diff --git a/src/cnetz/cnetz.c b/src/cnetz/cnetz.c
index df0968b..c97af0d 100644
--- a/src/cnetz/cnetz.c
+++ b/src/cnetz/cnetz.c
@@ -377,21 +377,23 @@ int cnetz_create(const char *kanal, enum cnetz_chan_type chan_type, const char *
 		goto error;
 
 	/* go into idle state */
-	cnetz_set_dsp_mode(cnetz, DSP_MODE_OGK);
-	cnetz_set_sched_dsp_mode(cnetz, DSP_MODE_OGK, 0);
+	if (chan_type == CHAN_TYPE_OGK || chan_type == CHAN_TYPE_OGK_SPK)
+		cnetz_set_dsp_mode(cnetz, DSP_MODE_OGK);
+	else
+		cnetz_set_dsp_mode(cnetz, DSP_MODE_OFF);
 	cnetz_go_idle(cnetz);
 
 #ifdef DEBUG_SPK
 	transaction_t *trans = create_transaction(cnetz, TRANS_DS, 2, 2, 22002, -1, -1);
 	trans->mo_call = 1;
-	cnetz_set_sched_dsp_mode(cnetz, DSP_MODE_SPK_K, 2);
+	cnetz_set_sched_dsp_mode(cnetz, DSP_MODE_SPK_K, (cnetz->sched_ts + 2) & 31);
 #else
 	/* create transaction for speech channel loopback */
 	if (loopback && chan_type == CHAN_TYPE_SPK) {
 		transaction_t *trans = create_transaction(cnetz, TRANS_VHQ_K, 2, 2, 22002, -1, -1);
 		trans->mo_call = 1;
 		cnetz_set_dsp_mode(cnetz, DSP_MODE_SPK_K);
-		cnetz_set_sched_dsp_mode(cnetz, DSP_MODE_SPK_K, 0);
+		cnetz_set_sched_dsp_mode(cnetz, DSP_MODE_SPK_K, (cnetz->sched_ts + 1) & 31);
 	}
 #endif
 
@@ -509,10 +511,11 @@ void cnetz_go_idle(cnetz_t *cnetz)
 
 	/* set scheduler to OgK or turn off SpK */
 	if (cnetz->dsp_mode == DSP_MODE_SPK_K || cnetz->dsp_mode == DSP_MODE_SPK_V) {
-		/* go idle after next frame/slot */
-		cnetz_set_sched_dsp_mode(cnetz, (atoi(cnetz->sender.kanal) == CNETZ_OGK_KANAL) ? DSP_MODE_OGK : DSP_MODE_OFF, 1);
+		/* switch next frame after distributed signaling boundary (mutliple of 8 slots) */
+		cnetz_set_sched_dsp_mode(cnetz, (atoi(cnetz->sender.kanal) == CNETZ_OGK_KANAL) ? DSP_MODE_OGK : DSP_MODE_OFF, (cnetz->sched_ts + 8) & 24);
 	} else {
-		cnetz_set_sched_dsp_mode(cnetz, (atoi(cnetz->sender.kanal) == CNETZ_OGK_KANAL) ? DSP_MODE_OGK : DSP_MODE_OFF, 0);
+		/* switch next frame */
+		cnetz_set_sched_dsp_mode(cnetz, (atoi(cnetz->sender.kanal) == CNETZ_OGK_KANAL) ? DSP_MODE_OGK : DSP_MODE_OFF, (cnetz->sched_ts + 1) & 31);
 		cnetz_set_dsp_mode(cnetz, (atoi(cnetz->sender.kanal) == CNETZ_OGK_KANAL) ? DSP_MODE_OGK : DSP_MODE_OFF);
 	}
 
@@ -533,7 +536,7 @@ static void cnetz_release(transaction_t *trans, uint8_t cause)
 	trans_new_state(trans, (trans->cnetz->dsp_mode == DSP_MODE_OGK) ? TRANS_VA : TRANS_AF);
 	trans->repeat = 0;
 	trans->release_cause = cause;
-	trans->cnetz->sched_switch_mode = 0;
+	trans->cnetz->sched_dsp_mode_ts = -1;
 	timer_stop(&trans->timer);
 }
 
