diff --git a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/Link.java b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/Link.java
index 6c84382..0fc72f6 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/Link.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/Link.java
@@ -1,14 +1,21 @@
 package net.onrc.onos.ofcontroller.networkgraph;
 
+/**
+ * Interface of Link Object exposed to the "NB" read-only Topology.
+ *
+ * Everything returned by these interfaces must be either Unmodifiable view,
+ * immutable object, or a copy of the original "SB" In-memory Topology.
+ *
+ */
 public interface Link {
 	public Port getSourcePort();
 	public Port getDestinationPort();
 	public Switch getSourceSwitch();
 	public Switch getDestinationSwitch();
-	
+
 	public long getLastSeenTime();
 	public int getCost();
-	
+
 	// Not sure if we want to expose these northbound
 	public long getSourceSwitchDpid();
 	public short getSourcePortNumber();