diff --git a/include/Makefile.am b/include/Makefile.am
index b341ee3..572c880 100644
--- a/include/Makefile.am
+++ b/include/Makefile.am
@@ -90,6 +90,7 @@
                        osmocom/coding/gsm0503_mapping.h \
                        osmocom/coding/gsm0503_interleaving.h \
                        osmocom/coding/gsm0503_coding.h \
+                       osmocom/coding/gsm0503_amr_dtx.h \
                        osmocom/gsm/gsm0808.h \
                        osmocom/gsm/gsm29205.h \
                        osmocom/gsm/gsm0808_utils.h \
diff --git a/include/osmocom/coding/gsm0503_amr_dtx.h b/include/osmocom/coding/gsm0503_amr_dtx.h
new file mode 100644
index 0000000..f048a6e
--- /dev/null
+++ b/include/osmocom/coding/gsm0503_amr_dtx.h
@@ -0,0 +1,40 @@
+/*! \file gsm0503_amr_dtx.h
+ *  GSM TS 05.03 coding
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+#include <osmocom/core/defs.h>
+#include <osmocom/core/bits.h>
+
+/*! \addtogroup coding
+ *  @{
+ * \file gsm0503_amr_dtx.h */
+
+enum gsm0503_amr_dtx_frames {
+	AMR_OTHER,
+	AFS_SID_FIRST,
+	AFS_SID_UPDATE,
+	AFS_SID_UPDATE_CN,
+	AFS_ONSET,
+	AHS_SID_UPDATE,
+	AHS_SID_UPDATE_CN,
+	AHS_SID_FIRST_P1,
+	AHS_SID_FIRST_P2,
+	AHS_ONSET,
+	AHS_SID_FIRST_INH,
+	AHS_SID_UPDATE_INH,
+};
+
+extern const struct value_string gsm0503_amr_dtx_frame_names[];
+static inline const char *gsm0503_amr_dtx_frame_name(enum gsm0503_amr_dtx_frames frame)
+{
+	return get_value_string(gsm0503_amr_dtx_frame_names, frame);
+}
+
+enum gsm0503_amr_dtx_frames gsm0503_detect_afs_dtx_frame(int *n_errors, int *n_bits_total, const ubit_t *ubits);
+enum gsm0503_amr_dtx_frames gsm0503_detect_ahs_dtx_frame(int *n_errors, int *n_bits_total, const ubit_t *ubits);
+
+/*! @} */
diff --git a/include/osmocom/coding/gsm0503_coding.h b/include/osmocom/coding/gsm0503_coding.h
index 98038f8..2afa049 100644
--- a/include/osmocom/coding/gsm0503_coding.h
+++ b/include/osmocom/coding/gsm0503_coding.h
@@ -58,12 +58,18 @@
 int gsm0503_tch_afs_decode(uint8_t *tch_data, const sbit_t *bursts,
 	int codec_mode_req, uint8_t *codec, int codecs, uint8_t *ft,
 	uint8_t *cmr, int *n_errors, int *n_bits_total);
+int gsm0503_tch_afs_decode_dtx(uint8_t *tch_data, const sbit_t *bursts,
+	int codec_mode_req, uint8_t *codec, int codecs, uint8_t *ft,
+	uint8_t *cmr, int *n_errors, int *n_bits_total, uint8_t *dtx);
 
 int gsm0503_tch_ahs_encode(ubit_t *bursts, const uint8_t *tch_data, int len,
 	int codec_mode_req, uint8_t *codec, int codecs, uint8_t ft, uint8_t cmr);
 int gsm0503_tch_ahs_decode(uint8_t *tch_data, const sbit_t *bursts, int odd,
 	int codec_mode_req, uint8_t *codec, int codecs, uint8_t *ft,
 	uint8_t *cmr, int *n_errors, int *n_bits_total);
+int gsm0503_tch_ahs_decode_dtx(uint8_t *tch_data, const sbit_t *bursts, int odd,
+	int codec_mode_req, uint8_t *codec, int codecs, uint8_t *ft,
+	uint8_t *cmr, int *n_errors, int *n_bits_total, uint8_t *dtx);
 
