diff --git a/trunk/src/core/srs_core_protocol.cpp b/trunk/src/core/srs_core_protocol.cpp
index 233655be0..6f546d93d 100755
--- a/trunk/src/core/srs_core_protocol.cpp
+++ b/trunk/src/core/srs_core_protocol.cpp
@@ -311,6 +311,12 @@ int SrsProtocol::recv_message(SrsMessage** pmsg)
 			continue;
 		}
 		
+		if ((ret = on_recv_message(msg)) != ERROR_SUCCESS) {
+			srs_error("update context when received msg. ret=%d", ret);
+			delete msg;
+			return ret;
+		}
+		
 		srs_verbose("get a msg with raw/undecoded payload");
 		*pmsg = msg;
 		break;
@@ -431,6 +437,35 @@ int SrsProtocol::send_message(SrsMessage* msg)
 	return ret;
 }
 
+int SrsProtocol::on_recv_message(SrsMessage* msg)
+{
+	int ret = ERROR_SUCCESS;
+	
+	srs_assert(msg != NULL);
+	
+	switch (msg->header.message_type) {
+		case RTMP_MSG_WindowAcknowledgementSize:
+			if ((ret = msg->decode_packet()) != ERROR_SUCCESS) {
+				srs_error("decode packet from message payload failed. ret=%d", ret);
+				return ret;
+			}
+			srs_verbose("decode packet from message payload success.");
+			break;
+	}
+	
+	switch (msg->header.message_type) {
+		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);
+			break;
+		}
+	}
+	
+	return ret;
+}
+
 int SrsProtocol::recv_interlaced_message(SrsMessage** pmsg)
 {
 	int ret = ERROR_SUCCESS;
@@ -816,22 +851,30 @@ int SrsMessage::decode_packet()
 	srs_assert(payload != NULL);
 	srs_assert(size > 0);
 	
+	if (packet) {
+		srs_verbose("msg already decoded");
+		return ret;
+	}
+	
 	if (!stream) {
 		srs_verbose("create decode stream for message.");
 		stream = new SrsStream();
 	}
 	
+	// initialize the decode stream for all message,
+	// it's ok for the initialize if fast and without memory copy.
+	if ((ret = stream->initialize((char*)payload, size)) != ERROR_SUCCESS) {
+		srs_error("initialize stream failed. ret=%d", ret);
+		return ret;
+	}
+	srs_verbose("decode stream initialized success");
+	
+	// decode specified packet type
 	if (header.message_type == RTMP_MSG_AMF0CommandMessage) {
 		srs_verbose("start to decode AMF0 command message.");
 		
 		// amf0 command message.
 		// need to read the command name.
-		if ((ret = stream->initialize((char*)payload, size)) != ERROR_SUCCESS) {
-			srs_error("initialize stream failed. ret=%d", ret);
-			return ret;
-		}
-		srs_verbose("decode stream initialized success");
-		
 		std::string command;
 		if ((ret = srs_amf0_read_string(stream, command)) != ERROR_SUCCESS) {
 			srs_error("decode AMF0 command name failed. ret=%d", ret);
@@ -850,12 +893,16 @@ int SrsMessage::decode_packet()
 		srs_trace("drop the AMF0 command message, command_name=%s", command.c_str());
 		packet = new SrsPacket();
 		return ret;
+	} else if(header.message_type == RTMP_MSG_WindowAcknowledgementSize) {
+		srs_verbose("start to decode set ack window size message.");
+		packet = new SrsSetWindowAckSizePacket();
+		return packet->decode(stream);
+	} else {
+		// default packet to drop message.
+		srs_trace("drop the unknown message, type=%d", header.message_type);
+		packet = new SrsPacket();
 	}
 	
-	// default packet to drop message.
-	srs_trace("drop the unknown message, type=%d", header.message_type);
-	packet = new SrsPacket();
-	
 	return ret;
 }
 
@@ -1137,6 +1184,22 @@ SrsSetWindowAckSizePacket::~SrsSetWindowAckSizePacket()
 {
 }
 
+int SrsSetWindowAckSizePacket::decode(SrsStream* stream)
+{
+	int ret = ERROR_SUCCESS;
+	
+	if (!stream->require(4)) {
+		ret = ERROR_RTMP_MESSAGE_DECODE;
+		srs_error("decode ack window size failed. ret=%d", ret);
+		return ret;
+	}
+	
+	ackowledgement_window_size = stream->read_4bytes();
+	srs_info("decode ack window size success");
+	
+	return ret;
+}
+
 int SrsSetWindowAckSizePacket::get_perfer_cid()
 {
 	return RTMP_CID_ProtocolControl;
diff --git a/trunk/src/core/srs_core_protocol.hpp b/trunk/src/core/srs_core_protocol.hpp
index 1a08644f8..eca407d90 100755
--- a/trunk/src/core/srs_core_protocol.hpp
+++ b/trunk/src/core/srs_core_protocol.hpp
@@ -107,6 +107,10 @@ public:
 	*/
 	virtual int send_message(SrsMessage* msg);
 private:
+	/**
+	* when recv message, update the context.
+	*/
+	virtual int on_recv_message(SrsMessage* msg);
 	/**
 	* try to recv interlaced message from peer,
 	* return error if error occur and nerver set the pmsg,
@@ -372,6 +376,8 @@ public:
 public:
 	SrsSetWindowAckSizePacket();
 	virtual ~SrsSetWindowAckSizePacket();
+public:
+	virtual int decode(SrsStream* stream);
 public:
 	virtual int get_perfer_cid();
 public: