diff --git a/incubator/api/src/main/java/org/onosproject/incubator/net/virtual/VirtualNetworkService.java b/incubator/api/src/main/java/org/onosproject/incubator/net/virtual/VirtualNetworkService.java
index 6357aee..ebe0b69 100644
--- a/incubator/api/src/main/java/org/onosproject/incubator/net/virtual/VirtualNetworkService.java
+++ b/incubator/api/src/main/java/org/onosproject/incubator/net/virtual/VirtualNetworkService.java
@@ -60,7 +60,9 @@
     Set<VirtualLink> getVirtualLinks(NetworkId networkId);
 
     /**
-     * Returns list of all virtual ports of the specified device.
+     * Returns list of all virtual ports of the specified device. If the
+     * device identifier is null then all of the virtual ports in the specified
+     * network will be returned.
      *
      * @param networkId network identifier
      * @param deviceId  device identifier