diff --git a/include/osmocom/gsm/lapd_core.h b/include/osmocom/gsm/lapd_core.h
new file mode 100644
index 0000000..0f4e889
--- /dev/null
+++ b/include/osmocom/gsm/lapd_core.h
@@ -0,0 +1,171 @@
+#ifndef _OSMOCOM_LAPD_H
+#define _OSMOCOM_LAPD_H
+
+#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.h */
+
+/* primitive related sutff */
+
+/*! \brief LAPD related primitives (L2<->L3 SAP)*/
+enum osmo_dl_prim {
+	PRIM_DL_UNIT_DATA,	/*!< \brief DL-UNIT-DATA */
+	PRIM_DL_DATA,		/*!< \brief DL-DATA */
+	PRIM_DL_EST,		/*!< \brief DL-ESTABLISH */
+	PRIM_DL_REL,		/*!< \brief DL-RLEEASE */
+	PRIM_DL_SUSP,		/*!< \brief DL-SUSPEND */
+	PRIM_DL_RES,		/*!< \brief DL-RESUME */
+	PRIM_DL_RECON,		/*!< \brief DL-RECONNECT */
+	PRIM_MDL_ERROR,		/*!< \brief 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
+
+/*! \brief for MDL-ERROR.ind */
+struct mdl_error_ind_param {
+	uint8_t cause;		/*!< \brief generic cause value */
+};
+
+/*! \brief for DL-REL.req */
+struct dl_rel_req_param {
+	uint8_t mode;		/*!< \brief release mode */
+};
+
+/*! \brief primitive header for LAPD DL-SAP primitives */
+struct osmo_dlsap_prim {
+	struct osmo_prim_hdr oph; /*!< \brief generic primitive header */
+	union {
+		struct mdl_error_ind_param error_ind;
+		struct dl_rel_req_param rel_req;
+	} u;			/*!< \brief request-specific data */
+};
+
+/*! \brief LAPD mode/role */
+enum lapd_mode {
+	LAPD_MODE_USER,		/*!< \brief behave like user */
+	LAPD_MODE_NETWORK,	/*!< \brief behave like network */
+};
+
+/*! \brief 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,
+};
+
+/*! \brief LAPD message format (I / S / U) */
+enum lapd_format {
+	LAPD_FORM_UKN = 0,
+	LAPD_FORM_I,
+	LAPD_FORM_S,
+	LAPD_FORM_U,
+};
+
+/*! \brief 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 */
+};
+
+/*! \brief 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);
+	struct {
+		/*! \brief filled-in once we set the lapd_mode above */
+		struct lapd_cr_ent loc2rem;
+		struct lapd_cr_ent rem2loc;
+	} cr;
+	enum lapd_mode mode; /*!< \brief current mode of link */
+	int use_sabme; /*!< \brief use SABME instead of SABM */
+	int reestablish; /*!< \brief enable reestablish support */
+	int n200, n200_est_rel; /*!< \brief number of retranmissions */
+	struct lapd_msg_ctx lctx; /*!< \brief LAPD context */
+	int maxf; /*!< \brief maximum frame size (after defragmentation) */ 
+	uint8_t k; /*!< \brief maximum number of unacknowledged frames */
+	uint8_t v_range; /*!< \brief range of sequence numbers */
+	uint8_t v_send;	/*!< \brief seq nr of next I frame to be transmitted */
+	uint8_t v_ack;	/*!< \brief last frame ACKed by peer */
+	uint8_t v_recv;	/*!< \brief seq nr of next I frame expected to be received */
+	uint32_t state; /*!< \brief LAPD state (\ref lapd_state) */
+	int seq_err_cond; /*!< \brief condition of sequence error */
+	uint8_t own_busy; /*!< \brief receiver busy on our side */
+	uint8_t peer_busy; /*!< \brief receiver busy on remote side */
+	int t200_sec, t200_usec; /*!< \brief retry timer (default 1 sec) */
+	int t203_sec, t203_usec; /*!< \brief retry timer (default 10 secs) */
+	struct osmo_timer_list t200; /*!< \brief T200 timer */
+	struct osmo_timer_list t203; /*!< \brief T203 timer */
+	uint8_t retrans_ctr; /*!< \brief re-transmission counter */
+	struct llist_head tx_queue; /*!< \brief frames to L1 */
+	struct llist_head send_queue; /*!< \brief frames from L3 */
+	struct msgb *send_buffer; /*!< \brief current frame transmitting */
+	int send_out; /*!< \brief how much was sent from send_buffer */
+	struct lapd_history *tx_hist; /*!< \brief tx history structure array */
+	uint8_t range_hist; /*!< \brief range of history buffer 2..2^n */
+	struct msgb *rcv_buffer; /*!< \brief buffer to assemble the received message */
+	struct msgb *cont_res; /*!< \brief buffer to store content resolution data on network side, to detect multiple phones on same channel */
+};
+
+void lapd_dl_init(struct lapd_datalink *dl, uint8_t k, uint8_t v_range,
+	int maxf);
+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);
+
+#endif /* _OSMOCOM_LAPD_H */