MTS/IMTS: (Improved) Mobile Telephone Service

Implementation of the 0G Mobile Phone Network of US and Canada

MTS or IMTS mode is selectable, als well as 5 or 7 digit mode.

11 files changed, 2834 insertions, 13 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index 4f1751f..3950a81 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -46,6 +46,7 @@ SUBDIRS += \
 	tacs \
 	jtacs \
 	r2000 \
+	imts \
 	jolly \
 	tv \
 	radio \
diff --git a/src/imts/Makefile.am b/src/imts/Makefile.am
new file mode 100644
index 0000000..c9f7dce
--- /dev/null
+++ b/src/imts/Makefile.am
@@ -0,0 +1,63 @@
+AM_CPPFLAGS = -Wall -Wextra -g $(all_includes)
+
+bin_PROGRAMS = \
+	imts \
+	imts-dialer
+
+imts_SOURCES = \
+	imts.c \
+	dsp.c \
+	image.c \
+	main.c
+imts_LDADD = \
+	$(COMMON_LA) \
+	../amps/libusatone.a \
+	$(top_builddir)/src/liboptions/liboptions.a \
+	$(top_builddir)/src/libdebug/libdebug.a \
+	$(top_builddir)/src/libmobile/libmobile.a \
+	$(top_builddir)/src/libdisplay/libdisplay.a \
+	$(top_builddir)/src/libjitter/libjitter.a \
+	$(top_builddir)/src/libsquelch/libsquelch.a \
+	$(top_builddir)/src/libtimer/libtimer.a \
+	$(top_builddir)/src/libsamplerate/libsamplerate.a \
+	$(top_builddir)/src/libemphasis/libemphasis.a \
+	$(top_builddir)/src/libfm/libfm.a \
+	$(top_builddir)/src/libfilter/libfilter.a \
+	$(top_builddir)/src/libwave/libwave.a \
+	$(top_builddir)/src/libmncc/libmncc.a \
+	$(top_builddir)/src/libsample/libsample.a \
+	-lm
+
+imts_dialer_SOURCES = \
+	dialer.c
+
+imts_dialer_LDADD = \
+	$(COMMON_LA) \
+	$(top_builddir)/src/liboptions/liboptions.a \
+	$(top_builddir)/src/libdebug/libdebug.a \
+	$(top_builddir)/src/libwave/libwave.a \
+	$(top_builddir)/src/libsample/libsample.a \
+	-lm
+
+if HAVE_ALSA
+imts_LDADD += \
+	$(top_builddir)/src/libsound/libsound.a \
+	$(ALSA_LIBS)
+
+imts_dialer_LDADD += \
+	$(top_builddir)/src/libsound/libsound.a \
+	$(ALSA_LIBS)
+endif
+
+if HAVE_SDR
+imts_LDADD += \
+	$(top_builddir)/src/libsdr/libsdr.a \
+	$(top_builddir)/src/libfft/libfft.a \
+	$(UHD_LIBS) \
+	$(SOAPY_LIBS)
+endif
+
+if HAVE_ALSA
+AM_CPPFLAGS += -DHAVE_ALSA
+endif
+
diff --git a/src/imts/dialer.c b/src/imts/dialer.c
new file mode 100644
index 0000000..a68ae05
--- /dev/null
+++ b/src/imts/dialer.c
@@ -0,0 +1,354 @@
+/* IMTS dialer
+ *
+ * (C) 2019 by Andreas Eversberg <jolly@eversberg.eu>
+ * All Rights Reserved
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <math.h>
+#include <errno.h>
+#include "../libsample/sample.h"
+#include "../libwave/wave.h"
+#include "../libdebug/debug.h"
+#ifdef HAVE_ALSA
+#include "../libsound/sound.h"
+#endif
+#include "../liboptions/options.h"
+
+/* presets */
+const char *station_id = "6681739";
+const char *dialing;
+const char *audiodev = "hw:0,0";
+int samplerate = 48000;
+const char *write_tx_wave = NULL;
+int latency = 50;
+
+#define TONE_DONE	-1
+#define TONE_SILENCE	0
+#define TONE_GUARD	2150
+#define TONE_CONNECT	1633
+#define TONE_DISCONNECT	1336
+
+/* states */
+static struct dial_string {
+	char console;
+	int tone;
+	int length;
+} dial_string[2048];
+static int dial_pos = 0;
+static int latspl;
+
+/* instances */
+#ifdef HAVE_ALSA
+void *audio = NULL;
+#endif
+wave_rec_t wave_tx_rec;
+
+/* dummy functions */
+int num_kanal = 1; /* only one channel used for debugging */
+void display_status_limit_scroll() {}
+void *get_sender_by_empfangsfrequenz() { return NULL; }
+void display_measurements_add() {}
+void display_measurements_update() {}
+
+static void print_help(const char *arg0)
+{
+	printf("Usage: %s [options] <number> | disconnect\n\n", arg0);
+	/*      -                                                                             - */
+	printf("This program generates a dialing sequence to make a call via IMTS base\n");
+	printf("station using an amateur radio transceiver.\n");
+	printf("Also it can write an audio file (wave) to be fed into IMTS base station for\n");
+	printf("showing how it simulates an IMTS phone doing an outgoing call.\n\n");
+	printf("Use 'disconnect' to generate a disconnect sequence.\n\n");
+	printf(" -h --help\n");
+	printf("        This help\n");
+	printf(" -i --station-id <station ID>\n");
+	printf("        7 Digits of ID of mobile station (default = '%s')\n", station_id);
+#ifdef HAVE_ALSA
+	printf(" -a --audio-device hw:<card>,<device>\n");
+	printf("        Sound card and device number (default = '%s')\n", audiodev);
+#endif
+	printf(" -s --samplerate <rate>\n");
+	printf("        Sample rate of sound device (default = '%d')\n", samplerate);
+	printf(" -w --write-tx-wave <file>\n");
+	printf("        Write audio to given wave file also.\n");
+}
+
+static void add_options(void)
+{
+	option_add('h', "help", 0);
+	option_add('i', "station-id", 1);
+	option_add('a', "audio-device", 1);
+	option_add('s', "samplerate", 1);
+	option_add('w', "write-tx-wave", 1);
+}
+
+static int handle_options(int short_option, int __attribute__((unused)) argi, char **argv)
+{
+	switch (short_option) {
+	case 'h':
+		print_help(argv[0]);
+		return 0;
+	case 'i':
+		station_id = strdup(argv[argi]);
+		break;
+	case 'a':
+		audiodev = strdup(argv[argi]);
+		break;
+	case 's':
+		samplerate = atoi(argv[argi]);
+		break;
+	case 'w':
+		write_tx_wave = strdup(argv[argi]);
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 1;
+}
+
+static double phase = 0;
+
+/* encode audio */
+static void encode_audio(sample_t *samples, uint8_t *power, int length)
+{
+	int count;
+	int i;
+
+	memset(power, 1, length);
+
+again:
+	count = length;
+	if (dial_string[dial_pos].length && dial_string[dial_pos].length < count)
+		count = dial_string[dial_pos].length;
+
+	switch (dial_string[dial_pos].tone) {
+	case TONE_DONE:
+	case TONE_SILENCE:
+		memset(samples, 0, count * sizeof(*samples));
+		phase = 0;
+		break;
+	default:
+		for (i = 0; i < count; i++) {
+			samples[i] = cos(2.0 * M_PI * (double)dial_string[dial_pos].tone * phase);
+			phase += 1.0 / samplerate;
+		}
+	}
+
+	if (dial_string[dial_pos].length) {
+		dial_string[dial_pos].length -= count;
+		if (dial_string[dial_pos].length == 0) {
+			if (dial_string[dial_pos].console) {
+				printf("%c", dial_string[dial_pos].console);
+				fflush(stdout);
+			}
+			dial_pos++;
+		}
+	}
+
+	samples += count;
+	length -= count;
+
+	if (length)
+		goto again;
+}
+
+/* loop that gets audio from encoder and fowards it to sound card.
+ * alternatively a sound file is written.
+ */
+static void process_signal(void)
+{
+	sample_t buff[latspl], *samples[1] = { buff };
+        uint8_t pbuff[latspl], *power[1] = { pbuff };
+	int count;
+	int __attribute__((unused)) rc;
+
+	while (dial_string[dial_pos].tone != TONE_DONE) {
+#ifdef HAVE_ALSA
+		count = sound_get_tosend(audio, latspl);
+#else
+		count = samplerate / 1000;
+#endif
+		if (count < 0) {
+			PDEBUG(DDSP, DEBUG_ERROR, "Failed to get number of samples in buffer (rc = %d)!\n", count);
+			break;
+		}
+
+		/* encode dial_string of tones and lengths */
+		encode_audio(samples[0], power[0], count);
+
+		/* write wave, if open */
+		if (wave_tx_rec.fp)
+			wave_write(&wave_tx_rec, samples, count);
+
+#ifdef HAVE_ALSA
+		/* write audio */
+		rc = sound_write(audio, samples, power, count, NULL, NULL, 1);
+		if (rc < 0) {
+			PDEBUG(DDSP, DEBUG_ERROR, "Failed to write TX data to audio device (rc = %d)\n", rc);
+			break;
+		}
+#endif
+
+		/* sleep a while */
+		usleep(1000);
+	}
+}
+
+int main(int argc, char *argv[])
+{
+	int i, d, p, pulses, tone = 0;
+	int rc, argi;
+
+	memset(dial_string, 0, sizeof(dial_string));
+
+	/* latency of send buffer in samples */
+	latspl = samplerate * latency / 1000;
+
+	/* handle options / config file */
+	add_options();
+	argi = options_command_line(argc, argv, handle_options);
+	if (argi <= 0)
+		return argi;
+
+	if (argi >= argc) {
+		printf("No phone number given!\n\n");
+		print_help(argv[0]);
+		goto exit;
+	}
+
+	/* check for valid station ID */
+	if (strlen(station_id) != 7) {
+		printf("Given station ID '%s' has invalid number of digits!\n", station_id);
+		goto exit;
+	}
+	for (i = 0; station_id[i]; i++) {
+		if (station_id[i] < '0' || station_id[i] > '9') {
+			printf("Given station ID '%s' has invalid digits!\n", station_id);
+			goto exit;
+		}
+	}
+
+	dialing = argv[argi];
+	d = 0;
+	dial_string[d].tone = TONE_SILENCE; dial_string[d++].length = 0.600 * (double)samplerate; /* pause */
+	if (!!strcasecmp(dialing, "disconnect")) {
+		/* check for valid phone number */
+		if (strlen(dialing) > 64) {
+			printf("Given phone number '%s' has too many digits! (more than allowed 64 digits)\n", dialing);
+			goto exit;
+		}
+		for (i = 0; dialing[i]; i++) {
+			if (dialing[i] < '0' || dialing[i] > '9') {
+				printf("Given phone number '%s' has invalid digits!\n", dialing);
+				goto exit;
+			}
+		}
+
+		dial_string[d].tone = TONE_GUARD; dial_string[d++].length = 0.350 * (double)samplerate; /* off-hook */
+		dial_string[d].console = 's';
+		dial_string[d].tone = TONE_CONNECT; dial_string[d++].length = 0.050 * (double)samplerate; /* seize */
+		dial_string[d].console = '-';
+		dial_string[d].tone = TONE_GUARD; dial_string[d++].length = 1.000 * (double)samplerate; /* pause */
+		for (i = 0; station_id[i]; i++) {
+			pulses = station_id[i] - '0';
+			if (pulses == 0)
+				pulses = 10;
+			dial_string[d].console = station_id[i];
+			for (p = 1; p <= pulses; p++) {
+				if ((p & 1) == 1)
+					tone = TONE_SILENCE;
+				else
+					tone = TONE_GUARD;
+				dial_string[d].tone = TONE_CONNECT; dial_string[d++].length = 0.025 * (double)samplerate; /* mark */
+				dial_string[d].tone = tone; dial_string[d++].length = 0.025 * (double)samplerate; /* space */
+			}
+			dial_string[d].tone = tone; dial_string[d++].length = 0.190 * (double)samplerate; /* after digit */
+		}
+		dial_string[d].console = '-';
+		dial_string[d].tone = TONE_SILENCE; dial_string[d++].length = 2.000 * (double)samplerate; /* pause */
+		for (i = 0; dialing[i]; i++) {
+			pulses = dialing[i] - '0';
+			if (pulses == 0)
+				pulses = 10;
+			dial_string[d].console = dialing[i];
+			for (p = 1; p <= pulses; p++) {
+				dial_string[d].tone = TONE_CONNECT; dial_string[d++].length = 0.060 * (double)samplerate; /* mark */
+				dial_string[d].tone = TONE_GUARD; dial_string[d++].length = 0.040 * (double)samplerate; /* space */
+			}
+			dial_string[d].tone = TONE_GUARD; dial_string[d++].length = 0.400 * (double)samplerate; /* after digit */
+		}
+		dial_string[d].console = '\n';
+	} else {
+		for (i = 0; i < 750; i += 50) {
+			dial_string[d].tone = TONE_DISCONNECT; dial_string[d++].length = 0.025 * (double)samplerate; /* mark */
+			dial_string[d].tone = TONE_GUARD; dial_string[d++].length = 0.025 * (double)samplerate; /* space */
+		}
+	}
+	dial_string[d].tone = TONE_SILENCE; dial_string[d++].length = 0.600 * (double)samplerate; /* pause */
+	dial_string[d].tone = TONE_DONE; dial_string[d++].length = 0; /* end */
+
+#ifdef HAVE_ALSA
+	/* init sound */
+	audio = sound_open(audiodev, NULL, NULL, 1, 0.0, samplerate, latspl, 1.0, 4000.0);
+	if (!audio) {
+		PDEBUG(DBNETZ, DEBUG_ERROR, "No sound device!\n");
+		goto exit;
+	}
+#endif
+
+	/* open wave */
+	if (write_tx_wave) {
+		rc = wave_create_record(&wave_tx_rec, write_tx_wave, samplerate, 1, 1.0);
+		if (rc < 0) {
+			PDEBUG(DBNETZ, DEBUG_ERROR, "Failed to create WAVE recoding instance!\n");
+			goto exit;
+		}
+	}
+#ifndef HAVE_ALSA
+	else {
+		PDEBUG(DBNETZ, DEBUG_ERROR, "No sound support compiled in, so you need to write to a wave file. See help!\n");
+		goto exit;
+	}
+#endif
+
+#ifdef HAVE_ALSA
+	/* start sound */
+	sound_start(audio);
+#endif
+
+	PDEBUG(DBNETZ, DEBUG_ERROR, "Start audio after pause...\n");
+
+	process_signal();
+
+exit:
+	/* close wave */
+	wave_destroy_record(&wave_tx_rec);
+
+#ifdef HAVE_ALSA
+	/* exit sound */
+	if (audio)
+		sound_close(audio);
+#endif
+
+	return 0;
+}
+
diff --git a/src/imts/dsp.c b/src/imts/dsp.c
new file mode 100644
index 0000000..52b388f
--- /dev/null
+++ b/src/imts/dsp.c
@@ -0,0 +1,564 @@
+/* MTS/IMTS signal processing
+ *
+ * (C) 2019 by Andreas Eversberg <jolly@eversberg.eu>
+ * All Rights Reserved
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#define CHAN imts->sender.kanal
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <math.h>
+#include "../libsample/sample.h"
+#include "../libdebug/debug.h"
+#include "../libtimer/timer.h"
+#include "../libmobile/call.h"
+#include "imts.h"
+#include "dsp.h"
+
+/* uncomment to debug decoder */
+//#define DEBUG_DECODER
+
+#define PI		3.1415927
+
+/* signaling */
+#define MAX_DEVIATION	7000.0				/* signaling tone plus some extra to calibrate */
+#define MAX_MODULATION	3000.0				/* FIXME */
+#define DBM0_DEVIATION	2500.0				/* deviation of dBm0 (with emphasis) */
+#define TX_PEAK_TONE	(5000.0 / DBM0_DEVIATION)	/* signaling tone level (5khz, no emphasis) */
+#define RX_MIN_AMPL	0.25				/* FIXME: Minimum level to detect tone */
+/* Note that 75 is half of the distance between two tones (2000 and 2150 Hz)
+ * An error of more than 50 causes too much toggeling between two tones,
+ * less would take too long to detect the tone and maybe not detect it, if
+ * it is too far off the expected frequency.
