diff --git a/src/main/java/net/onrc/onos/graph/GraphDBConnection.java b/src/main/java/net/onrc/onos/graph/GraphDBConnection.java
index bebcdd2..56a54f2 100644
--- a/src/main/java/net/onrc/onos/graph/GraphDBConnection.java
+++ b/src/main/java/net/onrc/onos/graph/GraphDBConnection.java
@@ -7,6 +7,7 @@
 
 import com.thinkaurelius.titan.core.TitanFactory;
 import com.thinkaurelius.titan.core.TitanGraph;
+import com.thinkaurelius.titan.diskstorage.StorageException;
 import com.tinkerpop.blueprints.TransactionalGraph;
 import com.tinkerpop.blueprints.Vertex;
 import com.tinkerpop.blueprints.util.wrappers.event.EventTransactionalGraph;
@@ -133,15 +134,17 @@
 
 	/**
 	 * Commit changes for the graph operations.
+	 * @throws Exception 
 	 */
 	@Override
 	public void commit() {
-		try {
+//		// Should not catch exception here! 
+//		try {
 			graph.commit();
-		}
-		catch (Exception e) {
-			log.error("{}", e.toString());
-		}
+//		}
+//		catch (Exception e) {
+//			log.error("{}", e.toString());
+//		}
 	}
 
 	/**
@@ -149,12 +152,13 @@
 	 */
 	@Override
 	public void rollback() {
-		try {
+		// Should not catch exception here! 
+//		try {
 			graph.rollback();
-		}
-		catch (Exception e) {
-			log.error("{}", e.toString());
-		}
+//		}
+//		catch (Exception e) {
+//			log.error("{}", e.toString());
+//		}
 	}
 
 	/**
@@ -162,6 +166,10 @@
 	 */
 	@Override
 	public void close() {
-		commit();
+		try {
+			commit();
+		} catch (Exception e) {
+			log.error("{}", e.toString());
+		}
 	}
 }
diff --git a/src/main/java/net/onrc/onos/ofcontroller/core/ILinkStorage.java b/src/main/java/net/onrc/onos/ofcontroller/core/ILinkStorage.java
index ce2379b..483fbda 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/core/ILinkStorage.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/core/ILinkStorage.java
@@ -15,26 +15,27 @@
 	/*
 	 * Generic operation method
 	 */
-	public void update(Link link, LinkInfo linkinfo, DM_OPERATION op);
+	public boolean update(Link link, LinkInfo linkinfo, DM_OPERATION op);
 	
 	/*
      * Link creation
      */
-	public void addLink(Link link);
-	public void addLinks(List<Link> links);
+	public boolean addLink(Link link);
+	public boolean addLink(Link link, LinkInfo linfo);
+	public boolean addLinks(List<Link> links);
 	
 	/*
 	 * Link deletion
 	 */
-	public void deleteLink(Link link);
-	public void deleteLinks(List<Link> links);
+	public boolean deleteLink(Link link);
+	public boolean deleteLinks(List<Link> links);
 
 	/*
 	 * Utility method to delete links associated with dpid and port 
 	 * If only dpid is used, All links associated for switch are removed
 	 * Useful for port up/down and also switch join/remove events
 	 */ 
-	public void deleteLinksOnPort(Long dpid, short port);
+	public boolean deleteLinksOnPort(Long dpid, short port);
 
 	/*
 	 * Get Links from Storage
diff --git a/src/main/java/net/onrc/onos/ofcontroller/core/ISwitchStorage.java b/src/main/java/net/onrc/onos/ofcontroller/core/ISwitchStorage.java
index bc50049..b7825f9 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/core/ISwitchStorage.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/core/ISwitchStorage.java
@@ -18,27 +18,29 @@
 	/*
 	 * Update the switch details
 	 */
-	public void update(String dpid,SwitchState state, DM_OPERATION op);
-	/*
-	 * Associate a port on switch
-	 */
-	public void addPort(String dpid, OFPhysicalPort port);
-	/*
-	 * Delete a port on a switch by num
-	 */
-	public void deletePort(String dpid, short port);
+	public boolean updateSwitch(String dpid, SwitchState state, DM_OPERATION op);
 	/*
 	 * Add a switch and all its associated ports
 	 */
-	public void addSwitch(IOFSwitch sw);
+	public boolean addSwitch(IOFSwitch sw);
 	/*
 	 * Add a switch
 	 */
-	public void addSwitch(String dpid);
+	public boolean addSwitch(String dpid);
 	/*
 	 * Delete switch and associated ports
 	 */
-	public void deleteSwitch(String dpid);
-	
-
+	public boolean deleteSwitch(String dpid);
+	/*
+	 * Update the port details
+	 */
+	public boolean updatePort(String dpid, short port, int state, String desc);
+	/*
+	 * Associate a port on switch
+	 */
+	public boolean addPort(String dpid, OFPhysicalPort port);
+	/*
+	 * Delete a port on a switch by num
+	 */
+	public boolean deletePort(String dpid, short port);
 }
diff --git a/src/main/java/net/onrc/onos/ofcontroller/core/internal/LinkStorageImpl.java b/src/main/java/net/onrc/onos/ofcontroller/core/internal/LinkStorageImpl.java
index 753563e..da34c22 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/core/internal/LinkStorageImpl.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/core/internal/LinkStorageImpl.java
@@ -14,7 +14,6 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import com.thinkaurelius.titan.core.TitanException;
 import com.tinkerpop.blueprints.Vertex;
 import com.tinkerpop.pipes.PipeFunction;
 import com.tinkerpop.pipes.transform.PathPipe;
@@ -25,7 +24,7 @@
 public class LinkStorageImpl implements ILinkStorage {
 	
 	protected static Logger log = LoggerFactory.getLogger(LinkStorageImpl.class);
-	protected GraphDBOperation dbop;
+	protected GraphDBOperation op;
 
