Band downsteer

README.md

@@ -10,6 +10,7 @@ Its goal is to optimize roaming behavior of wireless clients (STAs) in a ESS con
  - Policy-based decisions for probe- / association- / authentication requests received from STAs
  - Requesting clients to roam to a different BSS based on SNR / signal-level
  - Channel-load based client steering to different BSS
+ - Same-AP down-steering of clients stuck on a weak upper band (6->5->2.4) when no better AP is available
 
 ## Installation
 

band_steering.c

@@ -18,6 +18,32 @@
 #include "usteer.h"
 #include "node.h"
 
+/* Return a node of the SAME AP (local node) on the next-lower band (6->5->2.4).
+ * Used as a fallback when the roam state machine finds no measured better
+ * candidate: the same-AP lower band is guaranteed reachable and physically
+ * stronger than a weak upper band, even though its per-STA signal is unknown. */
+struct usteer_node *usteer_band_downsteer_target(struct usteer_local_node *ln)
+{
+	struct usteer_node *cur = &ln->node;
+	struct usteer_node *node, *best = NULL;
+
+	for_each_local_node(node) {
+		if (node == cur)
+			continue;
+		if (strcmp(cur->ssid, node->ssid) != 0)
+			continue;
+		if (node->freq >= cur->freq)
+			continue;
+		if (!usteer_policy_node_below_max_assoc(node))
+			continue;
+		/* Highest freq strictly below current => one band down. */
+		if (!best || node->freq > best->freq)
+			best = node;
+	}
+
+	return best;
+}
+
 void usteer_band_steering_sta_update(struct sta_info *si)
 {
 	if (si->connected == STA_NOT_CONNECTED) {

local_node.c

@@ -182,11 +182,13 @@ usteer_handle_bss_tm_response(struct usteer_local_node *ln, struct blob_attr *ms
 	si->bss_transition_response.status_code = blobmsg_get_u8(tb[BSS_TM_RESPONSE_STATUS_CODE]);
 	si->bss_transition_response.timestamp = current_time;
 
-	if (si->bss_transition_response.status_code && si->kick_time && si->sta->aggressiveness) {
-		/* Cancel imminent kick in case BSS transition was rejected */
-		si->kick_time = 0;
-		MSG(VERBOSE, "Kick canceled because transition rejected by station " MAC_ADDR_FMT "\n", MAC_ADDR_DATA(si->sta->addr));
-	}
+	/* PR#16 (openwrt/usteer): KEEP the already-scheduled fallback kick even if
+	 * the client REJECTS the BSS-TM (status_code != 0). Cancelling it here left
+	 * stubborn clients (notably iPhones) stuck for many minutes on soft-steering
+	 * retries and DEFEATED the forced band-downsteer (which schedules kick_time).
+	 * Ask nicely via BSS-TM first; if the client refuses, kick_time still deauths
+	 * it (roam_kick_delay / band_downsteer_disassoc), then assoc_min_snr keeps it
+	 * off the weak upper band. */
 
 	return 0;
 }

main.c

@@ -103,6 +103,10 @@ void usteer_init_defaults(void)
 
 	config.band_steering_interval = 30000;
 	config.band_steering_min_snr = -60;
+	config.band_downsteer_snr = 0;
+	config.band_downsteer_hold = 30 * 1000;
+	config.assoc_min_snr = 0;
+	config.band_downsteer_disassoc = 0;
 	config.band_steering_signal_threshold = 5;
 
 	config.link_measurement_interval = 30000;

openwrt/usteer/files/etc/config/usteer

@@ -143,6 +143,44 @@ config usteer
 	# steered to a higher frequency band
 	#option band_steering_min_snr -60
 
