diff --git a/openbsc/include/openbsc/gsm_04_08.h b/openbsc/include/openbsc/gsm_04_08.h
index 8c944e6..186a53f 100644
--- a/openbsc/include/openbsc/gsm_04_08.h
+++ b/openbsc/include/openbsc/gsm_04_08.h
@@ -42,7 +42,11 @@
 		 t3_low:3;
 } __attribute__ ((packed));
 
-/* Chapter 9.1.5 */
+/*
+ * Chapter 9.1.5/9.1.6
+ *
+ * For 9.1.6 the chan_desc has the meaning of 10.5.2.5a
+ */
 struct gsm48_chan_mode_modify {
 	struct gsm48_chan_desc chan_desc;
 	u_int8_t mode;
@@ -59,6 +63,15 @@
 	GSM48_CMODE_DATA_3k6	= 0x23,
 };
 
+/* Chapter 9.1.2 */
+struct gsm48_ass_cmd {
+	/* Semantic is from 10.5.2.5a */
+	struct gsm48_chan_desc chan_desc;
+	u_int8_t power_command;
+	u_int8_t data[0];
+} __attribute__((packed));
+
+
 /* Chapter 9.1.18 */
 struct gsm48_imm_ass {
 	u_int8_t l2_plen;
@@ -727,6 +740,7 @@
 int gsm48_send_rr_ciph_mode(struct gsm_lchan *lchan, int want_imeisv);
 int gsm48_send_rr_app_info(struct gsm_lchan *lchan, u_int8_t apdu_id,
 			   u_int8_t apdu_len, const u_int8_t *apdu);
+int gsm48_send_rr_ass_cmd(struct gsm_lchan *lchan, u_int8_t power_class);
 
 int bsc_upqueue(struct gsm_network *net);
 
@@ -744,4 +758,7 @@
 int gsm48_paging_extract_mi(struct msgb *msg, char *mi_string, u_int8_t *mi_type);
 int gsm48_handle_paging_resp(struct msgb *msg, struct gsm_subscriber *subscr);
 
+int gsm48_lchan_modify(struct gsm_lchan *lchan, u_int8_t lchan_mode);
+int gsm48_rx_rr_modif_ack(struct msgb *msg);
+
 #endif
diff --git a/openbsc/src/abis_rsl.c b/openbsc/src/abis_rsl.c
index 6b328bb..a4764f5 100644
--- a/openbsc/src/abis_rsl.c
+++ b/openbsc/src/abis_rsl.c
@@ -239,6 +239,7 @@
 	return lchan;
 }
 
+/* See Table 10.5.25 of GSM04.08 */
 u_int8_t lchan2chan_nr(struct gsm_lchan *lchan)
 {
 	struct gsm_bts_trx_ts *ts = lchan->ts;
diff --git a/openbsc/src/gsm_04_08.c b/openbsc/src/gsm_04_08.c
index 2373965..12cc362 100644
--- a/openbsc/src/gsm_04_08.c
+++ b/openbsc/src/gsm_04_08.c
@@ -1087,34 +1087,6 @@
 	return gsm0408_authorize(lchan, msg);
 }
 
