diff --git a/samples/main-simulator.cc b/samples/main-simulator.cc
index 89f043702..c1e43c332 100644
--- a/samples/main-simulator.cc
+++ b/samples/main-simulator.cc
@@ -15,22 +15,22 @@ private:
 void 
 MyModel::Start (void)
 {
-    Simulator::Schedule (Time::RelS (10.0), 
+    Simulator::Schedule (Now () + Seconds (10.0), 
                          &MyModel::DealWithEvent, 
-                         this, Simulator::Now ().S ());
+                         this, Simulator::Now ().ApproximateToSeconds ());
 }
 void
 MyModel::DealWithEvent (double value)
 {
-    std::cout << "Member method received event at " << Simulator::Now ().S () << 
-        "s started at " << value << "s" << std::endl;
+    std::cout << "Member method received event at " << Simulator::Now ().ApproximateToSeconds () 
+              << "s started at " << value << "s" << std::endl;
 }
 
 static void 
 random_function (MyModel *model)
 {
     std::cout << "random function received event at " << 
-        Simulator::Now ().S () << "s" << std::endl;
+        Simulator::Now ().ApproximateToSeconds () << "s" << std::endl;
     model->Start ();
 }
 
@@ -39,7 +39,7 @@ int main (int argc, char *argv[])
 {
     MyModel model;
 
-    Simulator::Schedule (Time::AbsS (10.0), &random_function, &model);
+    Simulator::Schedule (Now () + Seconds (10.0), &random_function, &model);
 
     Simulator::Run ();
 
diff --git a/src/common/pcap-writer.cc b/src/common/pcap-writer.cc
index 518737b3b..a835adc55 100644
--- a/src/common/pcap-writer.cc
+++ b/src/common/pcap-writer.cc
@@ -69,7 +69,7 @@ PcapWriter::WritePacket (Packet const packet)
 {
     if (m_writer != 0) 
       {
-        uint64_t current = Simulator::Now ().Us ();
+        uint64_t current = Simulator::Now ().ApproximateToMicroSeconds ();
         uint64_t s = current / 1000000;
         uint64_t us = current % 1000000;
         Write32 (s & 0xffffffff);
diff --git a/src/simulator/nstime.h b/src/simulator/nstime.h
index fcc407718..4cd8c54e6 100644
--- a/src/simulator/nstime.h
+++ b/src/simulator/nstime.h
@@ -32,78 +32,68 @@ namespace ns3 {
  * is expected to expire (see ns3::Simulator::schedule).
  */
 class Time {
-public:
+ public:
     Time (Time const &o);
     Time &operator = (Time const &o);
-    /**
-     * \returns the time stored in this
-     *          instance as seconds.
-     */
-    double S (void) const;
-    /**
-     * \returns the time stored in this
-     *          instance as microseconds.
-     */
-    uint64_t Us (void) const;
-    /**
-     * \returns the time stored in this
-     *          instance as nanoseconds.
-     */
-    uint64_t Ns (void) const;
-    /**
-     * \returns true if this instance represents
-     *          the "destroy" time.
-     */
-    bool IsDestroy (void) const;
-    /**
-     * \param s absolute time in seconds
-     * \returns a constructed Time object
-     */
-    static Time AbsS (double s);
-    /**
-     * \param us absolute time in microseconds
-     * \returns a constructed Time object
-     */
-    static Time AbsUs (uint64_t us);
-    /**
-     * \param ns absolute time in nanoseconds
-     * \returns a constructed Time object
-     */
-    static Time AbsNs (uint64_t ns);
-    /**
-     * \param s relative time in seconds
-     * \returns a constructed Time object
-     */
-    static Time RelS (double s);
-    /**
-     * \param us relative time in microseconds
-     * \returns a constructed Time object
-     */
-    static Time RelUs (uint64_t us);
-    /**
-     * \param ns relative time in nanoseconds
-     * \returns a constructed Time object
-     */
-    static Time RelNs (uint64_t ns);
-    /**
-     * \returns a constructed Time object which represents
-     *          the current simulation time
-     */
-    static Time Now (void);
-    /**
-     * \returns a constructed Time object which represents
-     *          the current "destroy" simulation time, that
-     *          is, the time when Simulator::destroy is
-     *          invoked by the user.
-     */
-    static Time Destroy (void);
-private:
-    Time (uint64_t ns);
+
+    bool IsNegative (void) const;
+    bool IsPositive (void) const;
+    bool IsStrictlyNegative (void) const;
+    bool IsStrictlyPositive (void) const;
+    bool IsZero (void) const;
+
+    Time operator += (Time const &o);
+    Time operator -= (Time const &o);
+
+    double ApproximateToSeconds (void) const;
+    uint64_t ApproximateToMilliSeconds (void) const;  
+    uint64_t ApproximateToMicroSeconds (void) const;
+    uint64_t ApproximateToNanoSeconds (void) const;
+  
+    /* semi-public method. */
+    uint64_t Get (void) const;
+ protected:
+    Time (int64_t ns);
+ private:
     Time ();
-    uint64_t m_ns;
-    bool m_isDestroy;
+    int64_t m_ns;
 };
 
