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);
+
+/*! @} */