+ */
+#define RX_MIN_FREQ	50.0				/* minimum frequency error to detect tone */
+#define MAX_DISPLAY	(MAX_DEVIATION / DBM0_DEVIATION)/* as much as MAX_DEVIATION */
+/* Note that FILTER_BW / SUSTAIN and QUAL_TIME sum up and should not exeed minimum tone length */
+#define RX_FILTER_BW	100.0				/* amplitude filter (causes delay) */
+#define RX_SUSTAIN	0.010				/* how long a tone must sustain until detected (causes delay) */
+#define RX_QUAL_TIME	0.005				/* how long a quality measurement lasts after detecting a tone */
+
+/* carrier loss detection */
+#define MUTE_TIME	0.1	/* time to mute after loosing signal */
+#define DELAY_TIME	0.15	/* delay, so we don't hear the noise before squelch mutes (MTS mode) */
+#define LOSS_TIME	12.0	/* duration of signal loss before release (FIXME: what was the actual duration ???) */
+#define SIGNAL_DETECT	0.3	/* time to have a steady signal to detect phone (used by MTS) */
+
+#define DISPLAY_INTERVAL 0.04
+
+/* signaling tones to be modulated */
+static double tones[NUM_SIG_TONES] = {
+	2150.0,		/* guard */
+	2000.0,		/* idle */
+	1800.0,		/* seize */
+	1633.0,		/* connect */
+	1336.0,		/* disconnect */
+	600.0,		/* MTS 600 Hz */
+	1500.0,		/* MTS 1500 Hz */
+};
+
+/* signaling tones to be demodulated (a subset of tones above) */
+static double tone_response[NUM_SIG_TONES] = {
+	0.71,		/* guard */
+	1.08,		/* idle */
+	1.01,		/* seize */
+	1.04,		/* connect */
+	0.71,		/* disconnect */
+	0.71,		/* MTS 600 Hz */
+	0.71,		/* MTS 1500 Hz */
+};
+
+/* all tone, with signaling tones first */
+static const char *tone_names[] = {
+	"GUARD tone",
+	"IDLE tone",
+	"SEIZE tone",
+	"CONNECT tone",
+	"DISCONNECT tone",
+	"600 Hz Tone",
+	"1500 Hz Tone",
+	"SILENCE",
+	"NOISE",
+	"DIALTONE",
+};
+
+#define DIALTONE1	350.0
+#define DIALTONE2	440.0
+
+/* table for fast sine generation */
+static sample_t dsp_sine_tone[65536];
+
+/* global init for audio processing */
+void dsp_init(void)
+{
+	int i;
+	double s;
+
+	PDEBUG(DDSP, DEBUG_DEBUG, "Generating sine tables.\n");
+	for (i = 0; i < 65536; i++) {
+		s = sin((double)i / 65536.0 * 2.0 * PI);
+		dsp_sine_tone[i] = s * TX_PEAK_TONE;
+	}
+}
+
+/* Init transceiver instance. */
+int dsp_init_transceiver(imts_t *imts, double squelch_db, int ptt)
+{
+	int rc = -1;
+
+	PDEBUG_CHAN(DDSP, DEBUG_DEBUG, "Init DSP for Transceiver.\n");
+
+	imts->sample_duration = 1.0 / (double)imts->sender.samplerate;
+
+	/* init squelch */
+	squelch_init(&imts->squelch, imts->sender.kanal, squelch_db, MUTE_TIME, LOSS_TIME);
+
+	/* set modulation parameters */
+	sender_set_fm(&imts->sender, MAX_DEVIATION, MAX_MODULATION, DBM0_DEVIATION, MAX_DISPLAY);
+
+	/* init FM demodulator for tone detection */
+	if (imts->mode == MODE_IMTS) {
+		imts->demod_center = (tones[TONE_GUARD] + tones[TONE_DISCONNECT]) / 2.0;
+		imts->demod_bandwidth = tones[TONE_GUARD] - tones[TONE_DISCONNECT];
+	} else {
+		imts->demod_center = (tones[TONE_1500] + tones[TONE_600]) / 2.0;
+		imts->demod_bandwidth = tones[TONE_1500] - tones[TONE_600];
+	}
+	rc = fm_demod_init(&imts->demod, (double)imts->sender.samplerate, imts->demod_center, imts->demod_bandwidth);
+	if (rc < 0)
+		goto error;
+	/* use fourth order (2 iter) filter, since it is as fast as second order (1 iter) filter */
+	/* NOTE: CHANGE TONE RESPONSES ABOVE, IF YOU CHANGE FILTER */
+	iir_lowpass_init(&imts->demod_freq_lp, RX_FILTER_BW, (double)imts->sender.samplerate, 2);
+	iir_lowpass_init(&imts->demod_ampl_lp, RX_FILTER_BW, (double)imts->sender.samplerate, 2);
+
+	/* tones */
+	imts->tone_idle_phaseshift65536 = 65536.0 / ((double)imts->sender.samplerate / tones[TONE_IDLE]);
+	imts->tone_seize_phaseshift65536 = 65536.0 / ((double)imts->sender.samplerate / tones[TONE_SEIZE]);
+	imts->tone_600_phaseshift65536 = 65536.0 / ((double)imts->sender.samplerate / tones[TONE_600]);
+	imts->tone_1500_phaseshift65536 = 65536.0 / ((double)imts->sender.samplerate / tones[TONE_1500]);
+	imts->tone_dialtone_phaseshift65536[0] = 65536.0 / ((double)imts->sender.samplerate / DIALTONE1);
+	imts->tone_dialtone_phaseshift65536[1] = 65536.0 / ((double)imts->sender.samplerate / DIALTONE2);
+
+	/* demod init */
+	imts->demod_current_tone = TONE_SILENCE;
+	imts->demod_sig_tone = 0;
+	imts->demod_last_tone = TONE_SILENCE;
+
+	/* delay buffer */
+	if (ptt) {
+		PDEBUG_CHAN(DDSP, DEBUG_DEBUG, "Push to talk: Adding delay buffer to remove noise when singal gets lost.\n");
+		imts->delay_max = (int)((double)imts->sender.samplerate * DELAY_TIME);
+		imts->delay_spl = calloc(imts->delay_max, sizeof(*imts->delay_spl));
+		if (!imts->delay_spl) {
+			PDEBUG(DDSP, DEBUG_ERROR, "No mem for delay buffer!\n");
+			goto error;
+		}
+	}
+
+	imts->dmp_tone_level = display_measurements_add(&imts->sender.dispmeas, "Tone Level", "%.1f %%", DISPLAY_MEAS_LAST, DISPLAY_MEAS_LEFT, 0.0, 150.0, 100.0);
+	imts->dmp_tone_quality = display_measurements_add(&imts->sender.dispmeas, "Tone Quality", "%.1f %%", DISPLAY_MEAS_LAST, DISPLAY_MEAS_LEFT, 0.0, 150.0, 100.0);
+
+	return 0;
+
+error:
+	dsp_cleanup_transceiver(imts);
+	return rc;
+}
+
+/* Cleanup transceiver instance. */
+void dsp_cleanup_transceiver(imts_t *imts)
+{
+	PDEBUG_CHAN(DDSP, DEBUG_DEBUG, "Cleanup DSP for Transceiver.\n");
+
+	fm_demod_exit(&imts->demod);
+	if (imts->delay_spl) {
+		free(imts->delay_spl);
+		imts->delay_spl = NULL;
+	}
+}
+
+/* Generate audio stream from tone. Keep phase for next call of function. */
+static int generate_tone(imts_t *imts, sample_t *samples, int length)
+{
+	double phaseshift[2] = {0,0}, phase[2]; // make gcc happy
+	int i;
+
+	switch (imts->tone) {
+	case TONE_IDLE:
+		phaseshift[0] = imts->tone_idle_phaseshift65536;
+		break;
+	case TONE_SEIZE:
+		phaseshift[0] = imts->tone_seize_phaseshift65536;
+		break;
+	case TONE_600:
+		phaseshift[0] = imts->tone_600_phaseshift65536;
+		break;
+	case TONE_1500:
+		phaseshift[0] = imts->tone_1500_phaseshift65536;
+		break;
+	case TONE_DIALTONE:
+		phaseshift[0] = imts->tone_dialtone_phaseshift65536[0];
+		phaseshift[1] = imts->tone_dialtone_phaseshift65536[1];
+		break;
+	case TONE_SILENCE:
+		break;
+	default:
+		PDEBUG_CHAN(DDSP, DEBUG_ERROR, "Software error, unsupported tone, please fix!\n");
+		return length;
+	}
+
+	/* don't send more than given length */
+	if (imts->tone_duration && length > imts->tone_duration)
+		length = imts->tone_duration;
+
+	phase[0] = imts->tone_phase65536[0];
+	phase[1] = imts->tone_phase65536[1];
+
+	switch (imts->tone) {
+	case TONE_SILENCE:
+		memset(samples, 0, length * sizeof(*samples));
+		phase[0] = phase[1] = 0;
+		break;
+	case TONE_DIALTONE:
+		for (i = 0; i < length; i++) {
+			*samples = dsp_sine_tone[(uint16_t)phase[0]];
+			*samples += dsp_sine_tone[(uint16_t)phase[1]];
+			*samples++ /= 4.0; /* not full volume */
+			phase[0] += phaseshift[0];
+			if (phase[0] >= 65536)
+				phase[0] -= 65536;
+			phase[1] += phaseshift[1];
+			if (phase[1] >= 65536)
+				phase[1] -= 65536;
+		}
+		break;
+	default:
+		for (i = 0; i < length; i++) {
+			*samples++ = dsp_sine_tone[(uint16_t)phase[0]];
+			phase[0] += phaseshift[0];
+			if (phase[0] >= 65536)
+				phase[0] -= 65536;
+		}
+	}
+
+	imts->tone_phase65536[0] = phase[0];
+	imts->tone_phase65536[1] = phase[1];
+
+	/* if tone has been sent completely, tell IMTS call process */
+	if (imts->tone_duration) {
+		imts->tone_duration -= length;
+		if (imts->tone_duration == 0)
+			imts_tone_sent(imts, imts->tone);
+	}
+
+	return length;
+}
+
+/* Provide stream of audio toward radio unit */
+void sender_send(sender_t *sender, sample_t *samples, uint8_t *power, int length)
+{
+	imts_t *imts = (imts_t *) sender;
+	int count;
+
+	memset(power, 1, length);
+
+again:
+	switch (imts->dsp_mode) {
+	case DSP_MODE_OFF:
+		memset(power, 0, length);
+		memset(samples, 0, length * sizeof(*samples));
+		break;
+	case DSP_MODE_TONE:
+		memset(power, 1, length);
+		count = generate_tone(imts, samples, length);
+		samples += count;
+		length -= count;
+		if (length)
+			goto again;
+		break;
+	case DSP_MODE_AUDIO:
+		memset(power, 1, length);
+		jitter_load(&imts->sender.dejitter, samples, length);
+		if (imts->pre_emphasis)
+			pre_emphasis(&imts->estate, samples, length);
+		break;
+	}
+}
+
+static void tone_demod(imts_t *imts, sample_t *samples, int length)
+{
+	sample_t frequency[length], amplitude[length];
+	sample_t I[length], Q[length];
+	double f, amp;
+	int i, t, tone = 0; // make GCC happy
+
+	/* demod frquency */
+	fm_demodulate_real(&imts->demod, frequency, length, samples, I, Q);
+	iir_process(&imts->demod_freq_lp, frequency, length);
+
+	/* demod amplitude
+	 * peak amplitude is the length of I/Q vector
+	 * since we filter out the unwanted modulation product, the vector is only half of length
+	 */
+	for (i = 0; i < length; i++)
+		amplitude[i] = sqrt(I[i] * I[i] + Q[i] * Q[i]) * 2.0;
+	iir_process(&imts->demod_ampl_lp, amplitude, length);
+
+	/* check result to detect tone or loss or change */
+	for (i = 0; i < length; i++) {
+		/* duration until change in tone */
+		imts->demod_duration += imts->sample_duration;
+		/* correct FSK amplitude */
+		amplitude[i] /= TX_PEAK_TONE;
+		/* see what we detect at this moment; tone is set */
+		if (amplitude[i] < RX_MIN_AMPL) {
+			/* silence */
+			tone = TONE_SILENCE;
+		} else {
+			/* tone */
+			f = frequency[i] + imts->demod_center;
+			if (imts->mode == MODE_IMTS) {
+				for (t = TONE_IDLE; t <= TONE_DISCONNECT; t++) {
+					/* check for frequency */
+					if (fabs(f - tones[t]) < RX_MIN_FREQ) {
+						tone = t;
+						break;
+					}
+				}
+			} else {
+				for (t = TONE_600; t <= TONE_1500; t++) {
+					/* check for frequency */
+					if (fabs(f - tones[t]) < RX_MIN_FREQ) {
+						tone = t;
+						break;
+					}
+				}
+			}
+			/* noise */
+			if (t == NUM_SIG_TONES)
+				tone = TONE_NOISE;