+Time operator + (Time const &lhs, Time const &rhs);
+Time operator - (Time const &lhs, Time const &rhs);
+bool operator == (Time const &lhs, Time const &rhs);
+bool operator != (Time const &lhs, Time const &rhs);
+bool operator <  (Time const &lhs, Time const &rhs);
+bool operator <= (Time const &lhs, Time const &rhs);
+bool operator >  (Time const &lhs, Time const &rhs);
+bool operator >= (Time const &lhs, Time const &rhs);
+
+
+class Now : public Time {
+public:
+    Now ();
+};
+
+class Seconds : public Time 
+{
+public:
+    Seconds (double s);
+};
+class MilliSeconds : public Time 
+{
+public:
+    MilliSeconds (int32_t ms);
+};
+class MicroSeconds : public Time 
+{
+public:
+    MicroSeconds (int32_t us);
+};
+class NanoSeconds : public Time 
+{
+public:
+    NanoSeconds (int64_t ns);
+};
 
 }; // namespace ns3
 
diff --git a/src/simulator/simulator.cc b/src/simulator/simulator.cc
index 348604ee6..ece48ad18 100644
--- a/src/simulator/simulator.cc
+++ b/src/simulator/simulator.cc
@@ -67,6 +67,7 @@ public:
 
 private:
     void ProcessOneEvent (void);
+    uint64_t NextNs (void) const;
 
     typedef std::list<std::pair<EventImpl *,uint32_t> > Events;
     Events m_destroy;
@@ -138,20 +139,26 @@ SimulatorPrivate::IsFinished (void) const
 {
     return m_events->IsEmpty ();
 }
-Time
-SimulatorPrivate::Next (void) const
+uint64_t
+SimulatorPrivate::NextNs (void) const
 {
     assert (!m_events->IsEmpty ());
     Scheduler::EventKey nextKey = m_events->PeekNextKey ();
-    return Time::AbsNs (nextKey.m_ns);
+    return nextKey.m_ns;
+}
+Time
+SimulatorPrivate::Next (void) const
+{
+    return NanoSeconds (NextNs ());
 }
 
