diff --git a/host/Makefile b/host/Makefile
new file mode 100644
index 0000000..4f46c8f
--- /dev/null
+++ b/host/Makefile
@@ -0,0 +1,15 @@
+LDFLAGS=`pkg-config --libs libusb-1.0 libosmocore` -losmocore
+
+all: simtrace2-remsim simtrace2-remsim-usb2udp
+
+simtrace2-remsim: simtrace2-remsim.o apdu_dispatch.o
+	$(CC) -o $@ $^ $(LDFLAGS) -losmosim
+
+simtrace2-remsim-usb2udp: usb2udp.o
+	$(CC) -o $@ $^ $(LDFLAGS)
+
+%.o: %.c
+	$(CC) $(CFLAGS) `pkg-config --cflags libusb-1.0 libosmocore` -o $@ -c $^
+
+clean:
+	@rm -f simtrace2-remsim simtrace2-remsim-usb2udp *.o
diff --git a/host/apdu_dispatch.c b/host/apdu_dispatch.c
new file mode 100644
index 0000000..6bdba9f
--- /dev/null
+++ b/host/apdu_dispatch.c
@@ -0,0 +1,173 @@
+/* apdu_dispatch - State machine to determine Rx/Tx phases of APDU
+ *
+ * (C) 2016 by Harald Welte <hwelte@hmw-consulting.de>
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License version 2 
+ *  as published by the Free Software Foundation
+ *
+ *  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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <errno.h>
+
+#include <osmocom/core/utils.h>
+#include <osmocom/sim/sim.h>
+#include <osmocom/sim/class_tables.h>
+
+#include "apdu_dispatch.h"
+
+/*! \brief Has the command-data phase been completed yet? */
+static inline bool is_dc_complete(struct apdu_context *ac)
+{
+	return (ac->lc.tot == ac->lc.cur);
+}
+
+/*! \brief Has the expected-data phase been completed yet? */
+static inline bool is_de_complete(struct apdu_context *ac)
+{
+	return (ac->le.tot == ac->le.cur);
+}
+
+static const char *dump_apdu_hdr(const struct osim_apdu_cmd_hdr *h)
+{
+	static char buf[256];
+	sprintf(buf, "CLA=%02x INS=%02x P1=%02x P2=%02x P3=%02x",
+		h->cla, h->ins, h->p1, h->p2, h->p3);
+
+	return buf;
+}
+
+static void dump_apdu_ctx(const struct apdu_context *ac)
+{
+	printf("%s; case=%d, lc=%d(%d), le=%d(%d)\n",
+		dump_apdu_hdr(&ac->hdr), ac->apdu_case,
+		ac->lc.tot, ac->lc.cur,
+		ac->le.tot, ac->le.cur);
+}
+
+/*! \brief input function for APDU segmentation
+ *  \param ac APDU context accross successive calls
+ *  \param[in] apdu_buf APDU inpud data buffer
+ *  \param[in] apdu_len Length of apdu_buf
+ *  \param[in] new_apdu Is this the beginning of a new APDU?
+ *
+ *  The function returns APDU_ACT_TX_CAPDU_TO_CARD once there is
+ *  sufficient data of the APDU received to transmit the command-APDU to
+ *  the actual card.
+ *
+ *  The function retunrs APDU_ACT_RX_MORE_CAPDU_FROM_READER when there
+ *  is more data to be received from the card reader (GSM Phone).
