diff --git a/.gitignore b/.gitignore
index 48dec50..6dfb660 100644
--- a/.gitignore
+++ b/.gitignore
@@ -40,6 +40,7 @@ src/liboptions/liboptions.a
 src/libosmocc/libosmocc.a
 src/libsample/libsample.a
 src/libtimer/libtimer.a
+src/libselect/libselect.a
 src/libph_socket/libph_socket.a
 src/libmisdn/libmisdn.a
 src/libmisdnuser/libmisdnuser.a
diff --git a/configure.ac b/configure.ac
index a7b8f30..8383c2e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -84,6 +84,7 @@ AC_OUTPUT(
 	src/libdebug/Makefile
 	src/libsample/Makefile
 	src/libtimer/Makefile
+	src/libselect/Makefile
 	src/libjitter/Makefile
 	src/libosmocc/Makefile
 	src/libg711/Makefile
diff --git a/src/Makefile.am b/src/Makefile.am
index a6c9d87..464280a 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -5,6 +5,7 @@ SUBDIRS = \
 	libdebug \
 	libsample \
 	libtimer \
+	libselect \
 	libjitter \
 	libosmocc \
 	libg711 \
diff --git a/src/isdn/Makefile.am b/src/isdn/Makefile.am
index 564dc82..e67590a 100644
--- a/src/isdn/Makefile.am
+++ b/src/isdn/Makefile.am
@@ -18,6 +18,7 @@ osmo_cc_misdn_endpoint_LDADD = \
 	../liboptions/liboptions.a \
 	../libsample/libsample.a \
 	../libtimer/libtimer.a \
+	../libselect/libselect.a \
 	../libjitter/libjitter.a \
 	../libosmocc/libosmocc.a \
 	../libg711/libg711.a \
diff --git a/src/isdn/bridge.c b/src/isdn/bridge.c
index eb0d5c8..d481bb9 100644
--- a/src/isdn/bridge.c
+++ b/src/isdn/bridge.c
@@ -113,7 +113,7 @@ static int num_slots;
 
 struct conn {
 	struct conn	*next;
-	int		socket;
+	struct osmo_fd	ofd;
 	int		rx_index;
 	struct msg_channel_info
 			rx_msg;
@@ -137,7 +137,8 @@ struct channel {
 	int		tx_bank;
 };
 
-static int server_socket;
+static struct osmo_fd server_ofd = { .fd = -1 };
+static struct timer server_timer;
 static struct conn *conn_list = NULL;
 static struct channel *channel_list = NULL;
 
@@ -190,18 +191,20 @@ static void free_all_connections(void)
 	while (c) {
 		PDEBUG(DISDN, DEBUG_INFO, "Free pending bridge connection.\n");
 		c2 = c;
-		close(c->socket);
+		osmo_fd_unregister(&c->ofd);
+		close(c->ofd.fd);
 		c = c->next;
 		free(c2);
 	}
 	conn_list = NULL;
 }
 
+static int bridge_socket_server_cb(struct osmo_fd *ofd, unsigned int when);
+
 /* function to open the server socket */
 static int open_server_socket(int daemon)
 {
 	struct sockaddr_un sock_address;
-	int flags;
 	int rc;
 
 	memset(&sock_address, 0, sizeof(sock_address));
@@ -213,64 +216,70 @@ static int open_server_socket(int daemon)
 		PDEBUG(DISDN, DEBUG_ERROR, "Failed to create UNIX socket.\n");
 		return rc;
 	}
-	server_socket = rc;
+	server_ofd.fd = rc;
+	server_ofd.cb = bridge_socket_server_cb;
+	server_ofd.data = NULL;
+	server_ofd.when = OSMO_FD_READ;
+	osmo_fd_register(&server_ofd);
 
-	rc = bind(server_socket, (struct sockaddr *)(&sock_address), sizeof(struct sockaddr_un));
+	rc = bind(server_ofd.fd, (struct sockaddr *)(&sock_address), sizeof(struct sockaddr_un));
 	if (rc < 0) {
 		if (!daemon || errno != EADDRINUSE)
 			PDEBUG(DISDN, DEBUG_INFO, "Failed to bind UNIX socket with path '%s' (errno = %d (%s)).\n", SOCKET_NAME, errno, strerror(errno));
-		close(server_socket);
+		osmo_fd_unregister(&server_ofd);
+		close(server_ofd.fd);
 		return -EADDRINUSE;
 	}
 
-	rc = listen(server_socket, 10);
+	rc = listen(server_ofd.fd, 10);
 	if (rc < 0) {
 		PDEBUG(DISDN, DEBUG_INFO, "Failed to listen to UNIX socket with path '%s' (errno = %d (%s)).\n", SOCKET_NAME, errno, strerror(errno));
-		close(server_socket);
+		osmo_fd_unregister(&server_ofd);
+		close(server_ofd.fd);
 		return rc;
 	}
 
-	/* set nonblocking io */
-	flags = fcntl(server_socket, F_GETFL);
-	flags |= O_NONBLOCK;
-	fcntl(server_socket, F_SETFL, flags);
-
 	return 0;
 }
 
-static void listen_server_socket(void)
+static int bridge_socket_conn_cb(struct osmo_fd *ofd, unsigned int when);
+
+static int bridge_socket_server_cb(struct osmo_fd __attribute__((unused)) *ofd, unsigned int when)
 {
 	struct sockaddr_un sock_address;
 	socklen_t sock_len = sizeof(sock_address);
 	struct conn *c;
-	int flags;
 	int rc;
 
-	rc = accept(server_socket, (struct sockaddr *)&sock_address, &sock_len);
-	if (rc > 0) {
-		PDEBUG(DISDN, DEBUG_INFO, "Connection from bridge socket client.\n");
-		/* create connection */
-		c = calloc(1, sizeof(*c));
-		if (!c) {
-			PDEBUG(DISDN, DEBUG_ERROR, "No mem!\n");
-			abort();
+	if ((when & OSMO_FD_READ)) {
+		rc = accept(server_ofd.fd, (struct sockaddr *)&sock_address, &sock_len);
+		if (rc > 0) {
+			PDEBUG(DISDN, DEBUG_INFO, "Connection from bridge socket client.\n");
+			/* create connection */
+			c = calloc(1, sizeof(*c));
+			if (!c) {
+				PDEBUG(DISDN, DEBUG_ERROR, "No mem!\n");
+				abort();
+			}
+			c->next = conn_list;
+			conn_list = c;
+			c->ofd.fd = rc;
+			c->ofd.cb = bridge_socket_conn_cb;
+			c->ofd.data = c;
+			c->ofd.when = OSMO_FD_READ;
+			osmo_fd_register(&c->ofd);
+			/* reset rx buffer */
+			c->rx_index = 0;
 		}
-		c->next = conn_list;
-		conn_list = c;
-		c->socket = rc;
-		/* set nonblocking io */
-		flags = fcntl(c->socket, F_GETFL);
-		flags |= O_NONBLOCK;
-		fcntl(c->socket, F_SETFL, flags);
-		/* reset rx buffer */
-		c->rx_index = 0;
 	}
+
+	return 0;
 }
 
 static void rx_channel_info(int socket, int card, int port, int channel, uint16_t orig_rtp_port, int can_bridge);
 
 /* close server socket and remove all channels that are associated with it */
-void close_server_connection(int socket)
+void close_server_connection(struct osmo_fd *ofd)
 {
 	struct channel *c;
 
@@ -278,7 +287,7 @@ void close_server_connection(int socket)
 	do {
 		c = channel_list;
 		while (c) {
-			if (c->socket == socket)
+			if (c->socket == ofd->fd)
 				break;
 			c = c->next;
 		}
@@ -288,36 +297,41 @@ void close_server_connection(int socket)
 		}
 	} while (c);
 
-	close(socket);
+	osmo_fd_unregister(ofd);
+	close(ofd->fd);
 }
 
 /* read message from server socket */
-static void read_server_socket(struct conn *c)
+static int bridge_socket_conn_cb(struct osmo_fd *ofd, unsigned int when)
 {
+	struct conn *c = ofd->data;
 	int rc;
 
