diff --git a/openbsc/src/osmo-bsc_mgcp/mgcp_transcode.c b/openbsc/src/osmo-bsc_mgcp/mgcp_transcode.c
new file mode 100644
index 0000000..cadc876
--- /dev/null
+++ b/openbsc/src/osmo-bsc_mgcp/mgcp_transcode.c
@@ -0,0 +1,452 @@
+/*
+ * (C) 2014 by Sysmocom s.f.m.c. GmbH
+ * (C) 2014 by On-Waves
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+
+#include "bscconfig.h"
+
+#include "g711common.h"
+#include <gsm.h>
+#ifdef HAVE_BCG729
+#include <bcg729/decoder.h>
+#include <bcg729/encoder.h>
+#endif
+
+#include <openbsc/debug.h>
+#include <openbsc/mgcp.h>
+#include <openbsc/mgcp_internal.h>
+
+#include <osmocom/core/talloc.h>
+
+enum audio_format {
+	AF_INVALID,
+	AF_S16,
+	AF_L16,
+	AF_GSM,
+	AF_G729,
+	AF_PCMA
+};
+
+struct mgcp_process_rtp_state {
+	/* decoding */
+	enum audio_format src_fmt;
+	union {
+		gsm gsm_handle;
+#ifdef HAVE_BCG729
+		bcg729DecoderChannelContextStruct *g729_dec;
+#endif
+	} src;
+	size_t src_frame_size;
+	size_t src_samples_per_frame;
+
+	/* processing */
+
+	/* encoding */
+	enum audio_format dst_fmt;
+	union {
+		gsm gsm_handle;
+#ifdef HAVE_BCG729
+		bcg729EncoderChannelContextStruct *g729_enc;
+#endif
+	} dst;
+	size_t dst_frame_size;
+	size_t dst_samples_per_frame;
+};
+
+static enum audio_format get_audio_format(const struct mgcp_rtp_end *rtp_end)
+{
+	if (rtp_end->subtype_name) {
+		if (!strcmp("GSM", rtp_end->subtype_name))
+			return AF_GSM;
+		if (!strcmp("PCMA", rtp_end->subtype_name))
+			return AF_PCMA;
+#ifdef HAVE_BCG729
+		if (!strcmp("G729", rtp_end->subtype_name))
+			return AF_G729;
+#endif
+		if (!strcmp("L16", rtp_end->subtype_name))
+			return AF_L16;
+	}
+
+	switch (rtp_end->payload_type) {
+	case 3 /* GSM */:
+		return AF_GSM;
+	case 8 /* PCMA */:
+		return AF_PCMA;
+#ifdef HAVE_BCG729
+	case 18 /* G.729 */:
+		return AF_G729;
+#endif
+	case 11 /* L16 */:
+		return AF_L16;
+	default:
+		return AF_INVALID;
+	}
+}
+
+static void l16_encode(short *sample, unsigned char *buf, size_t n)
+{
+	for (; n > 0; --n, ++sample, buf += 2) {
+		buf[0] = sample[0] >> 8;
+		buf[1] = sample[0] & 0xff;
+	}
+}
+
+static void l16_decode(unsigned char *buf, short *sample, size_t n)
+{
+	for (; n > 0; --n, ++sample, buf += 2)
+		sample[0] = ((short)buf[0] << 8) | buf[1];
+}
+
+static void alaw_encode(short *sample, unsigned char *buf, size_t n)
+{
+	for (; n > 0; --n)
+		*(buf++) = s16_to_alaw(*(sample++));
+}
+
+static void alaw_decode(unsigned char *buf, short *sample, size_t n)
+{
+	for (; n > 0; --n)
+		*(sample++) = alaw_to_s16(*(buf++));
+}
+
+static int processing_state_destructor(struct mgcp_process_rtp_state *state)
+{
+	switch (state->src_fmt) {
+	case AF_GSM:
+		if (state->dst.gsm_handle)
+			gsm_destroy(state->src.gsm_handle);
+		break;
+#ifdef HAVE_BCG729
+	case AF_G729:
+		if (state->src.g729_dec)
+			closeBcg729DecoderChannel(state->src.g729_dec);
+		break;
+#endif
+	default:
+		break;
+	}
+	switch (state->dst_fmt) {
+	case AF_GSM:
+		if (state->dst.gsm_handle)
+			gsm_destroy(state->dst.gsm_handle);
+		break;
+#ifdef HAVE_BCG729
+	case AF_G729:
+		if (state->dst.g729_enc)
+			closeBcg729EncoderChannel(state->dst.g729_enc);
+		break;
+#endif
+	default:
+		break;
+	}
+	return 0;
+}
+
+int mgcp_transcoding_setup(struct mgcp_endpoint *endp,
+			   struct mgcp_rtp_end *dst_end,
+			   struct mgcp_rtp_end *src_end)
+{
+	struct mgcp_process_rtp_state *state;
+	enum audio_format src_fmt, dst_fmt;
+
+	/* cleanup first */
+	if (dst_end->rtp_process_data) {
+		talloc_free(dst_end->rtp_process_data);
+		dst_end->rtp_process_data = NULL;
+	}
+
+	if (!src_end)
+		return 0;
+
+	src_fmt = get_audio_format(src_end);
+	dst_fmt = get_audio_format(dst_end);
+
+	LOGP(DMGCP, LOGL_ERROR,
