diff --git a/docs/c_its-messages.proto b/docs/c_its-messages.proto
index 9848910..af8f802 100644
--- a/docs/c_its-messages.proto
+++ b/docs/c_its-messages.proto
@@ -35,18 +35,17 @@ enum GNAreaShape {
   ETSI_AREASHAPE_CIRCLE                         =  0;
   ETSI_AREASHAPE_RECTANGLE                      =  1;
   ETSI_AREASHAPE_ELLIPSIS                       =  2;
-  ETSI_AREASHAPE_UNKNOWN                        = 15;
 }
 
 // GeoNetworking Destination Area/ Source Position
 message ITSPosition {
-  optional  int32         latitude              =  1; // Latitude in 1/10th of micro degrees
-  optional  int32         longitude             =  2; // Longitude in 1/10th of micro degrees
+  required  int32         latitude              =  1; // Latitude in 1/10th of micro degrees
+  required  int32         longitude             =  2; // Longitude in 1/10th of micro degrees
 }
 
 // GeoNetworking Destination Area
 message GNArea {
-  optional  GNAreaShape   area                  =  1 [default = ETSI_AREASHAPE_UNKNOWN];
+  optional  GNAreaShape   area                  =  1;
   optional  ITSPosition   position              =  2;
   optional  int32         distA                 =  3; // Distance A of the geometric shape in meters
   optional  int32         distB                 =  4; // Distance B of the geometric shape in meters, mandatory for rectangle and ellipsis
@@ -55,8 +54,6 @@ message GNArea {
 
 // GeoNetworking Transport
 enum GNTransport {
-  GN_TRANSPORT_DEFAULT                          =  0;
-  GN_TRANSPORT_GUC                              =  2; // GeoUnicast
   GN_TRANSPORT_GAC                              =  3; // Geographically-Scoped Anycast
   GN_TRANSPORT_GBC                              =  4; // Geographically-Scoped broadcast
   GN_TRANSPORT_TSB                              =  5; // Topologically-scoped broadcast
@@ -79,7 +76,8 @@ message RawMsgTx {
 // ------------------------------
 
 message PositionState {
-  required  Position      position              =  1;
+  required  sfixed64      timestamp_ms          =  1; // current UNIX time in milliseconds
+  required  Position      position              =  2;
   optional  uint32        heading               =  3; // heading in 1/10 deg
   optional  uint32        speed                 =  4; // speed in 1/100 m/s
 }