slow start and congestion avoidance

Streaming.cpp

@@ -17,7 +17,8 @@ namespace stream
 		m_IsReset (false), m_IsAckSendScheduled (false), m_LocalDestination (local), 
 		m_RemoteLeaseSet (remote), m_ReceiveTimer (m_Service), 
 		m_ResendTimer (m_Service), m_AckSendTimer (m_Service), 
-		m_NumSentBytes (0), m_NumReceivedBytes (0), m_Port (port)
+		m_NumSentBytes (0), m_NumReceivedBytes (0), m_Port (port), 
+		m_WindowSize (MIN_WINDOW_SIZE), m_LastWindowSizeIncreaseTime (0)
 	{
 		m_RecvStreamID = i2p::context.GetRandomNumberGenerator ().GenerateWord32 ();
 		UpdateCurrentRemoteLease ();
@@ -27,7 +28,8 @@ namespace stream
 		m_Service (service), m_SendStreamID (0), m_SequenceNumber (0), m_LastReceivedSequenceNumber (-1), 
 		m_IsOpen (false), m_IsReset (false), m_IsAckSendScheduled (false), m_LocalDestination (local),
 		m_ReceiveTimer (m_Service), m_ResendTimer (m_Service), m_AckSendTimer (m_Service), 
-		m_NumSentBytes (0), m_NumReceivedBytes (0), m_Port (0)
+		m_NumSentBytes (0), m_NumReceivedBytes (0), m_Port (0), 
+		m_WindowSize (MIN_WINDOW_SIZE), m_LastWindowSizeIncreaseTime (0)
 	{
 		m_RecvStreamID = i2p::context.GetRandomNumberGenerator ().GenerateWord32 ();
 	}
@@ -239,10 +241,29 @@ namespace stream
 				m_SentPackets.erase (it++);
 				delete sentPacket;	
 				acknowledged = true;
+				if (m_WindowSize < WINDOW_SIZE)
+					m_WindowSize++; // slow start
+				else
+				{
+					// linear growth
+					auto ts = i2p::util::GetMillisecondsSinceEpoch ();
+					if (ts > m_LastWindowSizeIncreaseTime + INITIAL_RTT)
+					{
+						m_WindowSize++;
+						if (m_WindowSize > MAX_WINDOW_SIZE) m_WindowSize = MAX_WINDOW_SIZE;
+						m_LastWindowSizeIncreaseTime = ts;
+					}
+				}
 			}
 			else
 				break;
 		}
+		if (nackCount > 0)
+		{
+			// congesion avoidance
+			m_WindowSize -= nackCount;
+			if (m_WindowSize < MIN_WINDOW_SIZE) m_WindowSize = MIN_WINDOW_SIZE; 
+		}		
 		if (m_SentPackets.empty ())
 			m_ResendTimer.cancel ();
 		if (acknowledged)
@@ -263,7 +284,7 @@ namespace stream
 
 	void Stream::SendBuffer ()
 	{	
-		int numMsgs = WINDOW_SIZE - m_SentPackets.size ();
+		int numMsgs = m_WindowSize - m_SentPackets.size ();
 		if (numMsgs <= 0) return; // window is full 
 		
 		bool isNoAck = m_LastReceivedSequenceNumber < 0; // first packet

Streaming.h

@@ -45,6 +45,9 @@ namespace stream
 	const int ACK_SEND_TIMEOUT = 200; // in milliseconds
 	const int MAX_NUM_RESEND_ATTEMPTS = 5;	
 	const int WINDOW_SIZE = 6; // in messages
+	const int MIN_WINDOW_SIZE = 1;
+	const int MAX_WINDOW_SIZE = 128;		
+	const int INITIAL_RTT = 8000; // in milliseconds
 	
 	struct Packet
 	{
@@ -157,6 +160,8 @@ namespace stream
 
 			std::mutex m_SendBufferMutex;
 			std::stringstream m_SendBuffer;
+			int m_WindowSize;
+			uint64_t m_LastWindowSizeIncreaseTime;
 	};
 
 	class StreamingDestination