diff --git a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/AbstractNetworkGraph.java b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/AbstractNetworkGraph.java
new file mode 100644
index 0000000..3fa4ad9
--- /dev/null
+++ b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/AbstractNetworkGraph.java
@@ -0,0 +1,96 @@
+package net.onrc.onos.ofcontroller.networkgraph;
+
+import java.net.InetAddress;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+
+import net.floodlightcontroller.util.MACAddress;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class AbstractNetworkGraph implements NetworkGraph {
+    @SuppressWarnings("unused")
+    private static final Logger log = LoggerFactory
+	    .getLogger(AbstractNetworkGraph.class);
+
+    // DPID -> Switch
+    protected ConcurrentMap<Long, Switch> switches;
+
+    protected ConcurrentMap<InetAddress, Set<Device>> addr2Device;
+    protected ConcurrentMap<MACAddress, Set<Device>> mac2Device;
+
+    public AbstractNetworkGraph() {
+	// TODO: Does these object need to be stored in Concurrent Collection?
+	switches = new ConcurrentHashMap<>();
+	addr2Device = new ConcurrentHashMap<>();
+	mac2Device = new ConcurrentHashMap<>();
+    }
+
+    @Override
+    public Switch getSwitch(long dpid) {
+	// TODO Check if it is safe to directly return this Object.
+	return switches.get(dpid);
+    }
+
+    @Override
+    public Iterable<Switch> getSwitches() {
+	// TODO Check if it is safe to directly return this Object.
+	return Collections.unmodifiableCollection(switches.values());
+    }
+
+    @Override
+    public Iterable<Link> getLinks() {
+	List<Link> linklist = new LinkedList<>();
+
+	for (Switch sw : switches.values()) {
+	    Iterable<Link> links = sw.getLinks();
+	    for (Link l : links) {
+		linklist.add(l);
+	    }
+	}
+	return linklist;
+    }
+
+    @Override
+    public Iterable<Link> getLinksFromSwitch(long dpid) {
+	Switch sw = getSwitch(dpid);
+	if (sw == null) {
+	    return Collections.emptyList();
+	}
+	Iterable<Link> links = sw.getLinks();
+	if (links instanceof Collection) {
+	    return Collections.unmodifiableCollection((Collection<Link>) links);
+	} else {
+	    List<Link> linklist = new LinkedList<>();
+	    for (Link l : links) {
+		linklist.add(l);
+	    }
+	    return linklist;
+	}
+    }
+
+    @Override
+    public Iterable<Device> getDeviceByIp(InetAddress ipAddress) {
+	Set<Device> devices = addr2Device.get(ipAddress);
+	if (devices == null) {
+	    return Collections.emptyList();
+	}
+	return Collections.unmodifiableCollection(devices);
+    }
+
+    @Override
+    public Iterable<Device> getDeviceByMac(MACAddress address) {
+	Set<Device> devices = mac2Device.get(address);
+	if (devices == null) {
+	    return Collections.emptyList();
+	}
+	return Collections.unmodifiableCollection(devices);
+    }
+
+}