wifi: APs store buffer status reports carried by QoS frames

src/wifi/model/ap-wifi-mac.cc

@@ -83,6 +83,11 @@ ApWifiMac::GetTypeId (void)
                    BooleanValue (true),
                    MakeBooleanAccessor (&ApWifiMac::m_enableNonErpProtection),
                    MakeBooleanChecker ())
+    .AddAttribute ("BsrLifetime",
+                   "Lifetime of Buffer Status Reports received from stations.",
+                   TimeValue (MilliSeconds (20)),
+                   MakeTimeAccessor (&ApWifiMac::m_bsrLifetime),
+                   MakeTimeChecker ())
   ;
   return tid;
 }
@@ -1614,4 +1619,53 @@ ApWifiMac::IncrementPollingListIterator (void)
     }
 }
 
+uint8_t
+ApWifiMac::GetBufferStatus (uint8_t tid, Mac48Address address) const
+{
+  auto it = m_bufferStatus.find (WifiAddressTidPair (address, tid));
+  if (it == m_bufferStatus.end ()
+      || it->second.timestamp + m_bsrLifetime < Simulator::Now ())
+    {
+      return 255;
+    }
+  return it->second.value;
+}
+
+void
+ApWifiMac::SetBufferStatus (uint8_t tid, Mac48Address address, uint8_t size)
+{
+  if (size == 255)
+    {
+      // no point in storing an unspecified size
+      m_bufferStatus.erase (WifiAddressTidPair (address, tid));
+    }
+  else
+    {
+      m_bufferStatus[WifiAddressTidPair (address, tid)] = {size, Simulator::Now ()};
+    }
+}
+
+uint8_t
+ApWifiMac::GetMaxBufferStatus (Mac48Address address) const
+{
+  uint8_t maxSize = 0;
+  bool found = false;
+
+  for (uint8_t tid = 0; tid < 8; tid++)
+    {
+      uint8_t size = GetBufferStatus (tid, address);
+      if (size != 255)
+        {
+          maxSize = std::max (maxSize, size);
+          found = true;
+        }
+    }
+
+  if (found)
+    {
+      return maxSize;
+    }
+  return 255;
+}
+
 } //namespace ns3

src/wifi/model/ap-wifi-mac.h

@@ -24,6 +24,7 @@
 #define AP_WIFI_MAC_H
 
 #include "infrastructure-wifi-mac.h"
+#include <unordered_map>
 
 namespace ns3 {
 
@@ -121,6 +122,42 @@ public:
    */
   int64_t AssignStreams (int64_t stream);
 
+  /**
+   * Return the value of the Queue Size subfield of the last QoS Data or QoS Null
+   * frame received from the station with the given MAC address and belonging to
+   * the given TID.
+   *
+   * The Queue Size value is the total size, rounded up to the nearest multiple
+   * of 256 octets and expressed in units of 256 octets, of all  MSDUs and A-MSDUs
+   * buffered at the STA (excluding the MSDU or A-MSDU of the present QoS Data frame).
+   * A queue size value of 254 is used for all sizes greater than 64 768 octets.
+   * A queue size value of 255 is used to indicate an unspecified or unknown size.
+   * See Section 9.2.4.5.6 of 802.11-2016
+   *
+   * \param tid the given TID
+   * \param address the given MAC address
+   * \return the value of the Queue Size subfield
+   */
+  uint8_t GetBufferStatus (uint8_t tid, Mac48Address address) const;
+  /**
+   * Store the value of the Queue Size subfield of the last QoS Data or QoS Null
+   * frame received from the station with the given MAC address and belonging to
+   * the given TID.
+   *
+   * \param tid the given TID
+   * \param address the given MAC address
+   * \param size the value of the Queue Size subfield
+   */
+  void SetBufferStatus (uint8_t tid, Mac48Address address, uint8_t size);
+  /**
+   * Return the maximum among the values of the Queue Size subfield of the last
+   * QoS Data or QoS Null frames received from the station with the given MAC address
+   * and belonging to any TID.
+   *
+   * \param address the given MAC address
+   * \return the maximum among the values of the Queue Size subfields
+   */
+  uint8_t GetMaxBufferStatus (Mac48Address address) const;
 
 private:
   void Receive (Ptr<WifiMacQueueItem> mpdu);
@@ -298,6 +335,11 @@ private:
   std::list<Mac48Address> m_cfPollingList;   //!< List of all PCF stations currently associated to the AP
   std::list<Mac48Address>::iterator m_itCfPollingList; //!< Iterator to the list of all PCF stations currently associated to the AP
   bool m_enableNonErpProtection;             //!< Flag whether protection mechanism is used or not when non-ERP STAs are present within the BSS
+  Time m_bsrLifetime;                        //!< Lifetime of Buffer Status Reports
+  //!< store value and timestamp for each Buffer Status Report
+  typedef struct { uint8_t value; Time timestamp; } bsrType;
+  //!< Per (MAC address, TID) buffer status reports
+  std::unordered_map<WifiAddressTidPair, bsrType, WifiAddressTidHash> m_bufferStatus;
 };
 
 } //namespace ns3

src/wifi/model/qos-utils.cc

@@ -28,6 +28,27 @@
 
 namespace ns3 {
 
+std::size_t
+WifiAddressTidHash::operator()(const WifiAddressTidPair& addressTidPair) const
+{
+  uint8_t buffer[7];
+  addressTidPair.first.CopyTo (buffer);
+  buffer[6] = addressTidPair.second;
+
+  std::string s (buffer, buffer + 7);
+  return std::hash<std::string>{} (s);
+}
+
+std::size_t
+WifiAddressHash::operator()(const Mac48Address& address) const
+{
+  uint8_t buffer[6];
+  address.CopyTo (buffer);
+
+  std::string s (buffer, buffer + 6);
+  return std::hash<std::string>{} (s);
+}
+
 AcIndex
 QosUtilsMapTidToAc (uint8_t tid)
 {

src/wifi/model/qos-utils.h

@@ -28,6 +28,25 @@ namespace ns3 {
 class Packet;
 class WifiMacHeader;
 class QueueItem;
+class Mac48Address;
+
+typedef std::pair<Mac48Address, uint8_t> WifiAddressTidPair;  //!< (MAC address, TID) pair
+
+/**
+ * Function object to compute the hash of a (MAC address, TID) pair
+ */
+struct WifiAddressTidHash
+{
+  std::size_t operator() (const WifiAddressTidPair& addressTidPair) const;
+};
+
+/**
+ * Function object to compute the hash of a MAC address
+ */
+struct WifiAddressHash
+{
+  std::size_t operator() (const Mac48Address& address) const;
+};
 
 /**
  * \ingroup wifi