-/* 9.1.5 Channel mode modify: Modify the mode on the MS side */
-int gsm48_tx_chan_mode_modify(struct gsm_lchan *lchan, u_int8_t mode)
-{
-	struct msgb *msg = gsm48_msgb_alloc();
-	struct gsm48_hdr *gh = (struct gsm48_hdr *) msgb_put(msg, sizeof(*gh));
-	struct gsm48_chan_mode_modify *cmm =
-		(struct gsm48_chan_mode_modify *) msgb_put(msg, sizeof(*cmm));
-	u_int16_t arfcn = lchan->ts->trx->arfcn & 0x3ff;
-
-	DEBUGP(DRR, "-> CHANNEL MODE MODIFY mode=0x%02x\n", mode);
-
-	lchan->tch_mode = mode;
-	msg->lchan = lchan;
-	gh->proto_discr = GSM48_PDISC_RR;
-	gh->msg_type = GSM48_MT_RR_CHAN_MODE_MODIF;
-
-	/* fill the channel information element, this code
-	 * should probably be shared with rsl_rx_chan_rqd() */
-	cmm->chan_desc.chan_nr = lchan2chan_nr(lchan);
-	cmm->chan_desc.h0.tsc = lchan->ts->trx->bts->tsc;
-	cmm->chan_desc.h0.h = 0;
-	cmm->chan_desc.h0.arfcn_high = arfcn >> 8;
-	cmm->chan_desc.h0.arfcn_low = arfcn & 0xff;
-	cmm->mode = mode;
-
-	return gsm48_sendmsg(msg, NULL);
-}
-
 #if 0
 static u_int8_t to_bcd8(u_int8_t val)
 {
@@ -1615,11 +1587,7 @@
 		rc = gsm48_rx_rr_pag_resp(msg);
 		break;
 	case GSM48_MT_RR_CHAN_MODE_MODIF_ACK:
-		DEBUGP(DRR, "CHANNEL MODE MODIFY ACK\n");
-		/* We've successfully modified the MS side of the channel,
-		 * now go on to modify the BTS side of the channel */
-		msg->lchan->rsl_cmode = RSL_CMOD_SPD_SPEECH;
-		rc = rsl_chan_mode_modify_req(msg->lchan);
+		rc = gsm48_rx_rr_modif_ack(msg);
 		break;
 	case GSM48_MT_RR_STATUS:
 		rc = gsm48_rx_rr_status(msg);
@@ -3167,22 +3135,11 @@
 	return mncc_recvmsg(trans->subscr->net, trans, MNCC_USERINFO_IND, &user);
 }
 
-static int gsm48_lchan_modify(struct gsm_trans *trans, void *arg)
+static int _gsm48_lchan_modify(struct gsm_trans *trans, void *arg)
 {
 	struct gsm_mncc *mode = arg;
-	int rc;
 
-	rc = gsm48_tx_chan_mode_modify(trans->lchan, mode->lchan_mode);
-	if (rc < 0)
-		return rc;
-
-	/* FIXME: we not only need to do this after mode modify, but
-	 * also after channel activation */
-	if (is_ipaccess_bts(trans->lchan->ts->trx->bts) &&
-	    mode->lchan_mode != GSM48_CMODE_SIGN)
-		rc = rsl_ipacc_bind(trans->lchan);
-
-	return rc;
+	return gsm48_lchan_modify(trans->lchan, mode->lchan_mode);
 }
 
 static struct downstate {
@@ -3240,7 +3197,7 @@
 	 MNCC_REL_REQ, gsm48_cc_tx_release},
 	/* special */
 	{ALL_STATES,
-	 MNCC_LCHAN_MODIFY, gsm48_lchan_modify},
+	 MNCC_LCHAN_MODIFY, _gsm48_lchan_modify},
 };
 
 #define DOWNSLLEN \
diff --git a/openbsc/src/gsm_04_08_utils.c b/openbsc/src/gsm_04_08_utils.c
index ef9e59c..2545f33 100644
--- a/openbsc/src/gsm_04_08_utils.c
+++ b/openbsc/src/gsm_04_08_utils.c
@@ -482,3 +482,116 @@
 	return rsl_encryption_cmd(msg);
 }
 