 
 void
 SimulatorPrivate::Run (void)
 {
+
     while (!m_events->IsEmpty () && !m_stop && 
-           (m_stopAt == 0 || m_stopAt > Next ().Ns ())) 
+           (m_stopAt == 0 || m_stopAt > NextNs ())) 
       {
         ProcessOneEvent ();
       }
@@ -167,29 +174,17 @@ SimulatorPrivate::Stop (void)
 void 
 SimulatorPrivate::StopAt (Time const &at)
 {
-    m_stopAt = at.Ns ();
+    m_stopAt = at.ApproximateToNanoSeconds ();
 }
 EventId
 SimulatorPrivate::Schedule (Time const &time, EventImpl *event)
 {
-    if (time.IsDestroy ()) 
-      {
-        m_destroy.push_back (std::make_pair (event, m_uid));
-        if (m_logEnable) 
-          {
-            m_log << "id " << m_currentUid << " " << Now ().Ns () << " "
-                  << m_uid << std::endl;
-          }
-        m_uid++;
-        //XXX
-        return EventId ();
-      }
-    assert (time.Ns () >= Now ().Ns ());
-    Scheduler::EventKey key = {time.Ns (), m_uid};
+    assert (time.ApproximateToNanoSeconds () >= m_currentNs);
+    Scheduler::EventKey key = {time.ApproximateToNanoSeconds (), m_uid};
     if (m_logEnable) 
       {
-        m_log << "i "<<m_currentUid<<" "<<Now ().Ns ()<<" "
-              <<m_uid<<" "<<time.Ns () << std::endl;
+        m_log << "i "<<m_currentUid<<" "<<m_currentNs<<" "
+              <<m_uid<<" "<<time.ApproximateToNanoSeconds () << std::endl;
       }
     m_uid++;
     return m_events->Insert (event, key);
@@ -197,7 +192,7 @@ SimulatorPrivate::Schedule (Time const &time, EventImpl *event)
 Time
 SimulatorPrivate::Now (void) const
 {
-    return Time::AbsNs (m_currentNs);
+    return NanoSeconds (m_currentNs);
 }
 
 void
@@ -208,7 +203,7 @@ SimulatorPrivate::Remove (EventId ev)
     delete impl;
     if (m_logEnable) 
       {
-        m_log << "r " << m_currentUid << " " << Now ().Ns () << " "
+        m_log << "r " << m_currentUid << " " << m_currentNs << " "
               << key.m_uid << " " << key.m_ns << std::endl;
       }
 }
@@ -225,7 +220,7 @@ bool
 SimulatorPrivate::IsExpired (EventId ev)
 {
     if (ev.GetEventImpl () != 0 &&
-        ev.GetNs () <= Now ().Ns () &&
+        ev.GetNs () <= m_currentNs &&
         ev.GetUid () < m_currentUid) 
       {
         return false;
@@ -405,6 +400,7 @@ public:
     virtual ~SimulatorTests ();
     virtual bool RunTests (void);
 private:
+    uint64_t NowUs ();
     bool RunOneTest (void);
     void A (int a);
     void B (int b);
@@ -422,6 +418,12 @@ SimulatorTests::SimulatorTests ()
 {}
 SimulatorTests::~SimulatorTests ()
 {}
+uint64_t
+SimulatorTests::NowUs (void)
+{
+    uint64_t ns = Now ().ApproximateToNanoSeconds ();
+    return ns / 1000;
+}  
 void
 SimulatorTests::A (int a)
 {
@@ -430,7 +432,7 @@ SimulatorTests::A (int a)
 void
 SimulatorTests::B (int b)
 {
-    if (b != 2 || Simulator::Now ().Us () != 11) 
+    if (b != 2 || NowUs () != 11) 
       {
         m_b = false;
       } 
@@ -439,7 +441,7 @@ SimulatorTests::B (int b)
         m_b = true;
       }
     Simulator::Remove (m_idC);
-    Simulator::Schedule (Time::RelUs (10), &SimulatorTests::D, this, 4);
+    Simulator::Schedule (Now () + MicroSeconds (10), &SimulatorTests::D, this, 4);
 }
 void
 SimulatorTests::C (int c)
@@ -449,7 +451,7 @@ SimulatorTests::C (int c)
 void
 SimulatorTests::D (int d)
 {
-    if (d != 4 || Simulator::Now ().Us () != (11+10)) 
+    if (d != 4 || NowUs () != (11+10)) 
       {
         m_d = false;
       } 
@@ -467,9 +469,9 @@ SimulatorTests::RunOneTest (void)
     m_c = true;
     m_d = false;
 
