diff --git a/automotive/vehicle/2.1/Android.mk b/automotive/vehicle/2.1/Android.mk
index 2dfbefc..3001da0 100644
--- a/automotive/vehicle/2.1/Android.mk
+++ b/automotive/vehicle/2.1/Android.mk
@@ -208,6 +208,25 @@
 LOCAL_GENERATED_SOURCES += $(GEN)
 
 #
+# Build types.hal (VmsAvailabilityStateIntegerValuesIndex)
+#
+GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsAvailabilityStateIntegerValuesIndex.java
+$(GEN): $(HIDL)
+$(GEN): PRIVATE_HIDL := $(HIDL)
+$(GEN): PRIVATE_DEPS := $(LOCAL_PATH)/types.hal
+$(GEN): PRIVATE_OUTPUT_DIR := $(intermediates)
+$(GEN): PRIVATE_CUSTOM_TOOL = \
+        $(PRIVATE_HIDL) -o $(PRIVATE_OUTPUT_DIR) \
+        -Ljava \
+        -randroid.hardware:hardware/interfaces \
+        -randroid.hidl:system/libhidl/transport \
+        android.hardware.automotive.vehicle@2.1::types.VmsAvailabilityStateIntegerValuesIndex
+
+$(GEN): $(LOCAL_PATH)/types.hal
+	$(transform-generated-source)
+LOCAL_GENERATED_SOURCES += $(GEN)
+
+#
 # Build types.hal (VmsBaseMessageIntegerValuesIndex)
 #
 GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsBaseMessageIntegerValuesIndex.java
@@ -227,25 +246,6 @@
 LOCAL_GENERATED_SOURCES += $(GEN)
 
 #
-# Build types.hal (VmsDataMessageIntegerValuesIndex)
-#
-GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsDataMessageIntegerValuesIndex.java
-$(GEN): $(HIDL)
-$(GEN): PRIVATE_HIDL := $(HIDL)
-$(GEN): PRIVATE_DEPS := $(LOCAL_PATH)/types.hal
-$(GEN): PRIVATE_OUTPUT_DIR := $(intermediates)
-$(GEN): PRIVATE_CUSTOM_TOOL = \
-        $(PRIVATE_HIDL) -o $(PRIVATE_OUTPUT_DIR) \
-        -Ljava \
-        -randroid.hardware:hardware/interfaces \
-        -randroid.hidl:system/libhidl/transport \
-        android.hardware.automotive.vehicle@2.1::types.VmsDataMessageIntegerValuesIndex
-
-$(GEN): $(LOCAL_PATH)/types.hal
-	$(transform-generated-source)
-LOCAL_GENERATED_SOURCES += $(GEN)
-
-#
 # Build types.hal (VmsMessageType)
 #
 GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsMessageType.java
@@ -265,6 +265,44 @@
 LOCAL_GENERATED_SOURCES += $(GEN)
 
 #
+# Build types.hal (VmsMessageWithLayerAndPublisherIdIntegerValuesIndex)
+#
+GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsMessageWithLayerAndPublisherIdIntegerValuesIndex.java
+$(GEN): $(HIDL)
+$(GEN): PRIVATE_HIDL := $(HIDL)
+$(GEN): PRIVATE_DEPS := $(LOCAL_PATH)/types.hal
+$(GEN): PRIVATE_OUTPUT_DIR := $(intermediates)
+$(GEN): PRIVATE_CUSTOM_TOOL = \
+        $(PRIVATE_HIDL) -o $(PRIVATE_OUTPUT_DIR) \
+        -Ljava \
+        -randroid.hardware:hardware/interfaces \
+        -randroid.hidl:system/libhidl/transport \
+        android.hardware.automotive.vehicle@2.1::types.VmsMessageWithLayerAndPublisherIdIntegerValuesIndex
+
+$(GEN): $(LOCAL_PATH)/types.hal
+	$(transform-generated-source)
+LOCAL_GENERATED_SOURCES += $(GEN)
+
+#
+# Build types.hal (VmsMessageWithLayerIntegerValuesIndex)
+#
+GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsMessageWithLayerIntegerValuesIndex.java
+$(GEN): $(HIDL)
+$(GEN): PRIVATE_HIDL := $(HIDL)
+$(GEN): PRIVATE_DEPS := $(LOCAL_PATH)/types.hal
+$(GEN): PRIVATE_OUTPUT_DIR := $(intermediates)
+$(GEN): PRIVATE_CUSTOM_TOOL = \
+        $(PRIVATE_HIDL) -o $(PRIVATE_OUTPUT_DIR) \
+        -Ljava \
+        -randroid.hardware:hardware/interfaces \
+        -randroid.hidl:system/libhidl/transport \
+        android.hardware.automotive.vehicle@2.1::types.VmsMessageWithLayerIntegerValuesIndex
+
+$(GEN): $(LOCAL_PATH)/types.hal
+	$(transform-generated-source)
+LOCAL_GENERATED_SOURCES += $(GEN)
+
+#
 # Build types.hal (VmsOfferingMessageIntegerValuesIndex)
 #
 GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsOfferingMessageIntegerValuesIndex.java
@@ -284,9 +322,9 @@
 LOCAL_GENERATED_SOURCES += $(GEN)
 
