diff --git a/gisi/modem.c b/gisi/modem.c
index 6699576d..72b90047 100644
--- a/gisi/modem.c
+++ b/gisi/modem.c
@@ -23,17 +23,968 @@
 #include <config.h>
 #endif
 
-#include <errno.h>
+#define _GNU_SOURCE
+#include <stdint.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/ioctl.h>
+#include <sys/uio.h>
 #include <net/if.h>
+#include <errno.h>
+#include <glib.h>
 
+#include "message.h"
+#include "common.h"
 #include "modem.h"
+#include "socket.h"
 
-GIsiModem *g_isi_modem_by_name(char const *name)
+struct _GIsiServiceMux {
+	uint8_t resource;
+	GIsiVersion version;
+	GIsiModem *modem;
+	GSList *pending;
+	uint8_t last_utid;
+	unsigned subscriptions;
+	unsigned registrations;
+	gboolean reachable;
+	gboolean version_pending;
+};
+typedef struct _GIsiServiceMux GIsiServiceMux;
+
+struct _GIsiModem {
+	unsigned index;
+	GHashTable *services;
+	gboolean subs_pending;
+	int fd;
+	guint source;
+	GIsiNotifyFunc debug;
+	void *ddata;
+};
+
+struct _GIsiPending {
+	enum GIsiMessageType type;
+	GIsiServiceMux *service;
+	guint timeout;
+	GIsiNotifyFunc notify;
+	GDestroyNotify destroy;
+	void *data;
+	uint8_t utid;
+	uint8_t msgid;
+};
+
+static const struct sockaddr_pn namesrv = {
+	.spn_family = AF_PHONET,
+	.spn_resource = PN_NAMESERVICE,
+};
+
+static const struct sockaddr_pn commgr = {
+	.spn_family = AF_PHONET,
+	.spn_resource = PN_COMMGR,
+};
+
+static unsigned *g_keydup(unsigned key)
 {
-	unsigned index = if_nametoindex(name);
+	unsigned *tmp = g_try_new0(unsigned, 1);
+	if (!tmp)
+		return NULL;
 
-	if (errno == 0)
-		errno = ENODEV;
-
-	return (GIsiModem *)(void *)(uintptr_t)index;
+	*tmp = key;
+	return tmp;
+}
+
+static GIsiServiceMux *service_get(GIsiModem *modem, uint8_t resource)
+{
+	GIsiServiceMux *mux;
+	unsigned key = resource;
+
+	mux = g_hash_table_lookup(modem->services, &key);
+	if (mux)
+		return mux;
+
+	mux = g_try_new0(GIsiServiceMux, 1);
+	if (!mux)
+		return NULL;
+
+	g_hash_table_insert(modem->services, g_keydup(key), mux);
+
+	mux->modem = modem;
+	mux->resource = resource;
+	mux->version.major = -1;
+	mux->version.minor = -1;
+	mux->reachable = FALSE;
+	mux->version_pending = FALSE;
+
+	return mux;
+}
+
+static gint utid_equal(gconstpointer a, gconstpointer b)
+{
+	const GIsiPending *pa = a;
+	const GIsiPending *pb = b;
+
+	return pa->utid - pb->utid;
+}
+
+static void pending_dispatch(GIsiPending *pend, GIsiMessage *msg)
+{
+	if (!pend->notify)
+		return;
+
+	pend->notify(msg, pend->data);
+}
+
+static void service_dispatch(GIsiServiceMux *mux, GIsiMessage *msg)
+{
+	uint8_t msgid = g_isi_msg_id(msg);
+	uint8_t utid = g_isi_msg_utid(msg);
+
+	GSList *l = mux->pending;
+
+	while (l) {
+		GSList *next = l->next;
+		GIsiPending *pend = l->data;
+		msg->private = pend;
+
+		/*
+		 * REQs, NTFs and INDs are dispatched on message ID.  While
+		 * INDs have the unique transaction ID set to zero, NTFs
+		 * typically mirror the UTID of the request that set up the
+		 * session, and REQs can naturally have any transaction ID.
+		 *
+		 * RESPs are dispatched on unique transaction ID, explicitly
+		 * ignoring the msgid.  A RESP also completes a transaction,
+		 * so it needs to be removed after being notified of.
