hostapd: Add Power Constraint element

Add Power Constraint information element to Beacon and Probe Response
frames when hostapd is configured on 5 GHz band and Country information
element is also added. According to IEEE Std 802.11-2012 a STA shall
determine a local maximum transmit power for the current channel based
on information derived from Country and Power Constraint elements.

In order to add Power Constraint element ieee80211d option need to be
enabled and new local_pwr_constraint config option need to be set to
unsigned value in units of decibels. For now this value is statically
configured but the future goal is to implement dynamic TPC algorithm
to control local power constraint.

Signed-hostap: Srinivasan <srinivasanb@posedge.com>
Signed-hostap: Chaitanya T K <chaitanyatk@posedge.com>
Signed-hostap: Marek Puzyniak <marek.puzyniak@tieto.com>

diff --git a/hostapd/config_file.c b/hostapd/config_file.c
index 19d6ad324296b5e07079138d0d653f8211ca0f34..0ec170131e6b79577f2071013cd0500e0b26d385 100644 (file)
--- a/hostapd/config_file.c
+++ b/hostapd/config_file.c
@@ -2907,6 +2907,14 @@ static int hostapd_config_fill(struct hostapd_config *conf,
                                           "sae_groups value '%s'", line, pos);
                                return 1;
                        }
+               } else if (os_strcmp(buf, "local_pwr_constraint") == 0) {
+                       int val = atoi(pos);
+                       if (val < 0 || val > 255) {
+                               wpa_printf(MSG_ERROR, "Line %d: Invalid local_pwr_constraint %d (expected 0..255)",
+                                          line, val);
+                               return 1;
+                       }
+                       conf->local_pwr_constraint = val;
                } else {
                        wpa_printf(MSG_ERROR, "Line %d: unknown configuration "
                                   "item '%s'", line, buf);

diff --git a/hostapd/hostapd.conf b/hostapd/hostapd.conf
index c503ce2905e896874e3d28e9442c0cbca293a204..63232d750df98a41ffd38ac0fcc126ed87398b04 100644 (file)
--- a/hostapd/hostapd.conf
+++ b/hostapd/hostapd.conf
@@ -108,6 +108,13 @@ ssid=test
 # (default: 0 = disabled)
 #ieee80211h=1
 
+# Add Power Constraint element to Beacon and Probe Response frames
+# This config option adds Power Constraint element when applicable and Country
+# element is added. Power Constraint element is required by Transmit Power
+# Control. This can be used only with ieee80211d=1.
+# Valid values are 0..255.
+#local_pwr_constraint=3
+
 # Operation mode (a = IEEE 802.11a, b = IEEE 802.11b, g = IEEE 802.11g,
 # ad = IEEE 802.11ad (60 GHz); a/g options are used with IEEE 802.11n, too, to
 # specify band)

diff --git a/src/ap/ap_config.c b/src/ap/ap_config.c
index 368b2020e8e5c83a03651a3062052afe9a5cc3fd..a9e8bfac13f094737730c1954aa90252f3ed12ae 100644 (file)
--- a/src/ap/ap_config.c
+++ b/src/ap/ap_config.c
@@ -154,6 +154,8 @@ struct hostapd_config * hostapd_config_defaults(void)
        conf->rts_threshold = -1; /* use driver default: 2347 */
        conf->fragm_threshold = -1; /* user driver default: 2346 */
        conf->send_probe_response = 1;
+       /* Set to invalid value means do not add Power Constraint IE */
+       conf->local_pwr_constraint = -1;
 
        conf->wmm_ac_params[0] = ac_be;
        conf->wmm_ac_params[1] = ac_bk;
@@ -829,6 +831,12 @@ int hostapd_config_check(struct hostapd_config *conf, int full_config)
                return -1;
        }
 
+       if (full_config && conf->local_pwr_constraint != -1 &&
+           !conf->ieee80211d) {
+               wpa_printf(MSG_ERROR, "Cannot add Power Constraint element without Country element");
+               return -1;
+       }
+
        for (i = 0; i < conf->num_bss; i++) {
                if (hostapd_config_check_bss(conf->bss[i], conf, full_config))
                        return -1;

diff --git a/src/ap/ap_config.h b/src/ap/ap_config.h
index 4631ca9ede642cbcd2034bbba37a6f9681fb4ae0..26a0ef6c9ec8d77d1e607180a1b3766bf3e1a238 100644 (file)
--- a/src/ap/ap_config.h
+++ b/src/ap/ap_config.h
@@ -519,6 +519,13 @@ struct hostapd_config {
 
        int ieee80211h; /* DFS */
 
+       /*
+        * Local power constraint is an octet encoded as an unsigned integer in
+        * units of decibels. Invalid value -1 indicates that Power Constraint
+        * element will not be added.
+        */
+       int local_pwr_constraint;
+
        struct hostapd_tx_queue_params tx_queue[NUM_TX_QUEUES];
 
        /*

diff --git a/src/ap/beacon.c b/src/ap/beacon.c
index b1ebf6e3a375e15909cec470bc1e55f6d36017d2..d84af95348bcc9981ba74796a67d96f88f1ef437 100644 (file)
--- a/src/ap/beacon.c
+++ b/src/ap/beacon.c
@@ -102,6 +102,36 @@ static u8 * hostapd_eid_erp_info(struct hostapd_data *hapd, u8 *eid)
 }
 
 
+static u8 * hostapd_eid_pwr_constraint(struct hostapd_data *hapd, u8 *eid)
+{
+       u8 *pos = eid;
+
+       if (hapd->iconf->local_pwr_constraint == -1 ||
+           hapd->iface->current_mode == NULL ||
+           hapd->iface->current_mode->mode != HOSTAPD_MODE_IEEE80211A)
+               return eid;
+
+       /*
+        * A STA that is not an AP shall use a transmit power less than or
+        * equal to the local maximum transmit power level for the channel.
+        * The local maximum transmit power can be calculated from the formula:
+        * local max TX pwr = max TX pwr - local pwr constraint
+        * Where max TX pwr is maximum transmit power level specified for
+        * channel in Country element and local pwr constraint is specified
+        * for channel in this Power Constraint element.
+        */
+
+       /* Element ID */
+       *pos++ = WLAN_EID_PWR_CONSTRAINT;
+       /* Length */
+       *pos++ = 1;
+       /* Local Power Constraint */
+       *pos++ = hapd->iconf->local_pwr_constraint;
+
+       return pos;
+}
+
+
 static u8 * hostapd_eid_country_add(u8 *pos, u8 *end, int chan_spacing,
                                    struct hostapd_channel_data *start,
                                    struct hostapd_channel_data *prev)
@@ -315,6 +345,9 @@ static u8 * hostapd_gen_probe_resp(struct hostapd_data *hapd,
 
        pos = hostapd_eid_country(hapd, pos, epos - pos);
 
+       /* Power Constraint element */
+       pos = hostapd_eid_pwr_constraint(hapd, pos);
+
        /* ERP Information element */
        pos = hostapd_eid_erp_info(hapd, pos);
 
@@ -721,6 +754,9 @@ int ieee802_11_build_ap_params(struct hostapd_data *hapd,
        tailpos = hostapd_eid_country(hapd, tailpos,
                                      tail + BEACON_TAIL_BUF_SIZE - tailpos);
 
+       /* Power Constraint element */
+       tailpos = hostapd_eid_pwr_constraint(hapd, tailpos);
+
        /* ERP Information element */
        tailpos = hostapd_eid_erp_info(hapd, tailpos);