Implementing base support for TCP-style window-based limiting on per-FIB-prefix and per-face granularity

Currently, limits are supported only by ndn::fw::Limits forwarding
strategy and only at the very basic (not fully tested) level.
diff --git a/utils/ndn-limits.h b/utils/ndn-limits.h
new file mode 100644
index 0000000..b8ca50d
--- /dev/null
+++ b/utils/ndn-limits.h
@@ -0,0 +1,106 @@
+/* -*- Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil -*- */
+/*
+ * Copyright (c) 2011 University of California, Los Angeles
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Author: Alexander Afanasyev <alexander.afanasyev@ucla.edu>
+ */
+
+#ifndef _NDN_LIMITS_H_
+#define	_NDN_LIMITS_H_
+
+#include "ns3/ptr.h"
+#include "ns3/object.h"
+#include "ns3/nstime.h"
+#include "ns3/traced-value.h"
+
+namespace ns3 {
+namespace ndn {
+
+/**
+ * \ingroup ndn
+ * \brief Structure to manage limits for outstanding interests
+ */
+class Limits :
+    public Object
+{
+public:
+  static TypeId
+  GetTypeId ();
+  
+  /**
+   * \brief Constructor
+   * \param prefix smart pointer to the prefix for the FIB entry
+   */
+  Limits ()
+  : m_maxLimit (0)
+  , m_curMaxLimit (0)
+  , m_outstanding (0)
+  { }
+ 
+  /**
+   * Set per-prefix limit
+   */
+  void
+  SetMaxLimit (uint32_t max);
+
+  /**
+   * Decay current limit (exponential decaying)
+   */
+  void
+  DecayCurrentLimit ();
+
+  /**
+   * Increase current limit (additive increase)
+   */
+  void
+  IncreaseLimit ();
+
+  /**
+   * Decrease current limit (multiplicative decrease)
+   */
+  void
+  DecreaseLimit ();
+
+  ////////////////////////////////////////////////////////////////////////////
+  ////////////////////////////////////////////////////////////////////////////
+  ////////////////////////////////////////////////////////////////////////////
+  
+  /**
+   * Check if new interest can be send out, if yes, number of outstanding will be increased
+   */
+  bool
+  IsBelowLimit ();
+
+  /**
+   * Remove outstanding interests
+   */
+  void
+  RemoveOutstanding ();
+  
+public:
+  uint32_t m_maxLimit;
+  
+  TracedValue< double >   m_curMaxLimit;
+  TracedValue< uint32_t > m_outstanding;
+
+  Time     m_lastDecrease;
+  Time     m_lastDecay;
+};
+
+} // namespace ndn
+} // namespace ns3
+
+#endif // _NDN_LIMITS_H_