+		 *
+		 * Version query responses aredispatched in a similar fashion
+		 * as RESPs, but based on the pending type and the message ID.
+		 * Some of these may be synthesized, but nevertheless need to
+		 * be removed.
+		 */
+		if (pend->type < GISI_MESSAGE_TYPE_RESP && pend->msgid == msgid) {
+
+			pending_dispatch(pend, msg);
+
+		} else if (pend->type == GISI_MESSAGE_TYPE_RESP &&
+				pend->utid == utid) {
+
+			pending_dispatch(pend, msg);
+			pend->notify = NULL;
+
+			g_isi_pending_remove(pend);
+			break;
+
+		} else if (pend->type == GISI_MESSAGE_TYPE_COMMON &&
+				msgid == COMMON_MESSAGE &&
+				pend->msgid == COMM_ISI_VERSION_GET_REQ) {
+
+			pending_dispatch(pend, msg);
+			pend->notify = NULL;
+
+			g_isi_pending_remove(pend);
+
+		}
+		l = next;
+	}
+}
+
+static void common_message_decode(GIsiServiceMux *mux, GIsiMessage *msg)
+{
+	uint8_t code;
+	uint8_t major;
+	uint8_t minor;
+
+	if (!g_isi_msg_data_get_byte(msg, 0, &code))
+		return;
+
+	switch (code) {
+	case COMM_ISI_VERSION_GET_RESP:
+
+		if (g_isi_msg_data_get_byte(msg, 1, &major) &&
+				g_isi_msg_data_get_byte(msg, 2, &minor)) {
+			mux->version.major = major;
+			mux->version.minor = minor;
+		}
+		mux->version_pending = FALSE;
+		break;
+
+	case COMM_ISA_ENTITY_NOT_REACHABLE_RESP:
+		mux->reachable = FALSE;
+		msg->error = ENOENT;
+		break;
+
+	case 0x00:
+		/*
+		 * PN_SIM doesn't support ISI version, but sends a
+		 * 0x00 message as a response.  Work around this modem
+		 * wart.
+		 */
+		mux->version_pending = FALSE;
+		break;
+	}
+	msg->version = &mux->version;
+}
+
+static gboolean isi_callback(GIOChannel *channel, GIOCondition cond,
+				gpointer data)
+{
+	GIsiModem *modem = data;
+	int len;
+
+	if (cond & (G_IO_NVAL|G_IO_HUP)) {
+		g_warning("Unexpected event on PhoNet channel %p", channel);
+		return FALSE;
+	}
+
+	len = g_isi_phonet_peek_length(channel);
+
+	if (len > 0) {
+		struct sockaddr_pn addr;
+		uint32_t buf[(len + 3) / 4];
+
+		GIsiServiceMux *mux;
+		GIsiMessage msg;
+		unsigned key;
+
+		len = g_isi_phonet_read(channel, buf, len, &addr);
+		if (len < 2)
+			return TRUE;
+
+		msg.addr = &addr;
+		msg.error = 0;
+		msg.data = buf;
+		msg.len = len;
+		msg.version = &mux->version;
+
+		if (modem->debug)
+			modem->debug(&msg, modem->ddata);
+
+		key = addr.spn_resource;
+		mux = g_hash_table_lookup(modem->services, &key);
+		if (!mux)
+			return TRUE;
+
+		/*
+		 * For now, assume any message received means that the
+		 * resource is reachable
+		 */
+		mux->reachable = TRUE;
+
+		if (g_isi_msg_id(&msg) == COMMON_MESSAGE)
+			common_message_decode(mux, &msg);
+
+		service_dispatch(mux, &msg);
+	}
+	return TRUE;
+}
+
+GIsiModem *g_isi_modem_create(unsigned index)
+{
+	GIsiModem *modem;
+	GIOChannel *channel;
+
+	if (index == 0) {
+		errno = ENODEV;
+		return NULL;
+	}
+
+	modem = g_try_new0(GIsiModem, 1);
+	if (!modem) {
+		errno = ENOMEM;
+		return NULL;
+	}
+
+	channel = g_isi_phonet_new(index);
+	if (!channel) {
