diff --git a/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowProgrammer.java b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowProgrammer.java
index bd54755..33c9a6a 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowProgrammer.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowProgrammer.java
@@ -25,8 +25,13 @@
 /**
  * FlowProgrammer is a module responsible to maintain flows installed to switches.
  * FlowProgrammer consists of FlowPusher and FlowSynchronizer.
- * FlowPusher manages the rate of installation, and FlowSynchronizer synchronizez
+ * FlowPusher manages the rate of installation, and FlowSynchronizer synchronizes
  * flows between GraphDB and switches.
+ * FlowProgrammer also watch the event of addition/deletion of switches to
+ * start/stop synchronization. When a switch is added to network, FlowProgrammer
+ * immediately kicks synchronization to keep switch's flow table latest state.
+ * Adversely, when a switch is removed from network, FlowProgrammer immediately
+ * stops synchronization.
  * @author Brian
  *
  */
@@ -40,7 +45,6 @@
     protected volatile IFloodlightProviderService floodlightProvider;
     protected volatile IControllerRegistryService registryService;
 
-
     protected FlowPusher pusher;
     private static final int NUM_PUSHER_THREAD = 1;
 
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 ba3602c..6f85c5d 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowPusher.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowPusher.java
@@ -40,17 +40,20 @@
 import net.onrc.onos.ofcontroller.util.Port;
 
 /**
- * FlowPusher intermediates FlowManager/FlowSynchronizer and switches to push OpenFlow
- * messages to switches in proper rate.
+ * FlowPusher is a implementation of FlowPusherService.
+ * FlowPusher assigns one message queue instance for each one switch.
+ * Number of message processing threads is configurable by constructor, and
+ * one thread can handle multiple message queues. Each queue will be assigned to 
+ * a thread according to hash function defined by getHash().
+ * Each processing thread reads messages from queues and sends it to switches
+ * in round-robin. Processing thread also calculates rate of sending to suppress
+ * excessive message sending.
  * @author Naoki Shiota
  *
  */
 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.
     // TODO: Values copied from elsewhere (class LearningSwitch).
     // The local copy should go away!
@@ -71,7 +74,7 @@
 	}
 	
 	/**
-	 * Message queue attached to a switch.
+	 * SwitchQueue represents message queue attached to a switch.
 	 * This consists of queue itself and variables used for limiting sending rate.
 	 * @author Naoki Shiota
 	 *
@@ -104,8 +107,7 @@
 			}
 			
 			// Check if sufficient time (from aspect of rate) elapsed or not.
-			long interval = (current - last_sent_time) / 1000000;
-			long rate = last_sent_size / interval;
+			long rate = last_sent_size / (current - last_sent_time);
 			return (rate < max_rate);
 		}
 		
@@ -126,7 +128,10 @@
 
 	private FloodlightContext context = null;
 	private BasicFactory factory = null;
+	
+	// Map of threads versus dpid
 	private Map<Long, FlowPusherThread> threadMap = null;
+	// Map of Future objects versus dpid and transaction ID.
 	private Map<Long, Map<Integer, OFBarrierReplyFuture>>
 		barrierFutures = new HashMap<Long, Map<Integer, OFBarrierReplyFuture>>();
 	
@@ -139,14 +144,12 @@
 	 */
 	private class FlowPusherThread extends Thread {
 		private Map<IOFSwitch,SwitchQueue> queues
-		= new HashMap<IOFSwitch,SwitchQueue>();
+			= new HashMap<IOFSwitch,SwitchQueue>();
 		
 		private Semaphore mutex = new Semaphore(0);
 		
 		@Override
 		public void run() {
-			log.debug("Begin Flow Pusher Process");
-			
 			while (true) {
 				try {
 					// wait for message pushed to queue
@@ -173,7 +176,7 @@
 					}
 					
