diff --git a/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowPusher.java b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowPusher.java
index f43a83e..ba3602c 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowPusher.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowPusher.java
@@ -48,6 +48,7 @@
 public class FlowPusher implements IFlowPusherService, IOFMessageListener {
     private final static Logger log = LoggerFactory.getLogger(FlowPusher.class);
 
+    // If this flag is true, barrier message will be sent when queue goes empty.
     private static boolean barrierIfEmpty = false;
     
     // NOTE: Below are moved from FlowManager.
@@ -57,10 +58,6 @@
     protected static final int OFMESSAGE_DAMPER_CAPACITY = 50000; // TODO: find sweet spot
     protected static final int OFMESSAGE_DAMPER_TIMEOUT = 250;	// ms
     
-    // Interval of sleep when queue is empty
-    protected static final long SLEEP_MILLI_SEC = 10;
-    protected static final int SLEEP_NANO_SEC = 0;
-    
     // Number of messages sent to switch at once
     protected static final int MAX_MESSAGE_SEND = 100;
 
@@ -83,11 +80,14 @@
 	private class SwitchQueue extends ArrayDeque<OFMessage> {
 		QueueState state;
 		
-		// Max rate of sending message (bytes/sec). 0 implies no limitation.
+		// Max rate of sending message (bytes/ms). 0 implies no limitation.
 		long max_rate = 0;	// 0 indicates no limitation
 		long last_sent_time = 0;
 		long last_sent_size = 0;
 		
+		// "To be deleted" flag
+		boolean toBeDeleted = false;
+		
 		/**
 		 * Check if sending rate is within the rate
 		 * @param current Current time
@@ -104,7 +104,8 @@
 			}
 			
 			// Check if sufficient time (from aspect of rate) elapsed or not.
-			long rate = last_sent_size / (current - last_sent_time);
+			long interval = (current - last_sent_time) / 1000000;
+			long rate = last_sent_size / interval;
 			return (rate < max_rate);
 		}
 		
@@ -200,8 +201,15 @@
 							sw.flush();
 							queue.logSentData(current_time, size);
 							
-							if (queue.isEmpty() && barrierIfEmpty) {
-								barrier(sw);
+							if (queue.isEmpty()) {
+								if (barrierIfEmpty) {
+									barrier(sw);
+								}
+								if (queue.toBeDeleted) {
+									synchronized (queues) {
+										queues.remove(sw);
+									}
+								}
 							}
 						}
 					}
@@ -341,11 +349,7 @@
 		}
 	}
 	
-	/**
-	 * Set sending rate to a switch.
-	 * @param sw Switch.
-	 * @param rate Rate in bytes/sec.
-	 */
+	@Override
 	public void setRate(IOFSwitch sw, long rate) {
 		SwitchQueue queue = getQueue(sw);
 		if (queue == null) {
@@ -356,6 +360,52 @@
 			queue.max_rate = rate;
 		}
 	}
+
+	@Override
+	public boolean createQueue(IOFSwitch sw) {
+		SwitchQueue queue = getQueue(sw);
+		if (queue != null) {
+			return false;
+		}
+		
+		FlowPusherThread proc = getProcess(sw);
+		queue = new SwitchQueue();
+		queue.state = QueueState.READY;
+		synchronized (proc) {
+			proc.queues.put(sw, queue);
+		}
+		
+		return true;
+	}
+
+	@Override
+	public boolean deleteQueue(IOFSwitch sw) {
+		return deleteQueue(sw, false);
+	}
+	
+	@Override
+	public boolean deleteQueue(IOFSwitch sw, boolean force) {
+		FlowPusherThread proc = getProcess(sw);
+		
+		if (force) {
+			synchronized (proc.queues) {
+				SwitchQueue queue = proc.queues.remove(sw);
+				if (queue == null) {
+					return false;
+				}
+			}
+			return true;
+		} else {
+			SwitchQueue queue = getQueue(sw);
+			if (queue == null) {
+				return false;
+			}
+			synchronized (queue) {
+				queue.toBeDeleted = true;
+			}
+			return true;
+		}
+	}
 	
 	/**
 	 * Add OFMessage to queue of the switch.
@@ -368,12 +418,10 @@
 		FlowPusherThread proc = getProcess(sw);
 		SwitchQueue queue = proc.queues.get(sw);
 
+		// create queue at first call
 		if (queue == null) {
-			queue = new SwitchQueue();
-			queue.state = QueueState.READY;
-			synchronized (proc) {
-				proc.queues.put(sw, queue);
-			}
+			createQueue(sw);
+			queue = getQueue(sw);
 		}
 		
 		synchronized (queue) {
@@ -705,7 +753,7 @@
 	 * @param sw Switch to which message is sent.
 	 * @param flowPath FlowPath.
 	 * @param flowEntry FlowEntry.
-	 * @return true if secceed.
+	 * @return true if succeed.
 	 */
 	@Override
 	public boolean add(IOFSwitch sw, FlowPath flowPath, FlowEntry flowEntry) {
@@ -1061,12 +1109,16 @@
 				barrierFutures.put(sw.getId(), map);
 			}
 			map.put(msg.getXid(), future);
-			log.debug("Inserted future for {}", msg.getXid());
 		}
 		
 		return future;
 	}
 
+	/**
+	 * Get a queue attached to a switch.
+	 * @param sw Switch object
+	 * @return Queue object
+	 */
 	protected SwitchQueue getQueue(IOFSwitch sw) {
 		if (sw == null)  {
 			return null;
@@ -1075,12 +1127,22 @@
 		return getProcess(sw).queues.get(sw);
 	}
 	
+	/**
+	 * Get a hash value correspondent to a switch.
+	 * @param sw Switch object
+	 * @return Hash value
+	 */
 	protected long getHash(IOFSwitch sw) {
 		// This code assumes DPID is sequentially assigned.
 		// TODO consider equalization algorithm
 		return sw.getId() % number_thread;
 	}
-	
+
+	/**
+	 * Get a Thread object which processes the queue attached to a switch.
+	 * @param sw Switch object
+	 * @return Thread object
+	 */
 	protected FlowPusherThread getProcess(IOFSwitch sw) {
 		long hash = getHash(sw);
 		
@@ -1119,4 +1181,5 @@
 		
 		return Command.CONTINUE;
 	}
+
 }