 	
 	/**
@@ -34,37 +33,105 @@
 	 */
 	@Override
 	public void init(String conf) {
-		this.dbop = new GraphDBOperation(conf);
+		this.op = new GraphDBOperation(conf);
 	}
 
+	// Method designing policy:
+	//  op.commit() and op.rollback() MUST called in public (first-class) methods.
+	//  A first-class method MUST NOT call other first-class method.
+	//  Routine process should be implemented in private method.
+	//  A private method MUST NOT call commit or rollback.
+
+	
 	/**
-	 * Update a record in the LinkStorage in a way provided by op.
+	 * Update a record in the LinkStorage in a way provided by dmop.
 	 * @param link Record of a link to be updated.
-	 * @param op Operation to be done.
+	 * @param linkinfo Meta-information of a link to be updated.
+	 * @param dmop Operation to be done.
 	 */
 	@Override
-	public void update(Link link, LinkInfo linkinfo, DM_OPERATION op) {
-		switch (op) {
+	public boolean update(Link link, LinkInfo linkinfo, DM_OPERATION dmop) {
+		boolean success = false;
+		
+		switch (dmop) {
 		case CREATE:
 		case INSERT:
-			addLinkImpl(link,op);
+			if (link != null) {
+				try {
+					if (addLinkImpl(link)) {
+						op.commit();
+						success = true;
+					}
+				} catch (Exception e) {
+					op.rollback();
+					e.printStackTrace();
+		        	log.error("LinkStorageImpl:update {} link:{} failed", dmop, link);
+				}
+			}
 			break;
 		case UPDATE:
-			if (linkinfo != null) {
-				setLinkInfo(link, linkinfo);
-			} else {
-				deleteLinkInfo(link);
+			if (link != null && linkinfo != null) {
+				try {
+					if (setLinkInfoImpl(link, linkinfo)) {
+						op.commit();
+						success = true;
+					}
+				} catch (Exception e) {
+					op.rollback();
+					e.printStackTrace();
+		        	log.error("LinkStorageImpl:update {} link:{} failed", dmop, link);
+				}
 			}
 			break;
 		case DELETE:
-			deleteLink(link);
+			if (link != null) {
+				try {
+					if (deleteLinkImpl(link)) {
+						op.commit();
+						success = true;
+		            	log.debug("LinkStorageImpl:update {} link:{} succeeded", dmop, link);
+		            } else {
+						op.rollback();
+		            	log.debug("LinkStorageImpl:update {} link:{} failed", dmop, link);
+					}
+				} catch (Exception e) {
+					op.rollback();
+					e.printStackTrace();
+					log.error("LinkStorageImpl:update {} link:{} failed", dmop, link);
+				}
+			}
 			break;
 		}
+		
+		return success;
 	}
 
 	@Override
-	public void addLink(Link link) {
-		addLinkImpl(link, DM_OPERATION.INSERT);
+	public boolean addLink(Link link) {
+		return addLink(link, null);
+	}
+
+	@Override
+	public boolean addLink(Link link, LinkInfo linfo) {
+		boolean success = false;
+		
+		try {
+			if (addLinkImpl(link)) {
+				// Set LinkInfo only if linfo is non-null.
+				if (linfo != null && (! setLinkInfoImpl(link, linfo))) {
+					op.rollback();
+				}
+				op.commit();
+				success = true;
+			} else {
+				op.rollback();
+			}
+		} catch (Exception e) {
+			e.printStackTrace();
+			log.error("LinkStorageImpl:addLink link:{} linfo:{} failed", link, linfo);
+		}
+		
+		return success;
 	}
 	
 	/**
@@ -73,143 +140,82 @@
 	 * @param op Operation to be done.
 	 */
 	@Override
-	public void addLinks(List<Link> links) {
+	public boolean addLinks(List<Link> links) {
+		boolean success = false;
+		
 		for (Link lt: links) {
-			addLinkImpl(lt, DM_OPERATION.INSERT);
+			if (! addLinkImpl(lt)) {
+				return false;
+			}
 		}
+		
+		try {
+			op.commit();
+			success = true;
+		} catch (Exception e) {
+			e.printStackTrace();
+			log.error("LinkStorageImpl:addLinks link:s{} failed", links);
+		}
+		
+		return success;
 	}
 
 	/**
-		 * Delete a record in the LinkStorage.
-		 * @param lt Record to be deleted.
-		 */
-		@Override
-		public void deleteLink(Link lt) {
-			IPortObject vportSrc = null, vportDst = null;
-			
-			log.debug("deleteLink(): {}", lt);
-			
-	        try {
-	            // get source port vertex
-	         	String dpid = HexString.toHexString(lt.getSrc());
-	         	short port = lt.getSrcPort();
-	         	vportSrc = dbop.searchPort(dpid, port);
-	            
-	            // get dst port vertex
-	         	dpid = HexString.toHexString(lt.getDst());
-	         	port = lt.getDstPort();
-	         	vportDst = dbop.searchPort(dpid, port);
-	     		// FIXME: This needs to remove all edges
-	         	
-	         	if (vportSrc != null && vportDst != null) {
-	         		vportSrc.removeLink(vportDst);
-	        		dbop.commit();
-	            	log.debug("deleteLink(): deleted edges src {} dst {}", new Object[]{
-	            			lt, vportSrc, vportDst});
-	            	
-	        		// TODO publish DELETE_LINK event here
-	            } else {
-	            	log.error("deleteLink(): failed invalid vertices {} src {} dst {}", new Object[]{lt, vportSrc, vportDst});
-	            	dbop.rollback();
-	            }
-	         	
-	        } catch (TitanException e) {
-	            /*
-	             * retry till we succeed?
-	             */
-	        	log.error("deleteLink(): titan exception {} {}", new Object[]{lt, e.toString()});
-	        	dbop.rollback();
-	        	e.printStackTrace();
-	        }
-		}
+	 * Delete a record in the LinkStorage.
+	 * @param lt Record to be deleted.
+	 */
+	@Override
+	public boolean deleteLink(Link lt) {
+		boolean success = false;
+		
+		log.debug("LinkStorageImpl:deleteLink(): {}", lt);
+		
+        try {
+         	if (deleteLinkImpl(lt)) {
+        		op.commit();
+        		success = true;
+            	log.debug("LinkStorageImpl:deleteLink(): deleted edges {}", lt);
+            } else {
+            	op.rollback();
+            	log.error("LinkStorageImpl:deleteLink(): failed invalid vertices {}", lt);
+            }
+        } catch (Exception e) {
+        	op.rollback();
+        	log.error("LinkStorageImpl:deleteLink(): failed {} {}",
+        			new Object[]{lt, e.toString()});
+        	e.printStackTrace();
+        }
+        
+        return success;
+	}
 