-	/* read message until complete */
-	rc = recv(c->socket, ((uint8_t *)&c->rx_msg) + c->rx_index, sizeof(c->rx_msg) - c->rx_index, 0);
-	if (rc > 0) {
-		c->rx_index += rc;
-		if (c->rx_index == sizeof(c->rx_msg)) {
-			PDEBUG(DISDN, DEBUG_DEBUG, "Message from bridge socket client.\n");
-			/* different version ? */
-			if (c->rx_msg.version != SOCKET_VERSION) {
-				PDEBUG(DISDN, DEBUG_ERROR, "Bridge client uses different version than bridge server. Please update all applications to use same server version\n");
-				return;
+	if ((when & OSMO_FD_READ)) {
+		rc = recv(c->ofd.fd, ((uint8_t *)&c->rx_msg) + c->rx_index, sizeof(c->rx_msg) - c->rx_index, 0);
+		if (rc > 0) {
+			c->rx_index += rc;
+			if (c->rx_index == sizeof(c->rx_msg)) {
+				PDEBUG(DISDN, DEBUG_DEBUG, "Message from bridge socket client.\n");
+				/* different version ? */
+				if (c->rx_msg.version != SOCKET_VERSION) {
+					PDEBUG(DISDN, DEBUG_ERROR, "Bridge client uses different version than bridge server. Please update all applications to use same server version\n");
+					return 0;
+				}
+				/* process message and reset buffer index */
+				rx_channel_info(c->ofd.fd, c->rx_msg.card, c->rx_msg.port, c->rx_msg.channel, c->rx_msg.orig_rtp_port, c->rx_msg.can_bridge);
+				c->rx_index = 0;
+				return 0;
 			}
-			/* process message and reset buffer index */
-			rx_channel_info(c->socket, c->rx_msg.card, c->rx_msg.port, c->rx_msg.channel, c->rx_msg.orig_rtp_port, c->rx_msg.can_bridge);
-			c->rx_index = 0;
-			return;
+		} else if (rc == 0 || errno != EAGAIN) {
+			PDEBUG(DISDN, DEBUG_DEBUG, "Close from bridge socket client.\n");
+			close_server_connection(&c->ofd);
+			/* destroy connection */
+			free_connection(c);
 		}
-	} else if (rc == 0 || errno != EAGAIN) {
-		PDEBUG(DISDN, DEBUG_DEBUG, "Close from bridge socket client.\n");
-		close_server_connection(c->socket);
-		/* destroy connection */
-		free_connection(c);
 	}
+
+	return 0;
 }
 
 static void sighandler(int sigset)
@@ -325,11 +339,34 @@ static void sighandler(int sigset)
 	PDEBUG(DISDN, DEBUG_DEBUG, "Signal %d received.\n", sigset);
 }
 
+static int quit = 0;
+
+static void server_exit_timeout(void __attribute__((unused)) *data)
+{
+	if (!conn_list) {
+		PDEBUG(DISDN, DEBUG_DEBUG, "All clients gone, exitting.\n");
+		quit = 1;
+		return;
+	}
+	timer_start(&server_timer, 0.3);
+}
+
+static void server_show_timeout(void __attribute__((unused)) *data)
+{
+	struct channel *ch = channel_list;
+
+	if (ch)
+		printf("Connections:\n");
+	while (ch) {
+		printf("Card=%d Port=%d Channel=%d Bridge=%d\n", ch->card, ch->port, ch->channel, ch->pcm_bridge);
+		ch = ch->next;
+	}
+	timer_start(&server_timer, 1.0);
+}
+
 /* open socket, wait for connections and read incoming messages */
 void bridge_socket_server_child(int slots, int daemon)
 {
-	struct conn *c, *c2;
-	int count_ms = 0, delay_ms = 10;
 	int rc;
 
 	num_slots = slots;
@@ -349,43 +386,27 @@ void bridge_socket_server_child(int slots, int daemon)
 		signal(SIGPIPE, sighandler);
 	}
 
-	while(42) {
-		listen_server_socket();
-		c = conn_list;
-		if (daemon) {
-			/* timeout after some time without a connection */
-			if (!c) {
-				count_ms += delay_ms;
-				if (count_ms >= 300) {
-					PDEBUG(DISDN, DEBUG_DEBUG, "All clients gone, exitting.\n");
-					break;
-				}
-			}
-		} else {
-			/* show all existing channels */
-			count_ms += delay_ms;
-			if (count_ms >= 1000) {
-				struct channel *ch = channel_list;
-				if (ch)
-					printf("Connections:\n");
-				while (ch) {
-					printf("Card=%d Port=%d Channel=%d Bridge=%d\n", ch->card, ch->port, ch->channel, ch->pcm_bridge);
-					ch = ch->next;
-				}
-				count_ms = 0;
-			}
-		}
-		while (c) {
-			c2 = c->next;
-			read_server_socket(c);
-			c = c2;
-		}
-		usleep(delay_ms * 1000);
+	if (daemon) {
+		timer_init(&server_timer, server_exit_timeout, NULL);
+		timer_start(&server_timer, 0.3);
+	} else {
+		timer_init(&server_timer, server_show_timeout, NULL);
+		timer_start(&server_timer, 1.0);
 	}
 
+	while(!quit) {
+		double timeout;
+
+		timeout = process_timer();
+		osmo_fd_select(timeout);
+	}
+
+	timer_exit(&server_timer);
+
 	free_all_channels();
 	free_all_connections();
-	close(server_socket);
+	osmo_fd_unregister(&server_ofd);
+	close(server_ofd.fd);
 }
 
 /* create socket server thread and return 0 on success, return -errno on failure */
@@ -599,15 +620,16 @@ void tx_bridge_order(int socket, int card, int port, int channel, int pcm_bridge
  * client
  */
 
-static int client_socket = -1;
+static struct osmo_fd client_ofd = { .fd = -1 };
 int client_rx_index = 0;
 struct msg_bridge_order client_rx_msg;
 
+static int bridge_socket_client_cb(struct osmo_fd *ofd, unsigned int when);
+
 /* function to open the client socket */
-int bridge_socket_client(void)
+int bridge_socket_client(isdn_t *isdn_ep)
 {
 	struct sockaddr_un sock_address;
-	int flags;
 	int rc;
 
 	memset(&sock_address, 0, sizeof(sock_address));
@@ -619,21 +641,21 @@ int bridge_socket_client(void)
 		PDEBUG(DISDN, DEBUG_ERROR, "Failed to create UNIX socket.\n");
 		return rc;
 	}
-	client_socket = rc;
+	client_ofd.fd = rc;
+	client_ofd.cb = bridge_socket_client_cb;
+	client_ofd.data = isdn_ep;
+	client_ofd.when = OSMO_FD_READ;
+	osmo_fd_register(&client_ofd);
 
-	rc = connect(client_socket, (struct sockaddr *)(&sock_address), sizeof(struct sockaddr_un));
+	rc = connect(client_ofd.fd, (struct sockaddr *)(&sock_address), sizeof(struct sockaddr_un));
 	if (rc < 0) {
 		PDEBUG(DISDN, DEBUG_DEBUG, "Failed to connect to UNIX socket with path '%s' (errno = %d (%s)).\n", SOCKET_NAME, errno, strerror(errno));
-		close(client_socket);
-		client_socket = 0;
+		osmo_fd_unregister(&client_ofd);
+		close(client_ofd.fd);
+		client_ofd.fd = -1;
 		return -errno;
 	}
 
-	/* set nonblocking io */
-	flags = fcntl(client_socket, F_GETFL);
-	flags |= O_NONBLOCK;
-	fcntl(client_socket, F_SETFL, flags);
-
 	PDEBUG(DISDN, DEBUG_DEBUG, "Created bridging socket client.\n");
 
 	return 0;
@@ -642,38 +664,37 @@ int bridge_socket_client(void)
 void rx_bridge_order(isdn_t *isdn_ep, int card, int port, int channel, int pcm_bridge, int rx_slot, int tx_slot, int rx_bank, int tx_bank);
 
 /* read message from client socket */
-void bridge_socket_client_work(isdn_t *isdn_ep)
+static int bridge_socket_client_cb(struct osmo_fd *ofd, unsigned int when)
 {
+	isdn_t *isdn_ep = ofd->data;
 	int rc;
 