+	# Signal level (dBm) below which a client on an upper band (5/6 GHz) is
+	# down-steered to the next-lower band of the SAME AP (6->5->2.4), but only
+	# when the roaming policy has found no better measured candidate on another
+	# AP. Fixes clients (notably iOS) that cling to a weak 6 GHz signal while a
+	# stronger lower band of the same AP is available. A value of 0 disables it.
+	# Pair with band_downsteer_hold (below) for durability: min_snr-style kicking
+	# tends to fight the client's own band preference and cause an assoc/kick
+	# storm, whereas the directed BSS-TM plus a hold moves the client gently.
+	#option band_downsteer_snr 0
+
+	# Time (ms) after a down-steer during which the client is not allowed back
+	# up to a higher band than it was moved to. Time-based hysteresis that stops
+	# bouncing on a fluctuating signal. 0 disables the hold. NOTE: the hold state
+	# is per-AP (not synced between nodes), so it stops bounce-back to the SAME
+	# AP's upper band but not a jump to another AP's upper band. Use assoc_min_snr
+	# (below) to close that cross-AP gap.
+	#option band_downsteer_hold 30000
+
+	# Admission floor (dBm): refuse a client's association to an UPPER band
+	# (5/6 GHz) on ANY AP when its signal is below this value; 2.4 GHz is always
+	# exempt. This closes cross-AP bouncing onto weak 5/6 GHz that the per-AP
+	# band_downsteer_hold cannot: a client that is weak everywhere on the upper
+	# bands can only land on 2.4 GHz, so it settles instead of thrashing.
+	# Unlike min_snr this is ADMISSION-ONLY -- it never kicks a connected client,
+	# so it cannot cause the assoc/kick storm that min_snr does; and because
+	# 2.4 GHz is exempt the client always has a landing band (no lockout).
+	# Enforced independently of assoc_steering. 0 disables it.
+	#option assoc_min_snr 0
+
+	# Forced down-steer (ms): a plain down-steer is a BSS-TM suggestion that some
+	# clients (notably iOS) ignore, clinging to a dying upper band. If set, then
+	# this many ms after down-steering a client that is still on the upper band
+	# is kicked (deauth). Paired with assoc_min_snr this is safe: the kicked
+	# client cannot reassociate to the weak upper band, so it lands on 2.4/5 GHz
+	# and cannot bounce back -- no kick storm (the failure mode of blind min_snr).
+	# 0 = gentle (suggestion only). Typical: 8000 (give the client ~8s to comply).
+	#option band_downsteer_disassoc 0
+
 	# SNR difference that the signal must be better compared to signal was on connection to node.
 	# Avoids conflicts between roaming and band-steering policies.
 	# A value of 0 disables threshold.

openwrt/usteer/files/etc/init.d/usteer

@@ -86,7 +86,7 @@ uci_usteer() {
 		roam_kick_delay roam_scan_tries roam_scan_timeout \
 		roam_scan_snr roam_scan_interval roam_trigger_snr roam_trigger_interval \
 		link_measurement_interval \
-		band_steering_interval band_steering_min_snr band_steering_signal_threshold \
+		band_steering_interval band_steering_min_snr band_downsteer_snr band_downsteer_hold assoc_min_snr band_downsteer_disassoc band_steering_signal_threshold \
 		load_kick_threshold load_kick_delay load_kick_min_clients \
 		load_kick_reason_code
 	do

policy.c

@@ -182,7 +182,34 @@ usteer_check_request(struct sta_info *si, enum usteer_event_type type)
 	if (type == EVENT_TYPE_AUTH)
 		goto out;
 