 	/**
 	 * Delete multiple records in LinkStorage.
 	 * @param links List of records to be deleted.
 	 */
 	@Override
-	public void deleteLinks(List<Link> links) {
-		for (Link lt : links) {
-			deleteLink(lt);
+	public boolean deleteLinks(List<Link> links) {
+		boolean success = false;
+		
+		try {
+			for (Link lt : links) {
+				if (! deleteLinkImpl(lt)) {
+					op.rollback();
+					return false;
+				}
+			}
+			op.commit();
+			success = true;
+		} catch (Exception e) {
+        	op.rollback();
+			e.printStackTrace();
+        	log.error("LinkStorageImpl:deleteLinks failed invalid vertices {}", links);
 		}
-	}
-
-	/**
-	 * Update a record of link with meta-information in the LinkStorage in a way provided by op.
-	 * @param link Record of a link to update.
-	 * @param linkinfo Meta-information of a link to be updated.
-	 * @param op Operation to be done.
-	 */
-	private void setLinkInfo(Link link, LinkInfo linkinfo) {
-		// TODO implement this
 		
-		// TODO publish UPDATE_LINK event here
-	}
-	
-	private void deleteLinkInfo(Link link) {
-		// TODO implement this
-		
-		// TODO publish UPDATE_LINK event here
+		return success;
 	}
 
 	/**
-	 * Perform INSERT/CREATE/UPDATE operation to update the LinkStorage.
-	 * @param lt Record of a link to be updated.
-	 * @param linkinfo Meta-information of a link to be updated.
-	 * @param op Operation to be done. (only INSERT/CREATE/UPDATE is acceptable)
-	 */
-	private void addLinkImpl(Link lt, DM_OPERATION op) {
-		IPortObject vportSrc = null, vportDst = null;
-	
-		log.trace("updateLink(): op {} {}", new Object[]{op, lt});
-		
-        try {
-            // get source port vertex
-        	String dpid = HexString.toHexString(lt.getSrc());
-        	short port = lt.getSrcPort();
-        	vportSrc = dbop.searchPort(dpid, port);
-            
-            // get dest port vertex
-            dpid = HexString.toHexString(lt.getDst());
-            port = lt.getDstPort();
-            vportDst = dbop.searchPort(dpid, port);
-                        
-            if (vportSrc != null && vportDst != null) {
-            	// check if the link exists
-            	
-            	Iterable<IPortObject> currPorts = vportSrc.getLinkedPorts();
-            	List<IPortObject> currLinks = new ArrayList<IPortObject>();
-            	for (IPortObject V : currPorts) {
-            		currLinks.add(V);
-            	}
-
-            	if (currLinks.contains(vportDst)) {
-            		if (op.equals(DM_OPERATION.INSERT) || op.equals(DM_OPERATION.CREATE)) {
-            			log.debug("addOrUpdateLink(): failed link exists {} {} src {} dst {}", 
-            					new Object[]{op, lt, vportSrc, vportDst});
-            		}
-            	} else {
-            		vportSrc.setLinkPort(vportDst);
-
-            		dbop.commit();
-            		log.debug("updateLink(): link added {} {} src {} dst {}", new Object[]{op, lt, vportSrc, vportDst});
-            		
-            		// TODO publish ADD_LINK event here
-            	}
-            } else {
-            	log.error("updateLink(): failed invalid vertices {} {} src {} dst {}", new Object[]{op, lt, vportSrc, vportDst});
-            	dbop.rollback();
-            }
-        } catch (TitanException e) {
-            /*
-             * retry till we succeed?
-             */
-        	e.printStackTrace();
-        	log.error("updateLink(): titan exception {} {} {}", new Object[]{op, lt, e.toString()});
-        }
-	}
-	
-	/**
 	 * Get list of all links connected to the port specified by given DPID and port number.
 	 * @param dpid DPID of desired port.
 	 * @param port Port number of desired port.
@@ -219,7 +225,7 @@
 	public List<Link> getLinks(Long dpid, short port) {
     	List<Link> links = new ArrayList<Link>();
     	
-    	IPortObject srcPort = dbop.searchPort(HexString.toHexString(dpid), port);
+    	IPortObject srcPort = op.searchPort(HexString.toHexString(dpid), port);
     	ISwitchObject srcSw = srcPort.getSwitch();
     	
     	if(srcSw != null && srcPort != null) {
@@ -243,12 +249,27 @@
 	 * @param port Port number of desired port.
 	 */
 	@Override
-	public void deleteLinksOnPort(Long dpid, short port) {
-		List<Link> linksToDelete = getLinks(dpid, port);
+	public boolean deleteLinksOnPort(Long dpid, short port) {
+		boolean success = false;
 		
