.. _headlabel-refx-cmd-ack:

ACK (Acknowledgement)
=====================

The `AT@ACK` command is used to configure the :ref:`SACK <refx-frames-report-sack>` feature.

When the backend server receives a report from the termainal, it will behave as defined in `AT@ACK` command.

When the terminal receives a command from a physical path (for example, Cellular Network, SMS, RS232.), it will replies ACK (or NACK) to that physical path.

.. code-block:: none

   Example:
   AT@ACK=gl601###,,,,0,,012F$
   +ACK:ACK,123456789012345,C031,10,0,,012F,20210407101530,1234$
   AT@ACK?gl601###,,0C37$
   +QRY:ACK,123456789012345,C031,10,0,1,1,,,,0,,0C37,20210407101530,1234$

.. tabularcolumns:: |p{2.2em}|p{7.2em}|p{5.8em}|p{19em}|p{4.8em}|

.. table::
   :width: 100%
   :widths: auto

   +-------+-----------------------------+---------------+-----------------------------------+---------------------+
   | Parts | Fields                      | Length (Byte) | Range/Format                      | Default             |
   +=======+=============================+===============+===================================+=====================+
   | Head  | Header                      | 3             | AT@                               | AT@                 |
   +       +-----------------------------+---------------+-----------------------------------+---------------------+
   |       | Command Word                | 3             | ACK                               | ACK                 |
   +       +-----------------------------+---------------+-----------------------------------+---------------------+
   |       | Leading Symbol              | 1             | =                                 | =                   |
   +       +-----------------------------+---------------+-----------------------------------+---------------------+
   |       | Password                    | 8-16          |                                   | gl601###            |
   +-------+-----------------------------+---------------+-----------------------------------+---------------------+
   | Body  | Reserved                    | 0             |                                   |                     |
   +       +-----------------------------+---------------+-----------------------------------+---------------------+
   |       | Reserved                    | 0             |                                   |                     |
   +       +-----------------------------+---------------+-----------------------------------+---------------------+
   |       | Reserved                    | 0             |                                   |                     |
   +       +-----------------------------+---------------+-----------------------------------+---------------------+
   |       | `SACK Mode`                 | 1             | 0-2                               | 0                   |
   +       +-----------------------------+---------------+-----------------------------------+---------------------+
   |       | Reserved                    | 0             |                                   |                     |
   +-------+-----------------------------+---------------+-----------------------------------+---------------------+
   | Tail  | Sequence Number             | 4             | 0000-FFFF ('0'-'9', 'A'-'F')      |                     |
   +       +-----------------------------+---------------+-----------------------------------+---------------------+
   |       | Tail                        | 1             | $                                 | $                   |
   +-------+-----------------------------+---------------+-----------------------------------+---------------------+

- `SACK Mode`

  - **0** - The backend server does not reply a SACK frame after receiving a report from the terminal.

  - **1** - The backend server not only replies a SACK frame after receiving a report from the terminal but also requires the device to check the count number in the SACK frame.

  - **2** - The backend server replies a SACK frame after receiving a report from the terminal, but does not require the device to check the count number in the SACK frame.