diff --git a/trunk/src/core/srs_core_log.hpp b/trunk/src/core/srs_core_log.hpp
index 8c91ca94b..d2627f6cf 100755
--- a/trunk/src/core/srs_core_log.hpp
+++ b/trunk/src/core/srs_core_log.hpp
@@ -78,7 +78,7 @@ extern ILogContext* log_context;
 	#undef srs_verbose
 	#define srs_verbose(msg, ...) (void)0
 #endif
-#if 0
+#if 1
 	#undef srs_info
 	#define srs_info(msg, ...) (void)0
 #endif
diff --git a/trunk/src/core/srs_core_protocol.cpp b/trunk/src/core/srs_core_protocol.cpp
index 0b007b8ac..6a7c0289e 100755
--- a/trunk/src/core/srs_core_protocol.cpp
+++ b/trunk/src/core/srs_core_protocol.cpp
@@ -249,6 +249,10 @@ messages.
 /****************************************************************************
 *****************************************************************************
 ****************************************************************************/
+SrsProtocol::AckWindowSize::AckWindowSize()
+{
+	ack_window_size = acked_size = 0;
+}
 
 SrsProtocol::SrsProtocol(st_netfd_t client_stfd)
 {
@@ -450,6 +454,21 @@ int SrsProtocol::on_recv_message(SrsCommonMessage* msg)
 	int ret = ERROR_SUCCESS;
 	
 	srs_assert(msg != NULL);
+		
+	// acknowledgement
+	if (skt->get_recv_bytes() - in_ack_size.acked_size > in_ack_size.ack_window_size) {
+		SrsCommonMessage* ack = new SrsCommonMessage();
+		SrsAcknowledgementPacket* pkt = new SrsAcknowledgementPacket();
+		
+		in_ack_size.acked_size = pkt->sequence_number = skt->get_recv_bytes();
+		ack->set_packet(pkt, 0);
+		
+		if ((ret = send_message(ack)) != ERROR_SUCCESS) {
+			srs_error("send acknowledgement failed. ret=%d", ret);
+			return ret;
+		}
+		srs_verbose("send acknowledgement success.");
+	}
 	
 	switch (msg->header.message_type) {
 		case RTMP_MSG_SetChunkSize:
@@ -466,8 +485,13 @@ int SrsProtocol::on_recv_message(SrsCommonMessage* msg)
 		case RTMP_MSG_WindowAcknowledgementSize: {
 			SrsSetWindowAckSizePacket* pkt = dynamic_cast<SrsSetWindowAckSizePacket*>(msg->get_packet());
 			srs_assert(pkt != NULL);
-			// TODO: take effect.
-			srs_trace("set ack window size to %d", pkt->ackowledgement_window_size);
+			
+			if (pkt->ackowledgement_window_size > 0) {
+				in_ack_size.ack_window_size = pkt->ackowledgement_window_size;
+				srs_trace("set ack window size to %d", pkt->ackowledgement_window_size);
+			} else {
+				srs_warn("ignored. set ack window size is %d", pkt->ackowledgement_window_size);
+			}
 			break;
 		}
 		case RTMP_MSG_SetChunkSize: {
@@ -2222,6 +2246,48 @@ int SrsSetWindowAckSizePacket::encode_packet(SrsStream* stream)
 	return ret;
 }
 
+SrsAcknowledgementPacket::SrsAcknowledgementPacket()
+{
+	sequence_number = 0;
+}
+
+SrsAcknowledgementPacket::~SrsAcknowledgementPacket()
+{
+}
+
+int SrsAcknowledgementPacket::get_perfer_cid()
+{
+	return RTMP_CID_ProtocolControl;
+}
+
+int SrsAcknowledgementPacket::get_message_type()
+{
+	return RTMP_MSG_Acknowledgement;
+}
+
+int SrsAcknowledgementPacket::get_size()
+{
+	return 4;
+}
+
+int SrsAcknowledgementPacket::encode_packet(SrsStream* stream)
+{
+	int ret = ERROR_SUCCESS;
+	
+	if (!stream->require(4)) {
+		ret = ERROR_RTMP_MESSAGE_ENCODE;
+		srs_error("encode acknowledgement packet failed. ret=%d", ret);
+		return ret;
+	}
+	
+	stream->write_4bytes(sequence_number);
+	
+	srs_verbose("encode acknowledgement packet "
+		"success. sequence_number=%d", sequence_number);
+	
+	return ret;
+}
+
 SrsSetChunkSizePacket::SrsSetChunkSizePacket()
 {
 	chunk_size = RTMP_DEFAULT_CHUNK_SIZE;
diff --git a/trunk/src/core/srs_core_protocol.hpp b/trunk/src/core/srs_core_protocol.hpp
index b526f0b31..755d9d3aa 100755
--- a/trunk/src/core/srs_core_protocol.hpp
+++ b/trunk/src/core/srs_core_protocol.hpp
@@ -75,6 +75,14 @@ class ISrsMessage;
 */
 class SrsProtocol
 {
+private:
+	struct AckWindowSize
+	{
+		int ack_window_size;
+		int64_t acked_size;
+		
+		AckWindowSize();
+	};
 // peer in/out
 private:
 	st_netfd_t stfd;
@@ -85,6 +93,7 @@ private:
 	std::map<int, SrsChunkStream*> chunk_streams;
 	SrsBuffer* buffer;
 	int32_t in_chunk_size;
+	AckWindowSize in_ack_size;
 // peer out
 private:
 	char out_header_fmt0[RTMP_MAX_FMT0_HEADER_SIZE];
@@ -849,6 +858,34 @@ protected:
 	virtual int encode_packet(SrsStream* stream);
 };
 
