diff -r 4ddcca845f07 src/internet-stack/tcp-socket-impl.cc
--- a/src/internet-stack/tcp-socket-impl.cc	Fri Nov 28 17:42:10 2008 +0100
+++ b/src/internet-stack/tcp-socket-impl.cc	Mon Dec 01 10:20:14 2008 -0500
@@ -1260,7 +1260,10 @@ void TcpSocketImpl::NewRx (Ptr<Packet> p
   }
   else
   {
-    m_delAckEvent = Simulator::Schedule (m_delAckTimeout, &TcpSocketImpl::DelAckTimeout, this);
+    if (m_delAckEvent.IsExpired())
+    {
+      m_delAckEvent = Simulator::Schedule (m_delAckTimeout, &TcpSocketImpl::DelAckTimeout, this);
+    }
   }
 }