 int gsm0503_rach_ext_encode(ubit_t *burst, uint16_t ra, uint8_t bsic, bool is_11bit);
 int gsm0503_rach_encode(ubit_t *burst, const uint8_t *ra, uint8_t bsic) OSMO_DEPRECATED("Use gsm0503_rach_ext_encode() instead");
diff --git a/src/coding/Makefile.am b/src/coding/Makefile.am
index f47fe45..b023668 100644
--- a/src/coding/Makefile.am
+++ b/src/coding/Makefile.am
@@ -20,7 +20,8 @@
 	gsm0503_mapping.c \
 	gsm0503_tables.c \
 	gsm0503_parity.c \
-	gsm0503_coding.c
+	gsm0503_coding.c \
+	gsm0503_amr_dtx.c
 libosmocoding_la_LDFLAGS = \
 	$(LTLDFLAGS_OSMOCODING) \
 	-version-info \
diff --git a/src/coding/gsm0503_amr_dtx.c b/src/coding/gsm0503_amr_dtx.c
new file mode 100644
index 0000000..724cf09
--- /dev/null
+++ b/src/coding/gsm0503_amr_dtx.c
@@ -0,0 +1,314 @@
+/*
+ * (C) 2020 by sysmocom - s.f.m.c. GmbH, Author: Philipp Maier
+ * All Rights Reserved
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ *
+ * 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 2 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 <string.h>
+#include <stdlib.h>
+#include <errno.h>
+
+#include <osmocom/core/bits.h>
+#include <osmocom/core/conv.h>
+#include <osmocom/core/utils.h>
+#include <osmocom/coding/gsm0503_amr_dtx.h>
+#include <osmocom/coding/gsm0503_parity.h>
+#include <osmocom/gsm/gsm0503.h>
+
+/* See also: 3GPP TS 05.03, chapter 3.10.1.3, 3.10.5.2 Identification marker */
+static const ubit_t id_marker_1[] = { 1, 0, 1, 1, 0, 0, 0, 0, 1 };
+
+/* See also: 3GPP TS 05.03, chapter 3.9.1.3, 3.10.2.2, 3.10.2.2 Identification marker */
+static const ubit_t id_marker_0[] = { 0, 1, 0, 0, 1, 1, 1, 1, 0 };
+
+/* See also: 3GPP TS 05.03, chapter 3.9 Adaptive multi rate speech channel at full rate (TCH/AFS) */
+static const ubit_t codec_mode_1_sid[] = { 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 1, 0, 1, 0 };
+static const ubit_t codec_mode_2_sid[] = { 0, 0, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 0 };
+static const ubit_t codec_mode_3_sid[] = { 1, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 0, 1 };
+static const ubit_t codec_mode_4_sid[] = { 0, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 0, 1, 1, 1 };
+
+const struct value_string gsm0503_amr_dtx_frame_names[] = {
+	{ AFS_SID_FIRST,	"AFS_SID_FIRST" },
+	{ AFS_SID_UPDATE,	"AFS_SID_UPDATE" },
+	{ AFS_ONSET,		"AFS_ONSET" },
+	{ AHS_SID_UPDATE,	"AHS_SID_UPDATE" },
+	{ AHS_SID_FIRST_P1,	"AHS_SID_FIRST_P1" },
+	{ AHS_SID_FIRST_P2,	"AHS_SID_FIRST_P2" },
+	{ AHS_ONSET,		"AHS_ONSET" },
+	{ AHS_SID_FIRST_INH,	"AHS_SID_FIRST_INH" },
+	{ AHS_SID_UPDATE_INH,	"AHS_SID_UPDATE_INH" },
+	{ AMR_OTHER,		"NON DTX FRAME (OTHER)" },
+	{ 0, NULL }
+};
+
+static bool detect_afs_id_marker(int *n_errors, int *n_bits_total, const ubit_t * ubits, uint8_t offset, uint8_t count,
+				 const ubit_t * id_marker, uint8_t id_marker_len)
+{
+	unsigned int i, k;
+	unsigned int id_bit_nr = 0;
+	int errors = 0;
+	int bits = 0;
+
+	/* Override coded in-band data */
+	ubits += offset;
+
+	/* Check for identification marker bits */
+	for (i = 0; i < count; i++) {
+		for (k = 0; k < 4; k++) {
+			if (id_marker[id_bit_nr % id_marker_len] != *ubits)
+				errors++;
+			id_bit_nr++;
+			ubits++;
+			bits++;
+		}
+
+		/* Jump to the next block of 4 bits */
+		ubits += 4;
+	}
+
+	*n_errors = errors;
+	*n_bits_total = bits;
+
+	/* Tolerate up to 1/8 errornous bits */
+	return *n_errors < *n_bits_total / 8;
+}
+
+static bool detect_ahs_id_marker(int *n_errors, int *n_bits_total, const ubit_t * ubits, const ubit_t * id_marker)
+{
+	unsigned int i, k;
+	int errors = 0;
+	int bits = 0;
+
+	/* Override coded in-band data */
+	ubits += 16;
+
+	/* Check first identification marker bits (23*9 bits) */
+	for (i = 0; i < 23; i++) {
+		for (k = 0; k < 9; k++) {
+			if (id_marker[k] != *ubits)
+				errors++;
+			ubits++;
+			bits++;
+		}
+	}
+
+	/* Check remaining identification marker bits (5 bits) */
+	for (k = 0; k < 5; k++) {
+		if (id_marker[k] != *ubits)
+			errors++;
+		ubits++;
+		bits++;
+	}
+
+	*n_errors = errors;
+	*n_bits_total = bits;
+
+	/* Tolerate up to 1/8 errornous bits */
+	return *n_errors < *n_bits_total / 8;
+}
+
+static bool detect_interleaved_ahs_id_marker(int *n_errors, int *n_bits_total, const ubit_t * ubits, uint8_t offset,
+					     uint8_t n_bits, const ubit_t * id_marker, uint8_t id_marker_len)
+{
+	unsigned int i, k;
+	int errors = 0;
+	int bits = 0;
+	uint8_t full_rounds = n_bits / id_marker_len;
+	uint8_t remainder = n_bits % id_marker_len;
+
+	/* Override coded in-band data */
+	ubits += offset;
+
+	/* Check first identification marker bits (23*9 bits) */
+	for (i = 0; i < full_rounds; i++) {
+		for (k = 0; k < id_marker_len; k++) {
+			if (id_marker[k] != *ubits)
+				errors++;
+			ubits += 2;
+			bits++;
+		}
+	}
+
+	/* Check remaining identification marker bits (5 bits) */
+	for (k = 0; k < remainder; k++) {
+		if (id_marker[k] != *ubits)
+			errors++;
+		ubits += 2;
+		bits++;
+	}
+
+	*n_errors = errors;
+	*n_bits_total = bits;
+
+	/* Tolerate up to 1/8 errornous bits */
+	return *n_errors < *n_bits_total / 8;
+}
+
+/* Detect a an FR AMR SID_FIRST frame by its identifcation marker */
+static bool detect_afs_sid_first(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	return detect_afs_id_marker(n_errors, n_bits_total, ubits, 32, 53, id_marker_0, 9);
