diff -r e101960f06de src/node/drop-tail-queue.cc
--- a/src/node/drop-tail-queue.cc	Thu Aug 07 11:14:32 2008 -0700
+++ b/src/node/drop-tail-queue.cc	Thu Aug 07 11:49:25 2008 -0700
@@ -87,7 +87,7 @@ DropTailQueue::DoDequeue (void)
   return p;
 }
 
-Ptr<Packet>
+Ptr<const Packet>
 DropTailQueue::DoPeek (void) const
 {
   NS_LOG_FUNCTION (this);
diff -r e101960f06de src/node/drop-tail-queue.h
--- a/src/node/drop-tail-queue.h	Thu Aug 07 11:14:32 2008 -0700
+++ b/src/node/drop-tail-queue.h	Thu Aug 07 11:49:25 2008 -0700
@@ -47,7 +47,7 @@ private:
 private:
   virtual bool DoEnqueue (Ptr<Packet> p);
   virtual Ptr<Packet> DoDequeue (void);
-  virtual Ptr<Packet> DoPeek (void) const;
+  virtual Ptr<const Packet> DoPeek (void) const;
 
 private:
   std::queue<Ptr<Packet> > m_packets;
diff -r e101960f06de src/node/queue.cc
--- a/src/node/queue.cc	Thu Aug 07 11:14:32 2008 -0700
+++ b/src/node/queue.cc	Thu Aug 07 11:49:25 2008 -0700
@@ -107,7 +107,7 @@ Queue::DequeueAll (void)
     }
 }
 
-Ptr<Packet>
+Ptr<const Packet>
 Queue::Peek (void) const
 {
   NS_LOG_FUNCTION (this);
diff -r e101960f06de src/node/queue.h
--- a/src/node/queue.h	Thu Aug 07 11:14:32 2008 -0700
+++ b/src/node/queue.h	Thu Aug 07 11:49:25 2008 -0700
@@ -68,7 +68,7 @@ public:
    * Get a copy of the item at the front of the queue without removing it
    * \return 0 if the operation was not successful; the packet otherwise.
    */
-  Ptr<Packet> Peek (void) const;
+  Ptr<const Packet> Peek (void) const;
 
   /**
    * Flush the queue.
@@ -142,7 +142,7 @@ private:
 
   virtual bool DoEnqueue (Ptr<Packet> p) = 0;
   virtual Ptr<Packet> DoDequeue (void) = 0;
-  virtual Ptr<Packet> DoPeek (void) const = 0;
+  virtual Ptr<const Packet> DoPeek (void) const = 0;
 
 protected:
   // called by subclasses to notify parent of packet drops.