+		g_free(modem);
+		return NULL;
+	}
+
+	modem->fd = g_io_channel_unix_get_fd(channel);
+	modem->source = g_io_add_watch(channel,
+					G_IO_IN|G_IO_ERR|G_IO_HUP|G_IO_NVAL,
+					isi_callback, modem);
+	g_io_channel_unref(channel);
+
+	modem->index = index;
+	modem->services = g_hash_table_new_full(g_int_hash, g_int_equal,
+						g_free, NULL);
+
+	return modem;
+}
+
+GIsiModem *g_isi_modem_create_by_name(const char *name)
+{
+	return g_isi_modem_create(if_nametoindex(name));
+}
+
+static void service_name_register(GIsiServiceMux *mux)
+{
+	uint8_t msg[] = {
+		0, PNS_NAME_ADD_REQ, 0, 0,
+		0, 0, 0, mux->resource,	/* 32-bit Big-Endian name */
+		0, 0,			/* device/object */
+		0, 0,			/* filler */
+	};
+	uint16_t object = 0;
+
+	if (ioctl(mux->modem->fd, SIOCPNGETOBJECT, &object) < 0) {
+		g_warning("ioctl(SIOCPNGETOBJECT): %s", strerror(errno));
+		return;
+	}
+
+	/* Fill in the object ID */
+	msg[8] = object >> 8;
+	msg[9] = object & 0xFF;
+
+	sendto(mux->modem->fd, msg, sizeof(msg), MSG_NOSIGNAL, (void *)&namesrv,
+		sizeof(namesrv));
+}
+
+static void service_name_deregister(GIsiServiceMux *mux)
+{
+	const uint8_t msg[] = {
+		0, PNS_NAME_REMOVE_REQ, 0, 0,
+		0, 0, 0, mux->resource,
+	};
+
+	sendto(mux->modem->fd, msg, sizeof(msg), MSG_NOSIGNAL, (void *)&namesrv,
+		sizeof(namesrv));
+}
+
+static gboolean modem_subs_update(gpointer data)
+{
+	GHashTableIter iter;
+	gpointer keyptr, value;
+
+	GIsiModem *modem = data;
+	uint8_t msg[3 + 256] = {
+		0, PNS_SUBSCRIBED_RESOURCES_IND,
+		0,
+	};
+	uint8_t count = 0;
+
+	g_hash_table_iter_init(&iter, modem->services);
+
+	while (g_hash_table_iter_next(&iter, &keyptr, &value)) {
+		GIsiServiceMux *mux = value;
+
+		if (mux->subscriptions > 0) {
+			msg[3 + count] = mux->resource;
+			count++;
+		}
+	}
+	msg[2] = count;
+
+	sendto(modem->fd, msg, 3 + msg[2], MSG_NOSIGNAL, (void *)&commgr,
+		sizeof(commgr));
+
+	modem->subs_pending = FALSE;
+
+	return FALSE;
+}
+
+static uint8_t service_next_utid(GIsiServiceMux *mux)
+{
+	if (mux->last_utid == 0x00 || mux->last_utid == 0xFF)
+		return 1;
+
+	return mux->last_utid + 1;
+}
+
+static void service_subs_incr(GIsiServiceMux *mux)
+{
+	GIsiModem *modem = mux->modem;
+
+	mux->subscriptions++;
+
+	if (mux->subscriptions == 1 && !modem->subs_pending) {
+		g_idle_add(modem_subs_update, modem);
+		modem->subs_pending = TRUE;
+	}
+}
+
+static void service_subs_decr(GIsiServiceMux *mux)
+{
+	GIsiModem *modem = mux->modem;
+
+	if (mux->subscriptions == 0)
+		return;
+
+	mux->subscriptions--;
+
+	if (mux->subscriptions == 0 && !modem->subs_pending) {
+		g_idle_add(modem_subs_update, modem);
+		modem->subs_pending = TRUE;
+	}
+}
+
+static void service_regs_incr(GIsiServiceMux *mux)
+{
+	mux->registrations++;
+
+	if (mux->registrations == 1)
+		service_name_register(mux);
+}
+
+static void service_regs_decr(GIsiServiceMux *mux)
+{
+	if (mux->registrations == 0)
+		return;
+
+	mux->registrations--;
+
+	if (mux->registrations == 0)
+		service_name_deregister(mux);