-again:
-	/* no client */
-	if (client_socket <= 0)
-		return;
-
-	/* read message until complete */
-	rc = recv(client_socket, ((uint8_t *)&client_rx_msg) + client_rx_index, sizeof(client_rx_msg) - client_rx_index, 0);
-	if (rc > 0) {
-		client_rx_index += rc;
-		if (client_rx_index == sizeof(client_rx_msg)) {
-			PDEBUG(DISDN, DEBUG_DEBUG, "Message from bridge socket server.\n");
-			/* different version ? */
-			if (client_rx_msg.version != SOCKET_VERSION) {
-				PDEBUG(DISDN, DEBUG_ERROR, "Bridge server uses different version than bridge client. Please update all applications to use same server version\n");
-				return;
+	if ((when & OSMO_FD_READ)) {
+		/* read message until complete */
+		rc = recv(client_ofd.fd, ((uint8_t *)&client_rx_msg) + client_rx_index, sizeof(client_rx_msg) - client_rx_index, 0);
+		if (rc > 0) {
+			client_rx_index += rc;
+			if (client_rx_index == sizeof(client_rx_msg)) {
+				PDEBUG(DISDN, DEBUG_DEBUG, "Message from bridge socket server.\n");
+				/* different version ? */
+				if (client_rx_msg.version != SOCKET_VERSION) {
+					PDEBUG(DISDN, DEBUG_ERROR, "Bridge server uses different version than bridge client. Please update all applications to use same server version\n");
+					return 0;
+				}
+				/* process message and reset buffer index */
+				rx_bridge_order(isdn_ep, client_rx_msg.card, client_rx_msg.port, client_rx_msg.channel, client_rx_msg.pcm_bridge, client_rx_msg.rx_slot, client_rx_msg.tx_slot, client_rx_msg.rx_bank, client_rx_msg.tx_bank);
+				client_rx_index = 0;
 			}
-			/* process message and reset buffer index */
-			rx_bridge_order(isdn_ep, client_rx_msg.card, client_rx_msg.port, client_rx_msg.channel, client_rx_msg.pcm_bridge, client_rx_msg.rx_slot, client_rx_msg.tx_slot, client_rx_msg.rx_bank, client_rx_msg.tx_bank);
-			client_rx_index = 0;
-			goto again;
+		} else if (rc == 0 || errno != EAGAIN) {
+			PDEBUG(DISDN, DEBUG_DEBUG, "Close from bridge socket client.\n");
+			osmo_fd_unregister(&client_ofd);
+			close(client_ofd.fd);
+			client_ofd.fd = -1;
 		}
-	} else if (rc == 0 || errno != EAGAIN) {
-		PDEBUG(DISDN, DEBUG_DEBUG, "Close from bridge socket client.\n");
-		close(client_socket);
-		client_socket = -1;
 	}
-}
 
+	return 0;
+}
 
 /* check if ip address is one of the local interfaces */
 int check_local_address(sa_family_t family, struct sockaddr *addr)
@@ -758,7 +779,7 @@ void bridge_socket_client_update(call_t *call, int enable)
 	int rc;
 
 	/* no client */
-	if (client_socket <= 0)
+	if (client_ofd.fd <= 0)
 		return;
 
 	PDEBUG(DISDN, DEBUG_INFO, "We got called with enable=%d\n", enable);
@@ -850,7 +871,7 @@ send:
 	else
 		orig_rtp_port = media->description.port_remote;
 
-	tx_channel_info(client_socket, call->isdn_ep->bridge_cardnum, call->isdn_ep->bridge_portnum, call->b_channel, orig_rtp_port, can_bridge);
+	tx_channel_info(client_ofd.fd, call->isdn_ep->bridge_cardnum, call->isdn_ep->bridge_portnum, call->b_channel, orig_rtp_port, can_bridge);
 }
 
 static void tx_channel_info(int socket, int card, int port, int channel, uint16_t orig_rtp_port, int can_bridge)
diff --git a/src/isdn/bridge.h b/src/isdn/bridge.h
index c2cef5c..b16e7fb 100644
--- a/src/isdn/bridge.h
+++ b/src/isdn/bridge.h
@@ -2,7 +2,6 @@
 int brigde_socket_server(int slots);
 void bridge_socket_server_child(int slots, int daemon);
 
-int bridge_socket_client(void);
-void bridge_socket_client_work(isdn_t *isdn_ep);
+int bridge_socket_client(isdn_t *isdn_ep);
 void bridge_socket_client_update(call_t *call, int enable);
 
diff --git a/src/isdn/dss1.c b/src/isdn/dss1.c
index 169fde2..d575df1 100644
--- a/src/isdn/dss1.c
+++ b/src/isdn/dss1.c
@@ -955,6 +955,9 @@ void hold_ind(call_t *call, uint32_t pid, struct l3_msg *l3m)
 	/* reset jitter buffer, to ignore packets coming from remote */
 	jitter_reset(&call->tx_dejitter);
 
+	/* generate hold tone, using local clock */
+	enable_hold_clock(call->isdn_ep);
+
 	/* acknowledge hold */
 	PDEBUG(DDSS1, DEBUG_INFO, "HOLD-ACKNOWLEDGE REQUEST (pid = 0x%x callref = %d)\n", pid, call->cc_callref);
 	l3m = create_l3msg();
@@ -1078,6 +1081,9 @@ void suspend_ind(call_t *call, uint32_t pid, struct l3_msg *l3m)
 	/* deactivate bchannel */
 	drop_bchannel(call);
 
+	/* generate hold tone, using local clock */
+	enable_hold_clock(call->isdn_ep);
+
 	/* sending SUSPEND_ACKNOWLEDGE */
 	PDEBUG(DDSS1, DEBUG_INFO, "SUSPEND-ACKNOWLEDGE REQUEST (pid = 0x%x callref = %d)\n", pid, call->cc_callref);
 	l3m = create_l3msg();
diff --git a/src/isdn/isdn.c b/src/isdn/isdn.c
index bfd2c2b..5076c6b 100644
--- a/src/isdn/isdn.c
+++ b/src/isdn/isdn.c
@@ -671,11 +671,15 @@ void isdn_destroy(isdn_t *isdn_ep)
 
 	timer_exit(&isdn_ep->l2establish_timer);
 
+	timer_exit(&isdn_ep->clock_timer);
+
 	free(isdn_ep);
 
 	PDEBUG(DISDN, DEBUG_DEBUG, "ISDN instance destroyed\n");
 }
 
+static void clock_timeout(void *data);
+
 /* initialization and configuration to isdn interface instance */
 int isdn_initialize(isdn_t *isdn_ep, ph_socket_t *ph_socket, char law, const char *portname, int ntmode, int ptp, int layer1hold, int layer2hold, const char *channel_out, const char *channel_in, const char *timeouts, int tx_delay, int local_tones, int serving_location)
 {
@@ -875,18 +879,19 @@ static void im_control(int sock, uint32_t op, uint32_t channel, uint32_t p1, uin
 		PDEBUG(DISDN, DEBUG_ERROR, "Failed to send IMCTRLREQ to socket %d (errno=%d:%s)\n", sock, errno, strerror(errno));
 }
 
+static int bchannel_kernel_sock_receive_cb(struct osmo_fd *ofd, unsigned int when);
+
 /* create B-channel stack */
 static int bchannel_create(isdn_t *isdn_ep, int index)
 {
 	int channel = index + 1 + (index >= 15);
 	struct sockaddr_mISDN addr;
-	int flags;
 	int rc;
 
 	memset(&addr, 0, sizeof(addr));
 
 	if (isdn_ep->l2sock) {
-		if (isdn_ep->b_sock[index] > 0) {
+		if (isdn_ep->b_sock[index].ofd.fd > 0) {
 			PDEBUG(DISDN, DEBUG_ERROR, "Socket already created for index %d\n", index);
 			return -EIO;
 		}
@@ -900,26 +905,31 @@ static int bchannel_create(isdn_t *isdn_ep, int index)
 			PDEBUG(DISDN, DEBUG_ERROR, "Failed to open bchannel-socket for index %d with mISDN-DSP layer. Did you load mISDN_dsp.ko?\n", index);
 			return(0);
 		}
-		isdn_ep->b_sock[index] = rc;
+		isdn_ep->b_sock[index].ofd.fd = rc;
 
-		/* set nonblocking io */
-		flags = fcntl(isdn_ep->b_sock[index], F_GETFL);
-		flags |= O_NONBLOCK;
-		fcntl(isdn_ep->b_sock[index], F_SETFL, flags);
+		/* register */
+		isdn_ep->b_sock[index].isdn_ep = isdn_ep;
+		isdn_ep->b_sock[index].index = index;
+		isdn_ep->b_sock[index].ofd.cb = bchannel_kernel_sock_receive_cb;
+		isdn_ep->b_sock[index].ofd.data = &isdn_ep->b_sock[index];
+		isdn_ep->b_sock[index].ofd.when = OSMO_FD_READ;
+		osmo_fd_register(&isdn_ep->b_sock[index].ofd);
 