+	     "Checking transcoding: %s (%d) -> %s (%d)\n",
+	     src_end->subtype_name, src_end->payload_type,
+	     dst_end->subtype_name, dst_end->payload_type);
+
+	if (src_fmt == AF_INVALID || dst_fmt == AF_INVALID) {
+		if (!src_end->subtype_name || !dst_end->subtype_name)
+			/* Not enough info, do nothing */
+			return 0;
+
+		if (strcmp(src_end->subtype_name, dst_end->subtype_name) == 0)
+			/* Nothing to do */
+			return 0;
+
+		LOGP(DMGCP, LOGL_ERROR,
+		     "Cannot transcode: %s codec not supported (%s -> %s).\n",
+		     src_fmt != AF_INVALID ? "destination" : "source",
+		     src_end->audio_name, dst_end->audio_name);
+		return -EINVAL;
+	}
+
+	if (src_end->rate && dst_end->rate && src_end->rate != dst_end->rate) {
+		LOGP(DMGCP, LOGL_ERROR,
+		     "Cannot transcode: rate conversion (%d -> %d) not supported.\n",
+		     src_end->rate, dst_end->rate);
+		return -EINVAL;
+	}
+
+	state = talloc_zero(endp->tcfg->cfg, struct mgcp_process_rtp_state);
+	talloc_set_destructor(state, processing_state_destructor);
+	dst_end->rtp_process_data = state;
+
+	state->src_fmt = src_fmt;
+
+	switch (state->src_fmt) {
+	case AF_L16:
+	case AF_S16:
+		state->src_frame_size = 80 * sizeof(short);
+		state->src_samples_per_frame = 80;
+		break;
+	case AF_GSM:
+		state->src_frame_size = sizeof(gsm_frame);
+		state->src_samples_per_frame = 160;
+		state->src.gsm_handle = gsm_create();
+		if (!state->src.gsm_handle) {
+			LOGP(DMGCP, LOGL_ERROR,
+			     "Failed to initialize GSM decoder.\n");
+			return -EINVAL;
+		}
+		break;
+#ifdef HAVE_BCG729
+	case AF_G729:
+		state->src_frame_size = 10;
+		state->src_samples_per_frame = 80;
+		state->src.g729_dec = initBcg729DecoderChannel();
+		if (!state->src.g729_dec) {
+			LOGP(DMGCP, LOGL_ERROR,
+			     "Failed to initialize G.729 decoder.\n");
+			return -EINVAL;
+		}
+		break;
+#endif
+	case AF_PCMA:
+		state->src_frame_size = 80;
+		state->src_samples_per_frame = 80;
+		break;
+	default:
+		break;
+	}
+
+	state->dst_fmt = dst_fmt;
+
+	switch (state->dst_fmt) {
+	case AF_L16:
+	case AF_S16:
+		state->dst_frame_size = 80*sizeof(short);
+		state->dst_samples_per_frame = 80;
+		break;
+	case AF_GSM:
+		state->dst_frame_size = sizeof(gsm_frame);
+		state->dst_samples_per_frame = 160;
+		state->dst.gsm_handle = gsm_create();
+		if (!state->dst.gsm_handle) {
+			LOGP(DMGCP, LOGL_ERROR,
+			     "Failed to initialize GSM encoder.\n");
+			return -EINVAL;
+		}
+		break;
+#ifdef HAVE_BCG729
+	case AF_G729:
+		state->dst_frame_size = 10;
+		state->dst_samples_per_frame = 80;
+		state->dst.g729_enc = initBcg729EncoderChannel();
+		if (!state->dst.g729_enc) {
+			LOGP(DMGCP, LOGL_ERROR,
+			     "Failed to initialize G.729 decoder.\n");
+			return -EINVAL;
+		}
+		break;
+#endif
+	case AF_PCMA:
+		state->dst_frame_size = 80;
+		state->dst_samples_per_frame = 80;
+		break;
+	default:
+		break;
+	}
+
+	LOGP(DMGCP, LOGL_INFO,
+	     "Initialized RTP processing on: 0x%x "
+	     "conv: %d (%d, %d, %s) -> %d (%d, %d, %s)\n",
+	     ENDPOINT_NUMBER(endp),
+	     src_fmt, src_end->payload_type, src_end->rate, src_end->fmtp_extra,
+	     dst_fmt, dst_end->payload_type, dst_end->rate, dst_end->fmtp_extra);
+
+	return 0;
+}
+
+void mgcp_transcoding_net_downlink_format(struct mgcp_endpoint *endp,
+					  int *payload_type,
+					  const char**audio_name,
+					  const char**fmtp_extra)
+{
+	struct mgcp_process_rtp_state *state = endp->net_end.rtp_process_data;
+	if (!state || endp->net_end.payload_type < 0) {
+		*payload_type = endp->bts_end.payload_type;
+		*audio_name = endp->bts_end.audio_name;
+		*fmtp_extra = endp->bts_end.fmtp_extra;
+		return;
+	}
+
+	*payload_type = endp->net_end.payload_type;