+}
+
+static void pending_destroy(gpointer value, gpointer user)
+{
+	GIsiPending *op = value;
+
+	if (!op)
+		return;
+
+	if (op->timeout > 0)
+		g_source_remove(op->timeout);
+
+	if (op->destroy)
+		op->destroy(op->data);
+
+	g_free(op);
+}
+
+static gboolean service_finalize(gpointer key, gpointer value, gpointer user)
+{
+	GIsiServiceMux *mux = value;
+	GIsiModem *modem = user;
+
+	if (mux->subscriptions > 0) {
+		mux->subscriptions = 0;
+
+		if (!modem->subs_pending) {
+			g_idle_add(modem_subs_update, modem);
+			modem->subs_pending = TRUE;
+		}
+	}
+
+	if (mux->registrations > 0)
+		service_name_deregister(mux);
+
+	g_slist_foreach(mux->pending, pending_destroy, NULL);
+	g_slist_free(mux->pending);
+	g_free(mux);
+
+	return TRUE;
+}
+
+void g_isi_modem_destroy(GIsiModem *modem)
+{
+	if (!modem)
+		return;
+
+	g_hash_table_foreach_remove(modem->services, service_finalize, modem);
+	g_hash_table_unref(modem->services);
+	g_free(modem);
+}
+
+unsigned g_isi_modem_index(GIsiModem *modem)
+{
+	return modem ? modem->index : 0;
+}
+
+GIsiPending *g_isi_request_send(GIsiModem *modem, uint8_t resource,
+					const void *__restrict buf, size_t len,
+					unsigned timeout, GIsiNotifyFunc notify,
+					void *data, GDestroyNotify destroy)
+{
+	struct sockaddr_pn dst = {
+		.spn_family = AF_PHONET,
+		.spn_resource = resource,
+	};
+
+	return g_isi_request_sendto(modem, &dst, buf, len, timeout, notify,
+					data, destroy);
+};
+
+GIsiPending *g_isi_request_vsend(GIsiModem *modem, uint8_t resource,
+					const struct iovec *__restrict iov,
+					size_t iovlen, unsigned timeout,
+					GIsiNotifyFunc notify, void *data,
+					GDestroyNotify destroy)
+{
+	struct sockaddr_pn dst = {
+		.spn_family = AF_PHONET,
+		.spn_resource = resource,
+	};
+
+	return g_isi_request_vsendto(modem, &dst, iov, iovlen, timeout, notify,
+					data, destroy);
+}
+
+GIsiPending *g_isi_request_sendto(GIsiModem *modem, struct sockaddr_pn *dst,
+					const void *__restrict buf, size_t len,
+					unsigned timeout, GIsiNotifyFunc notify,
+					void *data, GDestroyNotify destroy)
+{
+	const struct iovec iov = {
+		.iov_base = (void *)buf,
+		.iov_len = len,
+	};
+
+	return g_isi_request_vsendto(modem, dst, &iov, 1, timeout, notify, data,
+					destroy);
+}
+
+static void vdebug(struct sockaddr_pn *dst,
+			const struct iovec *__restrict iov, size_t iovlen,
+			size_t total_len, GIsiNotifyFunc debug, void *data)
+{
+	uint8_t buffer[total_len];
+	uint8_t *ptr = buffer;
+	GIsiMessage msg = {
+		.addr = dst,
+		.data = (const void *)buffer,
+		.len = total_len,
+	};
+	size_t i;
+
+	for (i = 0; i < iovlen; i++) {
+		memcpy(ptr, iov[i].iov_base, iov[i].iov_len);
+		ptr += iov[i].iov_len;
+	}
+
+	debug(&msg, data);
+}
+
+static gboolean resp_timeout(gpointer data)
+{
+	GIsiPending *resp = data;
+	GIsiMessage msg = {
+		.error = ETIMEDOUT,
+		.private = resp,
+	};
+
+	pending_dispatch(resp, &msg);
+	resp->notify = NULL;
+
+	g_isi_pending_remove(resp);