-    EventId a = Simulator::Schedule (Time::AbsUs (10), &SimulatorTests::A, this, 1);
-    Simulator::Schedule (Time::AbsUs (11), &SimulatorTests::B, this, 2);
-    m_idC = Simulator::Schedule (Time::AbsUs (12), &SimulatorTests::C, this, 3);
+    EventId a = Simulator::Schedule (Now () + MicroSeconds (10), &SimulatorTests::A, this, 1);
+    Simulator::Schedule (Now () + MicroSeconds (11), &SimulatorTests::B, this, 2);
+    m_idC = Simulator::Schedule (Now () + MicroSeconds (12), &SimulatorTests::C, this, 3);
 
     Simulator::Cancel (a);
     Simulator::Run ();
diff --git a/src/simulator/time.cc b/src/simulator/time.cc
index eb6853a7e..c039c99ca 100644
--- a/src/simulator/time.cc
+++ b/src/simulator/time.cc
@@ -24,94 +24,151 @@
 namespace ns3 {
 
 Time::Time ()
-    : m_ns (0),
-      m_isDestroy (true)
+    : m_ns (0)
 {}
 Time::Time (Time const &o)
-    : m_ns (o.m_ns),
-      m_isDestroy (o.m_isDestroy)
+    : m_ns (o.m_ns)
 {}
 Time &
 Time::operator = (Time const &o)
 {
-    m_ns = o.m_ns;
-    m_isDestroy = o.m_isDestroy;
-    return *this;
+  m_ns = o.m_ns;
+  return *this;
 }
-Time::Time (uint64_t ns)
-    : m_ns (ns),
-      m_isDestroy (false)
+Time::Time (int64_t ns)
+    : m_ns (ns)
 {}
 
+
+bool 
+Time::IsNegative (void) const
+{
+  return m_ns <= 0;
+}
+  
+bool 
+Time::IsPositive (void) const
+{
+  return m_ns >= 0;
+}
+  
+bool 
+Time::IsStrictlyNegative (void) const
+{
+  return m_ns < 0;
+}
+bool 
+Time::IsStrictlyPositive (void) const
+{
+  return m_ns > 0;
+}
+bool 
+Time::IsZero (void) const
+{
+  return m_ns == 0;
+}
+
+Time 
+Time::operator += (Time const &o)
+{
+  m_ns += o.m_ns;
+  return *this;
+}
+  
+Time 
+Time::operator -= (Time const &o)
+{
+  m_ns -= o.m_ns;
+  return *this;
+}
+
 double 
-Time::S (void) const
+Time::ApproximateToSeconds (void) const
 {
-    double ns = m_ns;
-    ns /= 1000000000;
-    return ns;
+  double s = m_ns;
+  s /= 1000000000;
+  return s;
 }
 uint64_t 
-Time::Us (void) const
+Time::ApproximateToMilliSeconds (void) const
 {
-    uint64_t us = m_ns / 1000;
-    return us;
+  uint64_t ms = m_ns;
+  ms /= 1000000;
+  return ms;
 }
-
 uint64_t 
-Time::Ns (void) const
+Time::ApproximateToMicroSeconds (void) const
 {
-    return m_ns;
+  uint64_t us = m_ns;
+  us /= 1000;
+  return us;
+}
+uint64_t 
+Time::ApproximateToNanoSeconds (void) const
+{
+  return m_ns;
 }
 
-bool
-Time::IsDestroy (void) const
+
+/* To decrease the number of keystrokes
+ */
+static uint64_t 
+GetNs (Time const &time)
 {
-    return m_isDestroy;
+  return time.ApproximateToNanoSeconds ();
 }
 
