diff --git a/src/internet/model/tcp-socket-base.cc b/src/internet/model/tcp-socket-base.cc
index 66a49b9fd..b72dfc32c 100644
--- a/src/internet/model/tcp-socket-base.cc
+++ b/src/internet/model/tcp-socket-base.cc
@@ -138,6 +138,10 @@ TcpSocketBase::GetTypeId (void)
                      "TCP state",
                      MakeTraceSourceAccessor (&TcpSocketBase::m_state),
                      "ns3::TcpStatesTracedValueCallback")
+    .AddTraceSource ("AckState",
+                     "TCP ACK machine state",
+                     MakeTraceSourceAccessor (&TcpSocketBase::m_ackState),
+                     "ns3::TcpAckStatesTracedValueCallback")
     .AddTraceSource ("RWND",
                      "Remote side's flow control window",
                      MakeTraceSourceAccessor (&TcpSocketBase::m_rWnd),
@@ -190,7 +194,8 @@ TcpSocketBase::TcpSocketBase (void)
     m_sndScaleFactor (0),
     m_rcvScaleFactor (0),
     m_timestampEnabled (true),
-    m_timestampToEcho (0)
+    m_timestampToEcho (0),
+    m_ackState (OPEN)
 
 {
   NS_LOG_FUNCTION (this);
@@ -237,7 +242,8 @@ TcpSocketBase::TcpSocketBase (const TcpSocketBase& sock)
     m_sndScaleFactor (sock.m_sndScaleFactor),
     m_rcvScaleFactor (sock.m_rcvScaleFactor),
     m_timestampEnabled (sock.m_timestampEnabled),
-    m_timestampToEcho (sock.m_timestampToEcho)
+    m_timestampToEcho (sock.m_timestampToEcho),
+    m_ackState (sock.m_ackState)
 
 {
   NS_LOG_FUNCTION (this);
@@ -2784,6 +2790,13 @@ TcpSocketBase::GetRxBuffer (void) const
   return m_rxBuffer;
 }
 
+const char* const
+TcpSocketBase::TcpAckStateName[TcpSocketBase::LAST_ACKSTATE] =
+{
+  "OPEN", "DISORDER", "CWR", "RECOVERY",
+  "LOSS"
+};
+
 
 //RttHistory methods
 RttHistory::RttHistory (SequenceNumber32 s, uint32_t c, Time t)
diff --git a/src/internet/model/tcp-socket-base.h b/src/internet/model/tcp-socket-base.h
index 20627d55d..6566aa163 100644
--- a/src/internet/model/tcp-socket-base.h
+++ b/src/internet/model/tcp-socket-base.h
@@ -166,6 +166,40 @@ public:
    */
   Ptr<TcpRxBuffer> GetRxBuffer (void) const;
 
+  /**
+   * \brief Definition of the ACK state machine
+   *
+   * The design of this state machine is taken from Linux v4.0, but it has been
+   * maintained in the Linux mainline from ages. It basically avoids to maintain
+   * a lot of boolean variables, and it allows to check the transitions from
+   * different algorithm in a cleaner way.
+   *
+   * These states represent the situation from a congestion control point of view:
+   * in fact, apart the OPEN state, the other states represent a situation in
+   * which there is a congestion, and different actions should be taken,
+   * depending on the case.
+   *
+   * \see ReceivedAck
+   * \see Retransmit
+   */
+  typedef enum
+  {
+    OPEN,        /**< Normal state, no dubious events */
+    DISORDER,    /**< In all the respects it is "Open",
+                  *  but requires a bit more attention. It is entered when
+                  *  we see some SACKs or dupacks. It is split of "Open" */
+    CWR,         /**< cWnd was reduced due to some Congestion Notification event.
+                  *  It can be ECN, ICMP source quench, local device congestion.
+                  *  Not used in NS-3 right now. */
+    RECOVERY,     /**< CWND was reduced, we are fast-retransmitting. */
+    LOSS,         /**< CWND was reduced due to RTO timeout or SACK reneging. */
+    LAST_ACKSTATE /**< Used only in debug messages */
+  } TcpAckState_t;
+
+  /**
+   * \brief Literal names of TCP states for use in log messages
+   */
+  static const char* const TcpAckStateName[TcpSocketBase::LAST_ACKSTATE];
 
   // Necessary implementations of null functions from ns3::Socket
   virtual enum SocketErrno GetErrno (void) const;    // returns m_errno
@@ -774,8 +808,20 @@ protected:
   uint32_t m_timestampToEcho;     //!< Timestamp to echo
 
   EventId m_sendPendingDataEvent; //!< micro-delay event to send pending data
+
+  TracedValue<TcpAckState_t> m_ackState; //!< State in the ACK state machine
 };
 
+/**
+ * \ingroup tcp
+ * TracedValue Callback signature for TcpAckState_t
+ *
+ * \param [in] oldValue original value of the traced variable
+ * \param [in] newValue new value of the traced variable
+ */
+typedef void (* TcpAckStatesTracedValueCallback)(const TcpSocketBase::TcpAckState_t oldValue,
+                                                 const TcpSocketBase::TcpAckState_t newValue);
+
 } // namespace ns3
 
 #endif /* TCP_SOCKET_BASE_H */