@@ -1068,7 +1071,7 @@ vak:
 			/* change state to busy */
 			cnetz_new_state(spk, CNETZ_BUSY);
 			/* schedule switching two slots ahead */
-			cnetz_set_sched_dsp_mode(spk, DSP_MODE_SPK_K, 2);
+			cnetz_set_sched_dsp_mode(spk, DSP_MODE_SPK_K, (cnetz->sched_ts + 2) & 31);
 			/* relink */
 			unlink_transaction(trans);
 			link_transaction(trans, spk);
@@ -1384,7 +1387,7 @@ no_auth:
 			/* next sub frame */
 			trans_new_state(trans, TRANS_VHQ_V);
 			trans->repeat = 0;
-			cnetz_set_sched_dsp_mode(cnetz, DSP_MODE_SPK_V, 1);
+			cnetz_set_sched_dsp_mode(cnetz, DSP_MODE_SPK_V, (cnetz->sched_ts + 1) & 31);
 #ifndef DEBUG_SPK
 			timer_start(&trans->timer, 0.075 + 0.6 * F_VHQ); /* one slot + F_VHQ frames */
 #endif
@@ -1401,7 +1404,7 @@ no_auth:
 			/* next sub frame */
 			trans_new_state(trans, TRANS_VHQ_V);
 			trans->repeat = 0;
-			cnetz_set_sched_dsp_mode(cnetz, DSP_MODE_SPK_V, 1);
+			cnetz_set_sched_dsp_mode(cnetz, DSP_MODE_SPK_V, (cnetz->sched_ts + 1) & 31);
 			timer_start(&trans->timer, 0.075 + 0.6 * F_VHQ); /* one slot + F_VHQ frames */
 		}
 		break;
diff --git a/src/cnetz/cnetz.h b/src/cnetz/cnetz.h
index 88e621f..f8b0e1a 100644
--- a/src/cnetz/cnetz.h
+++ b/src/cnetz/cnetz.h
@@ -94,8 +94,8 @@ struct cnetz {
 	int			sched_ts;		/* current time slot */
 	int			sched_last_ts;		/* last timeslot we transmitted, to sync time of the receiver */
 	int			sched_r_m;		/* Rufblock (0) / Meldeblock (1) */
-	int			sched_switch_mode;	/* counts slots until mode is switched */
-	enum dsp_mode		sched_dsp_mode;		/* what mode shall be switched to  */
+	enum dsp_mode		sched_dsp_mode;		/* what mode shall be switched to */
+	int			sched_dsp_mode_ts;	/* time slot when to switch mode (-1 = don't switch) */
 
 	/* dsp states */
 	enum dsp_mode		dsp_mode;		/* current mode: audio, "Telegramm", .... */
diff --git a/src/cnetz/dsp.c b/src/cnetz/dsp.c
index 91f967c..ecf26a4 100644
--- a/src/cnetz/dsp.c
+++ b/src/cnetz/dsp.c
@@ -54,6 +54,27 @@ scrambler_t scrambler_test_scrambler1;
 scrambler_t scrambler_test_scrambler2;
 #endif
 
+const char *cnetz_dsp_mode_name(enum dsp_mode mode)
+{
+        static char invalid[16];
+
+	switch (mode) {
+        case DSP_SCHED_NONE:
+		return "SCHED_NONE";
+	case DSP_MODE_OFF:
+		return "OFF";
+	case DSP_MODE_OGK:
+		return "OGK";
+	case DSP_MODE_SPK_K:
+		return "SPK_K";
+	case DSP_MODE_SPK_V:
+		return "SPK_V";
+	}
+
+	sprintf(invalid, "invalid(%d)", mode);
+	return invalid;
+}
+
 static sample_t ramp_up[256], ramp_down[256];
 
 void dsp_init(void)
@@ -166,6 +187,8 @@ int dsp_init_sender(cnetz_t *cnetz, int measure_speed, double clock_speed[2], en
 	scrambler_setup(&scrambler_test_scrambler2, cnetz->sender.samplerate);
 #endif
 