+}
+
+/* Detect an FR AMR SID_FIRST frame by its identification marker */
+static bool detect_afs_sid_update(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	return detect_afs_id_marker(n_errors, n_bits_total, ubits, 36, 53, id_marker_0, 9);
+}
+
+/* Detect an FR AMR SID_FIRST frame by its repeating coded inband data */
+static bool detect_afs_onset(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	bool rc;
+
+	rc = detect_afs_id_marker(n_errors, n_bits_total, ubits, 4, 57, codec_mode_1_sid, 16);
+	if (rc)
+		return true;
+
+	rc = detect_afs_id_marker(n_errors, n_bits_total, ubits, 4, 57, codec_mode_2_sid, 16);
+	if (rc)
+		return true;
+
+	rc = detect_afs_id_marker(n_errors, n_bits_total, ubits, 4, 57, codec_mode_3_sid, 16);
+	if (rc)
+		return true;
+
+	rc = detect_afs_id_marker(n_errors, n_bits_total, ubits, 4, 57, codec_mode_4_sid, 16);
+	if (rc)
+		return true;
+
+	return false;
+}
+
+/* Detect an HR AMR SID UPDATE frame by its identification marker */
+static bool detect_ahs_sid_update(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	return detect_ahs_id_marker(n_errors, n_bits_total, ubits, id_marker_1);
+}
+
+/* Detect an HR AMR SID FIRST (part 1) frame by its identification marker */
+static bool detect_ahs_sid_first_p1(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	return detect_ahs_id_marker(n_errors, n_bits_total, ubits, id_marker_0);
+}
+
+/* Detect an HR AMR SID FIRST (part 2) frame by its repeating coded inband data */
+static bool detect_ahs_sid_first_p2(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	bool rc;
+
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 0, 114, codec_mode_1_sid, 16);
+	if (rc)
+		return true;
+
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 0, 114, codec_mode_2_sid, 16);
+	if (rc)
+		return true;
+
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 0, 114, codec_mode_3_sid, 16);
+	if (rc)
+		return true;
+
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 0, 114, codec_mode_4_sid, 16);
+	if (rc)
+		return true;
+
+	return false;
+}
+
+/* Detect an HR AMR ONSET frame by its repeating coded inband data */
+static bool detect_ahs_onset(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	bool rc;
+
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 1, 114, codec_mode_1_sid, 16);
+	if (rc)
+		return true;
+
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 1, 114, codec_mode_2_sid, 16);
+	if (rc)
+		return true;
+
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 1, 114, codec_mode_3_sid, 16);
+	if (rc)
+		return true;
+
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 1, 114, codec_mode_4_sid, 16);
+	if (rc)
+		return true;
+
+	return false;
+}
+
+/* Detect an HR AMR SID FIRST INHIBIT frame by its identification marker */
+static bool detect_ahs_sid_first_inh(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	return detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 33, 212, id_marker_1, 9);
+}
+
+/* Detect an HR AMR SID UPDATE INHIBIT frame by its identification marker */
+static bool detect_ahs_sid_update_inh(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	return detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 33, 212, id_marker_0, 9);
+}
+
+/*! Detect FR AMR DTX frame in unmapped, deinterleaved frame bits.
+ *  \param[in] ubits input bits (456 bit).
+ *  \param[out] n_errors number of errornous bits.
+ *  \param[out] n_bits_total number of checked bits.
+ *  \returns dtx frame type. */
+enum gsm0503_amr_dtx_frames gsm0503_detect_afs_dtx_frame(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	if (detect_afs_sid_first(n_errors, n_bits_total, ubits))
+		return AFS_SID_FIRST;
+	if (detect_afs_sid_update(n_errors, n_bits_total, ubits))
+		return AFS_SID_UPDATE;
+	if (detect_afs_onset(n_errors, n_bits_total, ubits))
+		return AFS_ONSET;
+
+	*n_errors = 0;
+	*n_bits_total = 0;
+	return AMR_OTHER;
+}
+
+/*! Detect HR AMR DTX frame in unmapped, deinterleaved frame bits.
+ *  \param[in] ubits input bits (456 bit).
+ *  \param[out] n_errors number of errornous bits.
+ *  \param[out] n_bits_total number of checked bits.
+ *  \returns dtx frame type, */
+enum gsm0503_amr_dtx_frames gsm0503_detect_ahs_dtx_frame(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	if (detect_ahs_sid_update(n_errors, n_bits_total, ubits))
+		return AHS_SID_UPDATE;
+	if (detect_ahs_sid_first_inh(n_errors, n_bits_total, ubits))
+		return AHS_SID_FIRST_INH;
+	if (detect_ahs_sid_update_inh(n_errors, n_bits_total, ubits))
+		return AHS_SID_UPDATE_INH;
+	if (detect_ahs_sid_first_p1(n_errors, n_bits_total, ubits))
+		return AHS_SID_FIRST_P1;
+	if (detect_ahs_sid_first_p2(n_errors, n_bits_total, ubits))
+		return AHS_SID_FIRST_P2;
+	if (detect_ahs_onset(n_errors, n_bits_total, ubits))
+		return AHS_ONSET;
+
+	*n_errors = 0;
+	*n_bits_total = 0;
+	return AMR_OTHER;
+}
diff --git a/src/coding/gsm0503_coding.c b/src/coding/gsm0503_coding.c
index 5592433..1bec56e 100644
--- a/src/coding/gsm0503_coding.c
+++ b/src/coding/gsm0503_coding.c
@@ -47,6 +47,7 @@
 #include <osmocom/coding/gsm0503_tables.h>
 #include <osmocom/coding/gsm0503_coding.h>
 #include <osmocom/coding/gsm0503_parity.h>
+#include <osmocom/coding/gsm0503_amr_dtx.h>
 
