diff --git a/libi2pd/SSU2.cpp b/libi2pd/SSU2.cpp
index e4f70f7e..90a78bbd 100644
--- a/libi2pd/SSU2.cpp
+++ b/libi2pd/SSU2.cpp
@@ -32,7 +32,7 @@ namespace transport
 		TransportSession (in_RemoteRouter, SSU2_CONNECT_TIMEOUT),
 		m_Server (server), m_Address (addr), m_DestConnID (0), m_SourceConnID (0),
 		m_State (eSSU2SessionStateUnknown), m_SendPacketNum (0), m_ReceivePacketNum (0),
-		m_IsDataReceived (false)
+		m_IsDataReceived (false), m_WindowSize (SSU2_MAX_WINDOW_SIZE)
 	{
 		m_NoiseState.reset (new i2p::crypto::NoiseSymmetricState);
 		if (in_RemoteRouter && m_Address)
@@ -110,12 +110,12 @@ namespace transport
 		
 	void SSU2Session::SendQueue ()
 	{	
-		if (!m_SendQueue.empty ())
+		if (!m_SendQueue.empty () && m_SentPackets.size () <= m_WindowSize)
 		{
 			auto nextResend = i2p::util::GetSecondsSinceEpoch () + SSU2_RESEND_INTERVAL;
 			auto packet = std::make_shared<SentPacket>();
 			packet->payloadSize += CreateAckBlock (packet->payload + packet->payloadSize, SSU2_MAX_PAYLOAD_SIZE - packet->payloadSize);
-			while (!m_SendQueue.empty ())
+			while (!m_SendQueue.empty () && m_SentPackets.size () <= m_WindowSize)
 			{
 				auto msg = m_SendQueue.front ();
 				size_t len = msg->GetNTCP2Length ();
@@ -180,7 +180,7 @@ namespace transport
 		
 	void SSU2Session::Resend (uint64_t ts)
 	{
-		if (m_SendQueue.empty ()) return;
+		if (m_SentPackets.empty ()) return;
 		std::map<uint32_t, std::shared_ptr<SentPacket> > resentPackets;
 		for (auto it = m_SentPackets.begin (); it != m_SentPackets.end (); )
 			if (ts > it->second->nextResendTime)
@@ -207,6 +207,7 @@ namespace transport
 			m_SentPackets.insert (resentPackets.begin (), resentPackets.end ());		
 #endif			
 		}	
+		SendQueue ();
 	}	
 		
 	void SSU2Session::ProcessFirstIncomingMessage (uint64_t connID, uint8_t * buf, size_t len)
@@ -746,7 +747,10 @@ namespace transport
 		m_LastActivityTimestamp = i2p::util::GetSecondsSinceEpoch ();
 		m_NumReceivedBytes += len;
 		if (UpdateReceivePacketNum (packetNum))
+		{	
 			HandlePayload (payload, payloadSize);
+			SendQueue (); // if we have something to send
+		}	
 	}	
 		
 	void SSU2Session::HandlePayload (const uint8_t * buf, size_t len)
diff --git a/libi2pd/SSU2.h b/libi2pd/SSU2.h
index 41027c2e..e2222b46 100644
--- a/libi2pd/SSU2.h
+++ b/libi2pd/SSU2.h
@@ -33,6 +33,7 @@ namespace transport
 	const int SSU2_RESEND_INTERVAL = 3; // in seconds
 	const int SSU2_MAX_NUM_RESENDS = 5;
 	const int SSU2_INCOMPLETE_MESSAGES_CLEANUP_TIMEOUT = 30; // in seconds	
+	const size_t SSU2_MAX_WINDOW_SIZE = 128; // in packets
 	
 	enum SSU2MessageType
 	{
@@ -210,6 +211,7 @@ namespace transport
 			std::list<std::shared_ptr<I2NPMessage> > m_SendQueue;
 			i2p::I2NPMessagesHandler m_Handler;
 			bool m_IsDataReceived;
+			size_t m_WindowSize;
 	};
 
 	class SSU2Server:  private i2p::util::RunnableServiceWithWork