diff --git a/tools/pylibopenflow/pylib/of/simu.py b/tools/pylibopenflow/pylib/of/simu.py
new file mode 100644
index 0000000..508b076
--- /dev/null
+++ b/tools/pylibopenflow/pylib/of/simu.py
@@ -0,0 +1,144 @@
+"""This module simulates the network.
+
+Copyright(C) 2009, Stanford University
+Date November 2009
+Created by ykk
+"""
+import openflow
+import output
+import of.msg
+import of.network
+
+class network(of.network.network):
+    """Class to simulate OpenFlow network
+
+    Copyright(C) 2009, Stanford University
+    Date November 2009
+    Created by ykk
+    """
+    def __init__(self):
+        """Initialize network
+        """
+        of.network.network.__init__(self)
+        ##Name of use for output
+        self.name = self.__class__.__name__+str(id(self))
+
+class link(of.network.link):
+    """Class to simulate link
+
+    Copyright(C) 2009, Stanford University
+    Date November 2009
+    Created by ykk
+    """
+    def __init__(self, switch1, switch2, isUp=True):
+        """Initialize link
+        """
+        of.network.link.__init__(self, switch1, switch2)
+        ##Name of use for output
+        self.name = self.__class__.__name__+str(id(self))
+        ##Indicate if link is up
+        self.isUp = isUp
+
+class switch(of.network.switch):
+    """Class to simulate OpenFlow switch
+
+    Copyright(C) 2009, Stanford University
+    Date November 2009
+    Created by ykk
+    """
+    def __init__(self,  messages, controller, port, miss_send_len=128,
+                 dpid=None, n_buffers=100, n_tables=1,
+                 capability=None, parser=None, connection=None):
+        """Initialize switch
+        """
+        of.network.switch.__init__(self,  miss_send_len,
+                                   None, dpid, n_buffers, n_tables,
+                                   capability)
+        ##Name of use for output
+        self.name = self.__class__.__name__+str(id(self))
+        ##Reference to OpenFlow messages
+        self.__messages = messages
+        ##Reference to connection
+        self.connection = openflow.tcpsocket(messages, controller, port)
+        self.sock = self.connection.sock
+        ##Reference to Parser
+        self.parser = None
+        if (parser == None):
+            self.parser = of.msg.parser(messages)
+        else:
+            self.parser = parser
+
+    def receive_openflow(self, packet):
+        """Switch receive OpenFlow packet, and respond accordingly
+        """
+        dic = self.__messages.peek_from_front("ofp_header", packet)
+        if (dic["type"][0] == self.__messages.get_value("OFPT_HELLO")):
+            output.dbg("Receive hello", self.name)
+        elif (dic["type"][0] == self.__messages.get_value("OFPT_ECHO_REQUEST")):
+            self.reply_echo(dic["xid"][0])
+        elif (dic["type"][0] == self.__messages.get_value("OFPT_FEATURES_REQUEST")):
+            self.reply_features(dic["xid"][0])
+        elif (dic["type"][0] == self.__messages.get_value("OFPT_FLOW_MOD")):
+            self.handle_flow_mod(packet)
+        else:
+            output.dbg("Unprocessed message "+self.parser.header_describe(dic),
+                       self.name)
+
+    def send_hello(self):
+        """Send hello
+        """
+        self.connection.structsend("ofp_hello",
+                                   0, self.__messages.get_value("OFPT_HELLO"),
+                                   0, 0)
+        output.dbg("Send hello",self.name)
+
+    def send_packet(self, inport, bufferid=None, packet="", xid=0, reason=None):
+        """Send packet in
+        Assume no match as reason, bufferid = 0xFFFFFFFF,
+        and empty packet by default
+        """
+        if (reason == None):
+            reason = self.__messages.get_value("OFPR_NO_MATCH")
+        if (bufferid == None):
+            bufferid = int("0xFFFFFFFF",16)
+        pktin = self.__messages.pack("ofp_packet_in",
+                                     0, self.__messages.get_value("OFPT_PACKET_IN"),
+                                     0, xid, #header
+                                     bufferid, len(packet),
+                                     inport, reason, 0)
+        self.connection.structsend_raw(pktin+packet)
+        output.dbg("Send packet ",self.name)
+
+    def send_echo(self, xid=0):
+        """Send echo
+        """
+        self.connection.structsend_xid("ofp_header",
+                                       0, self.__messages.get_value("OFPT_ECHO_REQUEST"),
+                                       0, xid)
+        output.dbg("Send echo", self.name)
+
+    def reply_echo(self, xid):
+        """Reply to echo request
+        """
+        self.connection.structsend_xid("ofp_header",
+                                       0, self.__messages.get_value("OFPT_ECHO_REPLY"),
+                                       0, xid)                                 
+        output.dbg("Reply echo of xid:"+str(xid),self.name)
+
+    def reply_features(self, xid):
+        """Reply to feature request
+        """
+        self.connection.structsend_xid("ofp_switch_features",
+                                       0, self.__messages.get_value("OFPT_FEATURES_REPLY"),
+                                       0, xid,
+                                       self.datapath_id, self.n_buffers,
+                                       self.n_tables,0,0,0,
+                                       self.capability.get_capability(self.__messages),
+                                       self.capability.get_actions(self.__messages))
+        output.dbg("Replied features request of xid "+str(xid), self.name)
+        
+    def handle_flow_mod(self, packet):
+        """Handle flow mod: just print it here
+        """
+        output.dbg(self.parser.flow_mod_describe(packet), self.name)
+