+ */
+int apdu_segment_in(struct apdu_context *ac, const uint8_t *apdu_buf,
+		    unsigned int apdu_len, bool new_apdu)
+{
+	int rc = 0;
+
+	if (new_apdu) {
+		/* initialize the apdu context structure */
+		memset(ac, 0, sizeof(*ac));
+		/* copy APDU header over */
+		memcpy(&ac->hdr, apdu_buf, sizeof(ac->hdr));
+		ac->apdu_case = osim_determine_apdu_case(&osim_uicc_sim_cic_profile, apdu_buf);
+		switch (ac->apdu_case) {
+		case 1: /* P3 == 0, No Lc/Le */
+			ac->le.tot = ac->lc.tot = 0;
+			break;
+		case 2: /* P3 == Le */
+			ac->le.tot = ac->hdr.p3;
+			break;
+		case 3: /* P3 = Lc */
+			ac->lc.tot = ac->hdr.p3;
+			/* copy Dc */
+			ac->lc.cur = apdu_len - sizeof(ac->hdr);
+			memcpy(ac->dc, apdu_buf + sizeof(ac->hdr),
+				ac->lc.cur);
+			break;
+		case 4: /* P3 = Lc; SW with Le */
+			ac->lc.tot = ac->hdr.p3;
+			/* copy Dc */
+			ac->lc.cur = apdu_len - sizeof(ac->hdr);
+			memcpy(ac->dc, apdu_buf + sizeof(ac->hdr),
+				ac->lc.cur);
+			break;
+		case 0:
+		default:
+			fprintf(stderr, "Unknown APDU case %d\n", ac->apdu_case);
+			return -1;
+		}
+	} else {
+		/* copy more data, if available */
+		int cpy_len;
+		switch (ac->apdu_case) {
+		case 1:
+		case 2:
+			break;
+		case 3:
+		case 4:
+			cpy_len = ac->lc.tot - ac->lc.cur;
+			if (cpy_len > apdu_len)
+				cpy_len = apdu_len;
+			memcpy(ac->dc+ac->lc.cur, apdu_buf, cpy_len);
+			ac->lc.cur += cpy_len;
+			break;
+		default:
+			fprintf(stderr, "Unknown APDU case %d\n", ac->apdu_case);
+			break;
+		}
+	}
+
+	/* take some decisions... */
+	switch (ac->apdu_case) {
+	case 1: /* P3 == 0, No Lc/Le */
+		/* send C-APDU to card */
+		/* receive SW from card, forward to reader */
+		rc |= APDU_ACT_TX_CAPDU_TO_CARD;
+		break;
+	case 2: /* P3 == Le */
+		/* send C-APDU to card */
+		/* receive Le bytes + SW from card, forward to reader */
+		rc |= APDU_ACT_TX_CAPDU_TO_CARD;
+		break;
+	case 3: /* P3 = Lc */
+		if (!is_dc_complete(ac)) {
+			/* send PB + read further Lc bytes from reader */
+			rc |= APDU_ACT_RX_MORE_CAPDU_FROM_READER;
+		} else {
+			/* send C-APDU to card */
+			/* receive SW from card, forward to reader */
+			rc |= APDU_ACT_TX_CAPDU_TO_CARD;
+		}
+		break;
+	case 4: /* P3 = Lc; SW with Le */
+		if (!is_dc_complete(ac)) {
+			/* send PB + read further Lc bytes from reader */
+			rc |= APDU_ACT_RX_MORE_CAPDU_FROM_READER;
+		} else {
+			/* send C-APDU to card */
+			/* receive SW from card, forward to reader */
+			rc |= APDU_ACT_TX_CAPDU_TO_CARD;
+		}
+		break;
+	case 0:
+	default:
+		fprintf(stderr, "Unknown APDU case %d\n", ac->apdu_case);
+		break;
+	}
+
+	dump_apdu_ctx(ac);
+
+	return rc;
+}
diff --git a/host/apdu_dispatch.h b/host/apdu_dispatch.h
new file mode 100644
index 0000000..c76c8ec
--- /dev/null
+++ b/host/apdu_dispatch.h
@@ -0,0 +1,31 @@
+#pragma once
+
+#include <stdint.h>
+#include <stdbool.h>
+
+#include <osmocom/sim/sim.h>
+
+struct apdu_context {
+	struct osim_apdu_cmd_hdr hdr;
+	uint8_t dc[256];
+	uint8_t de[256];
+	uint8_t sw[2];
+	uint8_t apdu_case;
+	struct {
+		uint8_t tot;
+		uint8_t cur;
+	} lc;
+	struct {
+		uint8_t tot;
+		uint8_t cur;
+	} le;
+};
+
+enum apdu_action {
+	APDU_ACT_TX_CAPDU_TO_CARD		= 0x0001,
+	APDU_ACT_RX_MORE_CAPDU_FROM_READER	= 0x0002,