 		/* bind socket to bchannel */
 		addr.family = AF_ISDN;
 		addr.dev = isdn_ep->portnum;
 		addr.channel = channel;
-		rc = bind(isdn_ep->b_sock[index], (struct sockaddr *)&addr, sizeof(addr));
+		rc = bind(isdn_ep->b_sock[index].ofd.fd, (struct sockaddr *)&addr, sizeof(addr));
 		if (rc < 0) {
 			PDEBUG(DISDN, DEBUG_ERROR, "Failed to bind bchannel-socket for index %d with mISDN-DSP layer (errno=%d). Did you load mISDN_dsp.ko?\n", index, errno);
-			close(isdn_ep->b_sock[index]);
+			/* unregister and close */
+			osmo_fd_unregister(&isdn_ep->b_sock[index].ofd);
+			close(isdn_ep->b_sock[index].ofd.fd);
 			return -errno;
 		}
 	}
 
-	PDEBUG(DISDN, DEBUG_DEBUG, "created socket #%d for B-channel %d\n", isdn_ep->b_sock[index], channel);
+	PDEBUG(DISDN, DEBUG_DEBUG, "created socket #%d for B-channel %d\n", isdn_ep->b_sock[index].ofd.fd, channel);
 
 	return 0;
 }
@@ -932,14 +942,14 @@ static void bchannel_activate(isdn_t *isdn_ep, int index, int activate, int time
 	int rc;
 
 	if (isdn_ep->l2sock) {
-		if (isdn_ep->b_sock[index] <= 0)
+		if (isdn_ep->b_sock[index].ofd.fd <= 0)
 			return;
 
 		act.prim = (activate) ? PH_ACTIVATE_REQ : PH_DEACTIVATE_REQ;
 		act.id = 0;
-		rc = sendto(isdn_ep->b_sock[index], &act, MISDN_HEADER_LEN, 0, NULL, 0);
+		rc = sendto(isdn_ep->b_sock[index].ofd.fd, &act, MISDN_HEADER_LEN, 0, NULL, 0);
 		if (rc < 0)
-			PDEBUG(DISDN, DEBUG_ERROR, "Failed to send to socket #%d, of B-channel %d\n", isdn_ep->b_sock[index], channel);
+			PDEBUG(DISDN, DEBUG_ERROR, "Failed to send to socket #%d, of B-channel %d\n", isdn_ep->b_sock[index].ofd.fd, channel);
 	}
 
 	if (isdn_ep->l2inst) {
@@ -964,10 +974,10 @@ static void bchannel_configure(isdn_t *isdn_ep, int index)
 	call_t *call;
 	int handle;
 
-	if (isdn_ep->b_sock[index] <= 0)
+	if (isdn_ep->b_sock[index].ofd.fd <= 0)
 		return;
 
-	handle = isdn_ep->b_sock[index];
+	handle = isdn_ep->b_sock[index].ofd.fd;
 	call = isdn_ep->b_call[index];
 
 	/* set PCM bridge features */
@@ -1007,13 +1017,15 @@ static void bchannel_destroy(isdn_t *isdn_ep, int index)
 	int channel = index + 1 + (index >= 15);
 
 	if (isdn_ep->l2sock) {
-		if (isdn_ep->b_sock[index] <= 0)
+		if (isdn_ep->b_sock[index].ofd.fd <= 0)
 			return;
 
-		PDEBUG(DISDN, DEBUG_DEBUG, "destroyed socket #%d for B-channel %d\n", isdn_ep->b_sock[index], channel);
+		PDEBUG(DISDN, DEBUG_DEBUG, "destroyed socket #%d for B-channel %d\n", isdn_ep->b_sock[index].ofd.fd, channel);
 
-		close(isdn_ep->b_sock[index]);
-		isdn_ep->b_sock[index] = 0;
+		/* unregister and close */
+		osmo_fd_unregister(&isdn_ep->b_sock[index].ofd);
+		close(isdn_ep->b_sock[index].ofd.fd);
+		isdn_ep->b_sock[index].ofd.fd = 0;
 	}
 
 	if (isdn_ep->l2inst) {
@@ -1226,18 +1238,26 @@ static void bchannel_rx_tx(isdn_t *isdn_ep, int index, struct mISDNhead *hh, uns
 static void bchannel_confirm(isdn_t *isdn_ep, int index);
 
 /* handle frames from B-channel (kernel socket) */
-static int bchannel_kernel_sock_receive(isdn_t *isdn_ep, int index)
+static int bchannel_kernel_sock_receive_cb(struct osmo_fd *ofd, unsigned int when)
 {
+	struct isdn_b_sock *b_sock = ofd->data;
+	int index = b_sock->index;
+	isdn_t *isdn_ep = b_sock->isdn_ep;
 	int channel = index + 1 + (index >= 15);
 	unsigned char buffer[2048+MISDN_HEADER_LEN];
 	struct mISDNhead *hh = (struct mISDNhead *)buffer;
 	int rc;
 
-	rc = recv(isdn_ep->b_sock[index], buffer, sizeof(buffer), 0);
+	if (!(when & OSMO_FD_READ)) {
+		PDEBUG(DISDN, DEBUG_ERROR, "this should never happen!\n");
+		return 0;
+	}
+
+	rc = recv(ofd->fd, buffer, sizeof(buffer), 0);
 	if (rc < 0) {
 		if (errno == EAGAIN)
 			return 0;
-		PDEBUG(DISDN, DEBUG_ERROR, "read error B-channel data (socket #%d errno=%d:%s)\n", isdn_ep->b_sock[index], errno, strerror(errno));
+		PDEBUG(DISDN, DEBUG_ERROR, "read error B-channel data (socket #%d errno=%d:%s)\n", ofd->fd, errno, strerror(errno));
 		return 0;
 	}
 	if (rc < (int)MISDN_HEADER_LEN) {
@@ -1318,9 +1338,9 @@ void bchannel_ph_sock_receive(void *priv, int channel, uint8_t prim, uint8_t *da
 	}
 }
 
-static void b_timer_timeout(struct timer *timer)
+static void b_timer_timeout(void *data)
 {
-	struct b_timer_inst *ti = timer->priv;
+	struct b_timer_inst *ti = data;
 
 	bchannel_event(ti->isdn_ep, ti->index, B_EVENT_TIMEOUT);
 }
@@ -1618,9 +1638,9 @@ static void bchannel_rx_tx(isdn_t *isdn_ep, int index, struct mISDNhead *hh, uns
 	if (call->isdn_ep->ph_socket)
 		ph_socket_tx_msg(call->isdn_ep->ph_socket, call->b_channel, PH_PRIM_DATA_REQ, buf + MISDN_HEADER_LEN, offset + len);
 	else
-		rc = send(call->isdn_ep->b_sock[call->b_index], buf, MISDN_HEADER_LEN + offset + len, 0);
+		rc = send(call->isdn_ep->b_sock[call->b_index].ofd.fd, buf, MISDN_HEADER_LEN + offset + len, 0);
 	if (rc < 0)
-		PDEBUG(DISDN, DEBUG_ERROR, "Write error B-channel data (socket #%d errno=%d:%s)\n", call->isdn_ep->b_sock[call->b_index], errno, strerror(errno));
+		PDEBUG(DISDN, DEBUG_ERROR, "Write error B-channel data (socket #%d errno=%d:%s)\n", call->isdn_ep->b_sock[call->b_index].ofd.fd, errno, strerror(errno));
 	else
 		call->b_transmitting = 1;
 }
@@ -1643,18 +1663,6 @@ static void bchannel_confirm(isdn_t *isdn_ep, int index)
 	}
 }
 
-void isdn_rtp_work(isdn_t *isdn_ep)
-{
-	call_t *call;
-
-	call = isdn_ep->call_list;
-	while (call) {
-		if (call->cc_session)
-			osmo_cc_session_handle(call->cc_session, call);
-		call = call->next;
-	}
-}
-
 /* send audio from RTP to B-channel's jitter buffer */
 void rtp_receive(struct osmo_cc_session_codec *codec, uint8_t __attribute__((unused)) marker, uint16_t sequence_number, uint32_t timestamp, uint32_t ssrc, uint8_t *data, int len)
 {
@@ -1716,6 +1724,10 @@ int do_layer3(struct mlayer3 *ml3, unsigned int cmd, unsigned int pid, struct l3
 	mqueue_tail(&isdn_ep->upqueue, mb);
 	pthread_mutex_unlock(&isdn_ep->upqueue_lock);
 
+	/* wake main thread */
+	char wakeup = 0;
+	write(isdn_ep->upqueue_pipe[1], &wakeup, 1);
+
 	return 0;
 }
 