+		}
+#ifdef DEBUG_DECODER
+		/* debug decoder */
+		if (tone < NUM_SIG_TONES) {
+			static int debug_interval = 0;
+			if (++debug_interval == 30) {
+				debug_interval = 0;
+				printf("decoder debug: diff=%s %.0f  ", debug_amplitude((f - tones[t]) / RX_MIN_FREQ), fabs(f - tones[t]));
+				amp = amplitude[i] / tone_response[t];
+				printf("ampl=%s %.0f%%\n", debug_amplitude(amp), amp * 100.0);
+			}
+		}
+#endif
+		/* display level of tones, or zero at noise/silence */
+		imts->display_interval +=imts->sample_duration;
+		if (imts->display_interval >= DISPLAY_INTERVAL) {
+			if (tone < NUM_SIG_TONES)
+				amp = amplitude[i] / tone_response[tone];
+			else
+				amp = 0.0;
+			display_measurements_update(imts->dmp_tone_level, amp * 100.0, 0.0);
+			imts->display_interval -= DISPLAY_INTERVAL;
+		}
+		/* check for tone change */
+		if (tone != imts->demod_current_tone) {
+#ifdef DEBUG_DECODER
+			printf("decoder debug: %s detected, waiting to sustain\n", tone_names[tone]);
+#endif
+			if (imts->demod_sig_tone) {
+				PDEBUG_CHAN(DDSP, DEBUG_DEBUG, "Lost %s (duration %.0f ms)\n", tone_names[imts->demod_current_tone], imts->demod_duration * 1000.0);
+				imts_lost_tone(imts, imts->demod_current_tone, imts->demod_duration);
+				imts->demod_sig_tone = 0;
+			}
+			imts->demod_current_tone = tone;
+			imts->demod_sustain = 0.0;
+		} else if (imts->demod_sustain < RX_SUSTAIN) {
+			imts->demod_sustain += imts->sample_duration;
+			/* when sustained. also tone must change to prevent flapping; lost signaling tone can be detected again */
+			if (imts->demod_sustain >= RX_SUSTAIN && (imts->demod_current_tone != imts->demod_last_tone || !imts->demod_sig_tone)) {
+				if (imts->demod_current_tone < NUM_SIG_TONES) {
+					amp = amplitude[i] / tone_response[imts->demod_current_tone];
+					imts->demod_sig_tone = 1;
+					imts->demod_quality_time = 0.0;
+					imts->demod_quality_count = 0;
+					imts->demod_quality_value = 0.0;
+				} else {
+					amp = amplitude[i];
+					imts->demod_sig_tone = 0;
+				}
+				PDEBUG_CHAN(DDSP, DEBUG_DEBUG, "Detected %s (level %.0f%%)\n", tone_names[imts->demod_current_tone], amp * 100);
+				imts_receive_tone(imts, imts->demod_current_tone, imts->demod_duration, amp);
+				imts->demod_last_tone = imts->demod_current_tone;
+				imts->demod_duration = imts->demod_sustain;
+			} else if (imts->demod_sig_tone && imts->demod_quality_time < RX_QUAL_TIME) {
+				f = frequency[i] + imts->demod_center;
+				imts->demod_quality_time += imts->sample_duration;
+				imts->demod_quality_count++;
+				imts->demod_quality_value += fabs((f - tones[imts->demod_current_tone])) / RX_MIN_FREQ;
+				if (imts->demod_quality_time >= RX_QUAL_TIME) {
+					double quality = 1.0 - imts->demod_quality_value / (double)imts->demod_quality_count * 2.0;
+					if (quality < 0)
+						quality = 0;
+					PDEBUG_CHAN(DDSP, DEBUG_DEBUG, "Quality: %.0f%%\n", quality * 100.0);
+					display_measurements_update(imts->dmp_tone_quality, quality * 100.0, 0.0);
+				}
+			}	
+		}
+	}
+}
+
+static void delay_audio(imts_t *imts, sample_t *samples, int count)
+{
+	sample_t *spl, s;
+	int pos, max;
+	int i;
+
+	spl = imts->delay_spl;
+	pos = imts->delay_pos;
+	max = imts->delay_max;
+
+	/* feed audio though delay buffer */
+	for (i = 0; i < count; i++) {
+		s = samples[i];
+		samples[i] = spl[pos];
+		spl[pos] = s;
+		if (++pos == max)
+			pos = 0;
+	}
+
+	imts->delay_pos = pos;
+}
+
+/* Process received audio stream from radio unit. */
+void sender_receive(sender_t *sender, sample_t *samples, int length, double rf_level_db)
+{
+	imts_t *imts = (imts_t *) sender;
+
+	/* no processing if off */
+	if (imts->dsp_mode == DSP_MODE_OFF)
+		return;
+
+	/* process signal mute/loss, also for signalling tone */
+	switch (squelch(&imts->squelch, rf_level_db, (double)length * imts->sample_duration)) {
+	case SQUELCH_LOSS:
+		imts_loss_indication(imts, LOSS_TIME);
+		/* FALLTHRU */
+	case SQUELCH_MUTE:
+		if (imts->mode == MODE_MTS && !imts->is_mute) {
+			PDEBUG_CHAN(DDSP, DEBUG_INFO, "Low RF level, muting.\n");
+			memset(imts->delay_spl, 0, sizeof(*samples) * imts->delay_max);
+			imts->is_mute = 1;
+		}
+		memset(samples, 0, sizeof(*samples) * length);
+		/* signal is gone */
+		imts->rf_signal = 0;
+		break;
+	default:
+		if (imts->is_mute) {
+			PDEBUG_CHAN(DDSP, DEBUG_INFO, "High RF level, unmuting.\n");
+			imts->is_mute = 0;
+		}
+		/* detect signal, if it is steady for a while */
+		if (imts->rf_signal < SIGNAL_DETECT * (double)imts->sender.samplerate) {
+			/* only do this, if signal has not been detected yet */
+			imts->rf_signal += length;
+			if (imts->rf_signal >= SIGNAL_DETECT * (double)imts->sender.samplerate)
+				imts_signal_indication(imts);
+		}
+		break;
+	}
+
+	/* FM/AM demod */
+	tone_demod(imts, samples, length);
+
+	/* delay audio to prevent noise before squelch mutes (don't do that for signaling tones) */
+	if (imts->delay_spl)
+		delay_audio(imts, samples, length);
+
+	/* Forward audio to network (call process). */
+	if (imts->dsp_mode == DSP_MODE_AUDIO && imts->callref) {
+		sample_t *spl;
+		int pos;
+		int count;
+		int i;
+
+		if (imts->de_emphasis) {
+			dc_filter(&imts->estate, samples, length);
+			de_emphasis(&imts->estate, samples, length);
+		}
+		count = samplerate_downsample(&imts->sender.srstate, samples, length);
+		spl = imts->sender.rxbuf;
+		pos = imts->sender.rxbuf_pos;
+		for (i = 0; i < count; i++) {
+			spl[pos++] = samples[i];
+			if (pos == 160) {
+				call_up_audio(imts->callref, spl, 160);
+				pos = 0;
+			}
+		}
+		imts->sender.rxbuf_pos = pos;
+	} else
+		imts->sender.rxbuf_pos = 0;
+
+}
+
+const char *imts_dsp_mode_name(enum dsp_mode mode)
+{
+        static char invalid[16];
+
+	switch (mode) {
+	case DSP_MODE_OFF:
+		return "TRX OFF";
+	case DSP_MODE_TONE:
+		return "TONE";
+	case DSP_MODE_AUDIO:
+		return "AUDIO";
+	}
+
+	sprintf(invalid, "invalid(%d)", mode);
+	return invalid;
+}
+
+void imts_set_dsp_mode(imts_t *imts, enum dsp_mode mode, int tone, double duration, int reset_demod)
+{
+	/* reset demod */
+	if (reset_demod) {
+		imts->demod_current_tone = TONE_SILENCE;
+		imts->demod_sig_tone = 0;
+		imts->demod_last_tone = TONE_SILENCE;
+		imts->demod_duration = 0.0;
+	}
+
+	if (imts->dsp_mode != mode) {
+		PDEBUG_CHAN(DDSP, DEBUG_DEBUG, "DSP mode %s -> %s\n", imts_dsp_mode_name(imts->dsp_mode), imts_dsp_mode_name(mode));
+		imts->dsp_mode = mode;
+	}
+
+	if (mode == DSP_MODE_TONE) {
+		if (duration)
+			PDEBUG_CHAN(DDSP, DEBUG_DEBUG, "Start sending %s for %.3f seconds.\n", tone_names[tone], duration);
+		else
+			PDEBUG_CHAN(DDSP, DEBUG_DEBUG, "Start sending %s continuously.\n", tone_names[tone]);
+		imts->tone = tone;
+		imts->tone_duration = duration * (double)imts->sender.samplerate;
+	}
+}
+
diff --git a/src/imts/dsp.h b/src/imts/dsp.h
new file mode 100644
index 0000000..921d2d9
--- /dev/null
+++ b/src/imts/dsp.h
@@ -0,0 +1,6 @@
+
+void dsp_init(void);
+int dsp_init_transceiver(imts_t *imts, double squelch_db, int ptt);
+void dsp_cleanup_transceiver(imts_t *imts);
+void imts_set_dsp_mode(imts_t *imts, enum dsp_mode mode, int tone, double duration, int reset_demod);
+
diff --git a/src/imts/image.c b/src/imts/image.c
new file mode 100644
index 0000000..8557f1b
--- /dev/null
+++ b/src/imts/image.c
@@ -0,0 +1,77 @@
+#include <stdio.h>
+#include <string.h>
+#include "../libmobile/image.h"
+
+const char *image[] = {
+	"@W",
+	"IMTS / MTS is back!",
+	"",
+	NULL
+};
+
+void print_image(void)
+{
+	int i, j;
+
+	for (i = 0; image[i]; i++) {
+		for (j = 0; j < (int)strlen(image[i]); j++) {
+			if (image[i][j] == '@') {
+				j++;
+				switch(image[i][j]) {
+				case 'k': /* black */
+					printf("\033[0;30m");
+					break;
+				case 'r': /* red */
+					printf("\033[0;31m");
+					break;
+				case 'g': /* green */
+					printf("\033[0;32m");
+					break;
+				case 'y': /* yellow */
+					printf("\033[0;33m");
+					break;
+				case 'b': /* blue */
+					printf("\033[0;34m");
+					break;
+				case 'm': /* magenta */
+					printf("\033[0;35m");
+					break;
+				case 'c': /* cyan */
+					printf("\033[0;36m");
+					break;
+				case 'w': /* white */
+					printf("\033[0;37m");
+					break;
+				case 'K': /* bright black */
+					printf("\033[1;30m");
+					break;
+				case 'R': /* bright red */
+					printf("\033[1;31m");
+					break;
+				case 'G': /* bright green */
+					printf("\033[1;32m");
+					break;
+				case 'Y': /* bright yellow */
+					printf("\033[1;33m");
+					break;
+				case 'B': /* bright blue */
+					printf("\033[1;34m");
+					break;
+				case 'M': /* bright magenta */
+					printf("\033[1;35m");
+					break;
+				case 'C': /* bright cyan */
+					printf("\033[1;36m");
+					break;
+				case 'W': /* bright white */
+					printf("\033[1;37m");
+					break;
+				}
+			} else
+				printf("%c", image[i][j]);
+		}
+		printf("\n");
+	}
+	printf("\033[0;39m");
+}
+
diff --git a/src/imts/imts.c b/src/imts/imts.c
new file mode 100644
index 0000000..2056806
--- /dev/null
+++ b/src/imts/imts.c
@@ -0,0 +1,1326 @@
+/* MTS/IMTS protocol handling
+ *
+ * (C) 2019 by Andreas Eversberg <jolly@eversberg.eu>
+ * All Rights Reserved
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * 
+ * How it works:
+ *
+ * (There should be a more detailed description of the call process!)
+ *
+ * There are call states defined by imts->state.
+ * imts_receive_tone() is called whenever a tone/silence/noise is detected.
+ * imts_lost_tone() is calles as soon as (only) a tone is gone.
+ * imts_timeout() is called when the timer has timed out.
+ * All these callbacks are used to process the call setup and disconnect.
+ * The imts_timeout() function will not only handle failures due to timeouts,
+ * but also E.g. end of pulsed digit or seize detection.