 /*! \mainpage libosmocoding Documentation
  *
@@ -1635,6 +1636,39 @@
 		d_bits[i] = (tch_data[j >> 3] >> (7 - (j & 7))) & 1;
 }
 
+/* Append STI and MI bits to the SID_UPDATE frame, see also
+ * 3GPP TS 26.101, chapter 4.2.3 AMR Core Frame with comfort noise bits */
+static void tch_amr_sid_update_append(ubit_t *sid_update, uint8_t sti, uint8_t mi)
+{
+	/* Zero out the space that had been used by the CRC14 */
+	memset(sid_update + 35, 0, 14);
+
+	/* Append STI and MI parameters */
+	sid_update[35] = sti & 1;
+	sid_update[36] = mi & 1;
+	sid_update[37] = mi >> 1 & 1;
+	sid_update[38] = mi >> 2 & 1;
+}
+
+/* Extract a SID UPDATE fram the sbits of an FR AMR frame */
+static void extract_afs_sid_update(sbit_t *sid_update, const sbit_t *sbits)
+{
+
+	unsigned int i;
+
+	sbits += 32;
+
+	for (i = 0; i < 53; i++) {
+		sid_update[0] = sbits[0];
+		sid_update[1] = sbits[1];
+		sid_update[2] = sbits[2];
+		sid_update[3] = sbits[3];
+		sid_update += 4;
+		sbits += 8;
+	}
+
+}
+
 /* re-arrange according to TS 05.03 Table 2 (receiver) */
 static void tch_fr_d_to_b(ubit_t *b_bits, const ubit_t *d_bits)
 {
@@ -2101,10 +2135,37 @@
 	int codec_mode_req, uint8_t *codec, int codecs, uint8_t *ft,
 	uint8_t *cmr, int *n_errors, int *n_bits_total)
 {
+	return gsm0503_tch_afs_decode_dtx(tch_data, bursts, codec_mode_req,
+					  codec, codecs, ft, cmr, n_errors,
+					  n_bits_total, NULL);
+}
+
+/*! Perform channel decoding of a TCH/AFS channel according TS 05.03
+ *  \param[out] tch_data Codec frame in RTP payload format
+ *  \param[in] bursts buffer containing the symbols of 8 bursts
+ *  \param[in] codec_mode_req is this CMR (1) or CMC (0)
+ *  \param[in] codec array of active codecs (active codec set)
+ *  \param[in] codecs number of codecs in \a codec
+ *  \param ft Frame Type; Input if \a codec_mode_req = 1, Output *  otherwise
+ *  \param[out] cmr Output in \a codec_mode_req = 1
+ *  \param[out] n_errors Number of detected bit errors
+ *  \param[out] n_bits_total Total number of bits
+ *  \param[inout] dtx DTX frame type output, previous DTX frame type input
+ *  \returns (>=4) length of bytes used in \a tch_data output buffer; ([0,3])
+ *  	     codec out of range; negative on error
+ */
+int gsm0503_tch_afs_decode_dtx(uint8_t *tch_data, const sbit_t *bursts,
+	int codec_mode_req, uint8_t *codec, int codecs, uint8_t *ft,
+	uint8_t *cmr, int *n_errors, int *n_bits_total, uint8_t *dtx)
+{
 	sbit_t iB[912], cB[456], h;
 	ubit_t d[244], p[6], conv[250];
 	int i, j, k, best = 0, rv, len, steal = 0, id = 0;
+	ubit_t cBd[456];
 	*n_errors = 0; *n_bits_total = 0;
+	static ubit_t sid_first_dummy[64] = { 0 };
+	sbit_t sid_update_enc[256];
+	uint8_t dtx_prev;
 