+};
+
+
+int apdu_segment_in(struct apdu_context *ac, const uint8_t *apdu_buf,
+		    unsigned int apdu_len, bool new_apdu);
diff --git a/host/cardemu_prot.h b/host/cardemu_prot.h
new file mode 120000
index 0000000..a252a25
--- /dev/null
+++ b/host/cardemu_prot.h
@@ -0,0 +1 @@
+../firmware/src_simtrace/cardemu_prot.h
\ No newline at end of file
diff --git a/host/simtrace.h b/host/simtrace.h
new file mode 100644
index 0000000..0611f36
--- /dev/null
+++ b/host/simtrace.h
@@ -0,0 +1,13 @@
+#ifndef _SIMTRACE_H
+#define _SIMTRACE_H
+
+#define SIMTRACE_USB_VENDOR	0x1d50
+#define SIMTRACE_USB_PRODUCT	0x60e3
+
+/* FIXME: automatically determine those values based on the usb config /
+ * interface descriptors */
+#define SIMTRACE_OUT_EP	0x04
+#define SIMTRACE_IN_EP	0x85
+#define SIMTRACE_INT_EP	0x86
+
+#endif
diff --git a/host/simtrace2-remsim.c b/host/simtrace2-remsim.c
new file mode 100644
index 0000000..f22c341
--- /dev/null
+++ b/host/simtrace2-remsim.c
@@ -0,0 +1,476 @@
+/* simtrace2-remsim - main program for the host PC
+ *
+ * (C) 2010-2016 by Harald Welte <hwelte@hmw-consulting.de>
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License version 2 
+ *  as published by the Free Software Foundation
+ *
+ *  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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <errno.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <time.h>
+#define _GNU_SOURCE
+#include <getopt.h>
+
+#include <sys/time.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+#include <libusb.h>
+
+#include "simtrace.h"
+#include "cardemu_prot.h"
+#include "apdu_dispatch.h"
+
+#include <osmocom/core/gsmtap.h>
+#include <osmocom/core/gsmtap_util.h>
+#include <osmocom/core/utils.h>
+#include <osmocom/core/socket.h>
+#include <osmocom/sim/class_tables.h>
+#include <osmocom/sim/sim.h>
+
+static struct gsmtap_inst *g_gti;
+struct libusb_device_handle *g_devh;
+const struct osim_cla_ins_card_profile *g_prof;
+static int g_udp_fd = -1;
+static struct osim_chan_hdl *g_chan;
+
+static int gsmtap_send_sim(const uint8_t *apdu, unsigned int len)
+{
+	struct gsmtap_hdr *gh;
+	unsigned int gross_len = len + sizeof(*gh);
+	uint8_t *buf = malloc(gross_len);
+	int rc;
+
+	if (!buf)
+		return -ENOMEM;
+
+	memset(buf, 0, sizeof(*gh));
+	gh = (struct gsmtap_hdr *) buf;
+	gh->version = GSMTAP_VERSION;
+	gh->hdr_len = sizeof(*gh)/4;
+	gh->type = GSMTAP_TYPE_SIM;
+
+	memcpy(buf + sizeof(*gh), apdu, len);
+
+	rc = write(gsmtap_inst_fd(g_gti), buf, gross_len);
+	if (rc < 0) {
+		perror("write gsmtap");
+		free(buf);
+		return rc;
+	}
+
+	free(buf);
+	return 0;
+}
+
+#if 0
+static void apdu_out_cb(uint8_t *buf, unsigned int len, void *user_data)
+{
+	printf("APDU: %s\n", osmo_hexdump(buf, len));
+	gsmtap_send_sim(buf, len);
+}
+#endif
+
+/*! \brief Transmit a given command to the SIMtrace2 device */
+static int tx_to_dev(uint8_t *buf, unsigned int len)
+{
+	struct cardemu_usb_msg_hdr *mh = (struct cardemu_usb_msg_hdr *) buf;
+	int xfer_len;
+
+	mh->msg_len = len;
+
+	printf("<- %s\n", osmo_hexdump(buf, len));
+
+	if (g_udp_fd < 0) {
+		return libusb_bulk_transfer(g_devh, SIMTRACE_OUT_EP, buf, len,
+					    &xfer_len, 100000);
