diff --git a/src/main/java/net/onrc/onos/datastore/topology/KVDevice.java b/src/main/java/net/onrc/onos/datastore/topology/KVDevice.java
index e076c14..805be62 100644
--- a/src/main/java/net/onrc/onos/datastore/topology/KVDevice.java
+++ b/src/main/java/net/onrc/onos/datastore/topology/KVDevice.java
@@ -55,6 +55,10 @@
     private final byte[] mac;
     private TreeSet<byte[]> portIds;
     private transient boolean isPortIdsModified;
+    
+    // Assume there is only one ip on a device now.
+    private int ip;
+    private long lastSeenTime;
 
     // Assuming mac is unique cluster-wide
     public static byte[] getDeviceID(final byte[] mac) {
@@ -199,4 +203,20 @@
         return "[" + this.getClass().getSimpleName()
                 + " " + ByteArrayUtil.toHexStringBuffer(mac, ":") + "]";
     }
+    
+	public int getIp() {
+		return ip;
+	}
+
+	public void setIp(int ip) {
+		this.ip = ip;
+	}
+
+	public long getLastSeenTime() {
+		return lastSeenTime;
+	}
+
+	public void setLastSeenTime(long lastSeenTime) {
+		this.lastSeenTime = lastSeenTime;
+	}
 }
diff --git a/src/main/java/net/onrc/onos/ofcontroller/devicemanager/IOnosDeviceListener.java b/src/main/java/net/onrc/onos/ofcontroller/devicemanager/IOnosDeviceListener.java
new file mode 100644
index 0000000..da50d83
--- /dev/null
+++ b/src/main/java/net/onrc/onos/ofcontroller/devicemanager/IOnosDeviceListener.java
@@ -0,0 +1,7 @@
+package net.onrc.onos.ofcontroller.devicemanager;
+
+public interface IOnosDeviceListener {
+
+    public void onosDeviceAdded(OnosDevice device);
+    public void onosDeviceRemoved(OnosDevice device);
+}
diff --git a/src/main/java/net/onrc/onos/ofcontroller/devicemanager/IOnosDeviceService.java b/src/main/java/net/onrc/onos/ofcontroller/devicemanager/IOnosDeviceService.java
index 9125985..e860de7 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/devicemanager/IOnosDeviceService.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/devicemanager/IOnosDeviceService.java
@@ -1,6 +1,7 @@
 package net.onrc.onos.ofcontroller.devicemanager;
 
 import net.floodlightcontroller.core.module.IFloodlightService;
+import net.floodlightcontroller.util.MACAddress;
 
 /**
  * {@link OnosDeviceManager} doesn't yet provide any API to fellow modules,
@@ -11,8 +12,13 @@
  */
 public interface IOnosDeviceService extends IFloodlightService {
 
+	public void addOnosDeviceListener(IOnosDeviceListener listener);
+	
+	public void deleteOnosDeviceListener(IOnosDeviceListener listener);	
+	
 	public void deleteOnosDevice(OnosDevice dev);
 
+	public void deleteOnosDeviceByMac(MACAddress mac);
+	
 	public void addOnosDevice(Long mac, OnosDevice dev);
-
 }
diff --git a/src/main/java/net/onrc/onos/ofcontroller/devicemanager/OnosDeviceManager.java b/src/main/java/net/onrc/onos/ofcontroller/devicemanager/OnosDeviceManager.java
index bb2e387..d6dffac 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/devicemanager/OnosDeviceManager.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/devicemanager/OnosDeviceManager.java
@@ -9,6 +9,7 @@
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.TimeUnit;
@@ -29,6 +30,8 @@
 import net.onrc.onos.packet.Ethernet;
 import net.onrc.onos.packet.IPv4;
 import net.onrc.onos.packet.UDP;
+import net.onrc.onos.ofcontroller.networkgraph.INetworkGraphService;
+import net.onrc.onos.ofcontroller.networkgraph.NetworkGraph;
 
 import org.openflow.protocol.OFMessage;
 import org.openflow.protocol.OFPacketIn;
@@ -42,11 +45,14 @@
 	private static final int CLEANUP_SECOND = 60*60;
 	private static final int AGEING_MILLSEC = 60*60*1000;
 
