diff --git a/include/osmocom/isdn/Makefile.am b/include/osmocom/isdn/Makefile.am
new file mode 100644
index 0000000..bf33623
--- /dev/null
+++ b/include/osmocom/isdn/Makefile.am
@@ -0,0 +1,6 @@
+osmoisdn_HEADERS = \
+	i460_mux.h \
+	lapd_core.h \
+	$(NULL)
+
+osmoisdndir = $(includedir)/osmocom/isdn
diff --git a/include/osmocom/isdn/i460_mux.h b/include/osmocom/isdn/i460_mux.h
new file mode 100644
index 0000000..770b1e1
--- /dev/null
+++ b/include/osmocom/isdn/i460_mux.h
@@ -0,0 +1,116 @@
+/*! \file i460_mux.h
+ * ITU-T I.460 sub-channel multiplexer + demultiplexer */
+/*
+ * (C) 2020 by Harald Welte <laforge@gnumonks.org>
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ */
+
+#pragma once
+#include <stdint.h>
+#include <osmocom/core/bits.h>
+#include <osmocom/core/linuxlist.h>
+#include <osmocom/core/msgb.h>
+
+/* I.460 sub-slot rate */
+enum osmo_i460_rate {
+	OSMO_I460_RATE_NONE,		/* disabled */
+	OSMO_I460_RATE_64k,
+	OSMO_I460_RATE_32k,
+	OSMO_I460_RATE_16k,
+	OSMO_I460_RATE_8k,
+};
+
+struct osmo_i460_subchan;
+
+typedef void (*out_cb_bits_t)(struct osmo_i460_subchan *schan, void *user_data,
+			      const ubit_t *bits, unsigned int num_bits);
+typedef void (*out_cb_bytes_t)(struct osmo_i460_subchan *schan, void *user_data,
+			       const uint8_t *bytes, unsigned int num_bytes);
+
+struct osmo_i460_subchan_demux {
+	/*! bit-buffer for output bits */
+	uint8_t *out_bitbuf;
+	/*! size of out_bitbuf in bytes */
+	unsigned int out_bitbuf_size;
+	/*! offset of next bit to be written in out_bitbuf */
+	unsigned int out_idx;
+	/*! callback to be called once we have received out_bitbuf_size bits */
+	out_cb_bits_t out_cb_bits;
+	out_cb_bytes_t out_cb_bytes;
+	void *user_data;
+};
+
+typedef void (*in_cb_queue_empty_t)(struct osmo_i460_subchan *schan, void *user_data);
+
+struct osmo_i460_subchan_mux {
+	/*! list of to-be-transmitted message buffers */
+	struct llist_head tx_queue;
+	in_cb_queue_empty_t in_cb_queue_empty;
+	void *user_data;
+};
+
+struct osmo_i460_subchan {
+	struct osmo_i460_timeslot *ts;	/* back-pointer */
+	enum osmo_i460_rate rate;		/* 8/16/32/64k */
+	uint8_t bit_offset;		/* bit offset inside each byte of the B-channel */
+	struct osmo_i460_subchan_demux demux;
+	struct osmo_i460_subchan_mux mux;
+};
+
+struct osmo_i460_timeslot {
+	struct osmo_i460_subchan schan[8];
+};
+
+/*! description of a sub-channel; passed by caller */
+struct osmo_i460_schan_desc {
+	enum osmo_i460_rate rate;
+	uint8_t bit_offset;
+	struct {
+		/* size (in bits) of the internal buffer; determines granularity */
+		size_t num_bits;
+		/*! call-back function called whenever we received num_bits */
+		out_cb_bits_t out_cb_bits;
+		/*! out_cb_bytes call-back function called whenever we received num_bits.