+ *
+ */
+
+#define CHAN imts->sender.kanal
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include "../libsample/sample.h"
+#include "../libdebug/debug.h"
+#include "../libtimer/timer.h"
+#include "../libmobile/call.h"
+#include "../libmncc/cause.h"
+#include "imts.h"
+#include "dsp.h"
+
+#define CUT_OFF_EMPHASIS_IMTS	796.0 /* FIXME: really 200 uS time constant? */
+
+/* Call reference for calls from mobile station to network
+   This offset of 0x400000000 is required for MNCC interface. */
+static int new_callref = 0x40000000;
+
+/* band info */
+#define VHF_LOW 0
+#define VHF_HIGH 1
+#define UHF 2
+static const char *band_name[] = {
+	"VHF-Low Band",
+	"VHF-High Band",
+	"UHF Band",
+};
+
+/* I measured VHF_HIGH deviation with 5000, others told me that all bands are 5000. */
+#define DEV_VHF_LOW	5000.0
+#define DEV_VHF_HIGH	5000.0
+#define DEV_UHF		5000.0
+
+static struct channel_info {
+	int		band;		/* which band it belongs to */
+	char		*name;		/* name of channel */
+	double		downlink_mhz;	/* base station frequency */
+	double		uplink_mhz;	/* mobile station frequency */
+	int		canada_only;	/* channel used in canada only */
+} channel_info[] = {
+	{ VHF_LOW,	"ZO",	35.26,		43.26,		0 },
+	{ VHF_LOW,	"ZF",	35.30,		43.30,		0 },
+	{ VHF_LOW,	"ZM",	35.38,		43.38,		0 },
+	{ VHF_LOW,	"ZH",	35.34,		43.34,		0 },
+	{ VHF_LOW,	"ZA",	35.42,		43.32,		0 },
+	{ VHF_LOW,	"ZY",	35.46,		43.46,		0 },
+	{ VHF_LOW,	"ZR",	35.50,		43.50,		0 },
+	{ VHF_LOW,	"ZB",	35.54,		43.54,		0 },
+	{ VHF_LOW,	"ZW",	35.62,		43.62,		0 },
+	{ VHF_LOW,	"ZL",	35.66,		43.66,		0 },
+	{ VHF_HIGH,	"JJ",	152.48,		157.74,		1 },
+	{ VHF_HIGH,	"JL",	152.51,		157.77,		0 },
+	{ VHF_HIGH,	"YL",	152.54,		157.80,		0 },
+	{ VHF_HIGH,	"JP",	152.57,		157.83,		0 },
+	{ VHF_HIGH,	"YP",	152.60,		157.86,		0 },
+	{ VHF_HIGH,	"YJ",	152.63,		157.89,		0 },
+	{ VHF_HIGH,	"YK",	152.66,		157.92,		0 },
+	{ VHF_HIGH,	"JS",	152.69,		157.95,		0 },
+	{ VHF_HIGH,	"YS",	152.72,		157.98,		0 },
+	{ VHF_HIGH,	"YR",	152.75,		158.01,		0 },
+	{ VHF_HIGH,	"JK",	152.78,		158.04,		0 },
+	{ VHF_HIGH,	"JR",	152.81,		158.07,		0 },
+	{ VHF_HIGH,	"JW",	152.84,		158.10,		1 },
+	{ UHF,		"QC",	454.375,	459.375,	0 },
+	{ UHF,		"QJ",	454.40,		459.40,		0 },
+	{ UHF,		"QD",	454.425,	459.425,	0 },
+	{ UHF,		"QA",	454.45,		459.45,		0 },
+	{ UHF,		"QE",	454.475,	459.475,	0 },
+	{ UHF,		"QP",	454.50,		459.50,		0 },
+	{ UHF,		"QK",	454.525,	459.525,	0 },
+	{ UHF,		"QB",	454.55,		459.55,		0 },
+	{ UHF,		"QO",	454.575,	459.575,	0 },
+	{ UHF,		"QR",	454.60,		459.60,		0 },
+	{ UHF,		"QY",	454.625,	459.625,	0 },
+	{ UHF,		"QF",	454.65,		459.65,		0 },
+	{ 0, NULL, 0.0, 0.0, 0}
+};
+
+void imts_list_channels(void)
+{
+	int last_band = -1;
+	int i;
+
+	for (i = 0; channel_info[i].name; i++) {
+		if (last_band != channel_info[i].band) {
+			last_band = channel_info[i].band;
+			printf("\n%s:\n\n", band_name[channel_info[i].band]);
+			printf("Channel\t\tDownlink\tUplink\t\tCountry\n");
+			printf("----------------------------------------------------------------\n");
+		}
+		printf("%s\t\t%.3f MHz\t%.3f MHz\t%s\n", channel_info[i].name, channel_info[i].downlink_mhz, channel_info[i].uplink_mhz, (channel_info[i].canada_only) ? "USA + Canada" : "USA");
+	}
+	printf("\n");
+}
+
+/* Timers */
+#define PAGING_TO	4.0	/* Time to wait for the phone to respond */
+#define RINGING_TO	45.0	/* Time to wait for the mobile user to answer */
+#define SEIZE_TO	1.0	/* Time to wait for the phone to seize (Connect tone) */
+#define ANI_TO		1.000	/* Time to wait for first / next digit */
+#define DIALTONE_TO	10.0	/* Time to wait until dialing must be performed */
+#define DIALING_TO	3.0	/* Time to wait until number is recognized as complete */
+#define RELEASE_TO	0.350	/* Time to turn off transmitter before going idle ".. for about 300 ms .." */
+#define ANI_PULSE_TO	0.100	/* Time to detect end of digit */
+#define DIAL_PULSE_TO	0.200	/* Time to detect end of digit */
+#define DISC_PULSE_TO	0.100	/* Time until aborting disconnect detection */
+#define PAGE_PULSE_TO	0.200	/* Time to detect end of digit */
+
+/* Counters */
+#define DISC_COUNT	6	/* Number of pulses to detect disconnect FIXME */
+#define RING_PULSES	40	/* 2 seconds ringer on */
+
+/* Durations */
+#define IDLE_DETECT	0.500	/* Time to detect Idle signal (loopback) */
+#define PAGE_SEIZE	0.400	/* Time to seize channel until start paging pulses FIXME */
+#define PAGE_PAUSE	0.400	/* Time to pause after each digit FIXME */
+#define PAGE_MARK	0.050	/* Mark duration of page pulse */
+#define PAGE_SPACE	0.050	/* Space duration of page pulse */
+#define PAGE_PULSE	0.100	/* Duration of a complete pulse (MTS) */
+#define RING_MARK	0.025	/* Mark duration of ring pulse */
+#define RING_SPACE	0.025	/* Space duration of ring pulse */
+#define RING_OFF	4.0	/* 4 seconds ringer off */
+#define GUARD_TIME	0.200	/* Time until detecting Guard tone from mobile */
+#define SEIZE_TIME	0.300	/* Time until sending Seize tone >= 250 */
+#define SEIZE_LENGTH	0.250	/* Length of Seize */
+#define RECEIVE_TIME	0.200	/* Time until detecting receive signal (Guard tone) from mobile */
+#define ANSWER_TIME	0.200	/* Time until detecting answer signal (Connect tone) from mobile */
+
+const char *imts_state_name(enum imts_state state)
+{
+	static char invalid[16];
+
+	switch (state) {
+	case IMTS_NULL:
+		return "(NULL)";
+	case IMTS_OFF:
+		return "IDLE (off)";
+	case IMTS_IDLE:
+		return "IDLE (tone)";
+	case IMTS_SEIZE:
+		return "SEIZE (mobile call)";
+	case IMTS_ANI:
+		return "ANI (mobile call)";
+	case IMTS_DIALING:
+		return "DIALING (mobile call)";
+	case IMTS_PAGING:
+		return "PAGING (station call)";
+	case IMTS_RINGING:
+		return "RINGING (station call)";
+	case IMTS_CONVERSATION:
+		return "CONVERSATION";
+	case IMTS_RELEASE:
+		return "RELEASE";
+	case IMTS_PAGING_TEST:
+		return "PAGING TEST";
+	case IMTS_DETECTOR_TEST:
+		return "DETECTOR TEST";
+	}
+
+	sprintf(invalid, "invalid(%d)", state);
+	return invalid;
+}
+
+static void imts_display_status(void)
+{
+	sender_t *sender;
+	imts_t *imts;
+
+	display_status_start();
+	for (sender = sender_head; sender; sender = sender->next) {
+		imts = (imts_t *) sender;
+		display_status_channel(imts->sender.kanal, NULL, imts_state_name(imts->state));
+		if (imts->station_id[0])
+			display_status_subscriber(imts->station_id, NULL);
+	}
+	display_status_end();
+}
+
+static void imts_new_state(imts_t *imts, enum imts_state new_state)
+{
+	if (imts->state == new_state)
+		return;
+	PDEBUG_CHAN(DIMTS, DEBUG_DEBUG, "State change: %s -> %s\n", imts_state_name(imts->state), imts_state_name(new_state));
+	imts->state = new_state;
+	imts_display_status();
+}
+
+/* Convert channel name to frequency number of base station.
+   Set 'uplink' to 1 to get frequency of mobile station. */
+double imts_channel2freq(const char *kanal, int uplink)
+{
+	int i;
+
+	for (i = 0; channel_info[i].name; i++) {
+		if (!strcasecmp(channel_info[i].name, kanal)) {
+			if (uplink == 2)
+				return (channel_info[i].downlink_mhz - channel_info[i].uplink_mhz) * 1e6;
+			else if (uplink)
+				return channel_info[i].uplink_mhz * 1e6;
+			else
+				return channel_info[i].downlink_mhz * 1e6;
+		}
+	}
+
+	return 0.0;
+}
+
+int imts_channel2band(const char *kanal)
+{
+	int i;
+
+	for (i = 0; channel_info[i].name; i++) {
+		if (!strcasecmp(channel_info[i].name, kanal))
+			return channel_info[i].band;
+	}
+
+	return 0.0;
+}
+
+double imts_is_canada_only(const char *kanal)
+{
+	int i;
+
+	for (i = 0; channel_info[i].name; i++) {
+		if (!strcasecmp(channel_info[i].name, kanal))
+			return channel_info[i].canada_only;
+	}
+
+	return 0;
+}
+
+/* global init */
+int imts_init(void)
+{
+	return 0;
+}
+
+static void imts_timeout(struct timer *timer);
+static void imts_go_idle(imts_t *imts);
+static void imts_paging(imts_t *imts, const char *dial_string, int loopback);
+static void imts_detector_test(imts_t *imts, double length_1, double length_2, double length_3);
+
+/* Create transceiver instance and link to a list. */
+int imts_create(const char *kanal, const char *audiodev, int use_sdr, int samplerate, double rx_gain, int pre_emphasis, int de_emphasis, const char *write_rx_wave, const char *write_tx_wave, const char *read_rx_wave, const char *read_tx_wave, int loopback, double squelch_db, int ptt, int station_length, double fast_seize, enum mode mode, const char *operator, double length_1, double length_2, double length_3)
+{
+	imts_t *imts;
+	int rc;
+
+	if (imts_channel2freq(kanal, 0) == 0.0) {
+		PDEBUG(DIMTS, DEBUG_ERROR, "Channel number %s invalid.\n", kanal);
+		return -EINVAL;
+	}
+	if (imts_is_canada_only(kanal)) {
+		PDEBUG(DIMTS, DEBUG_NOTICE, "*******************************************************************************\n");
+		PDEBUG(DIMTS, DEBUG_NOTICE, "Given channel '%s' was only available in Canada with Canadian phones.\n", kanal);
+		PDEBUG(DIMTS, DEBUG_NOTICE, "*******************************************************************************\n");
+	}
+	if (mode == MODE_IMTS && imts_channel2band(kanal) == VHF_LOW) {
+		PDEBUG(DIMTS, DEBUG_NOTICE, "*******************************************************************************\n");
+		PDEBUG(DIMTS, DEBUG_NOTICE, "Given channel '%s' was only available at MTS network.\n", kanal);
+		PDEBUG(DIMTS, DEBUG_NOTICE, "*******************************************************************************\n");
+		return -EINVAL;
+	}
+	if (mode == MODE_MTS && imts_channel2band(kanal) == UHF) {
+		PDEBUG(DIMTS, DEBUG_NOTICE, "*******************************************************************************\n");
+		PDEBUG(DIMTS, DEBUG_NOTICE, "Given channel '%s' was only available at IMTS network.\n", kanal);
+		PDEBUG(DIMTS, DEBUG_NOTICE, "*******************************************************************************\n");
+		return -EINVAL;
+	}
+
+	imts = calloc(1, sizeof(imts_t));
+	if (!imts) {
+		PDEBUG(DIMTS, DEBUG_ERROR, "No memory!\n");
+		return -EIO;
+	}
+
+	PDEBUG(DIMTS, DEBUG_DEBUG, "Creating 'IMTS' instance for channel = %s (sample rate %d).\n", kanal, samplerate);
+
+	imts->station_length = station_length;
+	imts->fast_seize = fast_seize;
+	imts->mode = mode;
+	imts->operator = operator;
+	imts->ptt = ptt;
+
+	/* init general part of transceiver */
+	/* do not enable emphasis, since it is done by imts code, not by common sender code */
+	rc = sender_create(&imts->sender, kanal, imts_channel2freq(kanal, 0), imts_channel2freq(kanal, 1), audiodev, use_sdr, samplerate, rx_gain, 0, 0, write_rx_wave, write_tx_wave, read_rx_wave, read_tx_wave, loopback, PAGING_SIGNAL_NONE);
+	if (rc < 0) {
+		PDEBUG(DIMTS, DEBUG_ERROR, "Failed to init 'Sender' processing!\n");
+		goto error;
+	}
+
+	/* init audio processing */
+	rc = dsp_init_transceiver(imts, squelch_db, ptt);
+	if (rc < 0) {
+		PDEBUG(DIMTS, DEBUG_ERROR, "Failed to init signal processing!\n");
+		goto error;
+	}
+
+	timer_init(&imts->timer, imts_timeout, imts);
+
+	imts->pre_emphasis = pre_emphasis;
+	imts->de_emphasis = de_emphasis;
+	rc = init_emphasis(&imts->estate, samplerate, CUT_OFF_EMPHASIS_IMTS, CUT_OFF_HIGHPASS_DEFAULT, CUT_OFF_LOWPASS_DEFAULT);
+	if (rc < 0)
+		goto error;
+
+	if (length_1 > 0.0 || length_2 > 0.0 || length_3 > 0.0) {
+		imts_detector_test(imts, length_1, length_2, length_3);
+		/* go into detector test state */
+	} else if (loopback) {
+		/* go into loopback test state */
+		imts_paging(imts, "1234567890", loopback);
+	} else {
+		/* go into idle state */
+		imts_go_idle(imts);
+	}
+
+	PDEBUG(DIMTS, DEBUG_NOTICE, "Created channel #%s\n", kanal);
+
+	return 0;
+
+error:
+	imts_destroy(&imts->sender);
+
+	return rc;
+}
+
+/* Destroy transceiver instance and unlink from list. */
+void imts_destroy(sender_t *sender)
+{
+	imts_t *imts = (imts_t *) sender;
+
+	PDEBUG(DIMTS, DEBUG_DEBUG, "Destroying 'IMTS' instance for channel = %s.\n", sender->kanal);
+
+	timer_exit(&imts->timer);
+	dsp_cleanup_transceiver(imts);
+	sender_destroy(&imts->sender);
+	free(sender);
+}
+
+/* Return to IDLE */
+static void imts_go_idle(imts_t *imts)
+{
+	sender_t *sender;
+	imts_t *idle;
+
+	timer_stop(&imts->timer);
+	imts->station_id[0] = '\0'; /* remove station ID before state change, so status is shown correctly */
+
+	for (sender = sender_head; sender; sender = sender->next) {
+		idle = (imts_t *) sender;
+		if (idle == imts)
+			continue;
+		if (idle->state == IMTS_IDLE)
+			break;
+	}
+	if (sender) {
+		PDEBUG(DIMTS, DEBUG_INFO, "Entering IDLE state on channel %s, turning transmitter off.\n", imts->sender.kanal);
+		imts_new_state(imts, IMTS_OFF);
+		imts_set_dsp_mode(imts, DSP_MODE_OFF, 0, 0.0, 0);
+	} else {
+		if (imts->mode == MODE_IMTS) {
+			PDEBUG(DIMTS, DEBUG_INFO, "Entering IDLE state on channel %s, sending 2000 Hz tone.\n", imts->sender.kanal);
+			imts_new_state(imts, IMTS_IDLE);
+			/* also reset detector, so if there is a new call it is answered */
+			imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_IDLE, 0.0, 1);
+		} else {
+			PDEBUG(DIMTS, DEBUG_INFO, "Entering IDLE state on channel %s, sending 600 Hz tone.\n", imts->sender.kanal);
+			imts_new_state(imts, IMTS_IDLE);
+			/* also reset detector, so if there is a new call it is answered */
+			imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_600, 0.0, 1);
+		}
+	}
+}
+
+/* If a channel is occupied, we need to hunt for an IDLE channel to be turned on. */
+static void imts_activate_idle(void)
+{
+	sender_t *sender;
+	imts_t *idle;
+
+	for (sender = sender_head; sender; sender = sender->next) {
+		idle = (imts_t *) sender;
+		if (idle->state == IMTS_OFF)
+			break;
+	}
+	if (sender)
+		imts_go_idle(idle);
+	else
+		PDEBUG(DIMTS, DEBUG_INFO, "All channels are busy now, cannot activate any other channel.\n");
+}
+
+/* Release connection towards mobile station by sending pause for a while. */
+static void imts_release(imts_t *imts)
+{
+	timer_stop(&imts->timer);
+	/* remove station ID before state change, so status is shown correctly */
+	imts->station_id[0] = '\0';
+
+	if (imts->mode == MODE_MTS && imts->state == IMTS_RINGING) {
+		/*
+		 * In MTS mode we abort ringing by sending pulse.