 					// check sending rate and determine it to be sent or not
-					long current_time = System.nanoTime();
+					long current_time = System.currentTimeMillis();
 					long size = 0;
 					
 					synchronized (queue) {
@@ -202,9 +205,7 @@
 							queue.logSentData(current_time, size);
 							
 							if (queue.isEmpty()) {
-								if (barrierIfEmpty) {
-									barrier(sw);
-								}
+								// remove queue if flagged to be.
 								if (queue.toBeDeleted) {
 									synchronized (queues) {
 										queues.remove(sw);
@@ -255,7 +256,7 @@
 		if (damper != null) {
 			messageDamper = damper;
 		} else {
-			// use default value
+			// use default values
 			messageDamper = new OFMessageDamper(OFMESSAGE_DAMPER_CAPACITY,
 				    EnumSet.of(OFType.FLOW_MOD),
 				    OFMESSAGE_DAMPER_TIMEOUT);
@@ -280,10 +281,6 @@
 		}
 	}
 	
-	/**
-	 * Suspend sending messages to switch.
-	 * @param sw
-	 */
 	@Override
 	public boolean suspend(IOFSwitch sw) {
 		SwitchQueue queue = getQueue(sw);
@@ -301,9 +298,6 @@
 		}
 	}
 
-	/**
-	 * Resume sending messages to switch.
-	 */
 	@Override
 	public boolean resume(IOFSwitch sw) {
 		SwitchQueue queue = getQueue(sw);
@@ -321,9 +315,6 @@
 		}
 	}
 	
-	/**
-	 * Check if given switch is suspended.
-	 */
 	@Override
 	public boolean isSuspended(IOFSwitch sw) {
 		SwitchQueue queue = getQueue(sw);
@@ -384,10 +375,10 @@
 	}
 	
 	@Override
-	public boolean deleteQueue(IOFSwitch sw, boolean force) {
+	public boolean deleteQueue(IOFSwitch sw, boolean forceStop) {
 		FlowPusherThread proc = getProcess(sw);
 		
-		if (force) {
+		if (forceStop) {
 			synchronized (proc.queues) {
 				SwitchQueue queue = proc.queues.remove(sw);
 				if (queue == null) {
@@ -407,18 +398,12 @@
 		}
 	}
 	
-	/**
-	 * Add OFMessage to queue of the switch.
-	 * @param sw Switch to which message is sent.
-	 * @param msg Message to be sent.
-	 * @return true if succeed.
-	 */
 	@Override
 	public boolean add(IOFSwitch sw, OFMessage msg) {
 		FlowPusherThread proc = getProcess(sw);
 		SwitchQueue queue = proc.queues.get(sw);
 
-		// create queue at first call
+		// create queue at first addition of message
 		if (queue == null) {
 			createQueue(sw);
 			queue = getQueue(sw);
@@ -436,13 +421,6 @@
 		return true;
 	}
 	
-	/**
-	 * Create OFMessage from given flow information and add it to the queue.
-	 * @param sw Switch to which message is sent.
-	 * @param flowObj FlowPath.
-	 * @param flowEntryObj FlowEntry.
-	 * @return true if succeed.
-	 */
 	@Override
 	public boolean add(IOFSwitch sw, IFlowPath flowObj, IFlowEntry flowEntryObj) {
 		log.debug("sending : {}, {}", sw, flowObj);
@@ -748,13 +726,6 @@
 		return true;
 	}
 	
-	/**
-	 * Create OFMessage from given flow information and add it to the queue.
-	 * @param sw Switch to which message is sent.
-	 * @param flowPath FlowPath.
-	 * @param flowEntry FlowEntry.
-	 * @return true if succeed.
-	 */
 	@Override
 	public boolean add(IOFSwitch sw, FlowPath flowPath, FlowEntry flowEntry) {
 		//
diff --git a/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowSynchronizer.java b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowSynchronizer.java
index 3250eb4..0d6b0e8 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowSynchronizer.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/FlowSynchronizer.java
@@ -29,11 +29,10 @@
 import net.onrc.onos.ofcontroller.util.FlowEntryId;
 