-		for(Link l : linksToDelete) {
-			deleteLink(l);
+		List<Link> linksToDelete = getLinks(dpid, port);
+		try {
+			for(Link l : linksToDelete) {
+				if (! deleteLinkImpl(l)) {
+					op.rollback();
+					log.error("LinkStorageImpl:deleteLinksOnPort dpid:{} port:{} failed", dpid, port);
+					return false;
+				}
+			}
+			op.commit();
+			success = true;
+		} catch (Exception e) {
+        	op.rollback();
+			e.printStackTrace();
+        	log.error("LinkStorageImpl:deleteLinksOnPort dpid:{} port:{} failed", dpid, port);
 		}
+		
+		return success;
 	}
 
 	/**
@@ -260,7 +281,7 @@
 	public List<Link> getLinks(String dpid) {
 		List<Link> links = new ArrayList<Link>();
 
-		ISwitchObject srcSw = dbop.searchSwitch(dpid);
+		ISwitchObject srcSw = op.searchSwitch(dpid);
 		
 		if(srcSw != null) {
 			for(IPortObject srcPort : srcSw.getPorts()) {
@@ -285,7 +306,7 @@
 	 * @return List of active links. Empty list if no port was found.
 	 */
 	public List<Link> getActiveLinks() {
-		Iterable<ISwitchObject> switches = dbop.getActiveSwitches();
+		Iterable<ISwitchObject> switches = op.getActiveSwitches();
 
 		List<Link> links = new ArrayList<Link>(); 
 		
@@ -329,6 +350,79 @@
 //		graph.shutdown();		
 	}
 
+	/**
+	 * Update a record of link with meta-information in the LinkStorage.
+	 * @param link Record of a link to update.
+	 * @param linkinfo Meta-information of a link to be updated.
+	 */
+	private boolean setLinkInfoImpl(Link link, LinkInfo linkinfo) {
+		// TODO implement this
+		
+		return false;
+	}
+
+	private boolean addLinkImpl(Link lt) {
+		boolean success = false;
+		
+		IPortObject vportSrc = null, vportDst = null;
+		
+		// get source port vertex
+		String dpid = HexString.toHexString(lt.getSrc());
+		short port = lt.getSrcPort();
+		vportSrc = op.searchPort(dpid, port);
+		
+		// get dest port vertex
+		dpid = HexString.toHexString(lt.getDst());
+		port = lt.getDstPort();
+		vportDst = op.searchPort(dpid, port);
+		            
+		if (vportSrc != null && vportDst != null) {
+			IPortObject portExist = null;
+			// check if the link exists
+			for (IPortObject V : vportSrc.getLinkedPorts()) {
+				if (V.equals(vportDst)) {
+					portExist = V;
+					break;
+				}
+			}
+		
+			if (portExist == null) {
+				vportSrc.setLinkPort(vportDst);
+				success = true;
+			} else {
+				log.debug("LinkStorageImpl:addLinkImpl failed link exists {} {} src {} dst {}", 
+						new Object[]{op, lt, vportSrc, vportDst});
+			}
+		}
+		
+		return success;
+	}
+
+	private boolean deleteLinkImpl(Link lt) {
+		boolean success = false;
+		IPortObject vportSrc = null, vportDst = null;
+	
+	    // get source port vertex
+	 	String dpid = HexString.toHexString(lt.getSrc());
+	 	short port = lt.getSrcPort();
+	 	vportSrc = op.searchPort(dpid, port);
+	    
+	    // get dst port vertex
+	 	dpid = HexString.toHexString(lt.getDst());
+	 	port = lt.getDstPort();
+	 	vportDst = op.searchPort(dpid, port);
+	 	
+		// FIXME: This needs to remove all edges
+	 	if (vportSrc != null && vportDst != null) {
+	 		vportSrc.removeLink(vportDst);
+	    	log.debug("deleteLinkImpl(): deleted edges src {} dst {}", new Object[]{
+	    			lt, vportSrc, vportDst});
+	    	success = true;
+	    }
+	    
+	 	return success;
+	}
+
 	// TODO should be moved to TopoLinkServiceImpl (never used in this class)
 	static class ExtractLink implements PipeFunction<PathPipe<Vertex>, Link> {
 	
diff --git a/src/main/java/net/onrc/onos/ofcontroller/core/internal/SwitchStorageImpl.java b/src/main/java/net/onrc/onos/ofcontroller/core/internal/SwitchStorageImpl.java
index d9f24e0..8399d6f 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/core/internal/SwitchStorageImpl.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/core/internal/SwitchStorageImpl.java
@@ -1,8 +1,5 @@
 package net.onrc.onos.ofcontroller.core.internal;
 
-import java.util.ArrayList;
-import java.util.List;
-
 import net.floodlightcontroller.core.IOFSwitch;
 import net.onrc.onos.graph.GraphDBConnection;
 import net.onrc.onos.graph.GraphDBOperation;
@@ -17,7 +14,7 @@
 import org.slf4j.LoggerFactory;
 
 /**
- * This is the class for storing the information of switches into CassandraDB
+ * This is the class for storing the information of switches into GraphDB
  */
 public class SwitchStorageImpl implements ISwitchStorage {
 	protected GraphDBOperation op;
@@ -50,23 +47,12 @@
 		op.close();		
 	}
 	