+	cnetz->sched_dsp_mode_ts = -1;
+
 	return 0;
 
 error:
@@ -636,10 +659,11 @@ again:
 		}
 
 		/* switch to speech channel */
-		if (cnetz->sched_switch_mode && cnetz->sched_r_m == 0) {
-			if (--cnetz->sched_switch_mode == 0) {
+		if (cnetz->sched_dsp_mode_ts >= 0 && cnetz->sched_r_m == 0) {
+			if (cnetz->sched_dsp_mode_ts == cnetz->sched_ts) {
 				/* OgK / SpK(K) / SpK(V) */
-				PDEBUG_CHAN(DDSP, DEBUG_INFO, "Switching channel (mode)\n");
+				PDEBUG_CHAN(DDSP, DEBUG_INFO, "Now switchting channel mode to %s at timeslot %d\n", cnetz_dsp_mode_name(cnetz->sched_dsp_mode), cnetz->sched_dsp_mode_ts);
+				cnetz->sched_dsp_mode_ts = -1;
 				cnetz_set_dsp_mode(cnetz, cnetz->sched_dsp_mode);
 			}
 		}
@@ -843,39 +867,22 @@ void unshrink_speech(cnetz_t *cnetz, sample_t *speech_buffer, int count)
 	cnetz->sender.rxbuf_pos = pos;
 }
 
-const char *cnetz_dsp_mode_name(enum dsp_mode mode)
-{
-        static char invalid[16];
-
-	switch (mode) {
-        case DSP_SCHED_NONE:
-		return "SCHED_NONE";
-	case DSP_MODE_OFF:
-		return "OFF";
-	case DSP_MODE_OGK:
-		return "OGK";
-	case DSP_MODE_SPK_K:
-		return "SPK_K";
-	case DSP_MODE_SPK_V:
-		return "SPK_V";
-	}
-
-	sprintf(invalid, "invalid(%d)", mode);
-	return invalid;
-}
-
 void cnetz_set_dsp_mode(cnetz_t *cnetz, enum dsp_mode mode)
 {
-	PDEBUG_CHAN(DDSP, DEBUG_DEBUG, "DSP mode %s -> %s\n", cnetz_dsp_mode_name(cnetz->dsp_mode), cnetz_dsp_mode_name(mode));
-	cnetz->dsp_mode = mode;
+	if (mode != cnetz->dsp_mode) {
+		PDEBUG_CHAN(DDSP, DEBUG_INFO, "DSP mode %s -> %s\n", cnetz_dsp_mode_name(cnetz->dsp_mode), cnetz_dsp_mode_name(mode));
+		cnetz->dsp_mode = mode;
+	}
 	/* we must get rid of partly received frame */
 	fsk_demod_reset(&cnetz->fsk_demod);
 }
 
-void cnetz_set_sched_dsp_mode(cnetz_t *cnetz, enum dsp_mode mode, int frames_ahead)
+void cnetz_set_sched_dsp_mode(cnetz_t *cnetz, enum dsp_mode mode, int timeslot)
 {
-	PDEBUG_CHAN(DDSP, DEBUG_DEBUG, " Schedule DSP mode %s -> %s in %d frames\n", cnetz_dsp_mode_name(cnetz->dsp_mode), cnetz_dsp_mode_name(mode), frames_ahead);
-	cnetz->sched_dsp_mode = mode;
-	cnetz->sched_switch_mode = frames_ahead;
+	if (mode != cnetz->dsp_mode) {
+		PDEBUG_CHAN(DDSP, DEBUG_INFO, "Schedule DSP mode %s -> %s at timeslot %d\n", cnetz_dsp_mode_name(cnetz->dsp_mode), cnetz_dsp_mode_name(mode), timeslot);
+		cnetz->sched_dsp_mode = mode;
+		cnetz->sched_dsp_mode_ts = timeslot;
+	}
 }
 
diff --git a/src/cnetz/dsp.h b/src/cnetz/dsp.h
index f5e3506..7af7c94 100644
--- a/src/cnetz/dsp.h
+++ b/src/cnetz/dsp.h
@@ -5,5 +5,5 @@ void dsp_cleanup_sender(cnetz_t *cnetz);
 void calc_clock_speed(cnetz_t *cnetz, double samples, int tx, int result);
 void unshrink_speech(cnetz_t *cnetz, sample_t *speech_buffer, int count);
 void cnetz_set_dsp_mode(cnetz_t *cnetz, enum dsp_mode mode);
-void cnetz_set_sched_dsp_mode(cnetz_t *cnetz, enum dsp_mode mode, int frames_ahead);
+void cnetz_set_sched_dsp_mode(cnetz_t *cnetz, enum dsp_mode mode, int timeslot);