 #
-# Build types.hal (VmsSimpleMessageIntegerValuesIndex)
+# Build types.hal (VmsSubscriptionsStateIntegerValuesIndex)
 #
-GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsSimpleMessageIntegerValuesIndex.java
+GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsSubscriptionsStateIntegerValuesIndex.java
 $(GEN): $(HIDL)
 $(GEN): PRIVATE_HIDL := $(HIDL)
 $(GEN): PRIVATE_DEPS := $(LOCAL_PATH)/types.hal
@@ -296,26 +334,7 @@
         -Ljava \
         -randroid.hardware:hardware/interfaces \
         -randroid.hidl:system/libhidl/transport \
-        android.hardware.automotive.vehicle@2.1::types.VmsSimpleMessageIntegerValuesIndex
-
-$(GEN): $(LOCAL_PATH)/types.hal
-	$(transform-generated-source)
-LOCAL_GENERATED_SOURCES += $(GEN)
-
-#
-# Build types.hal (VmsSubscriptionResponseFormat)
-#
-GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsSubscriptionResponseFormat.java
-$(GEN): $(HIDL)
-$(GEN): PRIVATE_HIDL := $(HIDL)
-$(GEN): PRIVATE_DEPS := $(LOCAL_PATH)/types.hal
-$(GEN): PRIVATE_OUTPUT_DIR := $(intermediates)
-$(GEN): PRIVATE_CUSTOM_TOOL = \
-        $(PRIVATE_HIDL) -o $(PRIVATE_OUTPUT_DIR) \
-        -Ljava \
-        -randroid.hardware:hardware/interfaces \
-        -randroid.hidl:system/libhidl/transport \
-        android.hardware.automotive.vehicle@2.1::types.VmsSubscriptionResponseFormat
+        android.hardware.automotive.vehicle@2.1::types.VmsSubscriptionsStateIntegerValuesIndex
 
 $(GEN): $(LOCAL_PATH)/types.hal
 	$(transform-generated-source)
@@ -548,6 +567,25 @@
 LOCAL_GENERATED_SOURCES += $(GEN)
 
 #
+# Build types.hal (VmsAvailabilityStateIntegerValuesIndex)
+#
+GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsAvailabilityStateIntegerValuesIndex.java
+$(GEN): $(HIDL)
+$(GEN): PRIVATE_HIDL := $(HIDL)
+$(GEN): PRIVATE_DEPS := $(LOCAL_PATH)/types.hal
+$(GEN): PRIVATE_OUTPUT_DIR := $(intermediates)
+$(GEN): PRIVATE_CUSTOM_TOOL = \
+        $(PRIVATE_HIDL) -o $(PRIVATE_OUTPUT_DIR) \
+        -Ljava \
+        -randroid.hardware:hardware/interfaces \
+        -randroid.hidl:system/libhidl/transport \
+        android.hardware.automotive.vehicle@2.1::types.VmsAvailabilityStateIntegerValuesIndex
+
+$(GEN): $(LOCAL_PATH)/types.hal
+	$(transform-generated-source)
+LOCAL_GENERATED_SOURCES += $(GEN)
+
+#
 # Build types.hal (VmsBaseMessageIntegerValuesIndex)
 #
 GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsBaseMessageIntegerValuesIndex.java
@@ -567,25 +605,6 @@
 LOCAL_GENERATED_SOURCES += $(GEN)
 