+	} else {
+		return write(g_udp_fd, buf, len);
+	}
+}
+
+/*! \brief Request the SIMtrace2 to generate a card-insert signal */
+static int request_card_insert(bool inserted)
+{
+	struct cardemu_usb_msg_cardinsert cins;
+
+	memset(&cins, 0, sizeof(cins));
+	cins.hdr.msg_type = CEMU_USB_MSGT_DT_CARDINSERT;
+	if (inserted)
+		cins.card_insert = 1;
+
+	return tx_to_dev((uint8_t *)&cins, sizeof(cins));
+}
+
+/*! \brief Request the SIMtrace2 to transmit a Procedure Byte, then Rx */
+static int request_pb_and_rx(uint8_t pb, uint8_t le)
+{
+	struct cardemu_usb_msg_tx_data *txd;
+	uint8_t buf[sizeof(*txd) + 1];
+	txd = (struct cardemu_usb_msg_tx_data *) buf;
+
+	printf("<= request_pb_and_rx(%02x, %d)\n", pb, le);
+
+	memset(txd, 0, sizeof(*txd));
+	txd->data_len = 1;
+	txd->hdr.msg_type = CEMU_USB_MSGT_DT_TX_DATA;
+	txd->flags = CEMU_DATA_F_PB_AND_RX;
+	txd->data[0] = pb;
+
+	return tx_to_dev((uint8_t *)txd, sizeof(*txd)+txd->data_len);
+}
+
+/*! \brief Request the SIMtrace2 to transmit a Procedure Byte, then Tx */
+static int request_pb_and_tx(uint8_t pb, const uint8_t *data, uint8_t data_len_in)
+{
+	uint32_t data_len = data_len_in;
+	struct cardemu_usb_msg_tx_data *txd;
+	uint8_t buf[sizeof(*txd) + 1 + data_len_in];
+	txd = (struct cardemu_usb_msg_tx_data *) buf;
+
+	printf("<= request_pb_and_tx(%02x, %s, %d)\n", pb, osmo_hexdump(data, data_len_in), data_len_in);
+
+	memset(txd, 0, sizeof(*txd));
+	txd->hdr.msg_type = CEMU_USB_MSGT_DT_TX_DATA;
+	txd->data_len = 1 + data_len_in;
+	txd->flags = CEMU_DATA_F_PB_AND_TX;
+	txd->data[0] = pb;
+	memcpy(txd->data+1, data, data_len_in);
+
+	return tx_to_dev(buf, sizeof(*txd)+txd->data_len);
+}
+
+/*! \brief Request the SIMtrace2 to send a Status Word */
+static int request_sw_tx(const uint8_t *sw)
+{
+	struct cardemu_usb_msg_tx_data *txd;
+	uint8_t buf[sizeof(*txd) + 2];
+	txd = (struct cardemu_usb_msg_tx_data *) buf;
+
+	printf("<= request_sw_tx(%02x %02x)\n", sw[0], sw[1]);
+
+	memset(txd, 0, sizeof(*txd));
+	txd->hdr.msg_type = CEMU_USB_MSGT_DT_TX_DATA;
+	txd->data_len = 2;
+	txd->flags = CEMU_DATA_F_PB_AND_TX | CEMU_DATA_F_FINAL;
+	txd->data[0] = sw[0];
+	txd->data[1] = sw[1];
+
+	return tx_to_dev((uint8_t *)txd, sizeof(*txd)+txd->data_len);
+}
+
+/*! \brief Process a STATUS message from the SIMtrace2 */
+static int process_do_status(uint8_t *buf, int len)
+{
+	struct cardemu_usb_msg_status *status;
+	status = (struct cardemu_usb_msg_status *) buf;
+
+	printf("=> STATUS: flags=0x%x, fi=%u, di=%u, wi=%u wtime=%u\n",
+		status->flags, status->fi, status->di, status->wi,
+		status->waiting_time);
+
+	return 0;
+}
+
+/*! \brief Process a PTS indication message from the SIMtrace2 */
+static int process_do_pts(uint8_t *buf, int len)
+{
+	struct cardemu_usb_msg_pts_info *pts;
+	pts = (struct cardemu_usb_msg_pts_info *) buf;
+
+	printf("=> PTS req: %s\n", osmo_hexdump(pts->req, sizeof(pts->req)));
+
+	return 0;
+}
+
+/*! \brief Process a ERROR indication message from the SIMtrace2 */
+static int process_do_error(uint8_t *buf, int len)
+{
+	struct cardemu_usb_msg_error *err;
+	err = (struct cardemu_usb_msg_error *) buf;
+
+	printf("=> ERROR: %u/%u/%u: %s\n",
+		err->severity, err->subsystem, err->code,