 	for (i=0; i<8; i++) {
 		gsm0503_tch_burst_unmap(&iB[i * 114], &bursts[i * 116], &h, i >> 2);
@@ -2123,6 +2184,50 @@
 		return GSM_MACBLOCK_LEN;
 	}
 
+	/* Determine the DTX frame type (SID_UPDATE, ONSET etc...) */
+	if (dtx) {
+		osmo_sbit2ubit(cBd, cB, 456);
+		dtx_prev = *dtx;
+		*dtx = gsm0503_detect_afs_dtx_frame(n_errors, n_bits_total, cBd);
+
+		if (dtx_prev == AFS_SID_UPDATE && *dtx == AMR_OTHER) {
+			/* NOTE: The AFS_SID_UPDATE frame is splitted into
+			 * two half rate frames. If the id marker frame
+			 * (AFS_SID_UPDATE) is detected the following frame
+			 * contains the actual comfort noised data part of
+			 * (AFS_SID_UPDATE_CN). */
+			*dtx = AFS_SID_UPDATE_CN;
+
+			extract_afs_sid_update(sid_update_enc, cB);
+			osmo_conv_decode_ber(&gsm0503_tch_axs_sid_update,
+					     sid_update_enc, conv, n_errors,
+					     n_bits_total);
+			rv = osmo_crc16gen_check_bits(&gsm0503_amr_crc14, conv,
+						      35, conv + 35);
+			if (rv != 0) {
+				/* Error checking CRC14 for an AMR SID_UPDATE frame */
+				return -1;
+			}
+
+			tch_amr_sid_update_append(conv, 1,
+						  (codec_mode_req) ? codec[*ft]
+						  : codec[id]);
+			tch_amr_reassemble(tch_data, conv, 39);
+			len = 5;
+			goto out;
+		} else if (*dtx == AFS_SID_FIRST) {
+			tch_amr_sid_update_append(sid_first_dummy, 0,
+						  (codec_mode_req) ? codec[*ft]
+						  : codec[id]);
+			tch_amr_reassemble(tch_data, conv, 39);
+			len = 5;
+			goto out;
+		} else if (*dtx == AFS_ONSET) {
+			len = 0;
+			goto out;
+		}
+	}
+
 	for (i = 0; i < 4; i++) {
 		for (j = 0, k = 0; j < 8; j++)
 			k += abs(((int)gsm0503_afs_ic_sbit[i][j]) - ((int)cB[j]));
@@ -2283,6 +2388,7 @@
 		return -1;
 	}
 
+out:
 	/* Change codec request / indication, if frame is valid */
 	if (codec_mode_req)
 		*cmr = id;
@@ -2480,9 +2586,36 @@
 	int codec_mode_req, uint8_t *codec, int codecs, uint8_t *ft,
 	uint8_t *cmr, int *n_errors, int *n_bits_total)
 {
+	return gsm0503_tch_ahs_decode_dtx(tch_data, bursts, odd, codec_mode_req,
+					  codec, codecs, ft, cmr, n_errors,
+					  n_bits_total, NULL);
+}
+
+/*! Perform channel decoding of a TCH/AFS channel according TS 05.03
+ *  \param[out] tch_data Codec frame in RTP payload format
+ *  \param[in] bursts buffer containing the symbols of 8 bursts
+ *  \param[in] odd Is this an odd (1) or even (0) frame number?
+ *  \param[in] codec_mode_req is this CMR (1) or CMC (0)
+ *  \param[in] codec array of active codecs (active codec set)
+ *  \param[in] codecs number of codecs in \a codec
+ *  \param ft Frame Type; Input if \a codec_mode_req = 1, Output *  otherwise
+ *  \param[out] cmr Output in \a codec_mode_req = 1
+ *  \param[out] n_errors Number of detected bit errors
+ *  \param[out] n_bits_total Total number of bits
+ *  \param[inout] dtx DTX frame type output, previous DTX frame type input
+ *  \returns (>=4) length of bytes used in \a tch_data output buffer; ([0,3])
+ *  	     codec out of range; negative on error
+ */
+int gsm0503_tch_ahs_decode_dtx(uint8_t *tch_data, const sbit_t *bursts, int odd,
+	int codec_mode_req, uint8_t *codec, int codecs, uint8_t *ft,
+	uint8_t *cmr, int *n_errors, int *n_bits_total, uint8_t *dtx)
+{
 	sbit_t iB[912], cB[456], h;
 	ubit_t d[244], p[6], conv[135];
 	int i, j, k, best = 0, rv, len, steal = 0, id = 0;
+	ubit_t cBd[456];
+	static ubit_t sid_first_dummy[64] = { 0 };
+	uint8_t dtx_prev;
 