 #
-# Build types.hal (VmsDataMessageIntegerValuesIndex)
-#
-GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsDataMessageIntegerValuesIndex.java
-$(GEN): $(HIDL)
-$(GEN): PRIVATE_HIDL := $(HIDL)
-$(GEN): PRIVATE_DEPS := $(LOCAL_PATH)/types.hal
-$(GEN): PRIVATE_OUTPUT_DIR := $(intermediates)
-$(GEN): PRIVATE_CUSTOM_TOOL = \
-        $(PRIVATE_HIDL) -o $(PRIVATE_OUTPUT_DIR) \
-        -Ljava \
-        -randroid.hardware:hardware/interfaces \
-        -randroid.hidl:system/libhidl/transport \
-        android.hardware.automotive.vehicle@2.1::types.VmsDataMessageIntegerValuesIndex
-
-$(GEN): $(LOCAL_PATH)/types.hal
-	$(transform-generated-source)
-LOCAL_GENERATED_SOURCES += $(GEN)
-
-#
 # Build types.hal (VmsMessageType)
 #
 GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsMessageType.java
@@ -605,6 +624,44 @@
 LOCAL_GENERATED_SOURCES += $(GEN)
 
 #
+# Build types.hal (VmsMessageWithLayerAndPublisherIdIntegerValuesIndex)
+#
+GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsMessageWithLayerAndPublisherIdIntegerValuesIndex.java
+$(GEN): $(HIDL)
+$(GEN): PRIVATE_HIDL := $(HIDL)
+$(GEN): PRIVATE_DEPS := $(LOCAL_PATH)/types.hal
+$(GEN): PRIVATE_OUTPUT_DIR := $(intermediates)
+$(GEN): PRIVATE_CUSTOM_TOOL = \
+        $(PRIVATE_HIDL) -o $(PRIVATE_OUTPUT_DIR) \
+        -Ljava \
+        -randroid.hardware:hardware/interfaces \
+        -randroid.hidl:system/libhidl/transport \
+        android.hardware.automotive.vehicle@2.1::types.VmsMessageWithLayerAndPublisherIdIntegerValuesIndex
+
+$(GEN): $(LOCAL_PATH)/types.hal
+	$(transform-generated-source)
+LOCAL_GENERATED_SOURCES += $(GEN)
+
+#
+# Build types.hal (VmsMessageWithLayerIntegerValuesIndex)
+#
+GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsMessageWithLayerIntegerValuesIndex.java
+$(GEN): $(HIDL)
+$(GEN): PRIVATE_HIDL := $(HIDL)
+$(GEN): PRIVATE_DEPS := $(LOCAL_PATH)/types.hal
+$(GEN): PRIVATE_OUTPUT_DIR := $(intermediates)
+$(GEN): PRIVATE_CUSTOM_TOOL = \
+        $(PRIVATE_HIDL) -o $(PRIVATE_OUTPUT_DIR) \
+        -Ljava \
+        -randroid.hardware:hardware/interfaces \
+        -randroid.hidl:system/libhidl/transport \
+        android.hardware.automotive.vehicle@2.1::types.VmsMessageWithLayerIntegerValuesIndex
+
+$(GEN): $(LOCAL_PATH)/types.hal
+	$(transform-generated-source)
+LOCAL_GENERATED_SOURCES += $(GEN)
+
+#
 # Build types.hal (VmsOfferingMessageIntegerValuesIndex)
 #
 GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsOfferingMessageIntegerValuesIndex.java
@@ -624,9 +681,9 @@
 LOCAL_GENERATED_SOURCES += $(GEN)
 
