diff --git a/src/main/java/org/opencord/igmpproxy/StateMachine.java b/src/main/java/org/opencord/igmpproxy/StateMachine.java
new file mode 100644
index 0000000..6c12877
--- /dev/null
+++ b/src/main/java/org/opencord/igmpproxy/StateMachine.java
@@ -0,0 +1,97 @@
+package org.opencord.igmpproxy;
+
+import com.google.common.collect.Maps;
+import org.onlab.packet.Ip4Address;
+import org.onosproject.net.DeviceId;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * State machine for whole IGMP process. The state machine is implemented on 
+ * RFC 2236 "6. Host State Diagram".
+ */
+public final class StateMachine {
+    private StateMachine() {
+
+    }
+    private static Map<String, SingleStateMachine> map = Maps.newConcurrentMap();
+
+    private static String getId(DeviceId devId, Ip4Address groupIp) {
+        return devId.toString() + "Group" + groupIp.toString();
+    }
+
+    private static SingleStateMachine get(DeviceId devId, Ip4Address groupIp) {
+        String id = getId(devId, groupIp);
+        return map.get(id);
+    }
+
+    public static void destorySingle(DeviceId devId, Ip4Address groupIp) {
+        SingleStateMachine machine = get(devId, groupIp);
+        if (null == machine) {
+            return;
+        }
+        machine.cancelTimer();
+        map.remove(getId(devId, groupIp));
+    }
+
+    public static boolean join(DeviceId devId, Ip4Address groupIp, Ip4Address srcIP) {
+        SingleStateMachine machine = get(devId, groupIp);
+        if (null == machine) {
+            machine = new SingleStateMachine(devId, groupIp, srcIP);
+            map.put(getId(devId, groupIp), machine);
+            machine.join();
+            return true;
+        }
+        machine.increaseCounter();
+        return false;
+    }
+
+    public static boolean leave(DeviceId devId, Ip4Address groupIp) {
+        SingleStateMachine machine = get(devId, groupIp);
+        if (null == machine) {
+            return false;
+        }
+        machine.decreaseCounter();
+
+        if (machine.getCounter() == 0) {
+            machine.leave();
+            destorySingle(devId, groupIp);
+            return true;
+        }
+        return false;
+    }
+
+    static void specialQuery(DeviceId devId, Ip4Address groupIp, int maxResp) {
+        SingleStateMachine machine = get(devId, groupIp);
+        if (null == machine) {
+            return;
+        }
+        machine.query(maxResp);
+    }
+
+    static void generalQuery(DeviceId devId, int maxResp) {
+        for (Map.Entry<String, SingleStateMachine> entry : map.entrySet()) {
+            SingleStateMachine machine = entry.getValue();
+            if (devId.equals(machine.getDeviceId())) {
+                machine.query(maxResp);
+            }
+        }
+    }
+
+    public static Set<Map.Entry<String, SingleStateMachine>> entrySet() {
+        return map.entrySet();
+    }
+
+    public static void timeOut(DeviceId devId, Ip4Address groupIp) {
+        SingleStateMachine machine = get(devId, groupIp);
+        if (null == machine) {
+            return;
+        }
+        machine.timeOut();
+    }
+
+    public static void clearMap() {
+        map.clear();
+    }
+
+}