Define Lambda interface representing wavelength and implementations

Two Lambda implementations are defined.
- IndexedLambda
- OchSignal

Change-Id: I36763390f61abd9f861e76edab63f558ae97e8a2
diff --git a/core/api/src/main/java/org/onosproject/net/Lambda.java b/core/api/src/main/java/org/onosproject/net/Lambda.java
new file mode 100644
index 0000000..d0995be
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+++ b/core/api/src/main/java/org/onosproject/net/Lambda.java
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+/*
+ * Copyright 2015 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.onosproject.net;
+
+/**
+ * Abstraction of wavelength. Currently, this is just a marker interface
+ */
+public interface Lambda {
+    /**
+     * Create an Lambda instance with the specified wavelength index number.
+     *
+     * @param lambda index number
+     * @return an instance
+     */
+    static Lambda indexedLambda(long lambda) {
+        return new IndexedLambda(lambda);
+    }
+
+    /**
+     * Creates a Lambda instance with the specified arguments.
+     *
+     * @param gridType          grid type
+     * @param channelSpacing    channel spacing
+     * @param spacingMultiplier channel spacing multiplier
+     * @param slotGranularity   slot width granularity
+     */
+    static Lambda ochSignal(GridType gridType, ChannelSpacing channelSpacing,
+                            int spacingMultiplier, int slotGranularity) {
+        return new OchSignal(gridType, channelSpacing, spacingMultiplier, slotGranularity);
+    }
+}