+		err->msg_len ? err->msg : "");
+
+	return 0;
+}
+
+/*! \brief Process a RX-DATA indication message from the SIMtrace2 */
+static int process_do_rx_da(uint8_t *buf, int len)
+{
+	static struct apdu_context ac;
+	struct cardemu_usb_msg_rx_data *data;
+	const uint8_t sw_success[] = { 0x90, 0x00 };
+	int rc;
+
+	data = (struct cardemu_usb_msg_rx_data *) buf;
+
+	printf("=> DATA: flags=%x, %s: ", data->flags,
+		osmo_hexdump(data->data, data->data_len));
+
+	rc = apdu_segment_in(&ac, data->data, data->data_len,
+			     data->flags & CEMU_DATA_F_TPDU_HDR);
+
+	if (rc & APDU_ACT_TX_CAPDU_TO_CARD) {
+		struct msgb *tmsg = msgb_alloc(1024, "TPDU");
+		struct osim_reader_hdl *rh = g_chan->card->reader;
+		uint8_t *cur;
+
+		/* Copy TPDU header */
+		cur = msgb_put(tmsg, sizeof(ac.hdr));
+		memcpy(cur, &ac.hdr, sizeof(ac.hdr));
+		/* Copy D(c), if any */
+		if (ac.lc.tot) {
+			cur = msgb_put(tmsg, ac.lc.tot);
+			memcpy(cur, ac.dc, ac.lc.tot);
+		}
+		/* send to actual card */
+		tmsg->l3h = tmsg->tail;
+		rc = rh->ops->transceive(rh, tmsg);
+		if (rc < 0) {
+			fprintf(stderr, "error during transceive: %d\n", rc);
+			msgb_free(tmsg);
+			return rc;
+		}
+		msgb_apdu_sw(tmsg) = msgb_get_u16(tmsg);
+		ac.sw[0] = msgb_apdu_sw(tmsg) >> 8;
+		ac.sw[1] = msgb_apdu_sw(tmsg) & 0xff;
+		printf("SW=0x%04x, len_rx=%d\n", msgb_apdu_sw(tmsg), msgb_l3len(tmsg));
+		if (msgb_l3len(tmsg))
+			request_pb_and_tx(ac.hdr.ins, tmsg->l3h, msgb_l3len(tmsg));
+		request_sw_tx(ac.sw);
+	} else if (ac.lc.tot > ac.lc.cur) {
+		request_pb_and_rx(ac.hdr.ins, ac.lc.tot - ac.lc.cur);
+	}
+	return 0;
+}
+
+/*! \brief Process an incoming message from the SIMtrace2 */
+static int process_usb_msg(uint8_t *buf, int len)
+{
+	struct cardemu_usb_msg_hdr *sh = (struct cardemu_usb_msg_hdr *)buf;
+	uint8_t *payload;
+	int payload_len;
+	int rc;
+
+	printf("-> %s\n", osmo_hexdump(buf, len));
+
+	switch (sh->msg_type) {
+	case CEMU_USB_MSGT_DO_STATUS:
+		rc = process_do_status(buf, len);
+		break;
+	case CEMU_USB_MSGT_DO_PTS:
+		rc = process_do_pts(buf, len);
+		break;
+	case CEMU_USB_MSGT_DO_ERROR:
+		rc = process_do_error(buf, len);
+		break;
+	case CEMU_USB_MSGT_DO_RX_DATA:
+		rc = process_do_rx_da(buf, len);
+		break;
+	default:
+		printf("unknown simtrace msg type 0x%02x\n", sh->msg_type);
+		rc = -1;
+		break;
+	}
+
+	return rc;
+}
+
+static void print_welcome(void)
+{
+	printf("simtrace2-remsim - Remote SIM card forwarding\n"
+	       "(C) 2010-2016 by Harald Welte <laforge@gnumonks.org>\n\n");
+}
+
+static void print_help(void)
+{
+	printf( "\t-i\t--gsmtap-ip\tA.B.C.D\n"
+		"\t-a\t--skip-atr\n"
+		"\t-h\t--help\n"
+		"\t-k\t--keep-running\n"
+		"\n"
+		);
+}
+
+static const struct option opts[] = {
+	{ "gsmtap-ip", 1, 0, 'i' },
+	{ "skip-atr", 0, 0, 'a' },
+	{ "help", 0, 0, 'h' },
+	{ "keep-running", 0, 0, 'k' },
+	{ NULL, 0, 0, 0 }
+};
+
+static void run_mainloop(void)
+{
+	unsigned int msg_count, byte_count = 0;
+	char buf[16*265];
+	int xfer_len;
+	int rc;
+
+	printf("Entering main loop\n");
+
+	while (1) {
+		/* read data from SIMtrace2 device (local or via USB) */
+		if (g_udp_fd < 0) {
+			rc = libusb_bulk_transfer(g_devh, SIMTRACE_IN_EP, buf, sizeof(buf), &xfer_len, 100000);
