tune RTT calculations

libi2pd/SSU2Session.cpp

@@ -85,7 +85,7 @@ namespace transport
 		m_DestConnID (0), m_SourceConnID (0), m_State (eSSU2SessionStateUnknown),
 		m_SendPacketNum (0), m_ReceivePacketNum (0), m_LastDatetimeSentPacketNum (0),
 		m_IsDataReceived (false), m_WindowSize (SSU2_MIN_WINDOW_SIZE),
-		m_RTT (SSU2_RESEND_INTERVAL), m_RTO (SSU2_RESEND_INTERVAL*SSU2_kAPPA), m_RelayTag (0),
+		m_RTT (SSU2_UNKNOWN_RTT), m_RTO (SSU2_INITIAL_RTO), m_RelayTag (0),
 		m_ConnectTimer (server.GetService ()), m_TerminationReason (eSSU2TerminationReasonNormalClose),
 		m_MaxPayloadSize (SSU2_MIN_PACKET_SIZE - IPV6_HEADER_SIZE - UDP_HEADER_SIZE - 32) // min size
 	{
@@ -1753,7 +1753,10 @@ namespace transport
 				if (ts > it1->second->sendTime)
 				{
 					auto rtt = ts - it1->second->sendTime;
-					m_RTT = std::round ((m_RTT*m_SendPacketNum + rtt)/(m_SendPacketNum + 1.0));
+					if (m_RTT != SSU2_UNKNOWN_RTT)
+						m_RTT = SSU2_RTT_EWMA_ALPHA * rtt + (1.0 - SSU2_RTT_EWMA_ALPHA) * m_RTT;
+					else
+						m_RTT = rtt;
 					m_RTO = m_RTT*SSU2_kAPPA;
 					if (m_RTO < SSU2_MIN_RTO) m_RTO = SSU2_MIN_RTO;
 					if (m_RTO > SSU2_MAX_RTO) m_RTO = SSU2_MAX_RTO;

libi2pd/SSU2Session.h

@@ -36,7 +36,6 @@ namespace transport
 	const size_t SSU2_MAX_PACKET_SIZE = 1500;
 	const size_t SSU2_MIN_PACKET_SIZE = 1280;
 	const int SSU2_HANDSHAKE_RESEND_INTERVAL = 1000; // in milliseconds
-	const int SSU2_RESEND_INTERVAL = 300; // in milliseconds
 	const int SSU2_MAX_NUM_RESENDS = 5;
 	const int SSU2_INCOMPLETE_MESSAGES_CLEANUP_TIMEOUT = 30; // in seconds
 	const int SSU2_MAX_NUM_RECEIVED_I2NP_MSGIDS = 5000; // how many msgID we store for duplicates check
@@ -45,7 +44,10 @@ namespace transport
 	const size_t SSU2_MIN_WINDOW_SIZE = 16; // in packets
 	const size_t SSU2_MAX_WINDOW_SIZE = 256; // in packets
 	const size_t SSU2_MIN_RTO = 100; // in milliseconds
+	const size_t SSU2_INITIAL_RTO = 540; // in milliseconds
 	const size_t SSU2_MAX_RTO = 2500; // in milliseconds
+	const double SSU2_UNKNOWN_RTT = -1;
+	const double SSU2_RTT_EWMA_ALPHA = 0.125;
 	const float SSU2_kAPPA = 1.8;
 	const int SSU2_MAX_NUM_ACNT = 255; // acnt, acks or nacks
 	const int SSU2_MAX_NUM_ACK_PACKETS = 511; // ackthrough + acnt + 1 range
@@ -356,7 +358,8 @@ namespace transport
 			std::list<std::shared_ptr<I2NPMessage> > m_SendQueue;
 			i2p::I2NPMessagesHandler m_Handler;
 			bool m_IsDataReceived;
-			size_t m_WindowSize, m_RTT, m_RTO;
+			double m_RTT;
+			size_t m_WindowSize, m_RTO;
 			uint32_t m_RelayTag; // between Bob and Charlie
 			OnEstablished m_OnEstablished; // callback from Established
 			boost::asio::deadline_timer m_ConnectTimer;

libi2pd/Streaming.cpp

@@ -434,7 +434,7 @@ namespace stream
 					rtt = 1;
 				}
 				if (seqn)
-					m_RTT = std::round (RTT_EWMA_ALPHA * m_RTT + (1.0 - RTT_EWMA_ALPHA) * rtt);
+					m_RTT = RTT_EWMA_ALPHA * rtt + (1.0 - RTT_EWMA_ALPHA) * m_RTT;
 				else
 					m_RTT = rtt;
 				m_RTO = m_RTT*1.5; // TODO: implement it better
@@ -457,7 +457,7 @@ namespace stream
 				if (!seqn && m_RoutingSession) // first message confirmed
 					m_RoutingSession->SetSharedRoutingPath (
 						std::make_shared<i2p::garlic::GarlicRoutingPath> (
-							i2p::garlic::GarlicRoutingPath{m_CurrentOutboundTunnel, m_CurrentRemoteLease, m_RTT, 0, 0}));
+							i2p::garlic::GarlicRoutingPath{m_CurrentOutboundTunnel, m_CurrentRemoteLease, (int)m_RTT, 0, 0}));
 			}
 			else
 				break;

libi2pd/Streaming.h

@@ -57,7 +57,7 @@ namespace stream
 	const int MIN_WINDOW_SIZE = 1;
 	const int MAX_WINDOW_SIZE = 128;
 	const int WINDOW_SIZE_DROP_FRACTION = 10; // 1/10
-	const double RTT_EWMA_ALPHA = 0.5;
+	const double RTT_EWMA_ALPHA = 0.125;
 	const int INITIAL_RTT = 8000; // in milliseconds
 	const int INITIAL_RTO = 9000; // in milliseconds
 	const int MIN_SEND_ACK_TIMEOUT = 2; // in milliseconds
@@ -254,7 +254,8 @@ namespace stream
 			uint16_t m_Port;
 
 			SendBufferQueue m_SendBuffer;
-			int m_WindowSize, m_RTT, m_RTO, m_AckDelay;
+			double m_RTT;
+			int m_WindowSize, m_RTO, m_AckDelay;
 			uint64_t m_LastWindowSizeIncreaseTime;
 			int m_NumResendAttempts;
 			size_t m_MTU;