+/* Chapter 9.1.2: Assignment Command */
+int gsm48_send_rr_ass_cmd(struct gsm_lchan *lchan, u_int8_t power_command)
+{
+	struct msgb *msg = gsm48_msgb_alloc();
+	struct gsm48_hdr *gh = (struct gsm48_hdr *) msgb_put(msg, sizeof(*gh));
+	struct gsm48_ass_cmd *ass =
+		(struct gsm48_ass_cmd *) msgb_put(msg, sizeof(*ass));
+	u_int16_t arfcn = lchan->ts->trx->arfcn & 0x3ff;
+
+	DEBUGP(DRR, "-> ASSIGNMENT COMMAND tch_mode=0x%02x\n", lchan->tch_mode);
+
+	msg->lchan = lchan;
+	gh->proto_discr = GSM48_PDISC_RR;
+	gh->msg_type = GSM48_MT_RR_ASS_CMD;
+
+	/*
+	 * fill the channel information element, this code
+	 * should probably be shared with rsl_rx_chan_rqd(),
+	 * gsm48_tx_chan_mode_modify. But beware that 10.5.2.5
+	 * 10.5.2.5.a have slightly different semantic for
+	 * the chan_desc. But as long as multi-slot configurations
+	 * are not used we seem to be fine.
+	 */
+	ass->chan_desc.chan_nr = lchan2chan_nr(lchan);
+	ass->chan_desc.h0.tsc = lchan->ts->trx->bts->tsc;
+	ass->chan_desc.h0.h = 0;
+	ass->chan_desc.h0.arfcn_high = arfcn >> 8;
+	ass->chan_desc.h0.arfcn_low = arfcn & 0xff;
+	ass->power_command = power_command;
+
+	return gsm48_sendmsg(msg, NULL);
+}
+
+/* 9.1.5 Channel mode modify: Modify the mode on the MS side */
+int gsm48_tx_chan_mode_modify(struct gsm_lchan *lchan, u_int8_t mode)
+{
+	struct msgb *msg = gsm48_msgb_alloc();
+	struct gsm48_hdr *gh = (struct gsm48_hdr *) msgb_put(msg, sizeof(*gh));
+	struct gsm48_chan_mode_modify *cmm =
+		(struct gsm48_chan_mode_modify *) msgb_put(msg, sizeof(*cmm));
+	u_int16_t arfcn = lchan->ts->trx->arfcn & 0x3ff;
+
+	DEBUGP(DRR, "-> CHANNEL MODE MODIFY mode=0x%02x\n", mode);
+
+	lchan->tch_mode = mode;
+	msg->lchan = lchan;
+	gh->proto_discr = GSM48_PDISC_RR;
+	gh->msg_type = GSM48_MT_RR_CHAN_MODE_MODIF;
+
+	/* fill the channel information element, this code
+	 * should probably be shared with rsl_rx_chan_rqd() */
+	cmm->chan_desc.chan_nr = lchan2chan_nr(lchan);
+	cmm->chan_desc.h0.tsc = lchan->ts->trx->bts->tsc;
+	cmm->chan_desc.h0.h = 0;
+	cmm->chan_desc.h0.arfcn_high = arfcn >> 8;
+	cmm->chan_desc.h0.arfcn_low = arfcn & 0xff;
+	cmm->mode = mode;
+
+	return gsm48_sendmsg(msg, NULL);
+}
+
+int gsm48_lchan_modify(struct gsm_lchan *lchan, u_int8_t lchan_mode)
+{
+	int rc;
+
+	rc = gsm48_tx_chan_mode_modify(lchan, lchan_mode);
+	if (rc < 0)
+		return rc;
+
+	/* FIXME: we not only need to do this after mode modify, but
+	 * also after channel activation */
+	if (is_ipaccess_bts(lchan->ts->trx->bts) && lchan_mode != GSM48_CMODE_SIGN)
+		rc = rsl_ipacc_bind(lchan);
+
+	return rc;
+}
+
+int gsm48_rx_rr_modif_ack(struct msgb *msg)
+{
+	struct gsm48_hdr *gh = msgb_l3(msg);
+	struct gsm48_chan_mode_modify *mod =
+				(struct gsm48_chan_mode_modify *) gh->data;
+
+	DEBUGP(DRR, "CHANNEL MODE MODIFY ACK\n");
+
+	if (mod->mode != msg->lchan->tch_mode) {
+		DEBUGP(DRR, "CHANNEL MODE change failed. Wanted: %d Got: %d\n",
+			msg->lchan->tch_mode, mod->mode);
+		return -1;
+	}
+
+	/* update the channel type */
+	switch (mod->mode) {
+	case GSM48_CMODE_SIGN:
+		msg->lchan->rsl_cmode = RSL_CMOD_SPD_SIGN;
+		break;
+	case GSM48_CMODE_SPEECH_V1:
+	case GSM48_CMODE_SPEECH_EFR:
+	case GSM48_CMODE_SPEECH_AMR:
+		msg->lchan->rsl_cmode = RSL_CMOD_SPD_SPEECH;
+		break;
+	case GSM48_CMODE_DATA_14k5:
+	case GSM48_CMODE_DATA_12k0:
+	case GSM48_CMODE_DATA_6k0:
+	case GSM48_CMODE_DATA_3k6:
+		msg->lchan->rsl_cmode = RSL_CMOD_SPD_DATA;
+		break;
+	}
+
+	/* We've successfully modified the MS side of the channel,
+	 * now go on to modify the BTS side of the channel */
+	return rsl_chan_mode_modify_req(msg->lchan);
+}