+	/* Down-steer hold-down: for band_downsteer_hold ms after a down-steer,
+	 * refuse probe/assoc for a band higher than the one the client was moved
+	 * to. Time-based hysteresis stops a client bouncing back up on brief signal
+	 * peaks. */
+	if (config.band_downsteer_hold && si->sta->downsteer_hold_until &&
+	    current_time < si->sta->downsteer_hold_until &&
+	    si->node->freq > si->sta->downsteer_to_freq) {
+		ret = false;
+		goto out;
+	}
+
 	if (type == EVENT_TYPE_ASSOC) {
+		/* Band-aware admission floor (assoc_min_snr): refuse association to an
+		 * upper band (> 2.4 GHz) when the client's signal is below the floor,
+		 * regardless of assoc_steering. This closes cross-node bouncing onto
+		 * weak 5/6 GHz on ANY AP. 2.4 GHz is exempt, so the client always has a
+		 * landing band and cannot be locked out. Admission-only: a connected
+		 * client is never kicked, so unlike min_snr this cannot cause a kick
+		 * storm. */
+		if (config.assoc_min_snr && si->node->freq > 4000 &&
+		    si->signal < usteer_snr_to_signal(si->node, config.assoc_min_snr)) {
+			ev.reason = UEV_REASON_LOW_SIGNAL;
+			ev.threshold.cur = si->signal;
+			ev.threshold.ref = usteer_snr_to_signal(si->node, config.assoc_min_snr);
+			ret = false;
+			goto out;
+		}
+
 		/* Check if assoc request has lower signal than min_signal.
 		 * If this is the case, block assoc even when assoc steering is enabled.
 		 *
@@ -374,6 +401,34 @@ usteer_roam_trigger_sm(struct usteer_local_node *ln, struct sta_info *si)
 		candidate = usteer_roam_sm_found_better_node(si, &ev, ROAM_TRIGGER_SCAN_DONE);
 		/* Kick back in case no better node is found */
 		if (!candidate) {
+			/* No measured better route. Fall back to same-AP down-steering:
+			 * if the client sits on an upper band (5/6 GHz) below
+			 * band_downsteer_snr, push it to the next-lower band of the same
+			 * AP. min_snr / min_connect_snr then refuse a bounce back up to a
+			 * band below the threshold, so the move is durable. */
+			if (config.band_downsteer_snr && si->node->freq > 4000 &&
+			    si->signal < usteer_snr_to_signal(si->node, config.band_downsteer_snr)) {
+				struct usteer_node *lower = usteer_band_downsteer_target(ln);
+				if (lower) {
+					uint32_t bi = usteer_local_node_get_beacon_interval(ln);
+					uint32_t vp = 10000 / bi;
+					uint32_t dtimer = config.band_downsteer_disassoc ?
+					    config.band_downsteer_disassoc / bi : 0;
+					MSG(VERBOSE, "down-steer " MAC_ADDR_FMT " to %s (signal %d%s)\n",
+					    MAC_ADDR_DATA(si->sta->addr), usteer_node_name(lower), si->signal,
+					    config.band_downsteer_disassoc ? ", forced" : "");
+					usteer_ubus_bss_transition_request(si, 1, true, dtimer, true, vp, lower);
+					si->sta->downsteer_hold_until = current_time + config.band_downsteer_hold;
+					si->sta->downsteer_to_freq = lower->freq;
+					/* If the client ignores the BSS-TM (iOS often does) and is
+					 * still on this upper band after band_downsteer_disassoc ms,
+					 * kick it. assoc_min_snr then refuses reassoc to a weak upper
+					 * band, so it lands on 2.4/5 and cannot bounce back -> no
+					 * kick storm (unlike blind min_snr). */
+					if (config.band_downsteer_disassoc && !si->kick_time)
+						si->kick_time = current_time + config.band_downsteer_disassoc;
+				}
+			}
 			usteer_roam_set_state(si, ROAM_TRIGGER_IDLE, &ev);
 			break;
 		}

ubus.c

@@ -186,6 +186,11 @@ struct cfg_item {
 	_cfg(U32, load_kick_reason_code), \
 	_cfg(U32, band_steering_interval), \
 	_cfg(I32, band_steering_min_snr), \
+	_cfg(U32, band_steering_signal_threshold), \
+	_cfg(I32, band_downsteer_snr), \
+	_cfg(U32, band_downsteer_hold), \
+	_cfg(I32, assoc_min_snr), \
+	_cfg(U32, band_downsteer_disassoc), \
 	_cfg(U32, link_measurement_interval), \
 	_cfg(ARRAY_CB, interfaces), \
 	_cfg(STRING_CB, node_up_script), \

usteer.h

@@ -203,6 +203,14 @@ struct usteer_config {
 
 	uint32_t band_steering_interval;
 	int32_t band_steering_min_snr;
+	int32_t band_downsteer_snr;
+	uint32_t band_downsteer_hold;
+	/* Admission floor: refuse assoc to an upper band (>2.4 GHz) below this
+	 * SNR, regardless of assoc_steering; 2.4 GHz exempt. Admission-only. */
+	int32_t assoc_min_snr;
+	/* Forced down-steer: ms after a down-steer BSS-TM to kick (deauth) a
+	 * client still on the upper band. 0 = gentle (BSS-TM suggestion only). */
+	uint32_t band_downsteer_disassoc;
 	uint32_t band_steering_signal_threshold;
 
 	uint32_t link_measurement_interval;
@@ -303,6 +311,10 @@ struct sta {
 
 	uint32_t aggressiveness;
 
+	/* Down-steer hold: block upsteer above downsteer_to_freq until this time. */
+	uint64_t downsteer_hold_until;
+	uint32_t downsteer_to_freq;
+
 	uint8_t addr[6];
 };
 
@@ -350,6 +362,7 @@ bool usteer_policy_can_perform_roam(struct sta_info *si);
 void usteer_band_steering_perform_steer(struct usteer_local_node *ln);
 void usteer_band_steering_sta_update(struct sta_info *si);
 bool usteer_band_steering_is_target(struct usteer_local_node *ln, struct usteer_node *node);
+struct usteer_node *usteer_band_downsteer_target(struct usteer_local_node *ln);
 
 void usteer_ubus_init(struct ubus_context *ctx);
 void usteer_ubus_kick_client(struct sta_info *si, uint32_t kick_reason_code);