-	private void setStatus(String dpid, SwitchState state) {
-		ISwitchObject sw = op.searchSwitch(dpid);
-		
-		try {
-			if (sw != null) {
-				sw.setState(state.toString());
-				op.commit();
-				log.info("SwitchStorage:setStatus dpid:{} state: {} done", dpid, state);
-			    // TODO publish UPDATE_SWITCH event here
-			}
-		} catch(Exception e) {
-			e.printStackTrace();
-			op.rollback();
-			log.info("SwitchStorage:setStatus dpid:{} state: {} failed: switch not found", dpid, state);	
-		}
-	}
-
+	// Method designing policy:
+	//  op.commit() and op.rollback() MUST called in public (first-class) methods.
+	//  A first-class method MUST NOT call other first-class method.
+	//  Routine process should be implemented in private method.
+	//  A private method MUST NOT call commit or rollback.
+	
 	/***
 	 * This function is for updating the switch into the DB.
 	 * @param dpid The switch dpid you want to update from the DB
@@ -74,71 +60,221 @@
 	 * @param dmope	The DM_OPERATION of the switch
 	 */
 	@Override
-	public void update(String dpid, SwitchState state, DM_OPERATION dmope) {
-		log.info("SwitchStorage:update dpid:{} state: {} ", dpid, state);
+	public boolean updateSwitch(String dpid, SwitchState state, DM_OPERATION dmope) {
+		boolean success = false;
+		ISwitchObject sw = null;
+		
+		log.info("SwitchStorage:update {} dpid:{}", dmope, dpid);
 	    switch(dmope) {
 	    	case UPDATE:
+            	try {
+		    		sw = op.searchSwitch(dpid);
+		    		if (sw != null) {
+			            	setSwitchStateImpl(sw, state);
+							op.commit();
+							success = true;
+		    		}
+				} catch (Exception e) {
+					op.rollback();
+					e.printStackTrace();
+					log.info("SwitchStorage:update {} dpid:{} failed", dmope, dpid);
+				}
+	    		break;
 	    	case INSERT:
 	    	case CREATE:
-	            addSwitch(dpid);
-	            if (state != SwitchState.ACTIVE) {
-	            	setStatus(dpid, state);
-	            }
+            	try {
+		            sw = addSwitchImpl(dpid);
+		            if (sw != null) {
+			            if (state != SwitchState.ACTIVE) {
+			            	setSwitchStateImpl(sw, state);
+			            }
+						op.commit();
+						success = true;
+		            }
+				} catch (Exception e) {
+					op.rollback();
+					e.printStackTrace();
+					log.info("SwitchStorage:update {} dpid:{} failed", dmope, dpid);
+				}
 	            break;
 	    	case DELETE:
-	            deleteSwitch(dpid);
+	            try {
+		    		sw = op.searchSwitch(dpid);
+		    		if (sw != null) {
+				            deleteSwitchImpl(sw);
+							op.commit();
+							success = true;
+		    		}
+				} catch (Exception e) {
+					op.rollback();
+					e.printStackTrace();
+					log.info("SwitchStorage:update {} dpid:{} failed", dmope, dpid);
+				}
 	            break;
 	    	default:
 	    }
+	    
+	    return success;
+	}
+	
+	@Override
+	public boolean addSwitch(IOFSwitch sw) {
+		boolean success = false;
+		
+		String dpid = sw.getStringId();
+		log.info("SwitchStorage:addSwitch(): dpid {} ", dpid);
+		
+		try {
+			ISwitchObject curr = op.searchSwitch(dpid);
+			if (curr != null) {
+				//If existing the switch. set The SW state ACTIVE. 
+				log.info("SwitchStorage:addSwitch dpid:{} already exists", dpid);
+				setSwitchStateImpl(curr, SwitchState.ACTIVE);
+			} else {
+				curr = addSwitchImpl(dpid);
+			}
+	
+			for (OFPhysicalPort port: sw.getPorts()) {
+				IPortObject p = op.searchPort(dpid, port.getPortNumber());
+				if (p != null) {
+		    		log.error("SwitchStorage:addPort dpid:{} port:{} exists", dpid, port.getPortNumber());
+		    		setPortStateImpl(p, port.getState(), port.getName());
+		    		p.setState("ACTIVE");
+				} else {
+					p = addPortImpl(curr, port.getPortNumber());
+					setPortStateImpl(p, port.getState(), port.getName());
+				}         		
+			}
+			op.commit();
+			success = true;
+		} catch (Exception e) {
+			op.rollback();
+			e.printStackTrace();
+			log.error("SwitchStorage:addSwitch dpid:{} failed", dpid);
+		}
+		
+		return success;
+	}
+
+	/***
+	 * This function is for adding the switch into the DB.
+	 * @param dpid The switch dpid you want to add into the DB.
+	 */
+	@Override
+	public boolean addSwitch(String dpid) {
+		boolean success = false;
+		
+		log.info("SwitchStorage:addSwitch(): dpid {} ", dpid);
+		try {
+			ISwitchObject sw = op.searchSwitch(dpid);
+			if (sw != null) {
+				//If existing the switch. set The SW state ACTIVE. 
+				log.info("SwitchStorage:addSwitch dpid:{} already exists", dpid);
+				setSwitchStateImpl(sw, SwitchState.ACTIVE);
+			} else {
+				addSwitchImpl(dpid);
+			}
+			op.commit();
+			success = true;
+		} catch (Exception e) {
+			op.rollback();
+			e.printStackTrace();
+			log.info("SwitchStorage:addSwitch dpid:{} failed", dpid);
+		}
+		
+		return success;
+	}
+
+	/***
+	 * This function is for deleting the switch into the DB.
+	 * @param dpid The switch dpid you want to delete from the DB.
+	 */
+	@Override
+	public boolean deleteSwitch(String dpid) {
+		boolean success = false;
+		
+		try {
+			ISwitchObject sw = op.searchSwitch(dpid);
+			if (sw != null) {
+				deleteSwitchImpl(sw);
+	        	op.commit();
+			}
+			success = true;
+		} catch (Exception e) {
+			op.rollback();
+			e.printStackTrace();
+			log.error("SwitchStorage:deleteSwitch {} failed", dpid);
+		}
+	
+		return success;
+	}
+
+	public boolean updatePort(String dpid, short portNum, int state, String desc) {
+		boolean success = false;
+		
+		try {
+			ISwitchObject sw = op.searchSwitch(dpid);
+	
+	        if (sw != null) {
+	        	IPortObject p = sw.getPort(portNum);
+	        	log.info("SwitchStorage:updatePort dpid:{} port:{}", dpid, portNum);
+	        	if (p != null) {
+	        		setPortStateImpl(p, state, desc);
+	        	}
+	        	op.commit();
+        		success = true;
+	        } else {
+	    		log.error("SwitchStorage:updatePort dpid:{} port:{} : failed switch does not exist", dpid, portNum);
+	        }
+		} catch (Exception e) {
+			op.rollback();
+			e.printStackTrace();
+			log.error("SwitchStorage:addPort dpid:{} port:{} failed", dpid, portNum);
+		}	
+
+		return success;
 	}
 