+	private CopyOnWriteArrayList<IOnosDeviceListener> deviceListeners;
 	private IFloodlightProviderService floodlightProvider;
 	private final static ScheduledExecutorService executor = Executors.newSingleThreadScheduledExecutor();
 
 	private IDatagridService datagrid;
 	private Map<Long, OnosDevice> mapDevice = new ConcurrentHashMap<Long, OnosDevice>();
+	private INetworkGraphService networkGraphService;
+	private NetworkGraph networkGraph;
 
     public enum OnosDeviceUpdateType {
         ADD, DELETE, UPDATE;
@@ -63,14 +69,15 @@
 
 		@Override
 		public void dispatch() {
-		    // TODO: Fix the code below after deviceStorage was removed
-		    /*
 			if(type == OnosDeviceUpdateType.ADD) {
-				deviceStorage.addOnosDevice(device);
+				for(IOnosDeviceListener listener: deviceListeners) {
+					listener.onosDeviceAdded(device);
+				}
 			} else if (type == OnosDeviceUpdateType.DELETE){
-				deviceStorage.deleteOnosDevice(device);
+				for(IOnosDeviceListener listener: deviceListeners) {
+					listener.onosDeviceRemoved(device);
+				}
 			}
-		    */
 		}
 	}
 
@@ -132,37 +139,28 @@
 		        return Command.CONTINUE;
 	    	} else if (srcDevice.getIpv4Address() == null &&
 	    			exDev.getSwitchDPID().equals(srcDevice.getSwitchDPID()) &&
-	    			exDev.getSwitchPort() == srcDevice.getSwitchPort() &&
-	    			exDev.getVlan().equals(srcDevice.getVlan())) {
-	    		//Device attachment point and mac address are the same
-	    		//but the packet does not have an ip address.
-	        	exDev.setLastSeenTimestamp(new Date());
-	        	if(log.isTraceEnabled()) {
-		        	log.debug("In the datagrid, there is the same device with no ip."
-							+ "Keep ip and update last seen time. dpid {}, port {}, mac {}, ip {}, lastSeenTime {}",
-							dpid, portId, srcDevice.getMacAddress(), srcDevice.getIpv4Address(), srcDevice.getLastSeenTimestamp().getTime());
-	        	}
-	        	return Command.CONTINUE;
+	    			exDev.getSwitchPort() == srcDevice.getSwitchPort()) {
+	    			//Vlan should be handled based on the Onos spec. Until then, don't handle it.
+		    		//Device attachment point and mac address are the same
+		    		//but the packet does not have an ip address.
+		        	exDev.setLastSeenTimestamp(new Date());
+		        	if(log.isTraceEnabled()) {
+			        	log.debug("In the datagrid, there is the same device with no ip."
+								+ "Keep ip and update last seen time. dpid {}, port {}, mac {}, ip {} lastSeenTime {}",
+								dpid, portId, srcDevice.getMacAddress(), exDev.getIpv4Address(), srcDevice.getLastSeenTimestamp().getTime());
+		        	}
+		        	return Command.CONTINUE;
+	    		}
 	    	}
-        }
 
         //If the switch port we try to attach a new device already has a link, then stop adding device
-	// TODO: Fix/update this after we refactor the Device Discovery mechanism
-	/*
-        Collection<TopologyElement> list = datagrid.getAllTopologyElements();
-        for(TopologyElement elem: list) {
-        	if(elem.getType() == Type.ELEMENT_LINK) {
-        		if((elem.getFromPort() == portId && elem.getFromSwitch() == dpid) ||
-        				(elem.getToPort() == portId && elem.getToSwitch() == dpid)) {
-        			if(log.isTraceEnabled()) {
-	        			log.debug("Stop adding OnosDevice {} due to there is a link to: dpid {} port {}",
-	    						srcDevice.getMacAddress(), dpid, portId);
-        			}
-        			return Command.CONTINUE;
-        		}
-        	}
+        if(networkGraph.getLink(dpid, (long)portId) != null) {
+			if(log.isTraceEnabled()) {
+    			log.debug("Stop adding OnosDevice {} due to there is a link to: dpid {} port {}",
+						srcDevice.getMacAddress(), dpid, portId);
+			}
+			return Command.CONTINUE;
         }
-	*/
 
         addOnosDevice(mac, srcDevice);
 
@@ -279,6 +277,8 @@
 		List<Class<? extends IFloodlightService>> dependencies =
 				new ArrayList<Class<? extends IFloodlightService>>();
 		dependencies.add(IFloodlightProviderService.class);
+		dependencies.add(INetworkGraphService.class);
+		dependencies.add(IDatagridService.class);
 		return dependencies;
 	}
 