 /**
- * FlowSynchronizer is a sub-module of FlowProgrammer to keep switches' flow table
- * synchronized with GraphDB. FlowSynchronizer periodically read flow tables from
+ * FlowSynchronizer is an implementation of FlowSyncService.
+ * In addition to IFlowSyncService, FlowSynchronizer periodically reads flow tables from
  * switches and compare them with GraphDB to drop unnecessary flows and/or to install
- * missing flows. FlowSynchronizer also watch the event of addition/deletion of switches
- * and start synchronization.
+ * missing flows.
  * @author Brian
  *
  */
@@ -66,6 +65,10 @@
 	}	
     }
 
+    /**
+     * Initialize Synchronizer.
+     * @param pusherService FlowPusherService used for sending messages.
+     */
     public void init(IFlowPusherService pusherService) {
 	pusher = pusherService;
     }
@@ -210,7 +213,7 @@
 
 	/**
 	 * Install this FlowEntry to a switch via FlowPusher.
-	 * @param sw
+	 * @param sw Switch to which flow will be installed.
 	 */
 	public void addToSwitch(IOFSwitch sw) {
 	    if(iflowEntry != null) {
@@ -224,7 +227,7 @@
 	
 	/**
 	 * Remove this FlowEntry from a switch via FlowPusher.
-	 * @param sw
+	 * @param sw Switch from which flow will be removed.
 	 */
 	public void removeFromSwitch(IOFSwitch sw){
 	    if(iflowEntry != null) {
@@ -258,6 +261,7 @@
 	 * the same value; otherwise, returns false.
 	 * 
 	 * @param Object to compare
+	 * @return true if the object has the same Flow Entry ID.
 	 */
 	@Override
 	public boolean equals(Object obj){
diff --git a/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/IFlowPusherService.java b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/IFlowPusherService.java
index 570120f..20a6249 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/IFlowPusherService.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/IFlowPusherService.java
@@ -11,6 +11,15 @@
 import net.onrc.onos.ofcontroller.util.FlowEntry;
 import net.onrc.onos.ofcontroller.util.FlowPath;
 
+/**
+ * FlowPusherService is a service to send message to switches in proper rate.
+ * Conceptually a queue is attached to each switch, and FlowPusherService
+ * read a message from queue and send it to switch in order.
+ * To guarantee message has been installed, FlowPusherService can add barrier
+ * message to queue and can notify when barrier message is sent to switch.
+ * @author Naoki Shiota
+ *
+ */
 public interface IFlowPusherService extends IFloodlightService {
 	/**
 	 * Create a queue correspondent to the switch.
@@ -31,11 +40,13 @@
 	 * Delete a queue correspondent to the switch.
 	 * By setting force flag on, queue will be deleted immediately.
 	 * @param sw Switch of which queue is deleted.
-	 * @param force If this flag is on, queue will be deleted immediately
-	 *        regardless of any messages in the queue.
-	 * @return true if queue is successfully deleted.
+	 * @param forceStop If this flag is set to true, queue will be deleted
+	 *        immediately regardless of any messages in the queue.
+	 *        If false, all messages will be sent to switch and queue will
+	 *        be deleted after that.
+	 * @return true if queue is successfully deleted or flagged to be deleted.
 	 */
-	boolean deleteQueue(IOFSwitch sw, boolean force);
+	boolean deleteQueue(IOFSwitch sw, boolean forceStop);
 	
 	/**
 	 * Add a message to the queue of the switch.
diff --git a/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/IFlowSyncService.java b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/IFlowSyncService.java
index 2b9d51d..4e6efaf 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/IFlowSyncService.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/flowprogrammer/IFlowSyncService.java
@@ -5,7 +5,9 @@
 import net.floodlightcontroller.core.module.IFloodlightService;
 
 /**
- * @author bocon
+ * FlowSyncService is a service to synchronize GraphDB and switch's flow table.
+ * FlowSyncService offers APIs to trigger and interrupt synchronization explicitly.
+ * @author Brian
  *
  */
 public interface IFlowSyncService extends IFloodlightService {