 	/* only unmap the stealing bits */
 	if (!odd) {
@@ -2526,6 +2659,52 @@
 
 	gsm0503_tch_hr_deinterleave(cB, iB);
 
+	/* Determine the DTX frame type (SID_UPDATE, ONSET etc...) */
+	if (dtx) {
+		osmo_sbit2ubit(cBd, cB, 456);
+		dtx_prev = *dtx;
+		*dtx = gsm0503_detect_ahs_dtx_frame(n_errors, n_bits_total, cBd);
+
+		if (dtx_prev == AHS_SID_UPDATE && *dtx == AMR_OTHER) {
+			/* NOTE: The AHS_SID_UPDATE frame is splitted into
+			 * two half rate frames. If the id marker frame
+			 * (AHS_SID_UPDATE) is detected the following frame
+			 * contains the actual comfort noised data part of
+			 * (AHS_SID_UPDATE_CN). */
+			*dtx = AHS_SID_UPDATE_CN;
+
+			osmo_conv_decode_ber(&gsm0503_tch_axs_sid_update,
+					     cB + 16, conv, n_errors,
+					     n_bits_total);
+			rv = osmo_crc16gen_check_bits(&gsm0503_amr_crc14, conv,
+						      35, conv + 35);
+			if (rv != 0) {
+				/* Error checking CRC14 for an AMR SID_UPDATE frame */
+				return -1;
+			}
+
+			tch_amr_sid_update_append(conv, 1,
+						  (codec_mode_req) ? codec[*ft]
+						  : codec[id]);
+			tch_amr_reassemble(tch_data, conv, 39);
+			len = 5;
+			goto out;
+		} else if (*dtx == AHS_SID_FIRST_P2) {
+			tch_amr_sid_update_append(sid_first_dummy, 0,
+						  (codec_mode_req) ? codec[*ft]
+						  : codec[id]);
+			tch_amr_reassemble(tch_data, sid_first_dummy, 39);
+			len = 5;
+			goto out;
+		} else if (*dtx == AHS_SID_UPDATE || *dtx == AHS_ONSET
+			   || *dtx == AHS_SID_FIRST_INH
+			   || *dtx == AHS_SID_UPDATE_INH
+			   || *dtx == AHS_SID_FIRST_P1) {
+			len = 0;
+			goto out;
+		}
+	}
+
 	for (i = 0; i < 4; i++) {
 		for (j = 0, k = 0; j < 4; j++)
 			k += abs(((int)gsm0503_ahs_ic_sbit[i][j]) - ((int)cB[j]));
@@ -2670,6 +2849,7 @@
 		return -1;
 	}
 
+out:
 	/* Change codec request / indication, if frame is valid */
 	if (codec_mode_req)
 		*cmr = id;
diff --git a/src/coding/libosmocoding.map b/src/coding/libosmocoding.map
index 7f88111..325b6d8 100644
--- a/src/coding/libosmocoding.map
+++ b/src/coding/libosmocoding.map
@@ -107,8 +107,10 @@
 gsm0503_tch_hr_decode;
 gsm0503_tch_afs_encode;
 gsm0503_tch_afs_decode;
+gsm0503_tch_afs_decode_dtx;
 gsm0503_tch_ahs_encode;
 gsm0503_tch_ahs_decode;
+gsm0503_tch_ahs_decode_dtx;
 gsm0503_rach_ext_encode;
 gsm0503_rach_ext_decode;
 gsm0503_rach_ext_decode_ber;
@@ -117,6 +119,10 @@
 gsm0503_rach_decode_ber;
 gsm0503_sch_encode;
 gsm0503_sch_decode;
+gsm0503_amr_dtx_frame_names;
+gsm0503_amr_dtx_frame_name;
+gsm0503_detect_afs_dtx_frame;
+gsm0503_detect_ahs_dtx_frame;
 
 local: *;
 };
diff --git a/tests/Makefile.am b/tests/Makefile.am
index bf7017b..0d0327a 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -34,6 +34,7 @@
 		 use_count/use_count_test				\
 		 context/context_test					\
                  gsm0502/gsm0502_test					\
+                 dtx/dtx_gsm0503_test					\
 		 $(NULL)
 
 if ENABLE_MSGFILE
@@ -114,6 +115,10 @@
 gsm0502_gsm0502_test_SOURCES = gsm0502/gsm0502_test.c
 gsm0502_gsm0502_test_LDADD = $(LDADD) $(top_builddir)/src/gsm/libosmogsm.la
 