@@ -1745,7 +1757,8 @@ int mISDN_getportbyname(isdn_t *isdn_ep, int cnt, const char *portname)
 	return port;
 }
 
-static void l2establish_timeout(struct timer *timer);
+static void l2establish_timeout(void *data);
+static int isdn_upqueue_cb(struct osmo_fd *ofd, unsigned int what);
 
 /* open mISDN port */
 int isdn_open(isdn_t *isdn_ep)
@@ -1766,6 +1779,16 @@ int isdn_open(isdn_t *isdn_ep)
 	/* queue must be initializes, because l3-thread may send messages during open_layer3() */
 	mqueue_init(&isdn_ep->upqueue);
 	isdn_ep->upqueue_initialized = 1;
+	rc = pipe(isdn_ep->upqueue_pipe);
+	if (rc < 0) {
+		PDEBUG(DISDN, DEBUG_ERROR, "Failed to create pipe errno=%d:%s. (Please fix!)\n", errno, strerror(errno));
+		goto error;
+	}
+	isdn_ep->upqueue_ofd.fd = isdn_ep->upqueue_pipe[0];
+	isdn_ep->upqueue_ofd.cb = isdn_upqueue_cb;
+	isdn_ep->upqueue_ofd.data = isdn_ep;
+	isdn_ep->upqueue_ofd.when = OSMO_FD_READ;
+	osmo_fd_register(&isdn_ep->upqueue_ofd);
 
 	/* port number given ? */
 	for (i = 0; i < (int)strlen(portname); i++){
@@ -1878,6 +1901,8 @@ int isdn_open(isdn_t *isdn_ep)
 		i++;
 	}
 
+	timer_init(&isdn_ep->clock_timer, clock_timeout, isdn_ep);
+
 	timer_init(&isdn_ep->l2establish_timer, l2establish_timeout, isdn_ep);
 
 	isdn_ep->l1link = -1;
@@ -1975,7 +2000,7 @@ void isdn_close(isdn_t *isdn_ep)
 
 	/* free bchannels */
 	for (i = 0; i < isdn_ep->b_num; i++) {
-		if (isdn_ep->b_sock[i] > 0) {
+		if (isdn_ep->b_sock[i].ofd.fd > 0) {
 			bchannel_destroy(isdn_ep, i);
 			PDEBUG(DISDN, DEBUG_DEBUG, "freeing %s port %s bchannel (index %d).\n", (isdn_ep->ntmode) ? "NT" : "TE", isdn_ep->portname, i);
 		}
@@ -1988,9 +2013,18 @@ void isdn_close(isdn_t *isdn_ep)
 		close_layer3(isdn_ep->ml3);
 	}
 
-	/* purge upqueue */
+	/* purge and remove upqueue */
 	if (isdn_ep->upqueue_initialized)
 		mqueue_purge(&isdn_ep->upqueue);
+	if (isdn_ep->upqueue_pipe[0] > 0) {
+		osmo_fd_unregister(&isdn_ep->upqueue_ofd);
+		close(isdn_ep->upqueue_pipe[0]);
+		isdn_ep->upqueue_pipe[0] = 0;
+	}
+	if (isdn_ep->upqueue_pipe[1] > 0) {
+		close(isdn_ep->upqueue_pipe[1]);
+		isdn_ep->upqueue_pipe[1] = 0;
+	}
 
 	if (isdn_ep->portname) {
 		free(isdn_ep->portname);
@@ -2009,116 +2043,120 @@ void isdn_close(isdn_t *isdn_ep)
 	}
 }
 
-/* receive message from ISDN protocol stack (out of queue) */
-int isdn_dchannel_work(isdn_t *isdn_ep)
+/* receive message from ISDN protocol stack (out of the upqueue) */
+static int isdn_upqueue_cb(struct osmo_fd *ofd, unsigned __attribute__((unused)) int what)
 {
+	isdn_t *isdn_ep = ofd->data;
 	struct mbuffer *mb;
 	struct l3_msg *l3m;
-	int w = 0;
 
+	char wakeup = 0;
+	read(ofd->fd, &wakeup, 1);
+
+again:
 	/* handle queued up-messages (d-channel) */
 	pthread_mutex_lock(&isdn_ep->upqueue_lock);
 	mb = mdequeue(&isdn_ep->upqueue);
 	pthread_mutex_unlock(&isdn_ep->upqueue_lock);
-	if (mb) {
-		w |= 1;
-		l3m = &mb->l3;
-		switch(l3m->type) {
-			case MPH_ACTIVATE_IND:
-			if (isdn_ep->l1link != 1) {
-				PDEBUG(DISDN, DEBUG_INFO, "layer 1 becomes active\n");
-				isdn_ep->l1link = 1;
-			}
-			break;
-	
-			case MPH_DEACTIVATE_IND:
-			if (isdn_ep->l1link != 0) {
-				PDEBUG(DISDN, DEBUG_INFO, "layer 1 becomes inactive\n");
-				isdn_ep->l1link = 0;
-			}
-			break;
+	if (!mb)
+		return 0;
 
-			case MPH_INFORMATION_IND:
-			switch (l3m->pid) {
-				case L1_SIGNAL_LOS_ON:
-				PDEBUG(DISDN, DEBUG_DEBUG, "received LOS\n");
-				isdn_ep->los = 1;
-				break;
-				case L1_SIGNAL_LOS_OFF:
-				PDEBUG(DISDN, DEBUG_DEBUG, "LOS is gone\n");
-				isdn_ep->los = 0;
-				break;
-				case L1_SIGNAL_AIS_ON:
-				PDEBUG(DISDN, DEBUG_DEBUG, "received AIS\n");
-				isdn_ep->ais = 1;
-				break;
-				case L1_SIGNAL_AIS_OFF:
-				PDEBUG(DISDN, DEBUG_DEBUG, "AIS is gone\n");
-				isdn_ep->ais = 0;
-				break;
-				case L1_SIGNAL_RDI_ON:
-				PDEBUG(DISDN, DEBUG_DEBUG, "received RDI\n");
-				isdn_ep->rdi = 1;
-				break;
-				case L1_SIGNAL_RDI_OFF:
-				PDEBUG(DISDN, DEBUG_DEBUG, "RDI is gone\n");
-				isdn_ep->rdi = 0;
-				break;
-				case L1_SIGNAL_SLIP_TX:
-				isdn_ep->slip_tx++;
-				PDEBUG(DISDN, DEBUG_DEBUG, "received TX slip #%d\n", isdn_ep->slip_tx);
-				break;
-				case L1_SIGNAL_SLIP_RX:
-				isdn_ep->slip_rx++;
-				PDEBUG(DISDN, DEBUG_DEBUG, "received RX slip #%d\n", isdn_ep->slip_rx);
-				break;
-			}
-			break;
-
-			case MT_L2ESTABLISH:
-			PDEBUG(DISDN, DEBUG_INFO, "layer 2 becomes active (tei = %d)\n", l3m->pid);
-			isdn_ep->l2link = 1;
-			if (l3m->pid < 128)
-				isdn_ep->l2mask[l3m->pid >> 3] |= (1 << (l3m->pid & 7));
-			if ((!isdn_ep->ntmode || isdn_ep->ptp) && l3m->pid < 127) {
-				if (timer_running(&isdn_ep->l2establish_timer))
-					timer_stop(&isdn_ep->l2establish_timer);
-			}
-			break;
-
-			case MT_L2RELEASE:
-			if (l3m->pid < 128)
-				isdn_ep->l2mask[l3m->pid >> 3] &= ~(1 << (l3m->pid & 7));
-			if (!timer_running(&isdn_ep->l2establish_timer)) {
-				PDEBUG(DISDN, DEBUG_INFO, "layer 2 becomes inactive (tei = %d)\n", l3m->pid);
-				/* down if not nt-ptmp */ 
-				if (!isdn_ep->ntmode || isdn_ep->ptp)
-					isdn_ep->l2link = 0;
-			}
-			if ((!isdn_ep->ntmode || isdn_ep->ptp) && l3m->pid < 127) {
-				if (!timer_running(&isdn_ep->l2establish_timer) && isdn_ep->l2hold) {
-					timer_start(&isdn_ep->l2establish_timer, 5.0); /* 5 seconds */
-					isdn_ep->ml3->to_layer3(isdn_ep->ml3, MT_L2ESTABLISH, 0, NULL);
-				}
-			}
-			break;
-
-			default:
-			/* l3-data is sent to DSS1 handling */
-			dss1_receive(isdn_ep, l3m->type, l3m->pid, l3m);
+	l3m = &mb->l3;
+	switch(l3m->type) {
+		case MPH_ACTIVATE_IND:
+		if (isdn_ep->l1link != 1) {
+			PDEBUG(DISDN, DEBUG_INFO, "layer 1 becomes active\n");
+			isdn_ep->l1link = 1;
 		}
-		/* free message */
-		free_l3_msg(l3m);
-	}
+		break;
 