 	/***
 	 * This function is for adding the switch port into the DB.
 	 * @param dpid The switch dpid that has the port.
-	 * @param port The port you want to add the switch.
+	 * @param phport The port you want to add the switch.
 	 */
 	@Override
-	public void addPort(String dpid, OFPhysicalPort port) {
+	public boolean addPort(String dpid, OFPhysicalPort phport) {
+		boolean success = false;
 		
-	   if(((OFPortConfig.OFPPC_PORT_DOWN.getValue() & port.getConfig()) > 0) ||
-	    					((OFPortState.OFPPS_LINK_DOWN.getValue() & port.getState()) > 0)) {
-		     deletePort(dpid, port.getPortNumber());
-	         return;  
-	   }
+		if(((OFPortConfig.OFPPC_PORT_DOWN.getValue() & phport.getConfig()) > 0) ||
+				((OFPortState.OFPPS_LINK_DOWN.getValue() & phport.getState()) > 0)) {
+			// just dispatch to deletePort()
+			return deletePort(dpid, phport.getPortNumber());
+		}
 	
 		try {
 			ISwitchObject sw = op.searchSwitch(dpid);
 	
 	        if (sw != null) {
-	        	IPortObject p = op.searchPort(dpid, port.getPortNumber());
-	        	log.info("SwitchStorage:addPort dpid:{} port:{}", dpid, port.getPortNumber());
+	        	IPortObject p = sw.getPort(phport.getPortNumber());
+	        	log.info("SwitchStorage:addPort dpid:{} port:{}", dpid, phport.getPortNumber());
 	        	if (p != null) {
-	        		log.error("SwitchStorage:addPort dpid:{} port:{} exists setting as ACTIVE", dpid, port.getPortNumber());
-	        		p.setState("ACTIVE");
-	        		p.setPortState(port.getState());
-	        		p.setDesc(port.getName());
-	        		op.commit();
-	        		
-	    		    // TODO publish UPDATE_PORT event here
+	        		setPortStateImpl(p, phport.getState(), phport.getName());
+	        		log.error("SwitchStorage:addPort dpid:{} port:{} exists setting as ACTIVE", dpid, phport.getPortNumber());
 	        	} else {
-	        		p = op.newPort(dpid, port.getPortNumber());
-	        		p.setState("ACTIVE");
-	        		p.setPortState(port.getState());
-	        		p.setDesc(port.getName());
-	        		sw.addPort(p);
-	        		op.commit();
-	        		
-	    		    // TODO publish ADD_PORT event here
+	        		addPortImpl(sw, phport.getPortNumber());
+	        		setPortStateImpl(p, phport.getState(), phport.getName());
 	        	}
+        		op.commit();
+        		success = true;
 	        } else {
-	    		log.error("SwitchStorage:addPort dpid:{} port:{} : failed switch does not exist", dpid, port.getPortNumber());
+	    		log.error("SwitchStorage:addPort dpid:{} port:{} : failed switch does not exist", dpid, phport.getPortNumber());
 	        }
 		} catch (Exception e) {
-			e.printStackTrace();
 			op.rollback();
-			log.error("SwitchStorage:addPort dpid:{} port:{} failed", dpid, port.getPortNumber());
+			e.printStackTrace();
+			log.error("SwitchStorage:addPort dpid:{} port:{} failed", dpid, phport.getPortNumber());
 		}	
-	
+
+		return success;
 	}
 
 	/***
@@ -147,111 +283,36 @@
 	 * @param port The port you want to delete the switch.
 	 */
 	@Override
-	public void deletePort(String dpid, short port) {
+	public boolean deletePort(String dpid, short port) {
+		boolean success = false;
+		
 		try {
 			ISwitchObject sw = op.searchSwitch(dpid);
 	
 	        if (sw != null) {
-	        	IPortObject p = op.searchPort(dpid, port);
+	        	IPortObject p = sw.getPort(port);
 	            if (p != null) {
 	        		log.info("SwitchStorage:deletePort dpid:{} port:{} found and set INACTIVE", dpid, port);
-	        		p.setState("INACTIVE");
+	        		deletePortImpl(p);
 	        		op.commit();
-	    		    // TODO publish DELETE_PORT event here
 	        	}
 	        }
 		} catch (Exception e) {
-			e.printStackTrace();
 			op.rollback();
+			e.printStackTrace();
 			log.info("SwitchStorage:deletePort dpid:{} port:{} failed", dpid, port);
-		}	
-	}
-
-	@Override
-	public void addSwitch(IOFSwitch sw) {
-		String dpid = sw.getStringId();
-		log.info("SwitchStorage:addSwitch(): dpid {} ", dpid);
-		
-		ISwitchObject curr = op.searchSwitch(dpid);
-		if (curr != null) {
-			//If existing the switch. set The SW state ACTIVE. 
-			log.info("SwitchStorage:addSwitch dpid:{} already exists", dpid);
-			setSwitchStateImpl(curr, SwitchState.ACTIVE);
-		} else {
-			curr = addSwitchImpl(dpid);
 		}
 
