From c72e5070ef7b0ce7687faa57f1eb0f4085892cf5 Mon Sep 17 00:00:00 2001
From: Andreas Eversberg <jolly@eversberg.eu>
Date: Sun, 30 Oct 2022 16:14:17 +0100
Subject: [PATCH] Add comfort noise when call is on hold

This is required so that the RTP stream does not interrupt.
---
 src/isdn/dss1.c | 11 +++++++++--
 src/isdn/isdn.c | 31 ++++++++++++++++++++++++++++++-
 src/isdn/isdn.h |  3 ++-
 src/isdn/main.c | 12 ++++++++++++
 4 files changed, 53 insertions(+), 4 deletions(-)

diff --git a/src/isdn/dss1.c b/src/isdn/dss1.c
index 3fd6653..4f46cfe 100644
--- a/src/isdn/dss1.c
+++ b/src/isdn/dss1.c
@@ -951,7 +951,9 @@ void hold_ind(call_t *call, uint32_t pid, struct l3_msg *l3m)
 
 	/* set hold state */
 	call->hold = 1;
-#warning use clock to send empty packets/holdmusic
+
+	/* reset jitter buffer, to ignore packets coming from remote */
+	jitter_reset(&call->tx_dejitter);
 
 	/* acknowledge hold */
 	PDEBUG(DDSS1, DEBUG_INFO, "HOLD-ACKNOWLEDGE REQUEST (pid = 0x%x callref = %d)\n", pid, call->cc_callref);
@@ -1066,7 +1068,9 @@ void suspend_ind(call_t *call, uint32_t pid, struct l3_msg *l3m)
 	new_state(call, ISDN_STATE_SUSPENDED);
 	memcpy(call->park_callid, callid, len);
 	call->park_len = len;
-#warning use clock to send empty packets/holdmusic
+
+	/* reset jitter buffer, to ignore packets coming from remote */
+	jitter_reset(&call->tx_dejitter);
 
 	/* send message to osmo-cc */
 	osmo_cc_ll_msg(&call->isdn_ep->cc_ep, call->cc_callref, msg);
@@ -1149,6 +1153,9 @@ void resume_ind(isdn_t *isdn_ep, uint32_t pid, struct l3_msg *l3m)
 
 	new_state(call, ISDN_STATE_CONNECT);
 
+	/* reset jitter buffer */
+	jitter_reset(&call->tx_dejitter);
+
 	/* send message to osmo-cc */
 	osmo_cc_ll_msg(&call->isdn_ep->cc_ep, call->cc_callref, msg);
 
diff --git a/src/isdn/isdn.c b/src/isdn/isdn.c
index 22e4758..3634cfb 100644
--- a/src/isdn/isdn.c
+++ b/src/isdn/isdn.c
@@ -1656,7 +1656,7 @@ void isdn_rtp_work(isdn_t *isdn_ep)
 }
 
 /* send audio from RTP to B-channel's jitter buffer */
-void rtp_receive(struct osmo_cc_session_codec *codec, uint16_t sequence_number, uint32_t timestamp, uint32_t ssrc, uint8_t *data, int len)
+void rtp_receive(struct osmo_cc_session_codec *codec, uint8_t __attribute__((unused)) marker, uint16_t sequence_number, uint32_t timestamp, uint32_t ssrc, uint8_t *data, int len)
 {
 	call_t *call = codec->media->session->priv;
 
@@ -2140,3 +2140,32 @@ void isdn_bchannel_work(isdn_t *isdn_ep)
 		} while (w);
 	}
 }
+
+#define COMFORT_NOISE	(0.02 * SPEECH_LEVEL)	/* audio level of comfort noise (relative to ISDN level) */
+
+void hold_clock(isdn_t *isdn_ep, int len)
+{
+	call_t *call;
+
+	call = isdn_ep->call_list;
+	while (call) {
+		if ((call->state == ISDN_STATE_SUSPENDED || call->hold) && call->codec) {
+			int16_t noise[len];
+			uint8_t *data;
+			int i;
+			int16_t r;
+
+			for (i = 0; i < len; i++) {
+				r = random();
+				noise[i] = (double)r * COMFORT_NOISE;
+			}
+			if (call->isdn_ep->law == 'a')
+				g711_encode_alaw_flipped((uint8_t *)noise, len * 2, &data, &len);
+			else
+				g711_encode_ulaw_flipped((uint8_t *)noise, len * 2, &data, &len);
+			osmo_cc_rtp_send(call->codec, data, len, 0, 1, len);
+			free(data);
+		}
+		call = call->next;
+	}
+}
diff --git a/src/isdn/isdn.h b/src/isdn/isdn.h
index 1fab144..8fe2ad4 100644
--- a/src/isdn/isdn.h
+++ b/src/isdn/isdn.h
@@ -208,5 +208,6 @@ void bchannel_bridge(call_t *call, int pcm_bridge, int rx_slot, int tx_slot, int
 void bchannel_event(isdn_t *isdn_ep, int index, int event);
 int seize_bchannel(call_t *call, int channel, int exclusive);
 void drop_bchannel(call_t *call);
-void rtp_receive(struct osmo_cc_session_codec *codec, uint16_t sequence_number, uint32_t timestamp, uint32_t ssrc, uint8_t *data, int len);
+void rtp_receive(struct osmo_cc_session_codec *codec, uint8_t marker, uint16_t sequence_number, uint32_t timestamp, uint32_t ssrc, uint8_t *data, int len);
+void hold_clock(isdn_t *isdn_ep, int len);
 
diff --git a/src/isdn/main.c b/src/isdn/main.c
index 799f329..98f0b9d 100644
--- a/src/isdn/main.c
+++ b/src/isdn/main.c
@@ -307,6 +307,7 @@ static int mISDNlib_debug(const char *file, int line, const char *func, int __at
 
 int main(int argc, char *argv[])
 {
+	double last_time_call = 0, now;
 	int argi, rc;
 	int misdn_initialized = 0;
 	int ph_drv_initialized = 0;
@@ -412,6 +413,17 @@ int main(int argc, char *argv[])
 
 	while (!quit) {
 		int w;
+
+		/* send clock calls to provide audio to suspended/helt calls */
+		now = get_time();
+		if (now - last_time_call >= 0.1)
+			last_time_call = now;
+		if (now - last_time_call >= 0.020) {
+			last_time_call += 0.020;
+			/* call hold-clock every 20ms */
+			hold_clock(isdn_ep, 160);
+		}
+
 		process_timer();
 		isdn_bchannel_work(isdn_ep);
 		isdn_rtp_work(isdn_ep);