 #
-# Build types.hal (VmsSimpleMessageIntegerValuesIndex)
+# Build types.hal (VmsSubscriptionsStateIntegerValuesIndex)
 #
-GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsSimpleMessageIntegerValuesIndex.java
+GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsSubscriptionsStateIntegerValuesIndex.java
 $(GEN): $(HIDL)
 $(GEN): PRIVATE_HIDL := $(HIDL)
 $(GEN): PRIVATE_DEPS := $(LOCAL_PATH)/types.hal
@@ -636,26 +693,7 @@
         -Ljava \
         -randroid.hardware:hardware/interfaces \
         -randroid.hidl:system/libhidl/transport \
-        android.hardware.automotive.vehicle@2.1::types.VmsSimpleMessageIntegerValuesIndex
-
-$(GEN): $(LOCAL_PATH)/types.hal
-	$(transform-generated-source)
-LOCAL_GENERATED_SOURCES += $(GEN)
-
-#
-# Build types.hal (VmsSubscriptionResponseFormat)
-#
-GEN := $(intermediates)/android/hardware/automotive/vehicle/V2_1/VmsSubscriptionResponseFormat.java
-$(GEN): $(HIDL)
-$(GEN): PRIVATE_HIDL := $(HIDL)
-$(GEN): PRIVATE_DEPS := $(LOCAL_PATH)/types.hal
-$(GEN): PRIVATE_OUTPUT_DIR := $(intermediates)
-$(GEN): PRIVATE_CUSTOM_TOOL = \
-        $(PRIVATE_HIDL) -o $(PRIVATE_OUTPUT_DIR) \
-        -Ljava \
-        -randroid.hardware:hardware/interfaces \
-        -randroid.hidl:system/libhidl/transport \
-        android.hardware.automotive.vehicle@2.1::types.VmsSubscriptionResponseFormat
+        android.hardware.automotive.vehicle@2.1::types.VmsSubscriptionsStateIntegerValuesIndex
 
 $(GEN): $(LOCAL_PATH)/types.hal
 	$(transform-generated-source)
diff --git a/automotive/vehicle/2.1/types.hal b/automotive/vehicle/2.1/types.hal
index e5f9411..f614b8b 100644
--- a/automotive/vehicle/2.1/types.hal
+++ b/automotive/vehicle/2.1/types.hal
@@ -119,6 +119,8 @@
      * bytes is a serialized VMS message as defined in the vms protocol
      * which is opaque to the framework;
      *
+     * IVehicle#get must always return StatusCode::NOT_AVAILABLE.
+     *
      * @change_mode VehiclePropertyChangeMode:ON_CHANGE
      * @access VehiclePropertyAccess:READ_WRITE
      */
@@ -509,102 +511,196 @@
 };
 
 /**
- * This enum lists the types of supported VMS messages.
+ * This enum lists the types of supported VMS messages. It is used as the first
+ * integer in the vehicle property integers array and determines how the rest of
+ * the message is decoded.
  */
 enum VmsMessageType : int32_t {
-  /** A client subscribes to a layer. */
+  /**
+   * A request from the subscribers to the VMS service to subscribe to a layer.
+   *
+   * This message type uses enum VmsMessageWithLayerIntegerValuesIndex.
+   */
   SUBSCRIBE = 1,
 
-  /** A client unsubscribes from a layer. */
-  UNSUBSCRIBE = 2,
+  /**
+   * A request from the subscribers to the VMS service to subscribe to a layer from a specific publisher.
+   *
+   * This message type uses enum VmsMessageWithLayerAndPublisherIdIntegerValuesIndex.
+   */
+  SUBSCRIBE_TO_PUBLISHER = 2,
 
-  /** A client publishes a data packet. */
-  DATA = 3,
+  /**
+   * A request from the subscribers to the VMS service to unsubscribes from a layer.
+   *
+   * This message type uses enum VmsMessageWithLayerIntegerValuesIndex.
+   */
+  UNSUBSCRIBE = 3,
 
-  /** A client declaring layers offering. */
-  OFFERING = 4,
+  /**
+   * A request from the subscribers to the VMS service to unsubscribes from a layer from a specific publisher.
+   *
+   * This message type uses enum VmsMessageWithLayerAndPublisherIdIntegerValuesIndex.
+   */
+  UNSUBSCRIBE_TO_PUBLISHER = 4,
 
-  /** Requesting the list of available layers. */
-  AVAILABILITY_REQUEST = 5,
+  /**
+   * Information from the publishers to the VMS service about the layers which the client can publish.
+   *
+   * This message type uses enum VmsOfferingMessageIntegerValuesIndex.
+   */
+  OFFERING = 5,
 
-  /** Returning the list of available layers. */
-  AVAILABILITY_RESPONSE = 6,
+  /**
+   * A request from the subscribers to the VMS service to get the available layers.
+   *
+   * This message type uses enum VmsBaseMessageIntegerValuesIndex.
+   */
+  AVAILABILITY_REQUEST = 6,
 