-		try {
-			List<IPortObject> added_ports = new ArrayList<IPortObject>();
-			List<IPortObject> updated_ports = new ArrayList<IPortObject>();
-			for (OFPhysicalPort port: sw.getPorts()) {
-				IPortObject p = op.searchPort(dpid, port.getPortNumber());
-				if (p != null) {
-		    		log.error("SwitchStorage:addPort dpid:{} port:{} exists", dpid, port.getPortNumber());
-		    		p.setState("ACTIVE");
-		    		p.setPortState(port.getState());
-		    		p.setDesc(port.getName());
-		    		
-		       		added_ports.add(p);
-				} else {
-		    		p = op.newPort(dpid, port.getPortNumber());
-		    		p.setState("ACTIVE");
-		    		p.setPortState(port.getState());
-		    		p.setDesc(port.getName());           		
-		    		curr.addPort(p);
-		    		
-		       		updated_ports.add(p);
-				}         		
-			}
-	
-			op.commit();
-		    
-		    // TODO publish ADD_PORT event here
-		    // TODO publish UPDATE_PORT event here
-		} catch (Exception e) {
-			e.printStackTrace();
-			op.rollback();
-			log.info("SwitchStorage:addSwitch dpid:{} failed", dpid);
-		}		
+		return success;
 	}
 
-	/***
-	 * This function is for adding the switch into the DB.
-	 * @param dpid The switch dpid you want to add into the DB.
-	 */
-	@Override
-	public void addSwitch(String dpid) {
-		log.info("SwitchStorage:addSwitch(): dpid {} ", dpid);
-		
-		ISwitchObject sw = op.searchSwitch(dpid);
-		if (sw != null) {
-			//If existing the switch. set The SW state ACTIVE. 
-			log.info("SwitchStorage:addSwitch dpid:{} already exists", dpid);
-			setSwitchStateImpl(sw, SwitchState.ACTIVE);
-		} else {
-			addSwitchImpl(dpid);
-		}
-	}
-	
 	private ISwitchObject addSwitchImpl(String dpid) {
-		try {
+		if (dpid != null) {
 			ISwitchObject sw = op.newSwitch(dpid);
-			if (sw != null) {
-				sw.setState(SwitchState.ACTIVE.toString());
-				log.info("SwitchStorage:addSwitchImpl dpid:{} added", dpid);
-			} else {
-				log.error("switchStorage:addSwitchImpl dpid:{} failed", dpid);
-				throw new RuntimeException();
-			}
-
-            op.commit();
-            
-            // TODO publish ADD_SWITCH event here
-    		return sw;
-		} catch (Exception e) {
-			e.printStackTrace();
-			op.rollback();
-			log.info("SwitchStorage:addSwitchImpl dpid:{} failed", dpid);
+			sw.setState(SwitchState.ACTIVE.toString());
+			log.info("SwitchStorage:addSwitchImpl dpid:{} added", dpid);
+			return sw;
+		} else {
 			return null;
 		}
 	}
@@ -259,33 +320,48 @@
 	private void setSwitchStateImpl(ISwitchObject sw, SwitchState state) {
 		if (sw != null && state != null) {
 			sw.setState(state.toString());
-            op.commit();
-            
-			// TODO publish UPDATE_SWITCH event here
+			log.info("SwitchStorage:setSwitchStateImpl dpid:{} updated {}",
+					sw.getDPID(), state.toString());
 		}
 	}
-
-	/***
-	 * This function is for deleting the switch into the DB.
-	 * @param dpid The switch dpid you want to delete from the DB.
-	 */
-	@Override
-	public void deleteSwitch(String dpid) {
-		try {
-			ISwitchObject sw = op.searchSwitch(dpid);
-            if (sw  != null) {
-            	op.removeSwitch(sw);
-            	op.commit();
-            	log.info("SwitchStorage:DeleteSwitch dpid:{} done", dpid);
-
-            	// TODO publish DELETE_SWITCH event here
-            }
-		} catch (Exception e) {
-			e.printStackTrace();
-			op.rollback();			
-			log.error("SwitchStorage:deleteSwitch {} failed", dpid);
-		}
-
-	}
 	
+	private void deleteSwitchImpl(ISwitchObject sw) {
+        if (sw  != null) {
+        	op.removeSwitch(sw);
+        	log.info("SwitchStorage:DeleteSwitchImpl dpid:{} done",
+        			sw.getDPID());
+        }
+	}
+
+	private IPortObject addPortImpl(ISwitchObject sw, short portNum) {
+		IPortObject p = op.newPort(sw.getDPID(), portNum);
+		p.setState("ACTIVE");
+		sw.addPort(p);
+    	log.info("SwitchStorage:addPortImpl dpid:{} port:{} done",
+    			sw.getDPID(), portNum);
+		
+		return p;
+	}
+
+	private void setPortStateImpl(IPortObject port, Integer state, String desc) {
+		if (port != null) {
+			if (state != null) {
+				port.setPortState(state);
+			}
+			if (desc != null) {
+				port.setDesc(desc);
+			}
+			
+	    	log.info("SwitchStorage:setPortStateImpl port:{} state:{} desc:{} done",
+	    			new Object[] {port.getPortId(), state, desc});
+		}
+	}
+	
+	private void deletePortImpl(IPortObject port) {
+		if (port != null) {
+			op.removePort(port);
+	    	log.info("SwitchStorage:deletePortImpl port:{} done",
+	    			port.getPortId());
+		}
+	}
 }
\ No newline at end of file
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 852cbb8..23c0e78 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/floodlightlistener/NetworkGraphPublisher.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/floodlightlistener/NetworkGraphPublisher.java
@@ -91,12 +91,17 @@
 