+dtx_dtx_gsm0503_test_SOURCES = dtx/dtx_gsm0503_test.c
+dtx_dtx_gsm0503_test_LDADD = $(LDADD) $(top_builddir)/src/gsm/libosmogsm.la \
+			     $(top_builddir)/src/coding/libosmocoding.la
+
 conv_conv_gsm0503_test_SOURCES = conv/conv_gsm0503_test.c conv/conv.c conv/gsm0503_test_vectors.c
 conv_conv_gsm0503_test_LDADD = $(LDADD) $(top_builddir)/src/gsm/libgsmint.la
 conv_conv_gsm0503_test_CPPFLAGS = $(AM_CPPFLAGS) -I$(top_srcdir)/tests/conv
@@ -339,6 +344,7 @@
 	     use_count/use_count_test.ok use_count/use_count_test.err \
 	     context/context_test.ok \
 	     gsm0502/gsm0502_test.ok \
+	     dtx/dtx_gsm0503_test.ok \
 	     exec/exec_test.ok exec/exec_test.err \
 	     $(NULL)
 
diff --git a/tests/dtx/dtx_gsm0503_test.c b/tests/dtx/dtx_gsm0503_test.c
new file mode 100644
index 0000000..f300313
--- /dev/null
+++ b/tests/dtx/dtx_gsm0503_test.c
@@ -0,0 +1,130 @@
+/*
+ * (C) 2019 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ * Author: Philipp Maier <pmaier@sysmocom.de>
+ * All Rights Reserved
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ *
+ * 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 2 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <string.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <osmocom/core/utils.h>
+#include <osmocom/coding/gsm0503_amr_dtx.h>
+
+char sample_afs_sid_frame[] =
+    {
+"111111110000000011001100101010100100010011111111001000100111011110011001001100111100110010011001111011100100010011111111001000100111011110011001001100111100110010011001111011100100010011111111001000100111011110011001001100111100110010011001111011100100010011111111001000100111011110011001001100111100110010011001111011100100010011111111001000100111011110011001001100111100110010011001111011100100010011111111001000100111011110011001001100111100110010011001"
+};
+
+char sample_afs_sid_update_frame[] =
+    {
+"111111110000000011001100101010100000010000001111111100101011011110001001000000110111110000001001011111101111010011001111100000101000011111001001111100110111110011111001001111101100010001001111000000100100011100111001100000111000110000111001010011101111010011111111010000101100011100111001111100110111110011111001110011101000010010001111110000100000011111001001011100110011110010111001101111100011010001111111001100100100011111111001000000110000110000001001"
+};
+
+char sample_afs_onset_frame[] =
+    {
+"111111110000000011001100101010100000111100000000111111000100101000111111100000000111110010001010001111110100000011111100111110100100111111000000110011001011101001001111011100001011110000001010010011111100000000111100111110101000111110110000111111000000101011111111010000001100110000111010111111111000000010111100000010100100111100110000100011001000101000111111101100001011110000111010011111110011000010111100101110101100111111000000010011001111101000001111"
+};
+
+char sample_ahs_sid_update_frame[] =
+    {
+"111100001100101010110000110110000110110000110110000110110000110110000110110000110110000110110000110110000110110000110110000110110000110110000110110000110110000110110000110110000110110000110110000110110000110110000110110000110110100011001000011010000000000000001111010010000000000001000000000010110000000011001000000000000000100000101000000000000000001010100000010010000000000010000111110001110110110011001101000000000100100011001000001010000100100000000011"
+};
+
+char sample_ahs_sid_first_p1_frame[] =
+    {
+"111100001100101001001111001001111001001111001001111001001111001001111001001111001001111001001111001001111001001111001001111001001111001001111001001111001001111001001111001001111001001111001001111001001111001001111001001111001001001011010110001101100101001110001111001110100110010000111101110110110000100100011111001001110000011110110001010010101100001010100000111101110110001010000111110001110110110011001101001111000011101001010011100011000111010110000011"
+};
+
+char sample_ahs_sid_first_p2_frame[] =
+    {
