wifi: (fixes #2352) Add 'drop oldest' drop policy to WifiMacQueue (patch from Ali Rostami)

AUTHORS

@@ -189,3 +189,4 @@ He Wu (mdzz@u.washington.edu)
 Yoshihiko Yazawa (yoshiyaz@gmail.com)
 Dizhi Zhou (dizhi.zhou@gmail.com)
 Gaurav Sathe (gaurav.sathe@tcs.com)
+Ali Rostami (a.rostami@rutgers.edu)

RELEASE_NOTES

@@ -39,6 +39,7 @@ Bugs fixed
 - Bug 2329 - TCP Veno implementation
 - Bug 2333 - TCP Scalable implementation
 - Bug 2347 - LrWpan Ascii traces are hooked to the wrong traces.
+- Bug 2352 - Add 'drop oldest' drop policy to WifiMacQueue
 - Bug 2353 - TCP Vegas implementation
 - Bug 2375 - Flowmonitor parse crashes when no pkt is received
 - Bug 2377 - SocketIpTosTag and SocketIpv6TclassTag may be added twice in UDP

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

@@ -23,6 +23,7 @@
 #include "ns3/simulator.h"
 #include "ns3/packet.h"
 #include "ns3/uinteger.h"
+#include "ns3/enum.h"
 #include "wifi-mac-queue.h"
 #include "qos-blocked-destinations.h"
 
@@ -54,6 +55,11 @@ WifiMacQueue::GetTypeId (void)
                    TimeValue (MilliSeconds (500.0)),
                    MakeTimeAccessor (&WifiMacQueue::m_maxDelay),
                    MakeTimeChecker ())
+    .AddAttribute ("DropPolicy", "Upon enqueue with full queue, drop oldest (DropOldest) or newest (DropNewest) packet",
+                   EnumValue (DROP_NEWEST),
+                   MakeEnumAccessor (&WifiMacQueue::m_dropPolicy),
+                   MakeEnumChecker (WifiMacQueue::DROP_OLDEST, "DropOldest",
+                                    WifiMacQueue::DROP_NEWEST, "DropNewest"))
   ;
   return tid;
 }
@@ -98,7 +104,15 @@ WifiMacQueue::Enqueue (Ptr<const Packet> packet, const WifiMacHeader &hdr)
   Cleanup ();
   if (m_size == m_maxSize)
     {
-      return;
+      if (m_dropPolicy == DROP_NEWEST)
+        {
+          return;
+        }
+      else if (m_dropPolicy == DROP_OLDEST)
+        {
+          m_queue.pop_front ();
+          m_size--;
+        }
     }
   Time now = Simulator::Now ();
   m_queue.push_back (Item (packet, hdr, now));

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

@@ -55,6 +55,12 @@ public:
   WifiMacQueue ();
   ~WifiMacQueue ();
 
+  enum DropPolicy
+  {
+    DROP_NEWEST,
+    DROP_OLDEST
+  };
+
   /**
    * Set the maximum queue size.
    *
@@ -271,6 +277,7 @@ protected:
   uint32_t m_size;     //!< Current queue size
   uint32_t m_maxSize;  //!< Queue capacity
   Time m_maxDelay;     //!< Time to live for packets in the queue
+  enum DropPolicy m_dropPolicy; //!< Drop behavior of queue
 };
 
 } //namespace ns3