static void dissect_APP_ACK_CONF(tvbuff_t *tvb,
  packet_info *pinfo _U_,
  gint offset,
  guint8 flags,
  const guint encoding,
  int octets_to_next_header,
  proto_tree *tree,
  proto_item *item,
  endpoint_guid * guid)
  {
  /*
  * 0...2...........7...............15.............23...............31
  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  * |  APP_ACK_CONF |X|X|X|X|X|X|X|E|      octetsToNextHeader       |
  * +---------------+---------------+---------------+---------------+
  * | EntityId readerEntityId                                       |
  * +---------------+---------------+---------------+---------------+
  * | EntityId writerEntityId                                       |
  * +---------------+---------------+---------------+---------------+
  * + unsigned long virtualWriterCount                              +
  * +---------------+---------------+---------------+---------------+
  * | GuidPrefix  virtualWriterGuidPrefix                           |
  * +---------------+---------------+---------------+---------------+
  * EntityId virtualWriterObjectId
  *
  * (after last interval) unsigned long virtualWriterEpoch
  *
  */
  gint original_offset; /* Offset to the readerEntityId */
  gint32 virtual_writer_count;
  guint32 wid;
  proto_item *octet_item;
  proto_tree_add_bitmask_value(tree, tvb, offset + 1, hf_rtps_sm_flags, ett_rtps_flags, APP_ACK_CONF_FLAGS, flags);

  octet_item = proto_tree_add_item(tree, hf_rtps_sm_octets_to_next_header, tvb, offset + 2, 2, encoding);
  offset += 4;
  original_offset = offset;

  if (octets_to_next_header < 20) {
    expert_add_info_format(pinfo, octet_item, &ei_rtps_sm_octets_to_next_header_error, "(Error: should be >= %u)", 20);
    return;
  }

  /* readerEntityId */
  rtps_util_add_entity_id(tree,
    tvb,
    offset,
    hf_rtps_sm_rdentity_id,
    hf_rtps_sm_rdentity_id_key,
    hf_rtps_sm_rdentity_id_kind,
    ett_rtps_rdentity,
    "readerEntityId",
    NULL);
  offset += 4;

  /* writerEntityId */
  rtps_util_add_entity_id(tree,
    tvb,
    offset,
    hf_rtps_sm_wrentity_id,
    hf_rtps_sm_wrentity_id_key,
    hf_rtps_sm_wrentity_id_kind,
    ett_rtps_wrentity,
    "writerEntityId",
    &wid);
  offset += 4;
  guid->entity_id = wid;
  guid->fields_present |= GUID_HAS_ENTITY_ID;
  rtps_util_topic_info_add_tree(tree, tvb, offset, guid);


  /* virtualWriterCount */
  proto_tree_add_item_ret_uint(tree, hf_rtps_param_app_ack_conf_virtual_writer_count, tvb, offset, 4,
    encoding, &virtual_writer_count);
  offset += 4;

  {
    /* Deserialize Virtual Writers */
    proto_tree *sil_tree_writer_list;
    proto_tree *sil_tree_writer;

    gint32 current_writer_index = 0;

    /** Writer list **/

    sil_tree_writer_list = proto_tree_add_subtree_format(tree, tvb, offset, -1,
           ett_rtps_app_ack_virtual_writer_list, NULL, "Virtual Writer List");

    current_writer_index = 0;

    while (current_writer_index < virtual_writer_count) {
      sil_tree_writer = proto_tree_add_subtree_format(sil_tree_writer_list, tvb, offset, -1,
           ett_rtps_app_ack_virtual_writer, NULL, "virtualWriter[%d]", current_writer_index);

      /* Virtual Writer Guid */
      rtps_util_add_guid_prefix_v2(sil_tree_writer, tvb, offset,
        hf_rtps_sm_guid_prefix, hf_rtps_sm_host_id, hf_rtps_sm_app_id,
        hf_rtps_sm_instance_id, 0);

      rtps_util_add_entity_id(sil_tree_writer, tvb, offset+12,
        hf_rtps_sm_entity_id, hf_rtps_sm_entity_id_key, hf_rtps_sm_entity_id_kind,
        ett_rtps_entity, "virtualGUIDSuffix", NULL);

      offset += 16;

      /* Counter */
      proto_tree_add_item(tree, hf_rtps_param_app_ack_conf_count, tvb, offset, 4, encoding);
      offset += 4;

      current_writer_index++;

    } /* virtual_writer_count */
  }


  if (offset < original_offset + octets_to_next_header)
  {
    /* In this case there must be something wrong in the bitmap: there
    * are some extra bytes that we don't know how to decode
    */
    expert_add_info_format(pinfo, item, &ei_rtps_extra_bytes, "Don't know how to decode those extra bytes: %d", octets_to_next_header - offset);
  }
  else if (offset > original_offset + octets_to_next_header)
  {
    /* Decoding the bitmap went over the end of this submessage.
    * Enter an item in the protocol tree that spans over the entire
    * submessage.
    */
    expert_add_info(pinfo, item, &ei_rtps_missing_bytes);
  }
}