
+			break;
+	}
+	llist_add_tail(&new_msg->list, &old_msg->list);
+}
+
+static void trim_starting_sb(struct twrtp_jibuf_inst *twjit)
+{
+	struct twrtp_jibuf_sub *sb = &twjit->sb[twjit->write_sb];
+	struct msgb *msg;
+	uint32_t msg_ts, ts_adv, quantum_adv;
+
+	while (sb->depth > sb->conf.bd_start) {
+		msg = msgb_dequeue(&sb->queue);
+		OSMO_ASSERT(msg);
+		msgb_free(msg);
+		OSMO_ASSERT(!llist_empty(&sb->queue));
+		msg = llist_entry(sb->queue.next, struct msgb, list);
+		msg_ts = msg->cb[0];
+		ts_adv = msg_ts - sb->head_ts;
+		quantum_adv = ts_adv / twjit->ts_quantum;
+		OSMO_ASSERT(sb->depth > quantum_adv);
+		sb->head_ts = msg_ts;
+		sb->depth -= quantum_adv;
+	}
+}
+
+static void rx_raw_analytics(struct twrtp_jibuf_inst *twjit, uint32_t rx_ssrc,
+			     uint16_t rx_seq, uint32_t rx_ts)
+{
+	int16_t seq_delta;
+	int32_t ts_delta;
+
+	if (twjit->last_ssrc != rx_ssrc) {
+		twjit->stats.ssrc_changes++;
+		return;
+	}
+	seq_delta = (int16_t)(rx_seq - twjit->last_seq);
+	if (seq_delta < 0)
+		twjit->stats.seq_backwards++;
+	else if (seq_delta == 0)
+		twjit->stats.seq_repeats++;
+	else if (seq_delta == 1) {
+		ts_delta = (int32_t)(rx_ts - twjit->last_ts);
+		if (ts_delta != twjit->ts_quantum) {
+			if (ts_delta > 0 && (ts_delta % twjit->ts_quantum) == 0)
+				twjit->stats.intentional_gaps++;
+			else
+				twjit->stats.ts_resets++;
+		}
+	} else
+		twjit->stats.seq_skips++;
+}
+
+void twrtp_jibuf_input(struct twrtp_jibuf_inst *twjit, struct msgb *msg)
+{
+	struct rtp_hdr *rtph;
+	uint32_t rx_ssrc, rx_ts;
+	uint16_t rx_seq;
+	struct timeval new_time;
+	enum input_decision id;
+
+	rtph = osmo_rtp_get_hdr(msg);
+	if (!rtph) {
+		/* invalid packet, couldn't even get header from it */
+		twjit->stats.bad_packets++;
+		msgb_free(msg);
+		return;
+	}
+	rx_ssrc = ntohl(rtph->ssrc);
+	rx_ts = ntohl(rtph->timestamp);
+	rx_seq = ntohs(rtph->sequence);
+	get_current_time(&new_time);
+	if (twjit->got_first_packet)
+		rx_raw_analytics(twjit, rx_ssrc, rx_seq, rx_ts);
+	twjit->last_ssrc = rx_ssrc;
+	twjit->last_seq = rx_seq;
+	twjit->last_ts = rx_ts;
+	twjit->got_first_packet = true;
+	msg->cb[0] = rx_ts;
+
+	switch (twjit->state) {
+	case TWJIT_STATE_EMPTY:
+		/* first packet into totally empty buffer */
+		twjit->state = TWJIT_STATE_HUNT;
+		twjit->write_sb = 0;
+		init_subbuf_first_packet(twjit, msg, rx_ssrc, rx_ts, &new_time);
+		return;
+	case TWJIT_STATE_HUNT:
+	case TWJIT_STATE_HANDOVER:
+		id = check_input_for_subbuf(twjit, true, rx_ssrc, rx_ts,
+					    &new_time);
+		if (id == INPUT_TOO_OLD) {
+			msgb_free(msg);
+			return;
+		}
+		if (id == INPUT_RESET) {
+			toss_write_queue(twjit);
+			init_subbuf_first_packet(twjit, msg, rx_ssrc, rx_ts,
+						 &new_time);
+			return;
+		}
+		insert_pkt_write_sb(twjit, msg, rx_ts);
+		trim_starting_sb(twjit);
+		return;
+	case TWJIT_STATE_FLOWING:
+		id = check_input_for_subbuf(twjit, false, rx_ssrc, rx_ts,
+					    &new_time);
+		if (id == INPUT_TOO_OLD) {
+			twjit->stats.too_old++;