 		@Override
 		public void controlChanged(long dpid, boolean hasControl) {
-			// TODO Auto-generated method stub
-			
 			if (hasControl) {
 				log.debug("got control to set inactive sw {}", HexString.toHexString(dpid));
-				swStore.update(HexString.toHexString(dpid),SwitchState.INACTIVE, DM_OPERATION.UPDATE);
-			    registryService.releaseControl(dpid);	
+				try {
+					if (swStore.updateSwitch(HexString.toHexString(dpid), SwitchState.INACTIVE, DM_OPERATION.UPDATE)) {
+					    registryService.releaseControl(dpid);
+					    
+					    // TODO publish UPDATE_SWITCH event here
+					}
+				} catch (Exception e) {
+	                log.error("Error in SwitchCleanup:controlChanged ", e);
+				}
 			}						
 		}
     }
@@ -119,12 +124,12 @@
 				//	log.debug("sw {} is controlled by controller: {}",HexString.toHexString(dpid),controller);
 				}
 			} catch (NumberFormatException e) {
-				// TODO Auto-generated catch block
+				log.debug("Caught NumberFormatException trying to requestControl in cleanup thread");
 				e.printStackTrace();
 			} catch (RegistryException e) {
 				log.debug("Caught RegistryException trying to requestControl in cleanup thread");
 				e.printStackTrace();
-			}			
+			}
 		}
     	op.close();
     }
@@ -138,22 +143,27 @@
 		switch (update.getOperation()) {
 			case LINK_REMOVED:
 				log.debug("LinkDiscoveryUpdate(): Removing link {}", lt);
-				linkStore.deleteLink(lt);
-				// TODO: Move network map link removal here
-				// reconcile paths here
-//				IPortObject srcPort = conn.utils().searchPort(conn, HexString.toHexString(update.getSrc()), update.getSrcPort());
+				
+				if (linkStore.deleteLink(lt)) {
+				    // TODO publish DELETE_LINK event here
+				}
 				break;
 			case LINK_UPDATED:
 				log.debug("LinkDiscoveryUpdate(): Updating link {}", lt);
+				
 				LinkInfo linfo = linkStore.getLinkInfo(lt);
 				// TODO update "linfo" using portState derived using "update"
-				linkStore.update(lt, linfo, DM_OPERATION.UPDATE);
+				if (linkStore.update(lt, linfo, DM_OPERATION.UPDATE)) {
+				    // TODO publish UPDATE_LINK event here
+				}
 				break;
 			case LINK_ADDED:
 				log.debug("LinkDiscoveryUpdate(): Adding link {}", lt);
-				linkStore.addLink(lt);
+				
+				if (linkStore.addLink(lt)) {
+				    // TODO publish ADD_LINK event here
+				}
 				break;
-					
 			default:
 				break;
 		}
@@ -162,36 +172,41 @@
 
 	@Override
 	public void addedSwitch(IOFSwitch sw) {
-
 		if (registryService.hasControl(sw.getId())) {
-	        	swStore.addSwitch(sw);
+			if (swStore.addSwitch(sw)) {
+			    // TODO publish ADD_SWITCH event here
+			}
 		}
-
 	}
 
 	@Override
 	public void removedSwitch(IOFSwitch sw) {
-		// TODO Auto-generated method stub
-
+		if (registryService.hasControl(sw.getId())) {
+			if (swStore.deleteSwitch(sw.getStringId())) {
+			    // TODO publish DELETE_SWITCH event here
+			}
+		}
 	}
 
 	@Override
 	public void switchPortChanged(Long switchId) {
 		// TODO Auto-generated method stub
-
+		// NOTE: Event not needed here. This callback always coincide with add/remove callback.
 	}
 
 
 	@Override
 	public void switchPortAdded(Long switchId, OFPhysicalPort port) {
-		// TODO Auto-generated method stub
-		swStore.addPort(HexString.toHexString(switchId), port);
+		if (swStore.addPort(HexString.toHexString(switchId), port)) {
+		    // TODO publish ADD_PORT event here
+		}
 	}
 
 	@Override
 	public void switchPortRemoved(Long switchId, OFPhysicalPort port) {
-		// TODO Auto-generated method stub
-		swStore.deletePort(HexString.toHexString(switchId), port.getPortNumber());		
+		if (swStore.deletePort(HexString.toHexString(switchId), port.getPortNumber())) {
+		    // TODO publish DELETE_PORT event here
+		}
 	}
 
 	@Override
@@ -201,7 +216,6 @@
 
 	@Override
 	public void deviceAdded(IDevice device) {
-		// TODO Auto-generated method stub
 		log.debug("{}:deviceAdded(): Adding device {}",this.getClass(),device.getMACAddressString());
 		devStore.addDevice(device);
 	}
@@ -214,16 +228,12 @@
 
 	@Override
 	public void deviceMoved(IDevice device) {
-		// TODO Auto-generated method stub
 		devStore.changeDeviceAttachments(device);
-
 	}
 
 	@Override
 	public void deviceIPV4AddrChanged(IDevice device) {
-		// TODO Auto-generated method stub
 		devStore.changeDeviceIPv4Address(device);
-
 	}
 
 	@Override
@@ -263,7 +273,6 @@
 	@Override
 	public void init(FloodlightModuleContext context)
 			throws FloodlightModuleException {
-		// TODO Auto-generated method stub
 		Map<String, String> configMap = context.getConfigParams(this);
 		String conf = configMap.get(DBConfigFile);
 		op = new GraphDBOperation(conf);
@@ -291,7 +300,6 @@
 
 	@Override
 	public void startUp(FloodlightModuleContext context) {
-		// TODO Auto-generated method stub
 		Map<String, String> configMap = context.getConfigParams(this);
 		String cleanupNeeded = configMap.get(CleanupEnabled);