+		 * The user is usually expected to provide either out_cb_bits or out_cb_bytes.  If only
+		 * out_cb_bits is provided, output data will always be provided as unpacked bits;  if only
+		 * out_cb_bytes is provided, output data will always be provided as packet bits (bytes).  If
+		 * both are provided, it is up to the I.460 multiplex to decide if it calls either of the two,
+		 * depending on what can be provided without extra conversion. */
+		out_cb_bytes_t out_cb_bytes;
+		/* opaque user data pointer to pass to out_cb */
+		void *user_data;
+	} demux;
+
+	struct {
+		/* call-back function whenever the muxer requires more input data from the sub-channels,
+		 * but has nothing enqueued yet. A typical function would then call osmo_i460_mux_enqueue() */
+		in_cb_queue_empty_t in_cb_queue_empty;
+		/* opaque user data pointer to pass to in_cb */
+		void *user_data;
+	} mux;
+};
+
+void osmo_i460_demux_in(struct osmo_i460_timeslot *ts, const uint8_t *data, size_t data_len);
+
+void osmo_i460_mux_enqueue(struct osmo_i460_subchan *schan, struct msgb *msg);
+int osmo_i460_mux_out(struct osmo_i460_timeslot *ts, uint8_t *out, size_t out_len);
+
+void osmo_i460_ts_init(struct osmo_i460_timeslot *ts);
+
+struct osmo_i460_subchan *
+osmo_i460_subchan_add(void *ctx, struct osmo_i460_timeslot *ts, const struct osmo_i460_schan_desc *chd);
+
+void osmo_i460_subchan_del(struct osmo_i460_subchan *schan);
+
+/*! @} */
diff --git a/include/osmocom/isdn/lapd_core.h b/include/osmocom/isdn/lapd_core.h
new file mode 100644
index 0000000..e4e8b46
--- /dev/null
+++ b/include/osmocom/isdn/lapd_core.h
@@ -0,0 +1,176 @@
+/*! \file lapd_core.h
+ * primitive related stuff
+ */
+#pragma once
+
+#include <stdint.h>
+
+#include <osmocom/core/timer.h>
+#include <osmocom/core/msgb.h>
+#include <osmocom/gsm/prim.h>
+
+/*! \defgroup lapd LAPD implementation common part
+ *  @{
+ * \file lapd_core.h
+ */
+
+#define LOGDL(dl, level, fmt, args...) \
+	LOGP(DLLAPD, level, "(%s) "  fmt, (dl)->name, ## args)
+
+/*! LAPD related primitives (L2<->L3 SAP)*/
+enum osmo_dl_prim {
+	PRIM_DL_UNIT_DATA,	/*!< DL-UNIT-DATA */
+	PRIM_DL_DATA,		/*!< DL-DATA */
+	PRIM_DL_EST,		/*!< DL-ESTABLISH */
+	PRIM_DL_REL,		/*!< DL-RLEEASE */
+	PRIM_DL_SUSP,		/*!< DL-SUSPEND */
+	PRIM_DL_RES,		/*!< DL-RESUME */
+	PRIM_DL_RECON,		/*!< DL-RECONNECT */
+	PRIM_MDL_ERROR,		/*!< MDL-ERROR */
+};
+
+/* Uses the same values as RLL, so no conversion for GSM is required. */
+#define MDL_CAUSE_T200_EXPIRED		0x01
+#define MDL_CAUSE_REEST_REQ		0x02
+#define MDL_CAUSE_UNSOL_UA_RESP		0x03
+#define MDL_CAUSE_UNSOL_DM_RESP		0x04
+#define MDL_CAUSE_UNSOL_DM_RESP_MF	0x05
+#define MDL_CAUSE_UNSOL_SPRV_RESP	0x06
+#define MDL_CAUSE_SEQ_ERR		0x07
+#define MDL_CAUSE_UFRM_INC_PARAM	0x08
+#define MDL_CAUSE_SFRM_INC_PARAM	0x09
+#define MDL_CAUSE_IFRM_INC_MBITS	0x0a
+#define MDL_CAUSE_IFRM_INC_LEN		0x0b
+#define MDL_CAUSE_FRM_UNIMPL		0x0c
+#define MDL_CAUSE_SABM_MF		0x0d
+#define MDL_CAUSE_SABM_INFO_NOTALL	0x0e
+#define MDL_CAUSE_FRMR			0x0f
+
+/*! for MDL-ERROR.ind */
+struct mdl_error_ind_param {
+	uint8_t cause;		/*!< generic cause value */
+};
+
+/*! for DL-REL.req */
+struct dl_rel_req_param {
+	uint8_t mode;		/*!< release mode */
+};
+
+/*! primitive header for LAPD DL-SAP primitives */
+struct osmo_dlsap_prim {
+	struct osmo_prim_hdr oph; /*!< generic primitive header */
+	union {
+		struct mdl_error_ind_param error_ind;
+		struct dl_rel_req_param rel_req;
+	} u;			/*!< request-specific data */
+};
+
+/*! LAPD mode/role */
+enum lapd_mode {
+	LAPD_MODE_USER,		/*!< behave like user */
+	LAPD_MODE_NETWORK,	/*!< behave like network */
+};
+
+/*! LAPD state (Figure B.2/Q.921)*/
+enum lapd_state {
