diff --git a/src/internet/model/tcp-tx-buffer.cc b/src/internet/model/tcp-tx-buffer.cc
index eb14b1d7f..636cc5c73 100644
--- a/src/internet/model/tcp-tx-buffer.cc
+++ b/src/internet/model/tcp-tx-buffer.cc
@@ -670,6 +670,76 @@ TcpTxBuffer::Update (const TcpOptionSack::SackList &list)
   return modified;
 }
 
+bool
+TcpTxBuffer::IsLost (const SequenceNumber32 &seq, const PacketList::const_iterator &segment,
+                     uint32_t dupThresh, uint32_t segmentSize) const
+{
+  NS_LOG_FUNCTION (this << seq << dupThresh << segmentSize);
+  uint32_t count = 0;
+  uint32_t bytes = 0;
+  PacketList::const_iterator it;
+  TcpTxItem *item;
+  Ptr<const Packet> current;
+  SequenceNumber32 beginOfCurrentPacket = seq;
+
+  // From RFC 6675:
+  // > The routine returns true when either dupThresh discontiguous SACKed
+  // > sequences have arrived above 'seq' or more than (dupThresh - 1) * SMSS bytes
+  // > with sequence numbers greater than 'SeqNum' have been SACKed.  Otherwise, the
+  // > routine returns false.
+  for (it = segment; it != m_sentList.end (); ++it)
+    {
+      item = *it;
+      current = item->m_packet;
+
+      if (item->m_lost)
+        {
+          return true;
+        }
+
+      if (item->m_sacked)
+        {
+          NS_LOG_DEBUG ("Segment found to be SACKed, increasing counter and bytes by " <<
+                        current->GetSize ());
+          ++count;
+          bytes += current->GetSize ();
+          if ((count >= dupThresh) || (bytes > (dupThresh-1) * segmentSize))
+            {
+              return true;
+            }
+        }
+
+      beginOfCurrentPacket += current->GetSize ();
+    }
+
+  return false;
+}
+
+bool
+TcpTxBuffer::IsLost (const SequenceNumber32 &seq, uint32_t dupThresh,
+                     uint32_t segmentSize) const
+{
+  NS_LOG_FUNCTION (this << seq << dupThresh);
+
+  SequenceNumber32 beginOfCurrentPacket = m_firstByteSeq;
+  PacketList::const_iterator it;
+
+  // This O(n) method is called only once, and outside this class.
+  // It should not harm the performance
+  for (it = m_sentList.begin (); it != m_sentList.end (); ++it)
+    {
+      // Search for the right iterator before calling IsLost()
+      if (beginOfCurrentPacket > seq)
+        {
+          return IsLost (beginOfCurrentPacket, it, dupThresh, segmentSize);
+        }
+
+      beginOfCurrentPacket += (*it)->m_packet->GetSize ();
+    }
+
+  return false;
+}
+
 std::ostream &
 operator<< (std::ostream & os, TcpTxBuffer const & tcpTxBuf)
 {
diff --git a/src/internet/model/tcp-tx-buffer.h b/src/internet/model/tcp-tx-buffer.h
index b99c27f5b..a643d4972 100644
--- a/src/internet/model/tcp-tx-buffer.h
+++ b/src/internet/model/tcp-tx-buffer.h
@@ -214,11 +214,31 @@ public:
    */
   bool Update (const TcpOptionSack::SackList &list);
 
+  /**
+   * \brief Check if a segment is lost per RFC 6675
+   * \param seq sequence to check
+   * \param dupThresh dupAck threshold
+   * \param segmentSize segment size
+   * \return true if the sequence is supposed to be lost, false otherwise
+   */
+  bool IsLost (const SequenceNumber32 &seq, uint32_t dupThresh, uint32_t segmentSize) const;
+
 private:
   friend std::ostream & operator<< (std::ostream & os, TcpTxBuffer const & tcpTxBuf);
 
   typedef std::list<TcpTxItem*> PacketList; //!< container for data stored in the buffer
 
+  /**
+   * \brief Check if a segment is lost per RFC 6675
+   * \param seq sequence to check
+   * \param segment Iterator pointing at seq
+   * \param dupThresh dupAck threshold
+   * \param segmentSize segment size
+   * \return true if the sequence is supposed to be lost, false otherwise
+   */
+  bool IsLost (const SequenceNumber32 &seq, const PacketList::const_iterator &segment, uint32_t dupThresh,
+               uint32_t segmentSize) const;
+
   /**
    * \brief Get a block of data not transmitted yet and move it into SentList
    *