application_layer = {
  header : {
    source : bstr .size 16,
    msgType : tstr .regexp "(request|reply|notify)",
    devType : tstr .regexp "[a-zA-Z][a-zA-Z0-9_-]{1}\\.[a-zA-Z][a-zA-Z0-9_-]{1}",
    action : tstr
  },
  ? body : { }
}