+	return FALSE;
+}
+
+GIsiPending *g_isi_request_vsendto(GIsiModem *modem, struct sockaddr_pn *dst,
+					const struct iovec *__restrict iov,
+					size_t iovlen, unsigned timeout,
+					GIsiNotifyFunc notify, void *data,
+					GDestroyNotify destroy)
+{
+	struct iovec _iov[1 + iovlen];
+	struct msghdr msg = {
+		.msg_name = (void *)dst,
+		.msg_namelen = sizeof(struct sockaddr_pn),
+		.msg_iov = _iov,
+		.msg_iovlen = 1 + iovlen,
+		.msg_control = NULL,
+		.msg_controllen = 0,
+		.msg_flags = 0,
+	};
+	ssize_t ret;
+	size_t i, len;
+
+	GIsiServiceMux *mux;
+	GIsiPending *resp;
+
+	if (!modem) {
+		errno = EINVAL;
+		return NULL;
+	}
+
+	mux = service_get(modem, dst->spn_resource);
+	if (!mux) {
+		errno = ENOMEM;
+		return NULL;
+	}
+
+	resp = g_try_new0(GIsiPending, 1);
+	if (!resp) {
+		errno = ENOMEM;
+		return NULL;
+	}
+
+	resp->type = GISI_MESSAGE_TYPE_RESP;
+	resp->utid = service_next_utid(mux);
+	resp->service = mux;
+	resp->notify = notify;
+	resp->destroy = destroy;
+	resp->data = data;
+
+	if (g_slist_find_custom(mux->pending, resp, utid_equal)) {
+		/*
+		 * FIXME: perhaps retry with randomized access after
+		 * initial miss. Although if the rate at which
+		 * requests are sent is so high that the unique
+		 * transaction ID wraps, it's likely there is
+		 * something wrong and we might as well fail here.
+		 */
+		errno = EBUSY;
+		goto error;
+	}
+
+	_iov[0].iov_base = &resp->utid;
+	_iov[0].iov_len = 1;
+
+	for (i = 0, len = 1; i < iovlen; i++) {
+		_iov[1 + i] = iov[i];
+		len += iov[i].iov_len;
+	}
+
+	if (modem->debug)
+		vdebug(dst, _iov, 1 + iovlen, len, modem->debug, modem->ddata);
+
+	ret = sendmsg(modem->fd, &msg, MSG_NOSIGNAL);
+	if (ret == -1)
+		goto error;
+
+	if (ret != (ssize_t)len) {
+		errno = EMSGSIZE;
+		goto error;
+	}
+
+	mux->pending = g_slist_prepend(mux->pending, resp);
+
+	if (timeout)
+		resp->timeout = g_timeout_add_seconds(timeout, resp_timeout, resp);
+
+	mux->last_utid = resp->utid;
+	return resp;
+
+error:
+	g_free(resp);
+	return NULL;
+}
+
+uint8_t g_isi_request_utid(GIsiPending *resp)
+{
+	return resp ? resp->utid : 0;
+}
+
+GIsiPending *g_isi_pending_from_msg(const GIsiMessage *msg)
+{
+	return msg ? msg->private : NULL;
+}
+
+void g_isi_pending_remove(GIsiPending *op)
+{
+	if (!op)
+		return;
+
+	op->service->pending = g_slist_remove(op->service->pending, op);
+
+	if (op->type == GISI_MESSAGE_TYPE_IND)
+		service_subs_decr(op->service);
+
+	if (op->type == GISI_MESSAGE_TYPE_REQ)
+		service_regs_decr(op->service);
+
+	if (op->type == GISI_MESSAGE_TYPE_RESP && op->notify) {
+		GIsiMessage msg = {
+			.error = ESHUTDOWN,
+			.private = op,
+		};
+		op->notify(&msg, op->data);
+		op->notify = NULL;
+	}
+
+	pending_destroy(op, NULL);
+}
+
+GIsiPending *g_isi_ntf_subscribe(GIsiModem *modem, uint8_t resource,
+					uint8_t msgid, GIsiNotifyFunc notify,
+					void *data, GDestroyNotify destroy)
+{
+	GIsiServiceMux *mux;
+	GIsiPending *ntf;
+
+	mux = service_get(modem, resource);