-	return w;
+		case MPH_DEACTIVATE_IND:
+		if (isdn_ep->l1link != 0) {
+			PDEBUG(DISDN, DEBUG_INFO, "layer 1 becomes inactive\n");
+			isdn_ep->l1link = 0;
+		}
+		break;
+
+		case MPH_INFORMATION_IND:
+		switch (l3m->pid) {
+			case L1_SIGNAL_LOS_ON:
+			PDEBUG(DISDN, DEBUG_DEBUG, "received LOS\n");
+			isdn_ep->los = 1;
+			break;
+			case L1_SIGNAL_LOS_OFF:
+			PDEBUG(DISDN, DEBUG_DEBUG, "LOS is gone\n");
+			isdn_ep->los = 0;
+			break;
+			case L1_SIGNAL_AIS_ON:
+			PDEBUG(DISDN, DEBUG_DEBUG, "received AIS\n");
+			isdn_ep->ais = 1;
+			break;
+			case L1_SIGNAL_AIS_OFF:
+			PDEBUG(DISDN, DEBUG_DEBUG, "AIS is gone\n");
+			isdn_ep->ais = 0;
+			break;
+			case L1_SIGNAL_RDI_ON:
+			PDEBUG(DISDN, DEBUG_DEBUG, "received RDI\n");
+			isdn_ep->rdi = 1;
+			break;
+			case L1_SIGNAL_RDI_OFF:
+			PDEBUG(DISDN, DEBUG_DEBUG, "RDI is gone\n");
+			isdn_ep->rdi = 0;
+			break;
+			case L1_SIGNAL_SLIP_TX:
+			isdn_ep->slip_tx++;
+			PDEBUG(DISDN, DEBUG_DEBUG, "received TX slip #%d\n", isdn_ep->slip_tx);
+			break;
+			case L1_SIGNAL_SLIP_RX:
+			isdn_ep->slip_rx++;
+			PDEBUG(DISDN, DEBUG_DEBUG, "received RX slip #%d\n", isdn_ep->slip_rx);
+			break;
+		}
+		break;
+
+		case MT_L2ESTABLISH:
+		PDEBUG(DISDN, DEBUG_INFO, "layer 2 becomes active (tei = %d)\n", l3m->pid);
+		isdn_ep->l2link = 1;
+		if (l3m->pid < 128)
+			isdn_ep->l2mask[l3m->pid >> 3] |= (1 << (l3m->pid & 7));
+		if ((!isdn_ep->ntmode || isdn_ep->ptp) && l3m->pid < 127) {
+			if (timer_running(&isdn_ep->l2establish_timer))
+				timer_stop(&isdn_ep->l2establish_timer);
+		}
+		break;
+
+		case MT_L2RELEASE:
+		if (l3m->pid < 128)
+			isdn_ep->l2mask[l3m->pid >> 3] &= ~(1 << (l3m->pid & 7));
+		if (!timer_running(&isdn_ep->l2establish_timer)) {
+			PDEBUG(DISDN, DEBUG_INFO, "layer 2 becomes inactive (tei = %d)\n", l3m->pid);
+			/* down if not nt-ptmp */ 
+			if (!isdn_ep->ntmode || isdn_ep->ptp)
+				isdn_ep->l2link = 0;
+		}
+		if ((!isdn_ep->ntmode || isdn_ep->ptp) && l3m->pid < 127) {
+			if (!timer_running(&isdn_ep->l2establish_timer) && isdn_ep->l2hold) {
+				timer_start(&isdn_ep->l2establish_timer, 5.0); /* 5 seconds */
+				isdn_ep->ml3->to_layer3(isdn_ep->ml3, MT_L2ESTABLISH, 0, NULL);
+			}
+		}
+		break;
+
+		default:
+		/* l3-data is sent to DSS1 handling */
+		dss1_receive(isdn_ep, l3m->type, l3m->pid, l3m);
+	}
+	/* free message */
+	free_l3_msg(l3m);
+
+	goto again;
 }
 
 
 /* l2 establish timer fires */
-static void l2establish_timeout(struct timer *timer)
+static void l2establish_timeout(void *data)
 {
-	isdn_t *isdn_ep = timer->priv;
+	isdn_t *isdn_ep = data;
 
 	if (isdn_ep->l2hold && (isdn_ep->ptp || !isdn_ep->ntmode)) {
 		PDEBUG(DISDN, DEBUG_DEBUG, "the L2 establish timer expired, we try to establish the link portnum=%d.\n", isdn_ep->portnum);
@@ -2127,25 +2165,20 @@ static void l2establish_timeout(struct timer *timer)
 	}
 }
 
-void isdn_bchannel_work(isdn_t *isdn_ep)
-{
-	int w, i;
-
-	for (i = 0; i < isdn_ep->b_num; i++) {
-		do {
-			if (isdn_ep->b_sock[i] > 0)
-				w = bchannel_kernel_sock_receive(isdn_ep, i);
-			else
-				w = 0;
-		} while (w);
-	}
-}
+/*
+ * local clock to generate hold tone
+ */
 
 #define COMFORT_NOISE	(0.02 * SPEECH_LEVEL)	/* audio level of comfort noise (relative to ISDN level) */
+#define CHUNK_DURATION	0.020
+#define	CHUNK_LENGTH	160
 
-void hold_clock(isdn_t *isdn_ep, int len)
+static void clock_timeout(void *data)
 {
+	isdn_t *isdn_ep = data;
+	int len = CHUNK_LENGTH;
 	call_t *call;
+	int any = 0;
 
 	call = isdn_ep->call_list;
 	while (call) {
@@ -2165,7 +2198,40 @@ void hold_clock(isdn_t *isdn_ep, int len)
 				g711_encode_ulaw_flipped((uint8_t *)noise, len * 2, &data, &len, NULL);
 			osmo_cc_rtp_send(call->codec, data, len, 0, 1, len, call);
 			free(data);
+			any = 1;
 		}
 		call = call->next;
 	}
+
+	/* restart clock if there is still any call that requires it */
+	if (any) {
+		double now;
+
+		/* restart timer to wait for next 20ms */
+		now = get_time();
+		/* if there is too much jitter or if last_time_clock is not set */
+		if (now - isdn_ep->last_time_clock >= 0.1)
+			isdn_ep->last_time_clock = now;
+		/* advance clock */
+		isdn_ep->last_time_clock += CHUNK_DURATION;
+		/* if there is too much jitter */
+		if (isdn_ep->last_time_clock < now)
+			isdn_ep->last_time_clock = now;
+		timer_start(&isdn_ep->clock_timer, isdn_ep->last_time_clock - now);
+	}
 }
+
+void enable_hold_clock(isdn_t *isdn_ep)
+{
+	double now;
+
+	/* already running, so keep running without restart */
+	if (timer_running(&isdn_ep->clock_timer))
+		return;
+	/* start timer to wait for 20ms */
+	now = get_time();
+	isdn_ep->last_time_clock = now + CHUNK_DURATION;
+	timer_start(&isdn_ep->clock_timer, CHUNK_DURATION);
+}
+
+
diff --git a/src/isdn/isdn.h b/src/isdn/isdn.h
index 8fe2ad4..5ca723e 100644
--- a/src/isdn/isdn.h
+++ b/src/isdn/isdn.h
@@ -1,6 +1,7 @@
 
 #include <pthread.h>
 #include "../libtimer/timer.h"
+#include "../libselect/select.h"
 #include "../libosmocc/endpoint.h"
 #include "../libosmocc/helper.h"
 #include "../libsample/sample.h"
@@ -65,6 +66,14 @@ struct select_channel {
 	int channel;
 };
 