@@ -288,7 +288,10 @@
 		floodlightProvider = context.getServiceImpl(IFloodlightProviderService.class);
 		executor.scheduleAtFixedRate(new CleanDevice(), 30 ,CLEANUP_SECOND, TimeUnit.SECONDS);
 
+		deviceListeners = new CopyOnWriteArrayList<IOnosDeviceListener>();
 		datagrid = context.getServiceImpl(IDatagridService.class);
+		networkGraphService = context.getServiceImpl(INetworkGraphService.class);
+		networkGraph = networkGraphService.getNetworkGraph();
 	}
 
 	@Override
@@ -297,12 +300,18 @@
 		datagrid.registerMapDeviceEventHandler(new MapDevListener());
 	}
 
-	@Override
+    @Override
 	public void deleteOnosDevice(OnosDevice dev) {
 		datagrid.sendNotificationDeviceDeleted(dev);
 		floodlightProvider.publishUpdate(new OnosDeviceUpdate(dev, OnosDeviceUpdateType.DELETE));
 	}
-
+    
+    @Override
+	public void deleteOnosDeviceByMac(MACAddress mac) {
+    	OnosDevice deleteDevice = mapDevice.get(mac);
+    	deleteOnosDevice(deleteDevice);
+	}
+	
 	@Override
 	public void addOnosDevice(Long mac, OnosDevice dev) {
         datagrid.sendNotificationDeviceAdded(mac, dev);
@@ -330,4 +339,14 @@
 			log.debug("updateDeviceMap: device mac {}", mac);
 		}
     }
+
+	@Override
+	public void addOnosDeviceListener(IOnosDeviceListener listener) {
+		deviceListeners.add(listener);
+	}
+
+	@Override
+	public void deleteOnosDeviceListener(IOnosDeviceListener listener) {
+		deviceListeners.remove(listener);
+	}
 }
diff --git a/src/main/java/net/onrc/onos/ofcontroller/floodlightlistener/NetworkGraphPublisher.java b/src/main/java/net/onrc/onos/ofcontroller/floodlightlistener/NetworkGraphPublisher.java
index fba97f5..88d9475 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/floodlightlistener/NetworkGraphPublisher.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/floodlightlistener/NetworkGraphPublisher.java
@@ -1,5 +1,6 @@
 package net.onrc.onos.ofcontroller.floodlightlistener;
 
+import java.net.InetAddress;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
@@ -16,8 +17,12 @@
 import net.floodlightcontroller.threadpool.IThreadPoolService;
 import net.onrc.onos.datagrid.IDatagridService;
 import net.onrc.onos.ofcontroller.core.IOFSwitchPortListener;
+import net.onrc.onos.ofcontroller.devicemanager.IOnosDeviceListener;
+import net.onrc.onos.ofcontroller.devicemanager.IOnosDeviceService;
+import net.onrc.onos.ofcontroller.devicemanager.OnosDevice;
 import net.onrc.onos.ofcontroller.linkdiscovery.ILinkDiscoveryListener;
 import net.onrc.onos.ofcontroller.linkdiscovery.ILinkDiscoveryService;
+import net.onrc.onos.ofcontroller.networkgraph.DeviceEvent;
 import net.onrc.onos.ofcontroller.networkgraph.INetworkGraphService;
 import net.onrc.onos.ofcontroller.networkgraph.LinkEvent;
 import net.onrc.onos.ofcontroller.networkgraph.NetworkGraph;
@@ -25,6 +30,7 @@
 import net.onrc.onos.ofcontroller.networkgraph.PortEvent;
 import net.onrc.onos.ofcontroller.networkgraph.Switch;
 import net.onrc.onos.ofcontroller.networkgraph.SwitchEvent;
+import net.onrc.onos.ofcontroller.networkgraph.PortEvent.SwitchPort;
 import net.onrc.onos.registry.controller.IControllerRegistryService;
 import net.onrc.onos.registry.controller.IControllerRegistryService.ControlChangeCallback;
 import net.onrc.onos.registry.controller.RegistryException;
@@ -34,6 +40,8 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import com.google.common.net.InetAddresses;
+
 /*
  * I've created a copy of the old NetworkGraphPublisher so I can integrate
  * the new API with ONOS while still having the old NetworkGraphPublisher
@@ -47,7 +55,8 @@
 public class NetworkGraphPublisher implements /*IOFSwitchListener,*/
 												IOFSwitchPortListener,
 												ILinkDiscoveryListener,
-												IFloodlightModule {
+												IFloodlightModule,
+												IOnosDeviceListener {
 	private static final Logger log = LoggerFactory.getLogger(NetworkGraphPublisher.class);
 
 	private IFloodlightProviderService floodlightProvider;
@@ -56,6 +65,8 @@
 	private IDatagridService datagridService;
 	private INetworkGraphService networkGraphService;
 
