diff --git a/src/host/layer23/include/osmocom/bb/mobile/gapk_io.h b/src/host/layer23/include/osmocom/bb/mobile/gapk_io.h
index b9f1bc52d..ab8b65798 100644
--- a/src/host/layer23/include/osmocom/bb/mobile/gapk_io.h
+++ b/src/host/layer23/include/osmocom/bb/mobile/gapk_io.h
@@ -42,6 +42,6 @@ gapk_io_state_alloc_mode_rate(struct osmocom_ms *ms,
 void gapk_io_state_free(struct gapk_io_state *state);
 
 void gapk_io_enqueue_dl(struct gapk_io_state *state, struct msgb *msg);
-int gapk_io_serve_ms(struct osmocom_ms *ms, struct gapk_io_state *state);
+void gapk_io_dequeue_ul(struct osmocom_ms *ms, struct gapk_io_state *state);
 
 #endif /* WITH_GAPK_IO */
diff --git a/src/host/layer23/include/osmocom/bb/mobile/tch.h b/src/host/layer23/include/osmocom/bb/mobile/tch.h
index 293397ded..b026bd5d6 100644
--- a/src/host/layer23/include/osmocom/bb/mobile/tch.h
+++ b/src/host/layer23/include/osmocom/bb/mobile/tch.h
@@ -24,6 +24,5 @@ struct tch_state {
 };
 
 int tch_init(struct osmocom_ms *ms);
-int tch_serve_ms(struct osmocom_ms *ms);
 int tch_send_msg(struct osmocom_ms *ms, struct msgb *msg);
 int tch_send_mncc_frame(struct osmocom_ms *ms, const struct gsm_data_frame *frame);
diff --git a/src/host/layer23/src/mobile/app_mobile.c b/src/host/layer23/src/mobile/app_mobile.c
index 453990eec..477c4fa52 100644
--- a/src/host/layer23/src/mobile/app_mobile.c
+++ b/src/host/layer23/src/mobile/app_mobile.c
@@ -81,7 +81,6 @@ int mobile_work(struct osmocom_ms *ms)
 		w |= gsm322_cs_dequeue(ms);
 		w |= gsm_sim_job_dequeue(ms);
 		w |= mncc_dequeue(ms);
-		w |= tch_serve_ms(ms);
 		if (w)
 			work = 1;
 	} while (w);
diff --git a/src/host/layer23/src/mobile/gapk_io.c b/src/host/layer23/src/mobile/gapk_io.c
index 4699bae52..cc756b063 100644
--- a/src/host/layer23/src/mobile/gapk_io.c
+++ b/src/host/layer23/src/mobile/gapk_io.c
@@ -503,6 +503,7 @@ gapk_io_state_alloc_mode_rate(struct osmocom_ms *ms,
 	return gapk_io_state_alloc(ms, codec);
 }
 
+/* Enqueue a Downlink TCH frame */
 void gapk_io_enqueue_dl(struct gapk_io_state *state, struct msgb *msg)
 {
 	if (state->tch_dl_fb_len >= GAPK_ULDL_QUEUE_LIMIT) {
@@ -513,49 +514,23 @@ void gapk_io_enqueue_dl(struct gapk_io_state *state, struct msgb *msg)
 
 	msgb_enqueue_count(&state->tch_dl_fb, msg,
 			   &state->tch_dl_fb_len);
+
+	/* Decode and play a received DL TCH frame */
+	osmo_gapk_pq_execute(state->pq_sink);
 }
 
-/* Serves both UL/DL TCH frame I/O buffers */
-int gapk_io_serve_ms(struct osmocom_ms *ms, struct gapk_io_state *state)
+/* Dequeue an Uplink TCH frame */
+void gapk_io_dequeue_ul(struct osmocom_ms *ms, struct gapk_io_state *state)
 {
-	int work = 0;
+	struct msgb *msg;
 
-	/**
-	 * Make sure we have at least two DL frames
-	 * to prevent discontinuous playback.
-	 */
-	if (state->tch_dl_fb_len < 2)
-		return 0;
+	/* Record and encode an UL TCH frame */
+	osmo_gapk_pq_execute(state->pq_source);
 