+struct isdn;
+
+struct isdn_b_sock {
+	int index;
+	struct isdn *isdn_ep;
+	struct osmo_fd ofd;
+};
+
 struct call_list;
 
 typedef struct isdn {
@@ -98,6 +107,8 @@ typedef struct isdn {
 	pthread_mutex_t upqueue_lock;
         struct mqueue upqueue;
 	int upqueue_initialized;
+	int upqueue_pipe[2];
+	struct osmo_fd upqueue_ofd;
         struct mlayer3 *ml3;
         int los, ais, rdi, slip_rx, slip_tx;
         int l1link; /* current state */
@@ -107,7 +118,7 @@ typedef struct isdn {
 	int b_reserved;
 	int b_mode[128];
 	int b_state[128];
-	int b_sock[128];
+	struct isdn_b_sock b_sock[128];
 	struct call_list *b_call[128];
 	struct timer b_timer[128];
 	struct b_timer_inst b_timer_inst[128];
@@ -119,6 +130,10 @@ typedef struct isdn {
 	int bridge_possible;
 	int bridge_cardnum;
 	int bridge_portnum;
+
+	/* clock for tone on hold */
+	struct timer clock_timer;
+	double last_time_clock;
 } isdn_t;
 
 typedef struct call_list {
@@ -193,9 +208,6 @@ int isdn_initialize(isdn_t *isdn_ep, ph_socket_t *ph_socket, char law, const cha
 int isdn_open(isdn_t *isdn_ep);
 void isdn_close(isdn_t *isdn_ep);
 void isdn_add_msn(isdn_t *isdn_ep, const char *msn);
-int isdn_dchannel_work(isdn_t *isdn_ep);
-void isdn_bchannel_work(isdn_t *isdn_ep);
-void isdn_rtp_work(isdn_t *isdn_ep);
 
 /* call instance */
 call_t *call_create(isdn_t *isdn_ep, int direction, int channel, int exclusive, int mode);
@@ -209,5 +221,5 @@ void bchannel_event(isdn_t *isdn_ep, int index, int event);
 int seize_bchannel(call_t *call, int channel, int exclusive);
 void drop_bchannel(call_t *call);
 void rtp_receive(struct osmo_cc_session_codec *codec, uint8_t marker, uint16_t sequence_number, uint32_t timestamp, uint32_t ssrc, uint8_t *data, int len);
-void hold_clock(isdn_t *isdn_ep, int len);
+void enable_hold_clock(isdn_t *isdn_ep);
 
diff --git a/src/isdn/main.c b/src/isdn/main.c
index 98f0b9d..2f4ea5d 100644
--- a/src/isdn/main.c
+++ b/src/isdn/main.c
@@ -307,7 +307,6 @@ static int mISDNlib_debug(const char *file, int line, const char *func, int __at
 
 int main(int argc, char *argv[])
 {
-	double last_time_call = 0, now;
 	int argi, rc;
 	int misdn_initialized = 0;
 	int ph_drv_initialized = 0;
@@ -340,7 +339,7 @@ int main(int argc, char *argv[])
 	/* start bridge server */
 	if (use_hfc_bridging) {
 		brigde_socket_server(pcm_slots);
-		bridge_socket_client();
+		bridge_socket_client(isdn_ep);
 	}
 
 	if (!misdn_kernel && !misdn_user) {
@@ -412,37 +411,30 @@ int main(int argc, char *argv[])
 	signal(SIGPIPE, sighandler);
 
 	while (!quit) {
-		int w;
+		int work;
+		double timeout, misdn_timeout = 0.0;
 
-		/* send clock calls to provide audio to suspended/helt calls */
-		now = get_time();
-		if (now - last_time_call >= 0.1)
-			last_time_call = now;
-		if (now - last_time_call >= 0.020) {
-			last_time_call += 0.020;
-			/* call hold-clock every 20ms */
-			hold_clock(isdn_ep, 160);
-		}
-
-		process_timer();
-		isdn_bchannel_work(isdn_ep);
-		isdn_rtp_work(isdn_ep);
-		bridge_socket_client_work(isdn_ep);
-		if (misdn_user) {
-			/* run workers of mISDN stacks in user space */
-			mISDN_work();
-		}
 		do {
-			w = 0;
-			w |= osmo_cc_handle();
-			w |= isdn_dchannel_work(isdn_ep);
+			work = 0;
+			work |= osmo_cc_handle();
 			if (misdn_user) {
 				/* run workers of mISDN stacks in user space */
-				w |= ph_socket_work(&ph_drv.ph_socket);
-				w |= work_layer3(isdn_ep->ml3);
+				work |= mISDN_work();
+				work |= work_layer3(isdn_ep->ml3, &misdn_timeout);
 			}
-		} while (w);
-		usleep(1000);
+		} while (work);
+		/* handle all timers
+		 * timeout is 0, if there was an event
+		 * -> handle FDs without waiting, continue this loop
+		 * timeout is not 0, if there was no event
+		 * -> wait until FD or timeout
+		*/
+		timeout = process_timer();
+		/* reduce timer, if mISDN timer hits earlier */
+		if (misdn_timeout > 0.0 && misdn_timeout < timeout)
+		       timeout = misdn_timeout;	
+		/* wait for FD event until given timeout */
+		osmo_fd_select(timeout);
 	}
 
 	signal(SIGINT, SIG_DFL);
@@ -459,7 +451,7 @@ int main(int argc, char *argv[])
 		schedp.sched_priority = 0;
 		sched_setscheduler(0, SCHED_OTHER, &schedp);
 	}
-	
+
 error:
 	if (isdn_ep) {
 		osmo_cc_delete(&isdn_ep->cc_ep);
diff --git a/src/isdn/ph_driver.c b/src/isdn/ph_driver.c
index 06fb187..7daed8a 100644
--- a/src/isdn/ph_driver.c
+++ b/src/isdn/ph_driver.c
@@ -20,6 +20,9 @@
 
 #include <stdio.h>
 #include <stdint.h>
+#include <time.h>
+#include "../libtimer/timer.h"
+#include "../libselect/select.h"
 #include "../libph_socket/ph_socket.h"
 #include "ph_driver.h"
 #define __MISDNL1L2__
@@ -171,7 +174,7 @@ static void ph_socket_rx_msg(ph_socket_t *s, int channel, uint8_t prim, uint8_t
 /* init instance of PH-socket driver */
 int init_ph_socket_driver(struct ph_socket_driver *drv, void *priv, const char *socket_name, int pri, int nt, uint32_t debug)
 {
-	int ret = 0;
+	int rc = 0;
         struct dchannel *dch;
 
 
@@ -180,13 +183,10 @@ int init_ph_socket_driver(struct ph_socket_driver *drv, void *priv, const char *
 	drv->pri = pri;
 	drv->nt = nt;
 
-	/* socket client */
-	ph_socket_init(&drv->ph_socket, ph_socket_rx_msg, drv, socket_name, 0);
-
 	/* allocate dchannel structure */
         dch = kzalloc(sizeof(*dch), GFP_KERNEL);
         if (!dch) {
-		ret = -ENOMEM;
+		rc = -ENOMEM;
 		goto error;
 	}
 
@@ -215,21 +215,30 @@ int init_ph_socket_driver(struct ph_socket_driver *drv, void *priv, const char *
 	dch->dev.nrbchan = 0;
 
 	/* register dchannel to mISDN */
-        ret = mISDN_register_device(&dch->dev, NULL, socket_name);
-        if (ret) {
-		kfree(dch);
-                return ret;
+        rc = mISDN_register_device(&dch->dev, NULL, socket_name);
+        if (rc) {
+		goto error;
 	}
 
 	/* link */
         drv->dch = dch;
 
+	/* socket client, must be initialized here, because driver will receive PH_PRIM_CTRL_IND message during init */
+	rc = ph_socket_init(&drv->ph_socket, ph_socket_rx_msg, drv, socket_name, 0);
+	if (rc < 0)
+		goto error;
+
 	return 0;
 
 error:
+	if (dch) {
+		kfree(dch);
+		dch = NULL;
+	}
+
 	exit_ph_socket_driver(drv);
 
-	return ret;
+	return rc;
 }
 
 /* destroy instance of PH-socket driver */
diff --git a/src/libmisdn/core.c b/src/libmisdn/core.c
index 618004d..8c7d8ba 100644
--- a/src/libmisdn/core.c
+++ b/src/libmisdn/core.c
@@ -416,13 +416,16 @@ void mISDN_cleanup(void)
 	printk(KERN_DEBUG "mISDNcore unloaded\n");
 }
 
-void mISDN_work(void)
+int mISDN_work(void)
 {
 	struct mISDNdevice *dev;
+	int work = 0;
 
 	hlist_for_each_entry(dev, &dev_list.head, list) {
-		work_stack(dev);
+		work |= work_stack(dev);
 	}
+
+	return work;
 }
 