+	private IOnosDeviceService onosDeviceService;
+	
 	private NetworkGraph networkGraph;
 	private NetworkGraphDiscoveryInterface networkGraphDiscoveryInterface;
 	
@@ -311,6 +322,7 @@
 		linkDiscovery = context.getServiceImpl(ILinkDiscoveryService.class);
 		registryService = context.getServiceImpl(IControllerRegistryService.class);
 		datagridService = context.getServiceImpl(IDatagridService.class);
+		onosDeviceService = context.getServiceImpl(IOnosDeviceService.class);
 
 		networkGraphService = context.getServiceImpl(INetworkGraphService.class);
 	}
@@ -320,6 +332,7 @@
 		// TODO enable cleanup thread
 		floodlightProvider.addOFSwitchListener(this);
 		linkDiscovery.addListener(this);
+		onosDeviceService.addOnosDeviceListener(this);
 
 		networkGraph = networkGraphService.getNetworkGraph();
 		networkGraphDiscoveryInterface = 
@@ -343,4 +356,30 @@
 			cleanupTask.reschedule(0, TimeUnit.SECONDS);
 		}
 	}
+	
+	@Override
+	public void onosDeviceAdded(OnosDevice device) {
+		log.debug("Called onosDeviceAdded mac {}", device.getMacAddress());
+
+		SwitchPort sp = new SwitchPort(device.getSwitchDPID(), (long)device.getSwitchPort());
+		List<SwitchPort> spLists = new ArrayList<SwitchPort>();
+		spLists.add(sp);
+		DeviceEvent event = new DeviceEvent(device.getMacAddress());
+		event.setAttachmentPoints(spLists);	
+		event.setLastSeenTime(device.getLastSeenTimestamp().getTime());
+		if(device.getIpv4Address() != null) {
+			InetAddress ip = InetAddresses.fromInteger(device.getIpv4Address());	
+			event.addIpAddress(ip);
+		}
+		//Does not use Vlan info now.
+		
+		networkGraphDiscoveryInterface.putDeviceDiscoveryEvent(event);	
+	}
+
+	@Override
+	public void onosDeviceRemoved(OnosDevice device) {	
+		log.debug("Called onosDeviceRemoved");
+		DeviceEvent event = new DeviceEvent(device.getMacAddress());
+		networkGraphDiscoveryInterface.removeDeviceDiscoveryEvent(event);
+	}
 }
diff --git a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/DeviceEvent.java b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/DeviceEvent.java
index 8bea7f8..1846d8b 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/DeviceEvent.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/DeviceEvent.java
@@ -27,7 +27,7 @@
     private final MACAddress mac;
     protected List<SwitchPort> attachmentPoints;
     protected Set<InetAddress> ipAddresses;
-
+    private long lastSeenTime;
 
     /**
      * Default constructor for Serializer to use.
@@ -68,11 +68,11 @@
     }
 
 
-    boolean addIpAddress(InetAddress addr) {
+    public boolean addIpAddress(InetAddress addr) {
 	return this.ipAddresses.add(addr);
     }
 
-    boolean removeIpAddress(InetAddress addr) {
+    public boolean removeIpAddress(InetAddress addr) {
 	return this.ipAddresses.remove(addr);
     }
 
@@ -93,4 +93,12 @@
     public ByteBuffer getIDasByteBuffer() {
 	return getDeviceID(mac.toBytes());
     }
+
+	public long getLastSeenTime() {
+		return lastSeenTime;
+	}
+
+	public void setLastSeenTime(long lastSeenTime) {
+		this.lastSeenTime = lastSeenTime;
+	}
 }
diff --git a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/DeviceImpl.java b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/DeviceImpl.java
index 2b8930b..8f46f31 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/DeviceImpl.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/DeviceImpl.java
@@ -17,38 +17,42 @@
     private final MACAddress macAddr;
     protected LinkedList<Port> attachmentPoints;
     protected Set<InetAddress> ipAddresses;
+    private long lastSeenTime;
 
     public DeviceImpl(NetworkGraph graph, MACAddress mac) {
-	super(graph);
-	this.macAddr = mac;
-	this.attachmentPoints = new LinkedList<>();
-	this.ipAddresses = new HashSet<>();
+		super(graph);
+		this.macAddr = mac;
+		this.attachmentPoints = new LinkedList<>();
+		this.ipAddresses = new HashSet<>();
     }
 