+	if (!mux) {
+		errno = ENOMEM;
+		return NULL;
+	}
+
+	ntf = g_try_new0(GIsiPending, 1);
+	if (!ntf) {
+		errno = ENOMEM;
+		return NULL;
+	}
+
+	ntf->type = GISI_MESSAGE_TYPE_NTF;
+	ntf->service = mux;
+	ntf->notify = notify;
+	ntf->data = data;
+	ntf->destroy = destroy;
+	ntf->msgid = msgid;
+
+	mux->pending = g_slist_append(mux->pending, ntf);
+
+	return ntf;
+}
+
+GIsiPending *g_isi_service_bind(GIsiModem *modem, uint8_t resource,
+				uint8_t msgid, GIsiNotifyFunc notify,
+				void *data, GDestroyNotify destroy)
+{
+	GIsiServiceMux *mux;
+	GIsiPending *srv;
+
+	mux = service_get(modem, resource);
+	if (!mux) {
+		errno = ENOMEM;
+		return NULL;
+	}
+
+	srv = g_try_new0(GIsiPending, 1);
+	if (!srv) {
+		errno = ENOMEM;
+		return NULL;
+	}
+
+	srv->type = GISI_MESSAGE_TYPE_REQ;
+	srv->service = mux;
+	srv->notify = notify;
+	srv->data = data;
+	srv->destroy = destroy;
+	srv->msgid = msgid;
+
+	mux->pending = g_slist_append(mux->pending, srv);
+
+	service_regs_incr(mux);
+
+	return srv;
+}
+
+GIsiPending *g_isi_ind_subscribe(GIsiModem *modem, uint8_t resource,
+					uint8_t msgid, GIsiNotifyFunc notify,
+					void *data, GDestroyNotify destroy)
+{
+	GIsiServiceMux *mux;
+	GIsiPending *ind;
+
+	mux = service_get(modem, resource);
+	if (!mux) {
+		errno = ENOMEM;
+		return NULL;
+	}
+
+	ind = g_try_new0(GIsiPending, 1);
+	if (!ind) {
+		errno = ENOMEM;
+		return NULL;
+	}
+
+	ind->type = GISI_MESSAGE_TYPE_IND;
+	ind->service = mux;
+	ind->notify = notify;
+	ind->data = data;
+	ind->destroy = destroy;
+	ind->msgid = msgid;
+
+	mux->pending = g_slist_append(mux->pending, ind);
+
+	service_subs_incr(mux);
+
+	return ind;
+}
+
+int g_isi_response_send(GIsiModem *modem, const GIsiMessage *req,
+				const void *__restrict buf, size_t len)
+{
+	const struct iovec iov = {
+		.iov_base = (void *)buf,
+		.iov_len = len,
+	};
+
+	return g_isi_response_vsend(modem, req, &iov, 1);
+}
+
+int g_isi_response_vsend(GIsiModem *modem, const GIsiMessage *req,
+				const struct iovec *__restrict iov,
+				size_t iovlen)
+{
+	struct iovec _iov[1 + iovlen];
+	uint8_t utid;
+	size_t i;
+
+	utid = g_isi_msg_utid(req);
+
+	_iov[0].iov_base = &utid;
+	_iov[0].iov_len = 1;
+
+	for (i = 0; i < iovlen; i++)
+		_iov[1 + i] = iov[i];
+
+	return g_isi_modem_vsendto(modem, req->addr, _iov, 1 + iovlen);
+}
+
+int g_isi_modem_sendto(GIsiModem *modem, struct sockaddr_pn *dst,
+			const void *__restrict buf, size_t len)
+{
+	const struct iovec iov = {
+		.iov_base = (void *)buf,
+		.iov_len = len,
+	};
+
+	return g_isi_modem_vsendto(modem, dst, &iov, 1);
+}
+
+int g_isi_modem_vsendto(GIsiModem *modem, struct sockaddr_pn *dst,
+				const struct iovec *__restrict iov,
+				size_t iovlen)
+{
+	struct msghdr msg = {
+		.msg_name = (void *)dst,
+		.msg_namelen = sizeof(struct sockaddr_pn),
+		.msg_iov = (struct iovec *)iov,
+		.msg_iovlen = iovlen,
+		.msg_control = NULL,
+		.msg_controllen = 0,
+		.msg_flags = 0,
+	};
+	ssize_t ret;
+	size_t i, len;