 //module_init(mISDNInit);
diff --git a/src/libmisdn/core.h b/src/libmisdn/core.h
index c5c3ccb..94fe16f 100644
--- a/src/libmisdn/core.h
+++ b/src/libmisdn/core.h
@@ -73,5 +73,5 @@ extern void	mISDN_init_clock(u_int *);
 
 extern int	mISDNInit(uint debug);
 extern void	mISDN_cleanup(void);
-extern void	mISDN_work(void);
+extern int	mISDN_work(void);
 #endif
diff --git a/src/libmisdn/fsm.c b/src/libmisdn/fsm.c
index ac29e47..e24ca4f 100644
--- a/src/libmisdn/fsm.c
+++ b/src/libmisdn/fsm.c
@@ -92,9 +92,9 @@ mISDN_FsmChangeState(struct FsmInst *fi, int newstate)
 EXPORT_SYMBOL(mISDN_FsmChangeState);
 
 static void
-FsmExpireTimer(struct timer *t)
+FsmExpireTimer(void *data)
 {
-	struct FsmTimer *ft = t->priv;
+	struct FsmTimer *ft = data;
 #if FSM_TIMER_DEBUG
 	if (ft->fi->debug)
 		ft->fi->printdebug(ft->fi, "FsmExpireTimer %lx", (long) ft);
diff --git a/src/libmisdn/stack.c b/src/libmisdn/stack.c
index a906f89..825267a 100644
--- a/src/libmisdn/stack.c
+++ b/src/libmisdn/stack.c
@@ -190,6 +190,7 @@ int
 work_stack(struct mISDNdevice *dev)
 {
 	struct mISDNstack *st = dev->D.st;
+	int work = 0;
 #if 0
 #ifdef MISDN_MSG_STATS
 	u64 utime, stime;
@@ -229,6 +230,7 @@ work_stack(struct mISDNdevice *dev)
 				test_and_set_bit(mISDN_STACK_WORK,
 						 &st->status);
 			}
+			work = 1;
 #ifdef MISDN_MSG_STATS
 			st->msg_cnt++;
 #endif
@@ -322,7 +324,7 @@ work_stack(struct mISDNdevice *dev)
 		st->notify = NULL;
 	}
 #endif
-	return 0;
+	return work;
 }
 
 static int
diff --git a/src/libmisdnuser/include/layer3.h b/src/libmisdnuser/include/layer3.h
index 840fb5d..a25c0d5 100644
--- a/src/libmisdnuser/include/layer3.h
+++ b/src/libmisdnuser/include/layer3.h
@@ -171,7 +171,7 @@ extern void		init_l3(layer3_t *);
 extern void		release_l3(layer3_t *);
 extern int		l3_start(struct _layer3 *);
 extern void 		l3_stop(struct _layer3 *);
-extern int		layer3_work(struct _layer3 *l3);
+extern int		layer3_work(struct _layer3 *l3, double *misdn_timeout);
 extern void		mISDNl3New(void);
 extern void		mISDNl3Free(void);
 
diff --git a/src/libmisdnuser/include/mISDN/mlayer3.h b/src/libmisdnuser/include/mISDN/mlayer3.h
index 9484300..6d67802 100644
--- a/src/libmisdnuser/include/mISDN/mlayer3.h
+++ b/src/libmisdnuser/include/mISDN/mlayer3.h
@@ -231,7 +231,7 @@ extern void		close_layer3(struct mlayer3 *);
  * run stack for one loop
  * parameter1 - stack struct
  */
-extern int		work_layer3(struct mlayer3 *);
+extern int		work_layer3(struct mlayer3 *, double *);
 
 extern unsigned int	request_new_pid(struct mlayer3 *);
 extern int		mISDN_get_pcm_slots(struct mlayer3 *, int, int *, int *);
diff --git a/src/libmisdnuser/include/mtimer.h b/src/libmisdnuser/include/mtimer.h
index 48d0ef5..f966285 100644
--- a/src/libmisdnuser/include/mtimer.h
+++ b/src/libmisdnuser/include/mtimer.h
@@ -41,6 +41,6 @@ extern	int		init_timer(struct mtimer *, struct timer_base  *, void *, mtimer_fun
 extern	int		add_timer(struct mtimer *, int);
 extern	int		del_timer(struct mtimer *);
 extern	int		timer_pending(struct mtimer *);
-extern	int		expire_timer(struct timer_base *, int);
+extern	int		expire_timer(struct timer_base *, int, double *);
 
 #endif
diff --git a/src/libmisdnuser/layer3/layer3.c b/src/libmisdnuser/layer3/layer3.c
index a1d9399..8519d0a 100644
--- a/src/libmisdnuser/layer3/layer3.c
+++ b/src/libmisdnuser/layer3/layer3.c
@@ -888,7 +888,7 @@ to_l2(layer3_t *l3, struct l3_msg *l3m)
 
 /* one shot */
 int
-layer3_work(struct _layer3 *l3)
+layer3_work(struct _layer3 *l3, double *misdn_timeout)
 {
 	fd_set		rfd;
 	struct mbuffer	*mb;
@@ -916,14 +916,14 @@ again:
 				eprint("%s read timer error %s\n", __FUNCTION__, strerror(errno));
 			} else {
 				if (ret == sizeof(id) && id) {
-					work |= expire_timer(&l3->tbase, id);
+					work |= expire_timer(&l3->tbase, id, NULL);
 				}
 			}
 		}
 	}
 	if (l3->l2inst) {
 		/* loops through all timers until there is no expired timer anymore */
-		work |= expire_timer(&l3->tbase, -1);
+		work |= expire_timer(&l3->tbase, -1, misdn_timeout);
 	}
 	/* check rdf when using kernel mISDN, poll when using user space mISDN */
 	if ((l3->l2sock && FD_ISSET(l3->l2sock, &rfd))
@@ -1014,7 +1014,7 @@ layer3_thread(void *arg)
 	struct _layer3	*l3 = arg;
 
 	while(!test_bit(FLG_ABORT, &l3->ml3.options)) {
-		layer3_work(l3);
+		layer3_work(l3, NULL);
 		if (test_bit(FLG_RUN_WAIT, &l3->ml3.options)) {
 			test_and_clear_bit(FLG_RUN_WAIT, &l3->ml3.options);
 			pthread_mutex_unlock(&l3->run);
diff --git a/src/libmisdnuser/layer3/mlayer3.c b/src/libmisdnuser/layer3/mlayer3.c
index d3cdc37..be22a94 100755
--- a/src/libmisdnuser/layer3/mlayer3.c
+++ b/src/libmisdnuser/layer3/mlayer3.c
@@ -316,12 +316,12 @@ close_layer3(struct mlayer3 *ml3)
 }
 
 int
-work_layer3(struct mlayer3 *ml3)
+work_layer3(struct mlayer3 *ml3, double *misdn_timeout)
 {
 	struct _layer3	*l3;
 
 	l3 = container_of(ml3, struct _layer3, ml3);
-	return layer3_work(l3);
+	return layer3_work(l3, misdn_timeout);
 }
 
 int
diff --git a/src/libmisdnuser/misc/mtimer.c b/src/libmisdnuser/misc/mtimer.c
index eae1be5..c163a91 100644
--- a/src/libmisdnuser/misc/mtimer.c
+++ b/src/libmisdnuser/misc/mtimer.c
@@ -106,7 +106,8 @@ del_timer(struct mtimer *mt)
 #endif
 	if (mt->id) {
 		list_del(&mt->list);
-		ret = ioctl(mt->tb->tdev, IMDELTIMER, (long)&mt->id);
+		if (mt->tb->tdev)
+			ret = ioctl(mt->tb->tdev, IMDELTIMER, (long)&mt->id);
 		mt->id = 0;
 	}
 #ifdef DEBUG_TIMERS
@@ -122,11 +123,12 @@ timer_pending(struct mtimer *mt)
 	return mt->id;
 }
 
-int expire_timer(struct timer_base *tb, int id)
+int expire_timer(struct timer_base *tb, int id, double *misdn_timeout)
 {
 	struct mtimer	*mt;
 	double now = 0.0;
 	int work = 0;
+	double timeout = 0.0;
 
 	/* if id is < 0, then check for expired timer */
 	if (id < 0) {
@@ -170,6 +172,17 @@ again:
 #endif
 			goto again;
 		}
+		/* we look for the next unexpired timer */
+		if (!timeout || (mt->expires - now) < timeout)
+			timeout = mt->expires - now;
+	}
+
+	/* if no timer has expired, also present the timeout for the next timer */
+	if (misdn_timeout) {
+		if (work)
+			*misdn_timeout = 0.0;
+		else
+			*misdn_timeout = timeout;
 	}
 
 	return work;