-Time 
-Time::AbsS (double s)
+Time operator + (Time const &lhs, Time const &rhs)
 {
-    int64_t ns = (int64_t)(s * 1000000000.0);
-    return Time (ns);
+  return NanoSeconds (GetNs (lhs) + GetNs (rhs));
+}  
+Time operator - (Time const &lhs, Time const &rhs)
+{
+  return NanoSeconds (GetNs (lhs) - GetNs (rhs));
 }
-Time 
-Time::AbsUs (uint64_t us)
+bool operator == (Time const &lhs, Time const &rhs)
 {
-    int64_t ns = us * 1000;
-    return Time (ns);
-}
-Time 
-Time::AbsNs (uint64_t ns)
-{
-    return Time (ns);
-}
-Time 
-Time::RelS (double s)
-{
-    int64_t ns = (int64_t)(s * 1000000000.0);
-    return Time (Simulator::Now ().Ns () + ns);
-}
-Time 
-Time::RelUs (uint64_t us)
-{
-    return Time (Simulator::Now ().Ns () + us * 1000);
-}
-Time 
-Time::RelNs (uint64_t ns)
-{
-    return Time (Simulator::Now ().Ns () + ns);
+  return GetNs (lhs) == GetNs (rhs);
 }
 
-Time 
-Time::Now (void)
+bool operator != (Time const &lhs, Time const &rhs)
 {
-    return Time (Simulator::Now ().Ns ());
+  return GetNs (lhs) != GetNs (rhs);
 }
-Time 
-Time::Destroy (void)
+bool operator <  (Time const &lhs, Time const &rhs)
 {
-    return Time ();
+  return GetNs (lhs) < GetNs (rhs);
 }
+bool operator <= (Time const &lhs, Time const &rhs)
+{
+  return GetNs (lhs) <= GetNs (rhs);
+}
+bool operator >  (Time const &lhs, Time const &rhs)
+{
+  return GetNs (lhs) > GetNs (rhs);
+}
+bool operator >= (Time const &lhs, Time const &rhs)
+{
+  return GetNs (lhs) >= GetNs (rhs);
+}
+
+Now::Now ()
+    : Time (Simulator::Now ())
+{}
+Seconds::Seconds (double s)
+    : Time ((int64_t)(s * 1000000000))
+{}
+MilliSeconds::MilliSeconds (int32_t ms)
+    : Time ((int64_t)(ms * 1000000))
+{}
+MicroSeconds::MicroSeconds (int32_t us)
+    : Time ((int64_t)(us * 1000))
+{}
+NanoSeconds::NanoSeconds (int64_t ns)
+    : Time (ns)
+{}
+  
+
+
 
 }; // namespace ns3
diff --git a/utils/bench-simulator.cc b/utils/bench-simulator.cc
index fe37a2438..de0dfec31 100644
--- a/utils/bench-simulator.cc
+++ b/utils/bench-simulator.cc
@@ -73,7 +73,7 @@ Bench::RunBench (void)
     time.Start ();
     for (std::vector<uint64_t>::const_iterator i = m_distribution.begin ();
          i != m_distribution.end (); i++) {
-        Simulator::Schedule (Time::AbsNs (*i), &Bench::Cb, this);
+        Simulator::Schedule (Now () + NanoSeconds (*i), &Bench::Cb, this);
     }
     init = time.End ();
 
@@ -103,9 +103,9 @@ Bench::Cb (void)
         m_current = m_distribution.begin ();
     }
     if (gDebug) {
-        std::cerr << "event at " << Simulator::Now ().S () << "s" << std::endl;
+        std::cerr << "event at " << Simulator::Now ().ApproximateToSeconds () << "s" << std::endl;
     }
-    Simulator::Schedule (Time::AbsNs (*m_current), &Bench::Cb, this);
+    Simulator::Schedule (Now () + NanoSeconds (*m_current), &Bench::Cb, this);
     m_current++;
     m_n++;
 }