--- a/src/contrib/delay-jitter-estimation.cc	Wed Dec 19 13:22:55 2007 +0100
+++ b/src/contrib/delay-jitter-estimation.cc	Wed Dec 19 13:24:30 2007 +0100
@@ -75,7 +75,10 @@
   TimestampTag tag;
   bool found;
   found = packet->PeekTag (tag);
-  NS_ASSERT (found);
+  if (!found)
+    {
+      return;
+    }
   tag.GetTxTime ();
 
   Time delta = (Simulator::Now () - m_previousRx) - (tag.GetTxTime () - m_previousRxTx);