-  /** Sending to the HAL the current list of the available layers. */
-  AVAILABILITY_CHANGE = 7,
+  /**
+   * A request from the publishers to the VMS service to get the layers with subscribers.
+   *
+   * This message type uses enum VmsBaseMessageIntegerValuesIndex.
+   */
+  SUBSCRIPTIONS_REQUEST = 7,
 
-  /** Requesting layers that have subscribers. */
-  SUBSCRIPTIONS_REQUEST = 8,
+  /**
+   * A response from the VMS service to the subscribers to a VmsMessageType.AVAILABILITY_REQUEST
+   *
+   * This message type uses enum VmsAvailabilityStateIntegerValuesIndex.
+   */
+  AVAILABILITY_RESPONSE = 8,
 
-  /** Returning layers that have subscribers. */
-  SUBSCRIPTIONS_RESPONSE = 9,
+  /**
+   * A notification from the VMS service to the subscribers on a change in the available layers.
+   *
+   * This message type uses enum VmsAvailabilityStateIntegerValuesIndex.
+   */
+  AVAILABILITY_CHANGE = 9,
 
-  /** Sending to the HAL the current list of the subscribed layers. */
-  SUBSCRIPTIONS_CHANGE = 10,
+  /**
+   * A response from the VMS service to the publishers to a VmsMessageType.SUBSCRIPTIONS_REQUEST
+   *
+   * This message type uses enum VmsSubscriptionsStateIntegerValuesIndex.
+   */
+  SUBSCRIPTIONS_RESPONSE = 10,
+
+  /**
+   * A notification from the VMS service to the publishers on a change in the layers with subscribers.
+   *
+   * This message type uses enum VmsSubscriptionsStateIntegerValuesIndex.
+   */
+  SUBSCRIPTIONS_CHANGE = 11,
+
+  /**
+   * A message from the VMS service to the subscribers or from the publishers to the VMS service
+   * with a serialized VMS data packet as defined in the VMS protocol.
+   *
+   * This message type uses enum VmsBaseMessageIntegerValuesIndex.
+   */
+  DATA = 12,
 };
 
 /**
- * This enum provides the canonical mapping for VMS properties that have an
- * integer value.
+ * Every VMS message starts with the type of the message from the VmsMessageType enum.
+ * Messages with no parameters such as VmsMessageType.AVAILABILITY_REQUEST,
+ * VmsMessageType.SUBSCRIPTIONS_REQUEST and VmsMessageType.DATA are also based on this enum.
  */
 enum VmsBaseMessageIntegerValuesIndex : int32_t {
   /* The message type as enumerated by VmsMessageType enum. */
-  VMS_MESSAGE_TYPE = 0,
+  MESSAGE_TYPE = 0,
 };
 
 /*
- * This enum provides the canonical mapping for VMS SUBMIT and UNSUBMIT
- * messages integer value properties.
+ * A VMS message with a layer is sent as part of a VmsMessageType.SUBSCRIBE or
+ * VmsMessageType.UNSUBSCRIBE messages.
+ *
+ * The layer type is defined in the VMS protocol, and the subtype and version are
+ * controlled by the implementer of the publisher.
  */
-enum VmsSimpleMessageIntegerValuesIndex : VmsBaseMessageIntegerValuesIndex {
-  /* The layer ID as defined in the vms protocol. */
-  VMS_LAYER_ID = 1,
+enum VmsMessageWithLayerIntegerValuesIndex : VmsBaseMessageIntegerValuesIndex {
+  LAYER_TYPE = 1,
 
-  /* The version of the VMS layer. */
-  VMS_LAYER_VERSION = 2,
+  LAYER_SUBTYPE = 2,
 
-  /* The layer type as defined in the vms protocol */
-  VMS_LAYER_SUB_TYPE = 3,
+  LAYER_VERSION = 3,
 };
 
 /*
- * This enum provides the canonical mapping for VMS DATA
- * message integer value properties.
+ * A VMS message with a layer and publisher ID is sent as part of a
+ * VmsMessageType.SUBSCRIBE_TO_PUBLISHER and VmsMessageType.UNSUBSCRIBE_TO_PUBLISHER messages.
  */
-enum VmsDataMessageIntegerValuesIndex : VmsSimpleMessageIntegerValuesIndex {
-  /* A publisher ID of the client that published this message. */
-  VMS_PUBLISHER_ID = 4,
+enum VmsMessageWithLayerAndPublisherIdIntegerValuesIndex : VmsMessageWithLayerIntegerValuesIndex {
+  PUBLISHER_ID = 4,
 };
 