     @Override
     public MACAddress getMacAddress() {
-	return this.macAddr;
+    	return this.macAddr;
     }
 
     @Override
     public Collection<InetAddress> getIpAddress() {
-	return Collections.unmodifiableSet(ipAddresses);
+    	return Collections.unmodifiableSet(ipAddresses);
     }
 
     @Override
     public Iterable<Port> getAttachmentPoints() {
-	return Collections.unmodifiableList(this.attachmentPoints);
+    	return Collections.unmodifiableList(this.attachmentPoints);
     }
 
     @Override
     public long getLastSeenTime() {
-	// TODO Auto-generated method stub
-	return 0;
+    	return lastSeenTime;
     }
 
     @Override
     public String toString() {
-	return macAddr.toString();
+    	return macAddr.toString();
+    }
+    
+    void setLastSeenTime(long lastSeenTime) {
+    	this.lastSeenTime = lastSeenTime;
     }
 
     /**
@@ -56,8 +60,8 @@
      * @param p
      */
     void addAttachmentPoint(Port p) {
-	this.attachmentPoints.remove(p);
-	this.attachmentPoints.addFirst(p);
+    	this.attachmentPoints.remove(p);
+    	this.attachmentPoints.addFirst(p);
     }
 
     /**
@@ -65,7 +69,7 @@
      * @param p
      */
     boolean removeAttachmentPoint(Port p) {
-	return this.attachmentPoints.remove(p);
+    	return this.attachmentPoints.remove(p);
     }
 
     /**
@@ -73,7 +77,7 @@
      * @param p
      */
     boolean addIpAddress(InetAddress addr) {
-	return this.ipAddresses.add(addr);
+    	return this.ipAddresses.add(addr);
     }
 
     /**
@@ -81,6 +85,6 @@
      * @param p
      */
     boolean removeIpAddress(InetAddress addr) {
-	return this.ipAddresses.remove(addr);
+    	return this.ipAddresses.remove(addr);
     }
 }
diff --git a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/NetworkGraphDatastore.java b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/NetworkGraphDatastore.java
index 30b2f73..63f37d8 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/NetworkGraphDatastore.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/NetworkGraphDatastore.java
@@ -1,21 +1,27 @@
 package net.onrc.onos.ofcontroller.networkgraph;
 
+import java.net.Inet4Address;
+import java.net.InetAddress;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Collection;
 
 import net.onrc.onos.datastore.DataStoreClient;
 import net.onrc.onos.datastore.IKVClient;
+import net.onrc.onos.datastore.topology.KVDevice;
 import net.onrc.onos.datastore.topology.KVLink;
 import net.onrc.onos.datastore.topology.KVPort;
 import net.onrc.onos.datastore.topology.KVPort.STATUS;
 import net.onrc.onos.datastore.topology.KVSwitch;
 import net.onrc.onos.datastore.utils.KVObject;
 import net.onrc.onos.datastore.utils.KVObject.WriteOp;
+import net.onrc.onos.ofcontroller.networkgraph.PortEvent.SwitchPort;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import com.google.common.net.InetAddresses;
+
 /**
  * The southbound interface to the network graph which allows clients to
  * mutate the graph. This class will maintain the invariants of the network
@@ -186,8 +192,24 @@
 	 * @return true on success, otherwise false.
 	 */
 	public boolean addDevice(DeviceEvent device) {
-		// TODO implement
-		return false;			// Failure: not implemented yet
+		log.debug("Adding device into DB. mac {}", device.getMac());
+
+		KVDevice rcDevice = new KVDevice(device.getMac().toBytes());
+		rcDevice.setLastSeenTime(device.getLastSeenTime());
+		
+		for(SwitchPort sp : device.getAttachmentPoints()) {
+			byte[] portId = KVPort.getPortID(sp.getDpid(), sp.getNumber());		
+			rcDevice.addPortId(portId);
+		}
+		
+		for(InetAddress addr : device.getIpAddresses()) {
+			//It assume only one ip on a device now.
+			rcDevice.setIp(InetAddresses.coerceToInteger(addr));	
+		}
+
+		rcDevice.forceCreate();
+		
+		return true;
 	}
 
