diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiTopoLayoutId.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiTopoLayoutId.java
index 2fa8717..289cacd 100644
--- a/core/api/src/main/java/org/onosproject/ui/model/topo/UiTopoLayoutId.java
+++ b/core/api/src/main/java/org/onosproject/ui/model/topo/UiTopoLayoutId.java
@@ -23,6 +23,11 @@
  */
 public final class UiTopoLayoutId extends Identifier<String> {
 
+    /**
+     * Default topology layout identifier.
+     */
+    public static final UiTopoLayoutId DEFAULT_ID = UiTopoLayoutId.layoutId("_default_");
+
     // For serialization
     private UiTopoLayoutId() {
     }
diff --git a/core/common/src/main/java/org/onosproject/utils/Comparators.java b/core/common/src/main/java/org/onosproject/utils/Comparators.java
index c3cd07c..0f8d7d7 100644
--- a/core/common/src/main/java/org/onosproject/utils/Comparators.java
+++ b/core/common/src/main/java/org/onosproject/utils/Comparators.java
@@ -33,6 +33,7 @@
 import org.onosproject.net.region.Region;
 import org.onosproject.net.statistic.TypedFlowEntryWithLoad;
 import org.onosproject.net.topology.TopologyCluster;
+import org.onosproject.ui.model.topo.UiTopoLayout;
 
 import java.util.Comparator;
 
@@ -154,6 +155,12 @@
         }
     };
 
+    public static final Comparator<UiTopoLayout> LAYOUT_COMPARATOR = new Comparator<UiTopoLayout>() {
+        @Override
+        public int compare(UiTopoLayout l1, UiTopoLayout l2) {
+            return l1.id().toString().compareTo(l2.id().toString());
+        }
+    };
     public static final Comparator<TenantId> TENANT_ID_COMPARATOR = new Comparator<TenantId>() {
         @Override
         public int compare(TenantId tenant1, TenantId tenant2) {
diff --git a/core/store/serializers/src/main/java/org/onosproject/store/serializers/KryoNamespaces.java b/core/store/serializers/src/main/java/org/onosproject/store/serializers/KryoNamespaces.java
index 10cd72f..67d9df1 100644
--- a/core/store/serializers/src/main/java/org/onosproject/store/serializers/KryoNamespaces.java
+++ b/core/store/serializers/src/main/java/org/onosproject/store/serializers/KryoNamespaces.java
@@ -195,6 +195,9 @@
 import org.onosproject.net.packet.DefaultPacketRequest;
 import org.onosproject.net.packet.PacketPriority;
 import org.onosproject.net.provider.ProviderId;
+import org.onosproject.net.region.DefaultRegion;
+import org.onosproject.net.region.Region;
+import org.onosproject.net.region.RegionId;
 import org.onosproject.net.resource.ContinuousResource;
 import org.onosproject.net.resource.ContinuousResourceId;
 import org.onosproject.net.resource.DiscreteResource;
@@ -504,6 +507,10 @@
             .register(new AnnotationsSerializer(), DefaultAnnotations.class)
             .register(new ExtensionInstructionSerializer(), Instructions.ExtensionInstructionWrapper.class)
             .register(new ExtensionCriterionSerializer(), ExtensionCriterion.class)
+            .register(Region.class)
+            .register(Region.Type.class)
+            .register(RegionId.class)
+            .register(DefaultRegion.class)
             .register(ExtensionSelectorType.class)
             .register(ExtensionTreatmentType.class)
             .register(TransactionId.class)