-	/**
-	 * TODO: if there is an active call, but no TCH frames
-	 * in DL buffer, put silence frames using the upcoming
-	 * ECU (Error Concealment Unit) of libosmocodec.
-	 */
-	while (!llist_empty(&state->tch_dl_fb)) {
-		/* Decode and play a received DL TCH frame */
-		osmo_gapk_pq_execute(state->pq_sink);
-
-		/* Record and encode an UL TCH frame back */
-		osmo_gapk_pq_execute(state->pq_source);
-
-		work |= 1;
-	}
-
-	while (!llist_empty(&state->tch_ul_fb)) {
-		struct msgb *tch_msg;
-
-		/* Obtain one TCH frame from the UL buffer */
-		tch_msg = msgb_dequeue_count(&state->tch_ul_fb,
-					     &state->tch_ul_fb_len);
-
-		/* Push a voice frame to the lower layers */
-		tch_send_msg(ms, tch_msg);
-
-		work |= 1;
-	}
-
-	return work;
+	/* Obtain one TCH frame from the UL buffer */
+	msg = msgb_dequeue_count(&state->tch_ul_fb, &state->tch_ul_fb_len);
+	if (msg != NULL)
+		tch_send_msg(ms, msg);
 }
 
 /**
diff --git a/src/host/layer23/src/mobile/tch.c b/src/host/layer23/src/mobile/tch.c
index 5acdef2e4..b78682f5e 100644
--- a/src/host/layer23/src/mobile/tch.c
+++ b/src/host/layer23/src/mobile/tch.c
@@ -45,7 +45,6 @@ void tch_data_state_free(struct tch_data_state *state);
 
 int tch_voice_recv(struct osmocom_ms *ms, struct msgb *msg);
 int tch_data_recv(struct osmocom_ms *ms, struct msgb *msg);
-int tch_voice_serve_ms(struct osmocom_ms *ms);
 
 /* Receive a Downlink traffic (voice/data) frame from the lower layers */
 static int tch_recv_cb(struct osmocom_ms *ms, struct msgb *msg)
@@ -116,20 +115,6 @@ int tch_send_mncc_frame(struct osmocom_ms *ms, const struct gsm_data_frame *fram
 	return tch_send_msg(ms, nmsg);
 }
 
-int tch_serve_ms(struct osmocom_ms *ms)
-{
-	struct tch_state *state = ms->tch_state;
-	int rc = 0;
-
-	if (state == NULL)
-		return 0;
-	if (state->is_voice)
-		rc = tch_voice_serve_ms(ms);
-	/* TODO: else tch_data_serve_ms() */
-
-	return rc;
-}
-
 static void tch_trans_cstate_active_cb(struct gsm_trans *trans, bool rx_only)
 {
 	struct osmocom_ms *ms = trans->ms;
diff --git a/src/host/layer23/src/mobile/tch_voice.c b/src/host/layer23/src/mobile/tch_voice.c
index a85d7dcba..ac793e84c 100644
--- a/src/host/layer23/src/mobile/tch_voice.c
+++ b/src/host/layer23/src/mobile/tch_voice.c
@@ -90,11 +90,12 @@ int tch_voice_recv(struct osmocom_ms *ms, struct msgb *msg)
 		return tch_forward_mncc(ms, msg);
 	case TCH_VOICE_IOH_GAPK:
 #ifdef WITH_GAPK_IO
-		/* Enqueue a frame to the DL TCH buffer */
-		if (state->gapk_io != NULL)
+		if (state->gapk_io != NULL) {
 			gapk_io_enqueue_dl(state->gapk_io, msg);
-		else
+			gapk_io_dequeue_ul(ms, state->gapk_io);
+		} else {
 			msgb_free(msg);
+		}
 		break;
 #endif
 	case TCH_VOICE_IOH_L1PHY:
@@ -107,18 +108,6 @@ int tch_voice_recv(struct osmocom_ms *ms, struct msgb *msg)
 	return 0;
 }
 
-int tch_voice_serve_ms(struct osmocom_ms *ms)
-{
-#ifdef WITH_GAPK_IO
-	struct tch_voice_state *state = &ms->tch_state->voice;
-
-	if (state->handler == TCH_VOICE_IOH_GAPK)
-		return gapk_io_serve_ms(ms, state->gapk_io);
-#endif
-
-	return 0;
-}
-
 int tch_voice_state_init(struct gsm_trans *trans, struct tch_voice_state *state)
 {
 	struct osmocom_ms *ms = trans->ms;