 	/**
@@ -197,7 +219,11 @@
 	 * @return true on success, otherwise false.
 	 */
 	public boolean removeDevice(DeviceEvent device) {
-		// TODO implement
-		return false;			// Failure: not implemented yet
+		log.debug("Removing device into DB. mac {}", device.getMac());
+		
+		KVDevice rcDevice = new KVDevice(device.getMac().toBytes());
+		rcDevice.forceDelete();
+		
+		return true;
 	}
 }
diff --git a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/TopologyManager.java b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/TopologyManager.java
index a323726..ccd3601 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/TopologyManager.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/TopologyManager.java
@@ -493,7 +493,7 @@
 	    // Send out notification
 	    TopologyEvent topologyEvent = new TopologyEvent(switchEvent);
 	    eventChannel.addEntry(topologyEvent.getID(), topologyEvent);
-
+	    
 	    // Send out notification for each port
 	    for (PortEvent portEvent : portEvents) {
 		topologyEvent = new TopologyEvent(portEvent);
@@ -719,7 +719,8 @@
 	    // Send out notification
 	    TopologyEvent topologyEvent = new TopologyEvent(deviceEvent);
 	    eventChannel.addEntry(topologyEvent.getID(), topologyEvent);
-
+	    log.debug("Put the device info into the cache of the graph. mac {}", deviceEvent.getMac());
+	    
 	    // Store the new Device Event in the local cache
 	    // TODO: The implementation below is probably wrong
 	    for (SwitchPort swp : deviceEvent.getAttachmentPoints()) {
@@ -746,6 +747,7 @@
 	if (datastore.removeDevice(deviceEvent)) {
 	    // Send out notification
 	    eventChannel.removeEntry(deviceEvent.getID());
+	    log.debug("Remove the device info into the cache of the graph. mac {}", deviceEvent.getMac());
 
 	    // Cleanup the Device Event from the local cache
 	    // TODO: The implementation below is probably wrong
@@ -998,9 +1000,12 @@
      */
     private void addDevice(DeviceEvent deviceEvent) {
 	Device device = networkGraph.getDeviceByMac(deviceEvent.getMac());
+	
 	if (device == null) {
+		log.debug("Existing device was not found in networkGraph. New device. mac {}", deviceEvent.getMac());
 	    device = new DeviceImpl(networkGraph, deviceEvent.getMac());
 	}
+	
 	DeviceImpl deviceImpl = getDeviceImpl(device);
 
 	// Update the IP addresses
@@ -1036,6 +1041,7 @@
 
 	// Update the device in the Network Graph
 	if (attachmentFound) {
+    	log.debug("Storing the info into networkGraph. mac {}", deviceEvent.getMac());
 	    networkGraph.putDevice(device);
 	    apiAddedDeviceEvents.add(deviceEvent);
 	}
diff --git a/src/main/java/net/onrc/onos/ofcontroller/util/serializers/KryoFactory.java b/src/main/java/net/onrc/onos/ofcontroller/util/serializers/KryoFactory.java
index 9eb4e10..42a3a4d 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/util/serializers/KryoFactory.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/util/serializers/KryoFactory.java
@@ -1,8 +1,9 @@
 package net.onrc.onos.ofcontroller.util.serializers;
 
+import java.net.Inet4Address;
 import java.net.InetAddress;
 import java.util.ArrayList;
-
+import java.util.HashSet;
 import net.floodlightcontroller.util.MACAddress;
 import net.onrc.onos.intent.ConstrainedShortestPathIntent;
 import net.onrc.onos.intent.ErrorIntent;
@@ -44,6 +45,8 @@
 // import net.onrc.onos.ofcontroller.util.SwitchPort;
 
 
+
+
 import com.esotericsoftware.kryo.Kryo;
 
 /**
@@ -202,6 +205,10 @@
 	kryo.register(IntentOperationList.class);
 	kryo.register(IntentStateList.class);
 
+	// Device-related classes
+	kryo.register(HashSet.class);
+	kryo.register(Inet4Address.class);
+
 	return kryo;
     }
 }