+	GIsiServiceMux *mux;
+
+	if (!modem)
+		return -EINVAL;
+
+	mux = service_get(modem, dst->spn_resource);
+	if (!mux)
+		return -ENOMEM;
+
+	for (i = 0, len = 0; i < iovlen; i++)
+		len += iov[i].iov_len;
+
+	if (modem->debug)
+		vdebug(dst, iov, iovlen, len, modem->debug, modem->ddata);
+
+	ret = sendmsg(modem->fd, &msg, MSG_NOSIGNAL);
+	if (ret == -1)
+		return -errno;
+
+	if (ret != (ssize_t)len)
+		return -EMSGSIZE;
+
+	return 0;
+}
+
+void g_isi_modem_set_debug(GIsiModem *modem, GIsiNotifyFunc debug, void *data)
+{
+	if (!modem)
+		return;
+
+	modem->debug = debug;
+	modem->ddata = data;
+}
+
+static int version_get_send(GIsiModem *modem, GIsiPending *ping)
+{
+	GIsiServiceMux *mux = ping->service;
+	const struct sockaddr_pn dst = {
+		.spn_family = AF_PHONET,
+		.spn_resource = mux->resource,
+	};
+	uint8_t msg[] = {
+		ping->utid,	/* UTID */
+		COMMON_MESSAGE,
+		COMM_ISI_VERSION_GET_REQ,
+		0,		/* Filler */
+	};
+	ssize_t ret;
+
+	if (g_slist_find_custom(mux->pending, ping, utid_equal))
+		return -EBUSY;
+
+	ret = sendto(modem->fd, msg, sizeof(msg), MSG_NOSIGNAL, (void *)&dst,
+			sizeof(dst));
+
+	if (ret == -1)
+		return -errno;
+
+	if (ret != (ssize_t)sizeof(msg))
+		return -EMSGSIZE;
+
+	mux->last_utid = ping->utid;
+	mux->version_pending = TRUE;
+	return 0;
+}
+
+static gboolean reachable_notify(gpointer data)
+{
+	GIsiPending *pong = data;
+	GIsiServiceMux *mux = pong->service;
+
+	struct sockaddr_pn addr = {
+		.spn_resource = mux->resource,
+	};
+	GIsiMessage msg = {
+		.version = &mux->version,
+		.private = pong,
+		.addr = &addr,
+	};
+
+	pending_dispatch(pong, &msg);
+	pong->notify = NULL;
+
+	g_isi_pending_remove(pong);
+	return FALSE;
+}
+
+GIsiPending *g_isi_resource_ping(GIsiModem *modem, uint8_t resource,
+					GIsiNotifyFunc notify, void *data,
+					GDestroyNotify destroy)
+{
+	GIsiServiceMux *mux;
+	GIsiPending *ping;
+	int ret;
+
+	mux = service_get(modem, resource);
+	if (!mux) {
+		errno = ENOMEM;
+		return NULL;
+	}
+
+	ping = g_try_new0(GIsiPending, 1);
+	if (!ping) {
+		errno = ENOMEM;
+		return NULL;
+	}
+
+	ping->type = GISI_MESSAGE_TYPE_COMMON;
+	ping->utid = service_next_utid(mux);
+	ping->service = mux;
+	ping->notify = notify;
+	ping->data = data;
+	ping->destroy = destroy;
+	ping->msgid = COMM_ISI_VERSION_GET_REQ;
+
+	if (mux->reachable) {
+		g_idle_add(reachable_notify, ping);
+		return ping;
+	}
+
+	if (!mux->version_pending) {
+		ret = version_get_send(modem, ping);
+		if (ret < 0) {
+			g_free(ping);
+			errno = ret;
+			return NULL;
+		}
+		mux->last_utid = ping->utid;
+	}
+
+	ping->timeout = g_timeout_add_seconds(COMMON_TIMEOUT, resp_timeout,
+						ping);
+	mux->pending = g_slist_prepend(mux->pending, ping);
+	mux->version_pending = TRUE;
+
+	return ping;
 }
diff --git a/gisi/modem.h b/gisi/modem.h
index bf7286d7..50f1f05b 100644
--- a/gisi/modem.h
+++ b/gisi/modem.h
@@ -23,22 +23,87 @@
 #define __GISI_MODEM_H
 
 #include <stdint.h>
+#include <glib/gtypes.h>
+
+#include "phonet.h"