+		 * Afterwards we call imts_release again and turn transmitter off.
+		 */
+		int tone;
+		if (imts->tone == TONE_1500)
+			tone = TONE_600;
+		else
+			tone = TONE_1500;
+		PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Sending pulse to stop ringing of the phone.\n");
+		imts_new_state(imts, IMTS_RELEASE);
+		imts_set_dsp_mode(imts, DSP_MODE_TONE, tone, PAGE_PAUSE, 0);
+	} else {
+		PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Turing transmitter off.\n");
+		if (imts->state != IMTS_RELEASE)
+			imts_new_state(imts, IMTS_RELEASE);
+		imts_set_dsp_mode(imts, DSP_MODE_OFF, 0, 0.0, 0);
+		timer_start(&imts->timer, RELEASE_TO);
+	}
+}
+
+/* Enter detector test state */
+static void imts_detector_test(imts_t *imts, double length_1, double length_2, double length_3)
+{
+	PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Entering detector test state, sending test sequence.\n");
+	imts->detector_test_length_1 = length_1;
+	imts->detector_test_length_2 = length_2;
+	imts->detector_test_length_3 = length_3;
+	imts_new_state(imts, IMTS_DETECTOR_TEST);
+	imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_SILENCE, 1.0, 0);
+	
+}
+
+/* Enter paging state */
+static void imts_paging(imts_t *imts, const char *dial_string, int loopback)
+{
+	/* stop timer, since it may be running while measuring Guard tone at IDLE state */
+	timer_stop(&imts->timer);
+
+	if (loopback)
+		PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Entering paging test state, sending digits %s.\n", dial_string);
+	else
+		PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Entering paging state, sending phone's ID '%s'.\n", dial_string);
+	/* set station ID before state change, so status is shown correctly */
+	strncpy(imts->station_id, dial_string, sizeof(imts->station_id) - 1);
+	imts->tx_page_index = 0;
+	imts->tx_page_pulse = 0;
+	imts_new_state(imts, (loopback) ? IMTS_PAGING_TEST : IMTS_PAGING);
+	imts_activate_idle(); /* must activate another channel right after station is not idle anymore */
+	if (imts->mode == MODE_IMTS) {
+		/* seize channel before dialing */
+		imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_SEIZE, PAGE_SEIZE, 0);
+	} else {
+		/* send single pulse + pause, which causes the call selector to reset */
+		imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_1500, PAGE_PAUSE, 0);
+		/* for loopback test, we need time stamp */
+		imts->tx_page_timestamp = get_time();
+	}
+}
+
+/* Enter ringing state */
+static void imts_ringing(imts_t *imts)
+{
+	PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Received response from mobile phone, ringing.\n");
+	imts->tx_ring_pulse = 0;
+	imts_new_state(imts, IMTS_RINGING);
+	imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_IDLE, RING_MARK, 0);
+	timer_start(&imts->timer, RINGING_TO);
+}
+
+/* Enter conversation state */
+static void imts_answer(imts_t *imts)
+{
+	PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Received answer from mobile phone, conversation started.\n");
+	timer_stop(&imts->timer);
+	imts_new_state(imts, IMTS_CONVERSATION);
+	imts_set_dsp_mode(imts, DSP_MODE_AUDIO, 0, 0.0, 0);
+	imts->rx_disc_pulse = 0;
+}
+
+/* Loss of signal was detected, release active call. */
+void imts_loss_indication(imts_t *imts, double loss_time)
+{
+	/* stop timer */
+	if (imts->mode == MODE_MTS && (imts->state == IMTS_IDLE || imts->state == IMTS_RINGING))
+		timer_stop(&imts->timer);
+
+	if (!imts->ptt && imts->state == IMTS_CONVERSATION) {
+		PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Detected loss of signal after %.1f seconds, releasing.\n", loss_time);
+		imts_release(imts);
+		call_up_release(imts->callref, CAUSE_TEMPFAIL);
+		imts->callref = 0;
+	}
+}
+
+/* if signal is detected, phone picked up */
+void imts_signal_indication(imts_t *imts)
+{
+	/* setup a call from mobile to base station */
+	if (imts->mode == MODE_MTS && imts->state == IMTS_IDLE) {
+		int callref = ++new_callref;
+		int rc;
+
+		PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Detectes RF signal in IDLE mode, calling the opterator at '%s'.\n", imts->operator);
+		rc = call_up_setup(callref, NULL, imts->operator);
+		if (rc < 0) {
+			PDEBUG_CHAN(DANETZ, DEBUG_NOTICE, "Call rejected (cause %d), releasing!\n", -rc);
+			imts_release(imts);
+			return;
+		}
+		imts->callref = callref;
+		imts_new_state(imts, IMTS_CONVERSATION);
+		imts_set_dsp_mode(imts, DSP_MODE_AUDIO, 0, 0.0, 0);
+	}
+
+	/* answer a call from base station to mobile */
+	if (imts->mode == MODE_MTS && imts->state == IMTS_RINGING) {
+		PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Detected RF signal, mobile is now transmitting.\n");
+		call_up_answer(imts->callref, imts->station_id);
+		imts_answer(imts);
+	}
+}
+
+/* decode seize from mobile */
+static void imts_receive_seize(imts_t *imts, int tone)
+{
+	/* other tone stops IDLE / GUARD timer */
+	timer_stop(&imts->timer);
+
+	switch (tone) {
+	case TONE_IDLE:
+	case TONE_600:
+		timer_start(&imts->timer, IDLE_DETECT);
+		break;
+	case TONE_GUARD:
+		imts->rx_guard_timestamp = get_time();
+		if (imts->fast_seize)
+			timer_start(&imts->timer, imts->fast_seize);
+		break;
+	case TONE_CONNECT:
+		if (imts->last_tone == TONE_GUARD && imts->rx_guard_duration >= GUARD_TIME) {
+			PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Received seize (Guard + Connect tone) from mobile phone.\n");
+			PDEBUG_CHAN(DIMTS, DEBUG_INFO, " -> Guard tone duration: %.0f ms (level %.0f%%)\n", (get_time() - imts->rx_guard_timestamp) * 1000.0, imts->last_sigtone_amplitude * 100.0);
+			imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_SILENCE, 0.0, 0);
+			imts_new_state(imts, IMTS_SEIZE);
+			imts_activate_idle(); /* must activate another channel right after station is not idle anymore */
+			timer_start(&imts->timer, SEIZE_TIME);
+		}
+		break;
+	default:
+		;
+	}
+}
+
+/* decode ANI digits */
+static void imts_receive_ani(imts_t *imts, int tone)
+{
+	/* wait for connect tone the first time */
+	if (!imts->rx_ani_totpulses && tone != TONE_CONNECT)
+		return;
+
+	switch (tone) {
+	case TONE_CONNECT:
+		/* pulse detected */
+		imts->rx_ani_pulse++;
+		imts->rx_ani_totpulses++;
+		if (imts->rx_ani_pulse > 10) {
+			PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Received too many pulses, releasing!\n");
+			imts_release(imts);
+			break;
+		}
+		PDEBUG_CHAN(DIMTS, DEBUG_DEBUG, "Detected ANI pulse #%d.\n", imts->rx_ani_pulse);
+		timer_start(&imts->timer, ANI_PULSE_TO);
+		break;
+	case TONE_GUARD:
+		/* even pulse completed */
+		if ((imts->rx_ani_totpulses & 1)) {
+			PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Parity error: Received Guard tone after %d (odd) pulses, releasing!\n", imts->rx_ani_totpulses);
+			imts_release(imts);
+			break;
+		}
+		timer_start(&imts->timer, ANI_PULSE_TO);
+		break;
+	case TONE_SILENCE:
+		/* odd pulse completed */
+		if (!(imts->rx_ani_totpulses & 1)) {
+			PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Parity error: Received silence after %d (even) pulses, releasing!\n", imts->rx_ani_totpulses);
+			imts_release(imts);
+			break;
+		}
+		timer_start(&imts->timer, ANI_PULSE_TO);
+		break;
+	default:
+		/* received noise */
+		PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Received noise while dialing, releasing!\n");
+		imts_release(imts);
+	}
+}
+
+/* decode dialing digits */
+static void imts_receive_dialing(imts_t *imts, int tone)
+{
+	switch (tone) {
+	case TONE_CONNECT:
+		/* turn off dialtone */
+		if (!imts->dial_number[0] && !imts->rx_dial_pulse)
+			imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_SILENCE, 0.0, 0);
+		/* pulse detected */
+		imts->rx_dial_pulse++;
+		if (imts->rx_dial_pulse > 10) {
+			PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Received too many pulses, releasing!\n");
+			imts_release(imts);
+			break;
+		}
+		PDEBUG_CHAN(DIMTS, DEBUG_DEBUG, "Detected dialing pulse #%d.\n", imts->rx_dial_pulse);
+		timer_start(&imts->timer, DIAL_PULSE_TO);
+		break;
+	case TONE_GUARD:
+		/* pulse completed */
+		if (imts->rx_dial_pulse)
+			timer_start(&imts->timer, DIAL_PULSE_TO);
+		break;
+	default:
+		;
+#if 0
+		/* received noise */
+		PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Received noise while dialing, releasing!\n");
+		imts_release(imts);
+#endif
+	}
+}
+
+/* check for disconnect */
+static void imts_receive_disconnect(imts_t *imts, int tone, double elapsed, double amplitude)
+{
+	/* reset disc counter on timeout */
+	if (elapsed > DISC_PULSE_TO) {
+		if (imts->rx_disc_pulse) {
+			PDEBUG_CHAN(DIMTS, DEBUG_DEBUG, "Timeout Disconnect sequence\n");
+			imts->rx_disc_pulse = 0;
+		}
+		return;
+	}
+
+	switch (tone) {
+	case TONE_DISCONNECT:
+		imts->rx_disc_pulse++;
+		PDEBUG_CHAN(DIMTS, DEBUG_DEBUG, "Detected Disconnect pulse #%d.\n", imts->rx_disc_pulse);
+		break;
+	case TONE_GUARD:
+		if (imts->rx_disc_pulse == DISC_COUNT) {
+			PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Received disconnect sequence from mobile phone (level %.0f%%).\n", amplitude * 100.0);
+			if (imts->state == IMTS_SEIZE
+			 || imts->state == IMTS_ANI
+			 || imts->state == IMTS_DIALING
+			 || imts->state == IMTS_PAGING
+			 || imts->state == IMTS_RINGING
+			 || imts->state == IMTS_CONVERSATION) {
+				if (imts->callref)
+					call_up_release(imts->callref, CAUSE_NORMAL);
+				imts_release(imts);
+			}
+			break;
+		}
+		break;
+	default:
+		if (imts->rx_disc_pulse) {
+			PDEBUG_CHAN(DIMTS, DEBUG_DEBUG, "Disconnect sequence not detected anymore\n");
+			imts->rx_disc_pulse = 0;
+		}
+	}
+}
+
+/* decode page test digits */
+static void receive_page_imts(imts_t *imts, int tone)
+{
+	switch (tone) {
+	case TONE_IDLE:
+		/* pulse detected */
+		imts->rx_page_pulse++;
+		PDEBUG_CHAN(DIMTS, DEBUG_DEBUG, "Detected page test pulse #%d.\n", imts->rx_page_pulse);
+		if (imts->rx_page_pulse > 10) {
+			PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Received too many pulses!\n");
+		}
+		timer_start(&imts->timer, PAGE_PULSE_TO); // use for page test timeout
+		break;
+	case TONE_SEIZE:
+		/* pulse completed */
+		timer_start(&imts->timer, PAGE_PULSE_TO); // use for page test timeout
+		break;
+	default:
+		;
+	}
+}
+
+/* decode page test digits */
+static void receive_page_mts(imts_t *imts, int tone)
+{
+	if (tone == TONE_600 || tone == TONE_1500) {
+		/* pulse detected */
+		imts->rx_page_pulse++;
+		PDEBUG_CHAN(DIMTS, DEBUG_DEBUG, "Detected page test pulse #%d.\n", imts->rx_page_pulse);
+		if (imts->rx_page_pulse > 10) {
+			PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Received too many pulses!\n");
+		}
+		timer_start(&imts->timer, PAGE_PULSE_TO); // use for page test timeout
+	}
+}
+
+/* A tone was detected or is gone. */
+void imts_receive_tone(imts_t *imts, int tone, double elapsed, double amplitude)
+{
+	/* used for several states */
+	imts_receive_disconnect(imts, tone, elapsed, amplitude);
+
+	switch (imts->state) {
+	case IMTS_IDLE:
+		imts_receive_seize(imts, tone);
+		break;
+	case IMTS_ANI:
+		imts_receive_ani(imts, tone);
+		break;
+	case IMTS_DIALING:
+		imts_receive_dialing(imts, tone);
+		break;
+	case IMTS_CONVERSATION:
+		break;
+	case IMTS_PAGING_TEST:
+		if (imts->mode == MODE_IMTS)
+			receive_page_imts(imts, tone);
+		else
+			receive_page_mts(imts, tone);
+		break;
+	default:
+		;
+	}
+
+	/* remember last tone, also store amplitude of last signaling tone */
+	imts->last_tone = tone;
+	if (imts->last_tone < NUM_SIG_TONES)
+		imts->last_sigtone_amplitude = amplitude;
+}
+
+void imts_lost_tone(imts_t *imts, int tone, double elapsed)
+{
+	switch (imts->state) {
+	case IMTS_IDLE:
+		timer_stop(&imts->timer);
+		imts->rx_guard_duration = elapsed;
+		break;
+	case IMTS_PAGING:
+		if (elapsed >= 0.300 && tone == TONE_GUARD && timer_running(&imts->timer)) {
