Restructured api to multiple packages

Change-Id: I8a3bb2297ef55fa7749bb312b01a4929d1b360f6
diff --git a/src/main/java/org/opencord/cordvtn/api/net/PortId.java b/src/main/java/org/opencord/cordvtn/api/net/PortId.java
new file mode 100644
index 0000000..10c9e8d
--- /dev/null
+++ b/src/main/java/org/opencord/cordvtn/api/net/PortId.java
@@ -0,0 +1,43 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.opencord.cordvtn.api.net;
+
+import org.onlab.util.Identifier;
+
+/**
+ * Representation of the port identifier.
+ */
+public final class PortId extends Identifier<String> {
+
+    /**
+     * Default constructor.
+     *
+     * @param id string port identifier
+     */
+    private PortId(String id) {
+        super(id);
+    }
+
+    /**
+     * Returns the port identifier with the supplied value.
+     *
+     * @param id string port identifier
+     * @return port identifier
+     */
+    public static PortId of(String id) {
+        return new PortId(id);
+    }
+}