+"111110100100000010100000110111001110101100000100101001011101100011101010010000001010010010001100101010100100010111110101110011011110101000010100111000001001110111101110010101001110000010001101101011110000000011100100110110011111100011001000001101100101001110001111001110100110010000111101110110110000100100011111001001110000011110110001010010101100001010100000111101110110001010000111110001110110110011001101001111000011101001010011100011000111010110000011"
+};
+
+char sample_ahs_onset_frame[] =
+    {
+"111101011000101001010000111001000111011110000000011110001110010011011111100000101101101001101110011111010000000001010010110001101101110100000010011110101100010001011101101010000111100011101100111101011010100011110010110001001111100011001000011010000000000000001010010010000000000001000000000000100000000011001000000000000000100000101000000000000000010010000101010010000000000010101100111110101000110110011001000000000100100011001000001010000100100000001100"
+};
+
+char sample_sid_first_inh_frame[] =
+    {
+"xBxBxBxBxBxBxBxBxBxBxBxBxBxBxBxBx1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0x0x0x0x1x1x0x1x1x0"
+};
+
+char sample_sid_update_inh_frame[] =
+    {
+"xBxBxBxBxBxBxBxBxBxBxBxBxBxBxBxBx0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1x1x1x1x0x0x1x0x0x1"
+};
+
+unsigned int string_to_ubit(ubit_t * ubits, char *string)
+{
+	unsigned int len;
+	unsigned int i;
+
+	len = strlen(string);
+
+	for (i = 0; i < len; i++) {
+		ubits[i] = string[i] & 1;
+	}
+
+	return len;
+}
+
+void test_gsm0503_detect_afs_dtx_frame(char *string)
+{
+	ubit_t ubits[512];
+	uint8_t dtx_frame_type;
+	int n_errors;
+	int n_bits_total;
+
+	string_to_ubit(ubits, string);
+	dtx_frame_type = gsm0503_detect_afs_dtx_frame(&n_errors, &n_bits_total, ubits);
+	printf(" ==> %s, n_errors=%i, n_bits_total=%i\n", gsm0503_amr_dtx_frame_name(dtx_frame_type),
+	       n_errors, n_bits_total);
+}
+
+void test_gsm0503_detect_ahs_dtx_frame(char *string)
+{
+	ubit_t ubits[512];
+	uint8_t dtx_frame_type;
+	int n_errors;
+	int n_bits_total;
+
+	string_to_ubit(ubits, string);
+	dtx_frame_type = gsm0503_detect_ahs_dtx_frame(&n_errors, &n_bits_total, ubits);
+	printf(" ==> %s, n_errors=%i, n_bits_total=%i\n", gsm0503_amr_dtx_frame_name(dtx_frame_type),
+	       n_errors, n_bits_total);
+}
+
+int main(int argc, char **argv)
+{
+	printf("FR AMR DTX FRAMES:\n");
+	test_gsm0503_detect_afs_dtx_frame(sample_afs_sid_frame);
+	test_gsm0503_detect_afs_dtx_frame(sample_afs_sid_update_frame);
+	test_gsm0503_detect_afs_dtx_frame(sample_afs_onset_frame);
+	printf("HR AMR DTX FRAMES:\n");
+	test_gsm0503_detect_ahs_dtx_frame(sample_ahs_sid_update_frame);
+	test_gsm0503_detect_ahs_dtx_frame(sample_ahs_sid_first_p1_frame);
+	test_gsm0503_detect_ahs_dtx_frame(sample_ahs_sid_first_p2_frame);
+	test_gsm0503_detect_ahs_dtx_frame(sample_ahs_onset_frame);
+	test_gsm0503_detect_ahs_dtx_frame(sample_sid_first_inh_frame);
+	test_gsm0503_detect_ahs_dtx_frame(sample_sid_update_inh_frame);
+
+	return EXIT_SUCCESS;
+}
diff --git a/tests/dtx/dtx_gsm0503_test.ok b/tests/dtx/dtx_gsm0503_test.ok
new file mode 100644
index 0000000..a95a18b
--- /dev/null
+++ b/tests/dtx/dtx_gsm0503_test.ok
@@ -0,0 +1,11 @@
+FR AMR DTX FRAMES:
+ ==> AFS_SID_FIRST, n_errors=0, n_bits_total=212
+ ==> AFS_SID_UPDATE, n_errors=0, n_bits_total=212
+ ==> AFS_ONSET, n_errors=0, n_bits_total=228
+HR AMR DTX FRAMES:
+ ==> AHS_SID_UPDATE, n_errors=0, n_bits_total=212
+ ==> AHS_SID_FIRST_P1, n_errors=0, n_bits_total=212
+ ==> AHS_SID_FIRST_P2, n_errors=0, n_bits_total=114
+ ==> AHS_ONSET, n_errors=0, n_bits_total=114
+ ==> AHS_SID_FIRST_INH, n_errors=0, n_bits_total=212
+ ==> AHS_SID_UPDATE_INH, n_errors=0, n_bits_total=212
diff --git a/tests/testsuite.at b/tests/testsuite.at
index cb83ab9..bab5730 100644
--- a/tests/testsuite.at
+++ b/tests/testsuite.at
@@ -132,6 +132,12 @@
 AT_CHECK([$abs_top_builddir/tests/gsm0502/gsm0502_test], [0], [expout], [ignore])
 AT_CLEANUP
 
+AT_SETUP([dtx])
+AT_KEYWORDS([dtx])
+cat $abs_srcdir/dtx/dtx_gsm0503_test.ok > expout
+AT_CHECK([$abs_top_builddir/tests/dtx/dtx_gsm0503_test], [0], [expout], [ignore])
+AT_CLEANUP
+
 AT_SETUP([gsm0808])
 AT_KEYWORDS([gsm0808])
 cat $abs_srcdir/gsm0808/gsm0808_test.ok > expout