+			PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Received acknowledge (Guard tone) from mobile phone (level %.0f%%).\n", imts->last_sigtone_amplitude * 100.0);
+			call_up_alerting(imts->callref);
+			imts_ringing(imts);
+			break;
+		}
+		break;
+	case IMTS_RINGING:
+		if (elapsed >= 0.190 && tone == TONE_CONNECT) {
+			PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Received answer (Connect tone) from mobile phone (level %.0f%%).\n", imts->last_sigtone_amplitude * 100.0);
+			call_up_answer(imts->callref, imts->station_id);
+			imts_answer(imts);
+			break;
+		}
+		break;
+	default:
+		;
+	}
+}
+
+static void ani_after_digit(imts_t *imts)
+{
+	/* timeout after pulses: digit complete
+	 * timeout after digit: ANI in complete
+	 */
+	if (imts->rx_ani_pulse) {
+		if (imts->rx_ani_pulse == 10)
+			imts->rx_ani_pulse = 0;
+		imts->station_id[imts->rx_ani_index] = imts->rx_ani_pulse + '0';
+		imts->rx_ani_pulse = 0;
+		PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Received ANI digit '%c' from mobile phone (level %.0f%%).\n", imts->station_id[imts->rx_ani_index], imts->last_sigtone_amplitude * 100.0);
+		imts->station_id[++imts->rx_ani_index] = '\0';
+		/* update status while receiving station ID */
+		imts_display_status();
+		/* if all digits have been received */
+		if (imts->rx_ani_index == imts->station_length) {
+			PDEBUG_CHAN(DIMTS, DEBUG_INFO, "ANI '%s' complete, sending dial tone.\n", imts->station_id);
+			imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_DIALTONE, 0.0, 0);
+			timer_start(&imts->timer, DIALTONE_TO);
+			imts->dial_number[0] = '\0';
+			imts->rx_dial_index = 0;
+			imts->rx_dial_pulse = 0;
+			imts_new_state(imts, IMTS_DIALING);
+			return;
+		}
+		timer_start(&imts->timer, ANI_TO);
+	} else {
+		PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Timeout receiving ANI from mobile phone, releasing!\n");
+		imts_release(imts);
+	}
+}
+
+static void dial_after_digit(imts_t *imts)
+{
+	/* special case where nothing happens after dial tone */
+	if (!imts->rx_dial_pulse && !imts->rx_dial_index) {
+		PDEBUG_CHAN(DANETZ, DEBUG_NOTICE, "Mobile phone does not start dialing, releasing!\n");
+		imts_release(imts);
+		return;
+	}
+
+	/* timeout after pulses: digit complete
+	 * timeout after digit: number complete
+	 */
+	if (imts->rx_dial_pulse) {
+		if (imts->rx_dial_index == sizeof(imts->dial_number) - 1) {
+			PDEBUG_CHAN(DANETZ, DEBUG_NOTICE, "Mobile phone dials too many digits, releasing!\n");
+			imts_release(imts);
+			return;
+		}
+		if (imts->rx_dial_pulse == 10)
+			imts->rx_dial_pulse = 0;
+		imts->dial_number[imts->rx_dial_index] = imts->rx_dial_pulse + '0';
+		imts->rx_dial_pulse = 0;
+		PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Received dial digit '%c' from mobile phone. (level %.0f%%)\n", imts->dial_number[imts->rx_dial_index], imts->last_sigtone_amplitude * 100.0);
+		imts->dial_number[++imts->rx_dial_index] = '\0';
+		timer_start(&imts->timer, DIALING_TO);
+	} else {
+		int callref = ++new_callref;
+		int rc;
+
+		PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Timeout receiving dialing from mobile phone, number complete.\n");
+		rc = call_up_setup(callref, imts->station_id, imts->dial_number);
+		if (rc < 0) {
+			PDEBUG_CHAN(DANETZ, DEBUG_NOTICE, "Call rejected (cause %d), releasing!\n", -rc);
+			imts_release(imts);
+			return;
+		}
+		imts->callref = callref;
+		imts_new_state(imts, IMTS_CONVERSATION);
+		imts_set_dsp_mode(imts, DSP_MODE_AUDIO, 0, 0.0, 0);
+		imts->rx_disc_pulse = 0;
+	}
+}
+
+static void page_after_digit(imts_t *imts)
+{
+	char digit;
+	double delay;
+
+	/* timeout after pulses: digit complete */
+	if (imts->rx_page_pulse) {
+		if (imts->rx_page_pulse < 11) {
+			if (imts->rx_page_pulse == 10)
+				imts->rx_page_pulse = 0;
+			digit = imts->rx_page_pulse + '0';
+			delay = get_time() - imts->tx_page_timestamp - PAGE_PULSE_TO;
+			PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Received paging test digit '%c' (level %.0f%%  delay %.0f ms).\n", digit, imts->last_sigtone_amplitude * 100.0, delay * 1000.0);
+		}
+		imts->rx_page_pulse = 0;
+	}
+}
+
+/* Timeout handling */
+static void imts_timeout(struct timer *timer)
+{
+	imts_t *imts = (imts_t *)timer->priv;
+
+	switch (imts->state) {
+	case IMTS_IDLE:
+		switch (imts->last_tone) {
+		case TONE_IDLE:
+			PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Received idle tone (level of %.0f%%), loopback?\n", imts->last_sigtone_amplitude * 100.0);
+			/* trigger reset of decoder to force detection again and again */
+			imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_IDLE, 0.0, 1);
+			break;
+		case TONE_600:
+			PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Received 600 Hz tone with level of %.0f%%, loopback?\n", imts->last_sigtone_amplitude * 100.0);
+			/* trigger reset of decoder to force detection again and again */
+			imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_600, 0.0, 1);
+			break;
+		case TONE_GUARD:
+			PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Received Guard tone, turning off IDLE tone\n");
+			imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_SILENCE, 0.5, 0);
+			break;
+		}
+		break;
+	case IMTS_PAGING:
+		PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "No response from mobile phone.\n");
+		imts_go_idle(imts);
+		call_up_release(imts->callref, CAUSE_OUTOFORDER);
+		imts->callref = 0;
+		break;
+	case IMTS_RINGING:
+		PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "No answer from mobile phone's user, releasing.\n");
+		imts_release(imts);
+		call_up_release(imts->callref, CAUSE_NOANSWER);
+		imts->callref = 0;
+		break;
+	case IMTS_RELEASE:
+		imts_go_idle(imts);
+		break;
+	case IMTS_SEIZE:
+		PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Sending Seize to mobile phone.\n");
+		imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_SEIZE, SEIZE_LENGTH, 0);
+		timer_start(&imts->timer, SEIZE_LENGTH + ANI_TO);
+		imts->station_id[0] = '\0';
+		imts->rx_ani_index = 0;
+		imts->rx_ani_pulse = 0;
+		imts->rx_ani_totpulses = 0;
+		imts_new_state(imts, IMTS_ANI);
+		break;
+	case IMTS_ANI:
+		ani_after_digit(imts);
+		break;
+	case IMTS_DIALING:
+		dial_after_digit(imts);
+		break;
+	case IMTS_PAGING_TEST:
+		page_after_digit(imts);
+		break;
+	default:
+		;
+	}
+}
+
+/* generate pulse sequence to page phone */
+static void paging_pulses_imts(imts_t *imts, int tone)
+{
+	double duration;
+	int pulses;
+
+	pulses = imts->station_id[imts->tx_page_index] - '0';
+	if (pulses == 0)
+		pulses = 10;
+
+	if (tone == TONE_SEIZE) {
+		if (imts->tx_page_pulse == 0)
+			PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Sending paging digit '%c' as pulses.\n", imts->station_id[imts->tx_page_index]);
+		/* send mark (pulse start) */
+		imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_IDLE, PAGE_MARK, 0);
+		imts->tx_page_pulse++;
+	} else {
+		if (imts->tx_page_pulse <= pulses) {
+			/* send space (pulse end), use long space after last pulse */
+			if (imts->tx_page_pulse < pulses)
+				duration = PAGE_SPACE;
+			else {
+				imts->tx_page_pulse = 0;
+				imts->tx_page_index++;
+				imts->tx_page_timestamp = get_time();
+				/* restart test pattern */
+				if (!imts->station_id[imts->tx_page_index] && imts->state == IMTS_PAGING_TEST)
+					imts->tx_page_index = 0;
+				if (imts->station_id[imts->tx_page_index])
+					duration = PAGE_PAUSE;
+				else {
+					duration = 0;
+					timer_start(&imts->timer, PAGING_TO);
+				}
+			}
+			imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_SEIZE, duration, 0);
+		}
+	}
+}
+static void paging_pulses_mts(imts_t *imts, int tone)
+{
+	double duration;
+	int pulses;
+
+	pulses = imts->station_id[imts->tx_page_index] - '0';
+	if (pulses == 0)
+		pulses = 10;
+
+	if (tone == TONE_1500)
+		tone = TONE_600;
+	else
+		tone = TONE_1500;
+
+	if (imts->tx_page_pulse == 0) {
+		PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Sending paging digit '%c' as pulses.\n", imts->station_id[imts->tx_page_index]);
+	}
+	imts->tx_page_pulse++;
+	if (imts->tx_page_pulse < pulses)
+		duration = PAGE_PULSE;
+	else {
+		imts->tx_page_pulse = 0;
+		imts->tx_page_index++;
+		imts->tx_page_timestamp = get_time();
+		/* restart test pattern */
+		if (!imts->station_id[imts->tx_page_index] && imts->state == IMTS_PAGING_TEST)
+			imts->tx_page_index = 0;
+		if (imts->station_id[imts->tx_page_index])
+			duration = PAGE_PAUSE;
+		else {
+			PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Digits complete, assuming the phone is ringing.\n");
+			duration = 0;
+			imts_new_state(imts, IMTS_RINGING);
+			call_up_alerting(imts->callref);
+		}
+	}
+	imts_set_dsp_mode(imts, DSP_MODE_TONE, tone, duration, 0);
+}
+
+/* generate pulse sequence to ring phone */
+static void ringing_pulses(imts_t *imts, int tone)
+{
+	if (tone == TONE_IDLE) {
+		if (imts->tx_ring_pulse == 0)
+			PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Sending ringing signal as pulses.\n");
+		/* send space (pulse end) */
+		imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_SEIZE, RING_SPACE, 0);
+		imts->tx_ring_pulse++;
+	} else {
+		if (imts->tx_ring_pulse < RING_PULSES) {
+			/* send mark (pulse start) */
+			imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_IDLE, RING_MARK, 0);
+		} else {
+			PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Sending pause after ringing.\n");
+			/* send long space after last pulse */
+			imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_SEIZE, RING_OFF, 0);
+			imts->tx_ring_pulse = 0;
+		}
+	}
+}
+
+/* after sending Seize tone switch to silence and await ANI */
+static void seize_sent(imts_t *imts, int tone)
+{
+	if (tone == TONE_SEIZE) {
+		imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_SILENCE, 0.0, 0);
+	}
+}
+
+/* send test pattern (cycle through tones, skip if length is 0) */
+static void detector_test_imts(imts_t *imts, int tone)
+{
+	switch (tone) {
+	case TONE_SILENCE:
+tone_idle:
+		if (imts->detector_test_length_1 <= 0)
+			goto tone_seize;
+		PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Sending %.3fs IDLE tone.\n", imts->detector_test_length_1);
+		imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_IDLE, imts->detector_test_length_1, 0);
+		break;
+	case TONE_IDLE:
+tone_seize:
+		if (imts->detector_test_length_2 <= 0)
+			goto tone_silence;
+		PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Sending %.3fs SEIZE tone.\n", imts->detector_test_length_2);
+		imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_SEIZE, imts->detector_test_length_2, 0);
+		break;
+	case TONE_SEIZE:
+tone_silence:
+		if (imts->detector_test_length_3 <= 0)
+			goto tone_idle;
+		PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Sending %.3fs SILENCE.\n", imts->detector_test_length_3);
+		imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_SILENCE, imts->detector_test_length_3, 0);
+		break;
+	}
+}
+static void detector_test_mts(imts_t *imts, int tone)
+{
+	switch (tone) {
+	case TONE_SILENCE:
+tone_idle:
+		if (imts->detector_test_length_1 <= 0)
+			goto tone_seize;
+		PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Sending %.3fs 600 Hz tone.\n", imts->detector_test_length_1);
+		imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_600, imts->detector_test_length_1, 0);
+		break;
+	case TONE_600:
+tone_seize:
+		if (imts->detector_test_length_2 <= 0)
+			goto tone_silence;
+		PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Sending %.3fs 1500 Hz tone.\n", imts->detector_test_length_2);
+		imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_1500, imts->detector_test_length_2, 0);
+		break;
+	case TONE_1500:
+tone_silence:
+		if (imts->detector_test_length_3 <= 0)
+			goto tone_idle;
+		PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Sending %.3fs SILENCE.\n", imts->detector_test_length_3);
