aodv: (fixes #2517, 2911) Binary exponential backoff problem

RELEASE_NOTES

@@ -32,6 +32,7 @@ New user-visible features
 
 Bugs fixed
 ----------
+- Bug 2911 - aodv:  Binary exponential backoff can become unlimited
 - Bug 2901 - Add CommandLine::Parse (const std::vector<std::string>> args)
 - Bug 2461 - CommandLine should handle non-option arguments
 - Bug 2801 - FdNetDevice device MTU is not set correctly

scratch/scratch-simulator.cc

@@ -25,6 +25,10 @@ main (int argc, char *argv[])
 {
   NS_LOG_UNCOND ("Scratch Simulator");
 
+  Time retry = std::pow<uint16_t> (2, 3 - 1) * Seconds (3);
+  uint16_t backoffFactor  = 3 - 1;
+  Time retry2 = Seconds (3) * (1 << backoffFactor);
+  std::cout << "Retry " << retry.GetSeconds () << " " << retry2.GetSeconds () << std::endl;
   Simulator::Run ();
   Simulator::Destroy ();
 }

src/aodv/model/aodv-routing-protocol.cc

@@ -1100,8 +1100,10 @@ RoutingProtocol::ScheduleRreqRetry (Ipv4Address dst)
     }
   else
     {
-      // Binary exponential backoff
-      retry = std::pow<uint16_t> (2, rt.GetRreqCnt () - 1) * m_netTraversalTime;
+      NS_ABORT_MSG_UNLESS (rt.GetRreqCnt () > 0, "Unexpected value for GetRreqCount ()");
+      uint16_t backoffFactor = rt.GetRreqCnt () - 1;
+      NS_LOG_LOGIC ("Applying binary exponential backoff factor " << backoffFactor);
+      retry = m_netTraversalTime * (1 << backoffFactor);
     }
   m_addressReqTimer[dst].Schedule (retry);
   NS_LOG_LOGIC ("Scheduled RREQ retry in " << retry.GetSeconds () << " seconds");