+			if (rc < 0 && rc != LIBUSB_ERROR_TIMEOUT) {
+				fprintf(stderr, "BULK IN transfer error; rc=%d\n", rc);
+				return;
+			}
+		} else {
+			rc = read(g_udp_fd, buf, sizeof(buf));
+			if (rc <= 0) {
+				fprintf(stderr, "shor read from UDP\n");
+				return;
+			}
+			xfer_len = rc;
+		}
+		/* dispatch any incoming data */
+		if (xfer_len > 0) {
+			//printf("URB: %s\n", osmo_hexdump(buf, rc));
+			process_usb_msg(buf, xfer_len);
+			msg_count++;
+			byte_count += xfer_len;
+		}
+	}
+}
+
+int main(int argc, char **argv)
+{
+	char *gsmtap_host = "127.0.0.1";
+	int rc;
+	int c, ret = 1;
+	int skip_atr = 0;
+	int keep_running = 0;
+	int remote_udp_port = 52342;
+	char *remote_udp_host = NULL;
+	struct osim_reader_hdl *reader;
+	struct osim_card_hdl *card;
+
+	print_welcome();
+
+	while (1) {
+		int option_index = 0;
+
+		c = getopt_long(argc, argv, "r:p:hi:ak", opts, &option_index);
+		if (c == -1)
+			break;
+		switch (c) {
+		case 'r':
+			remote_udp_host = optarg;
+			break;
+		case 'p':
+			remote_udp_port = atoi(optarg);
+			break;
+		case 'h':
+			print_help();
+			exit(0);
+			break;
+		case 'i':
+			gsmtap_host = optarg;
+			break;
+		case 'a':
+			skip_atr = 1;
+			break;
+		case 'k':
+			keep_running = 1;
+			break;
+		}
+	}
+
+	g_prof = &osim_uicc_sim_cic_profile;
+
+	if (!remote_udp_host) {
+		rc = libusb_init(NULL);
+		if (rc < 0) {
+			fprintf(stderr, "libusb initialization failed\n");
+			goto do_exit;
+		}
+	} else {
+		g_udp_fd = osmo_sock_init(AF_INET, SOCK_DGRAM, IPPROTO_UDP, remote_udp_host,
+					  remote_udp_port, OSMO_SOCK_F_CONNECT);
+		if (g_udp_fd < 0) {
+			fprintf(stderr, "error binding UDP port\n");
+			goto do_exit;
+		}
+	}
+
+	g_gti = gsmtap_source_init(gsmtap_host, GSMTAP_UDP_PORT, 0);
+	if (!g_gti) {
+		perror("unable to open GSMTAP");
+		goto close_exit;
+	}
+	gsmtap_source_add_sink(g_gti);
+
+	reader = osim_reader_open(OSIM_READER_DRV_PCSC, 0, "", NULL);
+	if (!reader) {
+		perror("unable to open PC/SC reader");
+		goto close_exit;
+	}
+
+	card = osim_card_open(reader, OSIM_PROTO_T0);
+	if (!card) {
+		perror("unable to open SIM card");
+		goto close_exit;
+	}
+
+	g_chan = llist_entry(card->channels.next, struct osim_chan_hdl, list);
+	if (!g_chan) {
+		perror("SIM card has no channel?!?");
+		goto close_exit;
+	}
+
+	do {
+		if (g_udp_fd < 0) {
+			g_devh = libusb_open_device_with_vid_pid(NULL, SIMTRACE_USB_VENDOR, SIMTRACE_USB_PRODUCT);
+			if (!g_devh) {
+				fprintf(stderr, "can't open USB device\n");
+				goto close_exit;
+			}
+
+			rc = libusb_claim_interface(g_devh, 0);
+			if (rc < 0) {
+				fprintf(stderr, "can't claim interface; rc=%d\n", rc);
+				goto close_exit;
+			}
+		}
+
+		request_card_insert(true);
+
+		run_mainloop();
+		ret = 0;
+
+		if (g_udp_fd < 0)
+			libusb_release_interface(g_devh, 0);
+close_exit:
+		if (g_devh)
+			libusb_close(g_devh);
+		if (keep_running)
+			sleep(1);
+	} while (keep_running);
+
+release_exit:
+	if (g_udp_fd < 0)
+		libusb_exit(NULL);
+do_exit:
+	return ret;
+}
diff --git a/host/usb2udp.c b/host/usb2udp.c
new file mode 100644
index 0000000..fcf508a
--- /dev/null
+++ b/host/usb2udp.c
@@ -0,0 +1,280 @@
+/* simtrace - main program for the host PC