+		imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_SILENCE, imts->detector_test_length_3, 0);
+		break;
+	}
+}
+
+/* whenever a tone has been sent (only for tones with given duration) */
+void imts_tone_sent(imts_t *imts, int tone)
+{
+	switch (imts->state) {
+	case IMTS_IDLE:
+		PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "No Seize tone after Guard tone, turning on IDLE tone\n");
+		imts_set_dsp_mode(imts, DSP_MODE_TONE, TONE_IDLE, 0.0, 0);
+		break;
+	case IMTS_ANI:
+		seize_sent(imts, tone);
+		break;
+	case IMTS_PAGING:
+	case IMTS_PAGING_TEST:
+		if (imts->mode == MODE_IMTS)
+			paging_pulses_imts(imts, tone);
+		else
+			paging_pulses_mts(imts, tone);
+		break;
+	case IMTS_RINGING:
+		ringing_pulses(imts, tone);
+		break;
+	case IMTS_RELEASE:
+		imts_release(imts);
+		break;
+	case IMTS_DETECTOR_TEST:
+		if (imts->mode == MODE_IMTS)
+			detector_test_imts(imts, tone);
+		else
+			detector_test_mts(imts, tone);
+		break;
+	default:
+		;
+	}
+}
+
+/* Call control starts call towards mobile station. */
+int call_down_setup(int callref, const char __attribute__((unused)) *caller_id, enum number_type __attribute__((unused)) caller_type, const char *dialing)
+{
+	char number[8];
+	sender_t *sender;
+	imts_t *imts;
+	int i;
+
+	/* 1. check if given number is already in a call, return BUSY */
+	for (sender = sender_head; sender; sender = sender->next) {
+		imts = (imts_t *) sender;
+		if (!strcmp(imts->station_id, dialing))
+			break;
+	}
+	if (sender) {
+		PDEBUG(DIMTS, DEBUG_NOTICE, "Outgoing call to busy number, rejecting!\n");
+		return -CAUSE_BUSY;
+	}
+
+	/* 2. check if all channels are busy, return NOCHANNEL */
+	for (sender = sender_head; sender; sender = sender->next) {
+		imts = (imts_t *) sender;
+		if (imts->state == IMTS_IDLE)
+			break;
+	}
+	if (!sender) {
+		PDEBUG(DIMTS, DEBUG_NOTICE, "Outgoing call, but no free channel, rejecting!\n");
+		return -CAUSE_NOCHANNEL;
+	}
+
+	/* 3. check if number is invalid, return INVALNUMBER */
+	if (strlen(dialing) == 12 && !strncmp(dialing, "+1", 2))
+		dialing += 2;
+	if (strlen(dialing) == 11 && !strncmp(dialing, "1", 1))
+		dialing += 1;
+	if (strlen(dialing) == 10 && imts->station_length == 7) {
+		strncpy(number, dialing, 3);
+		strcpy(number + 3, dialing + 6);
+		dialing = number;
+	}
+	if (strlen(dialing) == 10 && imts->station_length == 5)
+		dialing += 5;
+	if ((int)strlen(dialing) != imts->station_length) {
+inval:
+		PDEBUG(DIMTS, DEBUG_NOTICE, "Outgoing call to invalid number '%s', rejecting!\n", dialing);
+		return -CAUSE_INVALNUMBER;
+	}
+	for (i = 0; i < (int)strlen(dialing); i++) {
+		if (dialing[i] < '0' || dialing[i] > '9')
+			goto inval;
+	}
+
+	PDEBUG_CHAN(DIMTS, DEBUG_INFO, "Call to mobile station, paging number: %s\n", dialing);
+
+	/* 4. trying to page mobile station */
+	imts->callref = callref;
+	imts_paging(imts, dialing, 0);
+
+	return 0;
+}
+
+void call_down_answer(int __attribute__((unused)) callref)
+{
+}
+
+/* Call control sends disconnect (with tones).
+ * An active call stays active, so tones and annoucements can be received
+ * by mobile station.
+ */
+void call_down_disconnect(int callref, int cause)
+{
+	sender_t *sender;
+	imts_t *imts;
+
+	PDEBUG(DIMTS, DEBUG_INFO, "Call has been disconnected by network.\n");
+
+	for (sender = sender_head; sender; sender = sender->next) {
+		imts = (imts_t *) sender;
+		if (imts->callref == callref)
+			break;
+	}
+	if (!sender) {
+		PDEBUG(DIMTS, DEBUG_NOTICE, "Outgoing disconnect, but no callref!\n");
+		call_up_release(callref, CAUSE_INVALCALLREF);
+		return;
+	}
+
+	/* Release when not active */
+	if (imts->state == IMTS_CONVERSATION)
+		return;
+	switch (imts->state) {
+	case IMTS_PAGING:
+	case IMTS_RINGING:
+		PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Outgoing disconnect, during paging/alerting, releasing!\n");
+	 	imts_release(imts);
+		break;
+	default:
+		break;
+	}
+
+	call_up_release(callref, cause);
+
+	imts->callref = 0;
+
+}
+
+/* Call control releases call toward mobile station. */
+void call_down_release(int callref, __attribute__((unused)) int cause)
+{
+	sender_t *sender;
+	imts_t *imts;
+
+	PDEBUG(DIMTS, DEBUG_INFO, "Call has been released by network, releasing call.\n");
+
+	for (sender = sender_head; sender; sender = sender->next) {
+		imts = (imts_t *) sender;
+		if (imts->callref == callref)
+			break;
+	}
+	if (!sender) {
+		PDEBUG(DIMTS, DEBUG_NOTICE, "Outgoing release, but no callref!\n");
+		/* don't send release, because caller already released */
+		return;
+	}
+
+	imts->callref = 0;
+
+	switch (imts->state) {
+	case IMTS_CONVERSATION:
+		PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Outgoing release, during call, releasing!\n");
+	 	imts_release(imts);
+		break;
+	case IMTS_PAGING:
+	case IMTS_RINGING:
+		PDEBUG_CHAN(DIMTS, DEBUG_NOTICE, "Outgoing release, during paging/alerting, releasing!\n");
+	 	imts_release(imts);
+		break;
+	default:
+		break;
+	}
+}
+
+/* Receive audio from call instance. */
+void call_down_audio(int callref, sample_t *samples, int count)
+{
+	sender_t *sender;
+	imts_t *imts;
+
+	for (sender = sender_head; sender; sender = sender->next) {
+		imts = (imts_t *) sender;
+		if (imts->callref == callref)
+			break;
+	}
+	if (!sender)
+		return;
+
+	if (imts->dsp_mode == DSP_MODE_AUDIO) {
+		sample_t up[(int)((double)count * imts->sender.srstate.factor + 0.5) + 10];
+		count = samplerate_upsample(&imts->sender.srstate, samples, count, up);
+		jitter_save(&imts->sender.dejitter, up, count);
+	}
+}
+
+void dump_info(void) {}
+
diff --git a/src/imts/imts.h b/src/imts/imts.h
new file mode 100644
index 0000000..88b3da8
--- /dev/null
+++ b/src/imts/imts.h
@@ -0,0 +1,139 @@
+#include "../libsquelch/squelch.h"
+#include "../libfm/fm.h"
+#include "../libmobile/sender.h"
+
+enum dsp_mode {
+	DSP_MODE_OFF = 0,	/* transmitter off */
+	DSP_MODE_TONE,		/* send tone or silence */
+	DSP_MODE_AUDIO,		/* send audio */
+};
+
+#define TONE_GUARD		0
+#define TONE_IDLE		1
+#define TONE_SEIZE		2
+#define TONE_CONNECT		3
+#define TONE_DISCONNECT		4
+
+#define TONE_600		5
+#define TONE_1500		6
+
+#define TONE_SILENCE		7
+#define TONE_NOISE		8
+#define TONE_DIALTONE		9
+
+#define NUM_SIG_TONES		7
+
+enum mode {
+	MODE_IMTS = 0,
+	MODE_MTS,
+};
+
+enum imts_state {
+	IMTS_NULL = 0,
+	/* channel is idle */
+	IMTS_OFF,		/* base station not in use and turned off */
+	IMTS_IDLE,		/* base station not in use and sending 2000 Hz Idle tone */
+	/* mobile originated */
+	IMTS_SEIZE,		/* base station sends seize to acknowldege call from mobile */
+	IMTS_ANI,		/* base station is receiving ANI from mobile */
+	IMTS_DIALING,		/* base station is receiving dial digits */
+	/* mobile terminated */
+	IMTS_PAGING,		/* base station is paging mobile */
+	IMTS_RINGING,		/* base station is ringing mobile */
+	/* active call */
+	IMTS_CONVERSATION,	/* base station and mobile have conversation */
+	/* releasing call */
+	IMTS_RELEASE,		/* base station turned off */
+	/* loopback test */
+	IMTS_PAGING_TEST,	/* loopback test sequence */
+	/* detector test */
+	IMTS_DETECTOR_TEST,	/* detector test sequence */
+};
+
+typedef struct imts {
+	sender_t		sender;
+
+	/* channel's states */
+	enum imts_state		state;			/* current sender's state */
+	int			pre_emphasis;		/* use pre_emphasis by this instance */
+	int			de_emphasis;		/* use de_emphasis by this instance */
+	emphasis_t		estate;
+	int			callref;		/* call reference */
+	char			station_id[11];		/* current station ID (also used for test pattern) */
+	int			station_length;		/* digit length of station ID */
+	char			dial_number[33];	/* number dialing */
+	struct timer		timer;
+	int			last_tone;		/* last tone received */
+	double			last_sigtone_amplitude;	/* amplitude of last signaling tone received */
+	double			fast_seize;		/* fast seize: guard-length - roundtrip-delay */
+	double			rx_guard_timestamp;	/* start of guard tone (seize by mobile) */
+	double			rx_guard_duration;	/* duration of guard (only long guards are detected) */
+	int			rx_ani_pulse;		/* current pulse # receiving */
+	int			rx_ani_index;		/* current digit # receiving */
+	int			rx_ani_totpulses;	/* total pulses count receiving */
+	int			rx_dial_pulse;		/* current pulse # receiving */
+	int			rx_dial_index;		/* current digit # receiving */
+	int			rx_disc_pulse;		/* current pulse # receiving */
+	int			tx_page_pulse;		/* current pulse # transmitting */
+	int			tx_page_index;		/* current digit # transmitting */
+	double			tx_page_timestamp;	/* last pulse of digit transmitting */
+	int			tx_ring_pulse;		/* current pulse # transmitting */
+	int			rx_page_pulse;		/* current pulse # receiving */
+	double			detector_test_length_1;	/* detector test tone duration */
+	double			detector_test_length_2;	/* detector test tone duration */
+	double			detector_test_length_3;	/* detector test tone duration */
+
+	/* MTS additional states */
+	enum mode		mode;			/* set if MTS mode is used */
+	const char		*operator;		/* operator's number to call when seizing the channel */
+
+	/* display measurements */
+	dispmeasparam_t		*dmp_tone_level;
+	dispmeasparam_t		*dmp_tone_quality;
+
+	/* dsp states */
+	double			sample_duration;	/* 1 / samplerate */
+	double			demod_center;		/* center frequency for tone demodulation */
+	double			demod_bandwidth;	/* bandwidth for tone demodulation */
+	fm_demod_t		demod;			/* demodulator for frequency / amplitude */
+	iir_filter_t		demod_freq_lp;		/* filter for frequency response */
+	iir_filter_t		demod_ampl_lp;		/* filter for amplitude response */
+	int			demod_current_tone;	/* current tone being detected */
+	int			demod_sig_tone;		/* current tone is a signaling tone */
+	int			demod_last_tone;	/* last tone being detected */
+	double			demod_sustain;		/* how long a tone must sustain */
+	double			demod_duration;		/* duration of last tone */
+	double			demod_quality_time;	/* time counter to measure quality */
+	int			demod_quality_count;	/* counter to measure quality */
+	double			demod_quality_value;	/* sum of quality samples (must be divided by count) */
+	double			display_interval;	/* used to update tone levels */
+	enum dsp_mode		dsp_mode;		/* current mode: audio, durable tone 0 or 1, paging */
+	int			ptt;			/* set, if push to talk is used (transmitter of phone off) */
+	int			tone;			/* current tone to send */
+	int			tone_duration;		/* if set, tone is limited to this duration (in samples) */
+	double			tone_idle_phaseshift65536;/* how much the phase of sine wave changes per sample */
+	double			tone_seize_phaseshift65536;/* how much the phase of sine wave changes per sample */
+	double			tone_600_phaseshift65536;/* how much the phase of sine wave changes per sample */
+	double			tone_1500_phaseshift65536;/* how much the phase of sine wave changes per sample */
+	double			tone_dialtone_phaseshift65536[2];/* how much the phase of sine wave changes per sample */
+	double			tone_phase65536[2];	/* current phase */
+	squelch_t		squelch;		/* squelch detection process */
+	int			is_mute;		/* set if quelch has muted */
+	int			rf_signal;		/* set if we have currently an RF signal */
+	sample_t		*delay_spl;		/* delay buffer for delaying audio */
+	int			delay_pos;		/* position in delay buffer */
+	int			delay_max;		/* number of samples in delay buffer */
+} imts_t;
+
+
+void imts_list_channels(void);
+double imts_channel2freq(const char *kanal, int uplink);
+int imts_init(void);
+int imts_create(const char *channel, const char *audiodev, int use_sdr, int samplerate, double rx_gain, int pre_emphasis, int de_emphasis, const char *write_rx_wave, const char *write_tx_wave, const char *read_rx_wave, const char *read_tx_wave, int loopback, double squelch_db, int ptt, int station_length, double fast_seize, enum mode mode, const char *operator, double length_1, double length_2, double length_3);
+void imts_destroy(sender_t *sender);