+	LAPD_STATE_NULL = 0,
+	LAPD_STATE_TEI_UNASS,
+	LAPD_STATE_ASS_TEI_WAIT,
+	LAPD_STATE_EST_TEI_WAIT,
+	LAPD_STATE_IDLE,
+	LAPD_STATE_SABM_SENT,
+	LAPD_STATE_DISC_SENT,
+	LAPD_STATE_MF_EST,
+	LAPD_STATE_TIMER_RECOV,
+};
+
+/*! LAPD message format (I / S / U) */
+enum lapd_format {
+	LAPD_FORM_UKN = 0,
+	LAPD_FORM_I,
+	LAPD_FORM_S,
+	LAPD_FORM_U,
+};
+
+/*! LAPD message context */
+struct lapd_msg_ctx {
+	struct lapd_datalink *dl;
+	int n201;
+	/* address */
+	uint8_t cr;
+	uint8_t sapi;
+	uint8_t tei;
+	uint8_t lpd;
+	/* control */
+	uint8_t format;
+	uint8_t p_f; /* poll / final bit */
+	uint8_t n_send;
+	uint8_t n_recv;
+	uint8_t s_u; /* S or repectivly U function bits */
+	/* length */
+	int	length;
+	uint8_t	more;
+};
+
+struct lapd_cr_ent {
+	uint8_t cmd;
+	uint8_t resp;
+};
+
+struct lapd_history {
+	struct msgb *msg; /* message to be sent / NULL, if histoy is empty */
+	int	more; /* if message is fragmented */
+};
+
+/*! LAPD datalink */
+struct lapd_datalink {
+	int (*send_dlsap)(struct osmo_dlsap_prim *dp, struct lapd_msg_ctx *lctx);
+	int (*send_ph_data_req)(struct lapd_msg_ctx *lctx, struct msgb *msg);
+	int (*update_pending_frames)(struct lapd_msg_ctx *lctx);
+	struct {
+		/*! filled-in once we set the lapd_mode above */
+		struct lapd_cr_ent loc2rem;
+		struct lapd_cr_ent rem2loc;
+	} cr;
+	enum lapd_mode mode; /*!< current mode of link */
+	int use_sabme; /*!< use SABME instead of SABM */
+	int reestablish; /*!< enable reestablish support */
+	int n200, n200_est_rel; /*!< number of retranmissions */
+	struct lapd_msg_ctx lctx; /*!< LAPD context */
+	int maxf; /*!< maximum frame size (after defragmentation) */
+	uint8_t k; /*!< maximum number of unacknowledged frames */
+	uint8_t v_range; /*!< range of sequence numbers */
+	uint8_t v_send;	/*!< seq nr of next I frame to be transmitted */
+	uint8_t v_ack;	/*!< last frame ACKed by peer */
+	uint8_t v_recv;	/*!< seq nr of next I frame expected to be received */
+	uint32_t state; /*!< LAPD state (\ref lapd_state) */
+	int seq_err_cond; /*!< condition of sequence error */
+	uint8_t own_busy; /*!< receiver busy on our side */
+	uint8_t peer_busy; /*!< receiver busy on remote side */
+	int t200_sec, t200_usec; /*!< retry timer (default 1 sec) */
+	int t203_sec, t203_usec; /*!< retry timer (default 10 secs) */
+	struct osmo_timer_list t200; /*!< T200 timer */
+	struct osmo_timer_list t203; /*!< T203 timer */
+	uint8_t retrans_ctr; /*!< re-transmission counter */
+	struct llist_head tx_queue; /*!< frames to L1 */
+	struct llist_head send_queue; /*!< frames from L3 */
+	struct msgb *send_buffer; /*!< current frame transmitting */
+	int send_out; /*!< how much was sent from send_buffer */
+	struct lapd_history *tx_hist; /*!< tx history structure array */
+	uint8_t range_hist; /*!< range of history buffer 2..2^n */
+	struct msgb *rcv_buffer; /*!< buffer to assemble the received message */
+	struct msgb *cont_res; /*!< buffer to store content resolution data on network side, to detect multiple phones on same channel */
+	char *name; /*!< user-provided name */
+};
+
+void lapd_dl_init(struct lapd_datalink *dl, uint8_t k, uint8_t v_range, int maxf)
+	OSMO_DEPRECATED("Use lapd_dl_init2() instead");
+void lapd_dl_init2(struct lapd_datalink *dl, uint8_t k, uint8_t v_range, int maxf, const char *name);
+void lapd_dl_set_name(struct lapd_datalink *dl, const char *name);
+void lapd_dl_exit(struct lapd_datalink *dl);
+void lapd_dl_reset(struct lapd_datalink *dl);
+int lapd_set_mode(struct lapd_datalink *dl, enum lapd_mode mode);
+int lapd_ph_data_ind(struct msgb *msg, struct lapd_msg_ctx *lctx);
+int lapd_recv_dlsap(struct osmo_dlsap_prim *dp, struct lapd_msg_ctx *lctx);
+
+/*! @} */