+ *
+ * (C) 2010-2016 by Harald Welte <hwelte@hmw-consulting.de>
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License version 2 
+ *  as published by the Free Software Foundation
+ *
+ *  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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <errno.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <time.h>
+#define _GNU_SOURCE
+#include <getopt.h>
+#include <poll.h>
+
+#include <sys/time.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+#include <libusb.h>
+
+#include "simtrace.h"
+#include "cardemu_prot.h"
+#include "apdu_dispatch.h"
+
+#include <osmocom/core/utils.h>
+#include <osmocom/core/socket.h>
+#include <osmocom/core/select.h>
+
+struct libusb_device_handle *g_devh;
+static struct sockaddr_in g_sa_remote;
+static struct osmo_fd g_udp_ofd;
+
+static void print_welcome(void)
+{
+	printf("usb2udp - UDP/IP forwarding of SIMtrace card emulation\n"
+	       "(C) 2016 by Harald Welte <laforge@gnumonks.org>\n\n");
+}
+
+static void print_help(void)
+{
+	printf( "\t-h\t--help\n"
+		"\n"
+		);
+}
+
+struct ep_buf {
+	uint8_t ep;
+	uint8_t buf[1024];
+	struct libusb_transfer *xfer;
+};
+static struct ep_buf g_buf_in;
+static struct ep_buf g_buf_out;
+
+static void usb_in_xfer_cb(struct libusb_transfer *xfer)
+{
+	int rc;
+
+	printf("xfer_cb(ep=%02x): status=%d, flags=0x%x, type=%u, len=%u, act_len=%u\n",
+		xfer->endpoint, xfer->status, xfer->flags, xfer->type, xfer->length, xfer->actual_length);
+	switch (xfer->status) {
+	case LIBUSB_TRANSFER_COMPLETED:
+		switch (xfer->endpoint) {
+		case SIMTRACE_IN_EP:
+			/* process the data */
+			printf("read %d bytes from SIMTRACE, forwarding to UDP\n", xfer->actual_length);
+			rc = sendto(g_udp_ofd.fd, xfer->buffer, xfer->actual_length, 0, (struct sockaddr *)&g_sa_remote, sizeof(g_sa_remote));
+			if (rc <= 0) {
+				fprintf(stderr, "error writing to UDP\n");
+			}
+			/* and re-submit the URB */
+			libusb_submit_transfer(xfer);
+			break;
+		case SIMTRACE_OUT_EP:
+			/* re-enable reading from the UDP side */
+			g_udp_ofd.when |= BSC_FD_READ;
+			break;
+		}
+		break;
+	default:
+		fprintf(stderr, "xfer_cb(ERROR '%s')\n", osmo_hexdump_nospc(xfer->buffer, xfer->actual_length));
+		break;
+	}
+}
+
+static void init_ep_buf(int ep, struct ep_buf *epb)
+{
+	epb->ep = ep;
+	if (!epb->xfer)
+		epb->xfer = libusb_alloc_transfer(0);
+
+	epb->xfer->flags = 0;
+
+	libusb_fill_bulk_transfer(epb->xfer, g_devh, epb->ep, epb->buf, sizeof(epb->buf), usb_in_xfer_cb, NULL, 0);
+}
+
+/***********************************************************************
+ * libosmocore main loop integration of libusb async I/O
+ ***********************************************************************/
+
+static int g_libusb_pending = 0;
+
+static int ofd_libusb_cb(struct osmo_fd *ofd, unsigned int what)
+{
+	/* FIXME */
+	g_libusb_pending = 1;
+
+	return 0;
+}
+
+/* call-back when libusb adds a FD */
+static void libusb_fd_added_cb(int fd, short events, void *user_data)
+{
+	struct osmo_fd *ofd = talloc_zero(NULL, struct osmo_fd);
+
+	printf("%s(%u, %x)\n", __func__, fd, events);
+
+	ofd->fd = fd;
+	ofd->cb = &ofd_libusb_cb;
+	if (events & POLLIN)