+void imts_loss_indication(imts_t *imts, double loss_time);
+void imts_signal_indication(imts_t *imts);
+void imts_receive_tone(imts_t *imts, int tone, double elapsed, double amplitude);
+void imts_lost_tone(imts_t *imts, int tone, double elapsed);
+void imts_tone_sent(imts_t *imts, int tone);
+
diff --git a/src/imts/main.c b/src/imts/main.c
new file mode 100644
index 0000000..7263542
--- /dev/null
+++ b/src/imts/main.c
@@ -0,0 +1,289 @@
+/* MTS/IMTS main
+ *
+ * (C) 2019 by Andreas Eversberg <jolly@eversberg.eu>
+ * All Rights Reserved
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <math.h>
+#include "../libsample/sample.h"
+#include "../libmobile/main_mobile.h"
+#include "../libdebug/debug.h"
+#include "../libtimer/timer.h"
+#include "../libmobile/call.h"
+#include "../liboptions/options.h"
+#include "../amps/tones.h"
+#include "../amps/outoforder.h"
+#include "../amps/noanswer.h"
+#include "../amps/invalidnumber.h"
+#include "../amps/congestion.h"
+#include "imts.h"
+#include "dsp.h"
+
+/* settings */
+static double squelch_db = -INFINITY;
+static int ptt = 0;
+static int station_length = 0; /* defined by mode */
+static double fast_seize = 0.0;
+static enum mode mode = MODE_IMTS;
+static char operator[32] = "010";
+static double detector_test_length_1 = 0.0;
+static double detector_test_length_2 = 0.0;
+static double detector_test_length_3 = 0.0;
+
+void print_help(const char *arg0)
+{
+	main_mobile_print_help(arg0, "-b 5 ");
+	/*      -                                                                             - */
+	printf(" -S --squelch <dB> | auto\n");
+	printf("        Use given RF level to detect loss of signal. When the signal gets lost\n");
+	printf("        and stays below this level, the connection is released.\n");
+	printf("        Use 'auto' to do automatic noise floor calibration to detect loss.\n");
+	printf("        Only works with SDR! (disabled by default)\n");
+	printf(" -P --push-to-talk\n");
+	printf("        Allow push-to-talk operation for IMTS mode. (MTS always uses it.)\n");
+	printf("        This adds extra delay to received audio, to eliminate noise when the\n");
+	printf("        transmitter of the phone is turned off. Also this disables release on\n");
+	printf("        loss of RF signal. (Squelch is required for this to operate.)\n");
+	printf(" -5 --five\n");
+	printf(" -7 --seven\n");
+	printf("        Force station ID length (default is 7 for IMTS, 5 for MTS)\n");
+	printf(" -F --fast-seize <delay in ms>\n");
+	printf("        To compensate audio processing latency, give delay when to respond,\n");
+	printf("        after detection of Guard tone from mobile phone.\n");
+	printf("        Run software in loopback mode '-l 2' to measure round trip delay.\n");
+	printf("        Substract delay from 350 ms. If the phone has different Guard tone\n");
+	printf("        length, substract from that value.\n");
+	printf(" -D --detector-test <idle length> <seize lenght> <silence length>\n");
+	printf("        Transmit detector test signal, to adjust decoder inside mobile phone.\n");
+	printf("        Give length of idle / seize and silence in seconds. Listen to it with\n");
+	printf("        a radio receiver. To exclude an element, set its length to '0'.\n");
+	printf("        Example: '-D 0.5 0.5 0' plays alternating idle/seize tone.\n");
+	printf("\nMTS mode options\n");
+	printf(" -M --mts\n");
+	printf("        Run base station in MTS mode, rather than in IMTS mode.\n");
+	printf(" -O --operator <number>\n");
+	printf("        Give number to dial when mobile station initiated a call in MTS mode.\n");
+	printf("        Because there is no dial on the mobile phone, operator assistance is\n");
+	printf("        required to complete the call.\n");
+	printf("        By default, the operator '%s' is dialed.\n", operator);
+	printf(" -D --detector-test <600 Hz length> <1500 Hz lenght> <silence length>\n");
+	printf("        Transmit detector test signal, to adjust decoder inside MTS phone.\n");
+	printf("        Give length of 600/1500 Hz and silence in seconds. Listen to it with\n");
+	printf("        a radio receiver. To exclude an element, set its length to '0'.\n");
+	printf("        Example: '-D 0.5 0.5 0' plays alternating 600/1500 Hz tone.\n");
+	printf("\nstation-id: Give %d digits of station-id, you don't need to enter it after\n", station_length);
+	printf("        every start of this program.\n");
+	main_mobile_print_hotkeys();
+}
+
+static void add_options(void)
+{
+	main_mobile_add_options();
+	option_add('S', "squelch", 1);
+	option_add('P', "push-to-talk", 0);
+	option_add('5', "five", 0);
+	option_add('7', "seven", 0);
+	option_add('F', "fast-seize", 1);
+	option_add('D', "decoder-test", 3);
+	option_add('M', "mts", 0);
+	option_add('O', "operator", 1);
+}
+
+static int handle_options(int short_option, int argi, char **argv)
+{
+	switch (short_option) {
+	case 'S':
+		if (!strcasecmp(argv[argi], "auto"))
+			squelch_db = 0.0;
+		else
+			squelch_db = atof(argv[argi]);
+		break;
+	case 'P':
+		ptt = 1;
+		break;
+	case '5':
+		station_length = 5;
+		break;
+	case '7':
+		station_length = 7;
+		break;
+	case 'F':
+		fast_seize = atof(argv[argi]) / 1000.0;
+		if (fast_seize < 0.0)
+			fast_seize = 0.0;
+		break;
+	case 'D':
+		detector_test_length_1 = atof(argv[argi++]);
+		detector_test_length_2 = atof(argv[argi++]);
+		detector_test_length_3 = atof(argv[argi++]);
+		break;
+	case 'M':
+		mode = MODE_MTS;
+		ptt = 1;
+		break;
+	case 'O':
+		strncpy(operator, argv[argi], sizeof(operator) - 1);
+		operator[sizeof(operator) - 1] = '\0';
+		break;
+	default:
+		return main_mobile_handle_options(short_option, argi, argv);
+	}
+
+	return 1;
+}
+
+int main(int argc, char *argv[])
+{
+	int rc, argi;
+	const char *station_id = "";
+	int i;
+
+	/* init common tones */
+	init_tones();
+	init_outoforder();
+	init_noanswer();
+	init_invalidnumber();
+	init_congestion();
+
+	main_mobile_init();
+
+	/* handle options / config file */
+	add_options();
+	rc = options_config_file("~/.osmocom/analog/imts.conf", handle_options);
+	if (rc < 0)
+		return 0;
+	argi = options_command_line(argc, argv, handle_options);
+	if (argi <= 0)
+		return argi;
+
+	if (!station_length) {
+		if (mode == MODE_IMTS)
+			station_length = 7;
+		else
+			station_length = 5;
+	}
+
+	if (argi < argc) {
+		station_id = argv[argi];
+		if ((int)strlen(station_id) != station_length) {
+			printf("Given station ID '%s' does not have %d digits\n", station_id, station_length);
+			return 0;
+		}
+	}
+
+	if (!num_kanal) {
+		printf("No channel (\"Kanal\") is specified, Use '-k list' to get a list of all channels.\n\n");
+		print_help(argv[0]);
+		return 0;
+	}
+	if (!strcasecmp(kanal[0], "list")) {
+		imts_list_channels();
+		goto fail;
+	}
+	if (use_sdr) {
+		/* set audiodev */
+		for (i = 0; i < num_kanal; i++)
+			audiodev[i] = "sdr";
+		num_audiodev = num_kanal;
+	}
+	if (num_kanal == 1 && num_audiodev == 0)
+		num_audiodev = 1; /* use default */
+	if (num_kanal != num_audiodev) {
+		fprintf(stderr, "You need to specify as many sound devices as you have channels.\n");
+		exit(0);
+	}
+
+	/* SDR always requires emphasis */
+	if (use_sdr) {
+		do_pre_emphasis = 1;
+		do_de_emphasis = 1;
+	}
+
+	if (!do_pre_emphasis || !do_de_emphasis) {
+		fprintf(stderr, "*******************************************************************************\n");
+		fprintf(stderr, "I suggest to let me do pre- and de-emphasis (options -p -d)!\n");
+		fprintf(stderr, "Use a transmitter/receiver without emphasis and let me do that!\n");
+		fprintf(stderr, "Because FSK signaling does not use emphasis, I like to control emphasis by\n");
+		fprintf(stderr, "myself for best results.\n");
+		fprintf(stderr, "*******************************************************************************\n");
+	}
+
+	if (mode == MODE_IMTS && !fast_seize && latency > 5 && loopback == 0) {
+		fprintf(stderr, "*******************************************************************************\n");
+		fprintf(stderr, "It is required to have a low latency in order to respond to phone's seizure\n");
+		fprintf(stderr, "fast enough! Please reduce buffer size to 5 ms via option: '-b 5'\n");
+		fprintf(stderr, "If this causes buffer underruns, use the 'Fast Seize' mode, see help.\n");
+		fprintf(stderr, "*******************************************************************************\n");
+		exit(0);
+	}
+
+	if (mode == MODE_MTS && !use_sdr && loopback == 0) {
+		fprintf(stderr, "*******************************************************************************\n");
+		fprintf(stderr, "MTS mode requires use of SDR, because base station is controlled by Squelch.\n");
+		fprintf(stderr, "*******************************************************************************\n");
+		exit(0);
+	}
+	if (mode == MODE_MTS && isinf(squelch_db) < 0 && loopback == 0) {
+		fprintf(stderr, "*******************************************************************************\n");
+		fprintf(stderr, "MTS mode requires use of Squelch. Please set Squelch level, see help.\n");
+		fprintf(stderr, "*******************************************************************************\n");
+		exit(0);
+	}
+
+	if (ptt && isinf(squelch_db) < 0 && loopback == 0) {
+		fprintf(stderr, "*******************************************************************************\n");
+		fprintf(stderr, "Cannot use push-to-talk feature without Squelch option.\n");
+		fprintf(stderr, "*******************************************************************************\n");
+		exit(0);
+	}
+
+	/* no squelch in loopback mode */
+	if (loopback)
+		squelch_db = -INFINITY;
+
+	/* inits */
+	fm_init(fast_math);
+	dsp_init();
+	imts_init();
+
+	/* create transceiver instance */
+	for (i = 0; i < num_kanal; i++) {
+		rc = imts_create(kanal[i], audiodev[i], use_sdr, samplerate, rx_gain, do_pre_emphasis, do_de_emphasis, write_rx_wave, write_tx_wave, read_rx_wave, read_tx_wave, loopback, squelch_db, ptt, station_length, fast_seize, mode, operator, detector_test_length_1, detector_test_length_2, detector_test_length_3);
+		if (rc < 0) {
+			fprintf(stderr, "Failed to create \"Sender\" instance. Quitting!\n");
+			goto fail;
+		}
+		printf("Base station on channel %s ready, please tune transmitter to %.3f MHz and receiver to %.3f MHz. (%.3f MHz offset)\n", kanal[i], imts_channel2freq(kanal[i], 0) / 1e6, imts_channel2freq(kanal[i], 1) / 1e6, imts_channel2freq(kanal[i], 2) / 1e6);
+	}
+
+	main_mobile(&quit, latency, interval, NULL, station_id, station_length);
+
+fail:
+	/* destroy transceiver instance */
+	while (sender_head)
+		imts_destroy(sender_head);
+
+	/* exits */
+	fm_exit();
+
+	return 0;
+}
+
diff --git a/src/libdebug/debug.c b/src/libdebug/debug.c
index cbafb4f..c22445f 100644
--- a/src/libdebug/debug.c
+++ b/src/libdebug/debug.c
@@ -51,6 +51,7 @@ struct debug_cat {
 	{ "nmt", "\033[1;34m" },
 	{ "amps", "\033[1;34m" },
 	{ "r2000", "\033[1;34m" },
+	{ "imts", "\033[1;34m" },
 	{ "jollycom", "\033[1;34m" },
 	{ "frame", "\033[0;36m" },
 	{ "call", "\033[0;37m" },
diff --git a/src/libdebug/debug.h b/src/libdebug/debug.h
index 6da992f..c399c4b 100644
--- a/src/libdebug/debug.h
+++ b/src/libdebug/debug.h
@@ -14,19 +14,20 @@
 #define DNMT		7
 #define DAMPS		8
 #define DR2000		9
-#define DJOLLY		10
-#define DFRAME		11
-#define DCALL		12
-#define DMNCC		13
-#define DDB		14
-#define DTRANS		15
-#define DDMS		16
-#define DSMS		17
-#define DSDR		18
-#define DUHD		19
-#define DSOAPY		20
-#define DWAVE		21
-#define DRADIO		22
+#define DIMTS		10
+#define DJOLLY		11
+#define DFRAME		12
+#define DCALL		13
+#define DMNCC		14
+#define DDB		15
+#define DTRANS		16
+#define DDMS		17
+#define DSMS		18
+#define DSDR		19
+#define DUHD		20
+#define DSOAPY		21
+#define DWAVE		22
+#define DRADIO		23
 
 void get_win_size(int *w, int *h);