 /*
- * This enum provides the canonical mapping for VMS offering messages integer
- * value properties
+ * An offering can be sent by publishers as part of VmsMessageType.OFFERING in order to
+ * advertise which layers they can publish and under which constraints: e.g., I can publish Layer X
+ * if someone else will publish Layer Y.
+ * The offering contains the publisher ID which was assigned to the publisher by the VMS service.
+ * A single offering is represented as:
+ * - Layer type
+ * - Layer subtype
+ * - Layer version
+ * - Number of dependencies (N)
+ * - N x (Layer type, Layer subtype, Layer version)
  */
 enum VmsOfferingMessageIntegerValuesIndex : VmsBaseMessageIntegerValuesIndex {
-  /* The ID assigend to the publisher by the VMS core. */
   PUBLISHER_ID = 1,
 
-  /* The number of VMS layer dependencies. */
-  VMS_NUMBER_OF_LAYERS_DEPENDENCIES = 2,
+  NUMBER_OF_OFFERS = 2,
 
-  /* The first index that contain dependencies */
-  FIRST_DEPENDENCIES_INDEX = 3,
+  OFFERING_START = 3,
 };
 
 /**
- * A VMS subscription request only contains its message type. The format of a VMS subscription
- * response is described below.
+ * A subscriptions state is sent to the publishers in response to a change in the subscriptions
+ * as part of a VmsMessageType.SUBSCRIPTIONS_CHANGE, or in response to a
+ * VmsMessageType.SUBSCRIPTIONS_REQUEST message as part of VmsMessageType.SUBSCRIPTIONS_RESPONSE.
+ * The VMS service issues monotonically increasing sequence numbers, and in case a subscriber receives
+ * a smaller sequnce number it should ignore the message.
+ * The subscriptions are sent as a list of layers followed by a list of associated layers:
+ * {Sequence number, N, M, N x layer, M x associated layer}
+ * A subscribed layer is represented as three integers:
+ * - Layer type
+ * - Layer subtype
+ * - Layer version
+ * A subscribed associated layer is a layer with a list of publisher IDs. It is represented as:
+ * - Layer type
+ * - Layer subtype
+ * - Layer version
+ * - Number of publisher IDs (N)
+ * - N x publisher ID
  */
-enum VmsSubscriptionResponseFormat : VmsBaseMessageIntegerValuesIndex {
-  /**
-    * Recipients should ignore any packet with a sequence number that is less than the highest
-    * sequence number they have seen thus far.
-    */
+enum VmsSubscriptionsStateIntegerValuesIndex : VmsBaseMessageIntegerValuesIndex {
   SEQUENCE_NUMBER = 1,
 
-  /** The number of VMS layers. Each layer has two integers: type and version. */
   NUMBER_OF_LAYERS = 2,
 
-  /** The first index that contains a layer. */
-  FIRST_LAYER = 3,
+  NUMBER_OF_ASSOCIATED_LAYERS = 3,
+
+  SUBSCRIPTIONS_START = 4,
+};
+
+/**
+ * An availability state is sent to the subscribers in response to a change in the available
+ * layers as part of a VmsMessageType.AVAILABILITY_CHANGE message, or in response to a
+ * VmsMessageType.AVAILABILITY_REQUEST message as part of a VmsMessageType.AVAILABILITY_RESPONSE.
+ * The VMS service issues monotonically increasing sequence numbers, and in case a subscriber receives
+ * a smaller sequnce number, it should ignore the message.
+ * An available associated layer is a layer with a list of publisher IDs:
+ * - Layer type
+ * - Layer subtype
+ * - Layer version
+ * - Number of publisher IDs (N)
+ * - N x publisher ID
+*/
+enum VmsAvailabilityStateIntegerValuesIndex : VmsBaseMessageIntegerValuesIndex {
+  SEQUENCE_NUMBER = 1,
+
+  NUMBER_OF_ASSOCIATED_LAYERS = 2,
+
+  LAYERS_START = 3,
 };