+		ofd->when |= BSC_FD_READ;
+	if (events & POLLOUT)
+		ofd->when |= BSC_FD_WRITE;
+
+	osmo_fd_register(ofd);
+}
+
+/* call-back when libusb removes a FD */
+static void libusb_fd_removed_cb(int fd, void *user_data)
+{
+	struct osmo_fd *ofd;
+
+	printf("%s(%u)\n", __func__, fd);
+#if 0
+	/* FIXME: This needs new export in libosmocore! */
+	ofd = osmo_fd_get_by_fd(fd);
+
+	if (ofd) {
+		osmo_fd_unregister(ofd);
+		talloc_free(ofd);
+	}
+#endif
+}
+
+/* call-back when the UDP socket is readable */
+static int ofd_udp_cb(struct osmo_fd *ofd, unsigned int what)
+{
+	int rc;
+	int addrlen = sizeof(g_sa_remote);
+
+	rc = recvfrom(ofd->fd, g_buf_out.buf, sizeof(g_buf_out.buf), 0,
+			(struct sockaddr *)&g_sa_remote, &addrlen);
+	if (rc <= 0) {
+		fprintf(stderr, "error reading from UDP\n");
+		return 0;
+	}
+	printf("read %d bytes from UDP, forwarding to SIMTRACE\n", rc);
+	g_buf_out.xfer->length = rc;
+
+	/* disable further READ interest for the UDP socket */
+	ofd->when &= ~BSC_FD_READ;
+
+	/* submit the URB on the OUT end point */
+	libusb_submit_transfer(g_buf_out.xfer);
+
+	return 0;
+}
+
+static void run_mainloop(void)
+{
+	int rc;
+
+	printf("Entering main loop\n");
+
+	while (1) {
+		osmo_select_main(0);
+		if (g_libusb_pending) {
+			struct timeval tv;
+			memset(&tv, 0, sizeof(tv));
+			rc = libusb_handle_events_timeout_completed(NULL, &tv, NULL);
+			if (rc != 0) {
+				fprintf(stderr, "handle_events_timeout_completed == %d\n", rc);
+				break;
+			}
+		}
+	}
+}
+
+int main(int argc, char **argv)
+{
+	int rc;
+	int c, ret = 1;
+	char *remote_host = NULL;
+	int local_udp_port = 52342;
+
+	print_welcome();
+
+	while (1) {
+		int option_index = 0;
+		static const struct option opts[] = {
+			{ "udp-port", 1, 0, 'u' },
+			{ "help", 0, 0, 'h' },
+			{ NULL, 0, 0, 0 }
+		};
+
+		c = getopt_long(argc, argv, "u:p:h", opts, &option_index);
+		if (c == -1)
+			break;
+		switch (c) {
+		case 'u':
+			local_udp_port = atoi(optarg);
+			break;
+		case 'h':
+			print_help();
+			exit(0);
+			break;
+		}
+	}
+
+	rc = libusb_init(NULL);
+	if (rc < 0) {
+		fprintf(stderr, "libusb initialization failed\n");
+		goto close_exit;
+	}
+
+	libusb_set_pollfd_notifiers(NULL, &libusb_fd_added_cb, &libusb_fd_removed_cb, NULL);
+
+	g_devh = libusb_open_device_with_vid_pid(NULL, SIMTRACE_USB_VENDOR, SIMTRACE_USB_PRODUCT);
+	if (!g_devh) {
+		fprintf(stderr, "can't open USB device\n");
+		goto close_exit;
+	}
+
+	rc = libusb_claim_interface(g_devh, 0);
+	if (rc < 0) {
+		fprintf(stderr, "can't claim interface; rc=%d\n", rc);
+		goto close_exit;
+	}
+
+	/* open UDP socket, register with select handling and mark it
+	 * readable */
+	g_udp_ofd.cb = ofd_udp_cb;
+	osmo_sock_init_ofd(&g_udp_ofd, AF_INET, SOCK_DGRAM, IPPROTO_UDP, NULL, local_udp_port, OSMO_SOCK_F_BIND);
+
+	/* initialize USB buffers / transfers */
+	init_ep_buf(SIMTRACE_OUT_EP, &g_buf_out);
+	init_ep_buf(SIMTRACE_IN_EP, &g_buf_in);
+
+	/* submit the first transfer for the IN endpoint */
+	libusb_submit_transfer(g_buf_in.xfer);
+
+	run_mainloop();
+
+	ret = 0;
+
+	libusb_release_interface(g_devh, 0);
+close_exit:
+	if (g_devh)
+		libusb_close(g_devh);
+
+release_exit:
+	libusb_exit(NULL);
+	return ret;
+}