+			msgb_free(msg);
+			return;
+		}
+		if (id == INPUT_RESET) {
+			twjit->state = TWJIT_STATE_HANDOVER;
+			twjit->write_sb = !twjit->write_sb;
+			init_subbuf_first_packet(twjit, msg, rx_ssrc, rx_ts,
+						 &new_time);
+			twjit->stats.handovers++;
+			return;
+		}
+		insert_pkt_write_sb(twjit, msg, rx_ts);
+		return;
+	default:
+		OSMO_ASSERT(0);
+	}
+}
+
+/* Output from twjit to the fixed timing system */
+
+static bool starting_sb_is_ready(struct twrtp_jibuf_inst *twjit)
+{
+	struct twrtp_jibuf_sub *sb = &twjit->sb[twjit->write_sb];
+
+	if (sb->depth < sb->conf.bd_start)
+		return false;
+	if (sb->delta_ms < sb->conf.start_min_delta)
+		return false;
+	return true;
+}
+
+static bool read_sb_is_empty(struct twrtp_jibuf_inst *twjit)
+{
+	struct twrtp_jibuf_sub *sb = &twjit->sb[twjit->read_sb];
+
+	return sb->depth == 0;
+}
+
+static struct msgb *pull_from_read_sb(struct twrtp_jibuf_inst *twjit)
+{
+	struct twrtp_jibuf_sub *sb = &twjit->sb[twjit->read_sb];
+	struct msgb *msg;
+
+	OSMO_ASSERT(!llist_empty(&sb->queue));
+	OSMO_ASSERT(sb->depth > 0);
+	msg = llist_entry(sb->queue.next, struct msgb, list);
+	if (msg->cb[0] == sb->head_ts) {
+		llist_del(&msg->list);
+		twjit->stats.delivered_pkt++;
+		twjit->stats.delivered_bytes += msg->len;
+	} else {
+		msg = NULL;
+		twjit->stats.output_gaps++;
+	}
+	sb->head_ts += twjit->ts_quantum;
+	sb->depth--;
+	return msg;
+}
+
+static void read_sb_thinning(struct twrtp_jibuf_inst *twjit)
+{
+	struct twrtp_jibuf_sub *sb = &twjit->sb[twjit->read_sb];
+	struct msgb *msg;
+
+	if (sb->drop_int_count) {
+		sb->drop_int_count--;
+		return;
+	}
+	if (sb->depth <= sb->conf.bd_hiwat)
+		return;
+	twjit->stats.thinning_drops++;
+	msg = pull_from_read_sb(twjit);
+	if (msg)
+		msgb_free(msg);
+	sb->drop_int_count = sb->conf.thinning_int - 2;
+}
+
+static void toss_read_queue(struct twrtp_jibuf_inst *twjit)
+{
+	struct twrtp_jibuf_sub *sb = &twjit->sb[twjit->read_sb];
+
+	msgb_queue_free(&sb->queue);
+	sb->depth = 0;
+}
+
+struct msgb *twrtp_jibuf_output(struct twrtp_jibuf_inst *twjit)
+{
+	switch (twjit->state) {
+	case TWJIT_STATE_EMPTY:
+		return NULL;
+	case TWJIT_STATE_HUNT:
+		if (!starting_sb_is_ready(twjit))
+			return NULL;
+		twjit->state = TWJIT_STATE_FLOWING;
+		twjit->read_sb = twjit->write_sb;
+		return pull_from_read_sb(twjit);
+	case TWJIT_STATE_FLOWING:
+		if (read_sb_is_empty(twjit)) {
+			twjit->state = TWJIT_STATE_EMPTY;
+			twjit->stats.underruns++;
+			return NULL;
+		}
+		read_sb_thinning(twjit);
+		return pull_from_read_sb(twjit);
+	case TWJIT_STATE_HANDOVER:
+		if (starting_sb_is_ready(twjit)) {
+			toss_read_queue(twjit);
+			twjit->state = TWJIT_STATE_FLOWING;
+			twjit->read_sb = twjit->write_sb;
+			return pull_from_read_sb(twjit);
+		}
+		if (read_sb_is_empty(twjit)) {
+			twjit->state = TWJIT_STATE_HUNT;
+			twjit->stats.underruns++;
+			return NULL;
+		}
+		read_sb_thinning(twjit);
+		return pull_from_read_sb(twjit);
+	default:
+		OSMO_ASSERT(0);
+	}
+}