+#include "message.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-typedef void (*GIsiDebugFunc) (const void *restrict data, size_t len,
-		void *opaque);
-
+struct _GIsiModem;
 typedef struct _GIsiModem GIsiModem;
 
-static inline unsigned g_isi_modem_index(GIsiModem *m)
-{
-	return (uintptr_t)m;
-}
+struct _GIsiPending;
+typedef struct _GIsiPending GIsiPending;
 
-GIsiModem *g_isi_modem_by_name(const char *name);
+typedef void (*GIsiNotifyFunc)(const GIsiMessage *msg, void *opaque);
+
+GIsiModem *g_isi_modem_create(unsigned index);
+GIsiModem *g_isi_modem_create_by_name(const char *name);
+void g_isi_modem_destroy(GIsiModem *modem);
+unsigned g_isi_modem_index(GIsiModem *modem);
+void g_isi_modem_set_debug(GIsiModem *modem, GIsiNotifyFunc notify,
+				void *opaque);
+
+GIsiPending *g_isi_request_send(GIsiModem *modem, uint8_t resource,
+					const void *__restrict buf, size_t len,
+					unsigned timeout, GIsiNotifyFunc notify,
+					void *data, GDestroyNotify destroy);
+
+GIsiPending *g_isi_request_vsend(GIsiModem *modem, uint8_t resource,
+					const struct iovec *__restrict iov,
+					size_t iovlen, unsigned timeout,
+					GIsiNotifyFunc notify, void *data,
+					GDestroyNotify destroy);
+
+GIsiPending *g_isi_request_sendto(GIsiModem *modem, struct sockaddr_pn *dst,
+					const void *__restrict buf, size_t len,
+					unsigned timeout, GIsiNotifyFunc notify,
+					void *data, GDestroyNotify destroy);
+
+GIsiPending *g_isi_request_vsendto(GIsiModem *modem, struct sockaddr_pn *dst,
+					const struct iovec *__restrict iov,
+					size_t iovlen, unsigned timeout,
+					GIsiNotifyFunc notify, void *data,
+					GDestroyNotify destroy);
+
+int g_isi_modem_sendto(GIsiModem *modem, struct sockaddr_pn *dst,
+			const void *__restrict buf, size_t len);
+
+int g_isi_modem_vsendto(GIsiModem *modem, struct sockaddr_pn *dst,
+				const struct iovec *__restrict iov,
+				size_t iovlen);
+
+uint8_t g_isi_request_utid(GIsiPending *resp);
+
+GIsiPending *g_isi_ind_subscribe(GIsiModem *modem, uint8_t resource,
+					uint8_t type, GIsiNotifyFunc notify,
+					void *data, GDestroyNotify destroy);
+
+GIsiPending *g_isi_ntf_subscribe(GIsiModem *modem, uint8_t resource,
+					uint8_t type, GIsiNotifyFunc notify,
+					void *data, GDestroyNotify destroy);
+
+GIsiPending *g_isi_service_bind(GIsiModem *modem, uint8_t resource,
+				uint8_t type, GIsiNotifyFunc notify,
+				void *data, GDestroyNotify destroy);
+
+int g_isi_response_send(GIsiModem *modem, const GIsiMessage *req,
+			const void *__restrict buf, size_t len);
+
+int g_isi_response_vsend(GIsiModem *modem, const GIsiMessage *req,
+				const struct iovec *__restrict iov,
+				size_t iovlen);
+
+GIsiPending *g_isi_pending_from_msg(const GIsiMessage *msg);
+
+void g_isi_pending_remove(GIsiPending *operation);
+
+GIsiPending *g_isi_resource_ping(GIsiModem *modem, uint8_t resource,
+					GIsiNotifyFunc notify, void *data,
+					GDestroyNotify destroy);
 
 #ifdef __cplusplus
 }