+/**
+* 5.3. Acknowledgement (3)
+* The client or the server sends the acknowledgment to the peer after
+* receiving bytes equal to the window size.
+*/
+class SrsAcknowledgementPacket : public SrsPacket
+{
+private:
+	typedef SrsPacket super;
+protected:
+	virtual const char* get_class_name()
+	{
+		return CLASS_NAME_STRING(SrsAcknowledgementPacket);
+	}
+public:
+	int32_t sequence_number;
+public:
+	SrsAcknowledgementPacket();
+	virtual ~SrsAcknowledgementPacket();
+public:
+	virtual int get_perfer_cid();
+public:
+	virtual int get_message_type();
+protected:
+	virtual int get_size();
+	virtual int encode_packet(SrsStream* stream);
+};
+
 /**
 * 7.1. Set Chunk Size
 * Protocol control message 1, Set Chunk Size, is used to notify the
diff --git a/trunk/src/core/srs_core_socket.cpp b/trunk/src/core/srs_core_socket.cpp
index 41abcea6a..5f540baf0 100755
--- a/trunk/src/core/srs_core_socket.cpp
+++ b/trunk/src/core/srs_core_socket.cpp
@@ -28,8 +28,8 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 SrsSocket::SrsSocket(st_netfd_t client_stfd)
 {
     stfd = client_stfd;
-	recv_timeout = ST_UTIME_NO_TIMEOUT;
-	send_timeout = ST_UTIME_NO_TIMEOUT;
+	send_timeout = recv_timeout = ST_UTIME_NO_TIMEOUT;
+	recv_bytes = send_bytes = 0;
 }
 
 SrsSocket::~SrsSocket()
@@ -46,6 +46,16 @@ void SrsSocket::set_send_timeout(int timeout_ms)
 	send_timeout = timeout_ms * 1000;
 }
 
+int64_t SrsSocket::get_recv_bytes()
+{
+	return recv_bytes;
+}
+
+int64_t SrsSocket::get_send_bytes()
+{
+	return send_bytes;
+}
+
 int SrsSocket::read(const void* buf, size_t size, ssize_t* nread)
 {
     int ret = ERROR_SUCCESS;
@@ -63,8 +73,10 @@ int SrsSocket::read(const void* buf, size_t size, ssize_t* nread)
             errno = ECONNRESET;
         }
         
-        ret = ERROR_SOCKET_READ;
+        return ERROR_SOCKET_READ;
     }
+    
+    recv_bytes += *nread;
         
     return ret;
 }
@@ -86,9 +98,11 @@ int SrsSocket::read_fully(const void* buf, size_t size, ssize_t* nread)
             errno = ECONNRESET;
         }
         
-        ret = ERROR_SOCKET_READ_FULLY;
+        return ERROR_SOCKET_READ_FULLY;
     }
     
+    recv_bytes += *nread;
+    
     return ret;
 }
 
@@ -103,8 +117,10 @@ int SrsSocket::write(const void* buf, size_t size, ssize_t* nwrite)
 			return ERROR_SOCKET_TIMEOUT;
 		}
 		
-        ret = ERROR_SOCKET_WRITE;
+        return ERROR_SOCKET_WRITE;
     }
+    
+    send_bytes += *nwrite;
         
     return ret;
 }
@@ -120,9 +136,11 @@ int SrsSocket::writev(const iovec *iov, int iov_size, ssize_t* nwrite)
 			return ERROR_SOCKET_TIMEOUT;
 		}
 		
-        ret = ERROR_SOCKET_WRITE;
+        return ERROR_SOCKET_WRITE;
     }
     
+    send_bytes += *nwrite;
+    
     return ret;
 }
 
diff --git a/trunk/src/core/srs_core_socket.hpp b/trunk/src/core/srs_core_socket.hpp
index e680aac17..320487a03 100755
--- a/trunk/src/core/srs_core_socket.hpp
+++ b/trunk/src/core/srs_core_socket.hpp
@@ -41,6 +41,8 @@ class SrsSocket
 private:
 	int64_t recv_timeout;
 	int64_t send_timeout;
+	int64_t recv_bytes;
+	int64_t send_bytes;
     st_netfd_t stfd;
 public:
     SrsSocket(st_netfd_t client_stfd);
@@ -48,6 +50,9 @@ public:
 public:
 	virtual void set_recv_timeout(int timeout_ms);
 	virtual void set_send_timeout(int timeout_ms);
+	virtual int64_t get_recv_bytes();
+	virtual int64_t get_send_bytes();
+public:
     virtual int read(const void* buf, size_t size, ssize_t* nread);
     virtual int read_fully(const void* buf, size_t size, ssize_t* nread);
     virtual int write(const void* buf, size_t size, ssize_t* nwrite);