+	*fmtp_extra = endp->net_end.fmtp_extra;
+	*audio_name = endp->net_end.audio_name;
+}
+
+
+int mgcp_transcoding_process_rtp(struct mgcp_endpoint *endp,
+				 struct mgcp_rtp_end *dst_end,
+				 char *data, int *len, int buf_size)
+{
+	struct mgcp_process_rtp_state *state = dst_end->rtp_process_data;
+	size_t rtp_hdr_size = 12;
+	char *payload_data = data + rtp_hdr_size;
+	int payload_len = *len - rtp_hdr_size;
+	size_t sample_cnt = 0;
+	size_t sample_idx;
+	int16_t samples[10*160];
+	uint8_t *src = (uint8_t *)payload_data;
+	uint8_t *dst = (uint8_t *)payload_data;
+	size_t nbytes = payload_len;
+	size_t frame_remainder;
+
+	if (!state)
+		return 0;
+
+	if (state->src_fmt == state->dst_fmt)
+		return 0;
+
+	/* TODO: check payload type (-> G.711 comfort noise) */
+
+	/* Decode src into samples */
+	while (nbytes >= state->src_frame_size) {
+		if (sample_cnt + state->src_samples_per_frame > ARRAY_SIZE(samples)) {
+			LOGP(DMGCP, LOGL_ERROR,
+			     "Sample buffer too small: %d > %d.\n",
+			     sample_cnt + state->src_samples_per_frame,
+			     ARRAY_SIZE(samples));
+			return -ENOSPC;
+		}
+		switch (state->src_fmt) {
+		case AF_GSM:
+			if (gsm_decode(state->src.gsm_handle,
+				       (gsm_byte *)src, samples + sample_cnt) < 0) {
+				LOGP(DMGCP, LOGL_ERROR,
+				     "Failed to decode GSM.\n");
+				return -EINVAL;
+			}
+			break;
+#ifdef HAVE_BCG729
+		case AF_G729:
+			bcg729Decoder(state->src.g729_dec, src, 0, samples + sample_cnt);
+			break;
+#endif
+		case AF_PCMA:
+			alaw_decode(src, samples + sample_cnt,
+				    state->src_samples_per_frame);
+			break;
+		case AF_S16:
+			memmove(samples + sample_cnt, src,
+				state->src_frame_size);
+			break;
+		case AF_L16:
+			l16_decode(src, samples + sample_cnt,
+				   state->src_samples_per_frame);
+			break;
+		default:
+			break;
+		}
+		src        += state->src_frame_size;
+		nbytes     -= state->src_frame_size;
+		sample_cnt += state->src_samples_per_frame;
+	}
+
+	/* Add silence if necessary */
+	frame_remainder = sample_cnt % state->dst_samples_per_frame;
+	if (frame_remainder) {
+		size_t silence = state->dst_samples_per_frame - frame_remainder;
+		if (sample_cnt + silence > ARRAY_SIZE(samples)) {
+			LOGP(DMGCP, LOGL_ERROR,
+			     "Sample buffer too small for silence: %d > %d.\n",
+			     sample_cnt + silence,
+			     ARRAY_SIZE(samples));
+			return -ENOSPC;
+		}
+
+		while (silence > 0) {
+			samples[sample_cnt] = 0;
+			sample_cnt += 1;
+			silence -= 1;
+		}
+	}
+
+	/* Encode samples into dst */
+	sample_idx = 0;
+	nbytes = 0;
+	while (sample_idx + state->dst_samples_per_frame <= sample_cnt) {
+		if (nbytes + state->dst_frame_size > buf_size) {
+			LOGP(DMGCP, LOGL_ERROR,
+			     "Encoding (RTP) buffer too small: %d > %d.\n",
+			     nbytes + state->dst_frame_size, buf_size);
+			return -ENOSPC;
+		}
+		switch (state->dst_fmt) {
+		case AF_GSM:
+			gsm_encode(state->dst.gsm_handle,
+				   samples + sample_idx, dst);
+			break;
+#ifdef HAVE_BCG729
+		case AF_G729:
+			bcg729Encoder(state->dst.g729_enc,
+				      samples + sample_idx, dst);
+			break;
+#endif
+		case AF_PCMA:
+			alaw_encode(samples + sample_idx, dst,
+				    state->src_samples_per_frame);
+			break;
+		case AF_S16:
+			memmove(dst, samples + sample_idx, state->dst_frame_size);
+			break;
+		case AF_L16:
+			l16_encode(samples + sample_idx, dst,
+				   state->src_samples_per_frame);
+			break;
+		default:
+			break;
+		}
+		dst        += state->dst_frame_size;
+		nbytes     += state->dst_frame_size;
+		sample_idx += state->dst_samples_per_frame;
+	}
+
+	*len = rtp_hdr_size + nbytes;
+	/* Patch payload type */
+	data[1] = (data[1] & 0x80) | (dst_end->payload_type & 0x7f);
+
+	return 0;
+}