.. _headlabel-refx-cmd-bss2:

BSS2 (Backup Backend Server Settings)
=====================================

The `AT@BSS2` command is used to configure the IP address (or domain name) and port of the backup backend server.
The connection parameters (i.e, 'Transmission Mode', 'Connection Mode', 'Stay Time', 'Connection Time', etc.) of
the backup backend server are same as those of the corresponding primary backend server (please refer to the :ref:`AT@BSS <headlabel-refx-cmd-bss>` command for more information).

.. code-block:: none

   Example:
   AT@BSS2=gv500cna,,,192.168.1.12,590,0,,,012F$
   +ACK:BSS2,123456789012345,8203,3,0,,012F,20210407101530,1234$
   AT@BSS2?gv500cna,,0C37$
   +QRY:BSS2,123456789012345,8203,3,0,1,1,,,192.168.1.12,590,0,,,0C37,20210407101530,1234$

.. tabularcolumns:: |p{2.2em}|p{14.2em}|p{5.8em}|p{12em}|p{4.8em}|

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

   +-------+----------------------------------+---------------+------------------------------------+-----------------+
   | Parts | Fields                           | Length (Byte) | Range/Format                       | Default         |
   +=======+==================================+===============+====================================+=================+
   | Head  | Header                           | 3             | AT@                                | AT@             |
   +       +----------------------------------+---------------+------------------------------------+-----------------+
   |       | Command Word                     | 4             | BSS2                               | BSS2            |
   +       +----------------------------------+---------------+------------------------------------+-----------------+
   |       | Leading Symbol                   | 1             | =                                  | =               |
   +       +----------------------------------+---------------+------------------------------------+-----------------+
   |       | Password                         | 8-16          |                                    | gv500cna        |
   +-------+----------------------------------+---------------+------------------------------------+-----------------+
   | Body  | Reserved                         | 0             |                                    |                 |
   +       +----------------------------------+---------------+------------------------------------+-----------------+
   |       | Reserved                         | 0             |                                    |                 |
   +       +----------------------------------+---------------+------------------------------------+-----------------+
   |       | `IP Address/Domain Name`         | <=128         |                                    |                 |
   +       +----------------------------------+---------------+------------------------------------+-----------------+
   |       | `Port`                           | <=11          | 1-65535 or 1-65535|1-65535         | 30059           |
   +       +----------------------------------+---------------+------------------------------------+-----------------+
   |       | `Mode`                           | 1             | 0-1                                | 0               |
   +       +----------------------------------+---------------+------------------------------------+-----------------+
   |       | Reserved                         | 0             |                                    |                 |
   +       +----------------------------------+---------------+------------------------------------+-----------------+
   |       | Reserved                         | 0             |                                    |                 |
   +-------+----------------------------------+---------------+------------------------------------+-----------------+
   | Tail  | Sequence Number                  | 4             | 0000-FFFF ('0'-'9', 'A'-'F')       |                 |
   +       +----------------------------------+---------------+------------------------------------+-----------------+
   |       | Tail                             | 1             | $                                  | $               |
   +-------+----------------------------------+---------------+------------------------------------+-----------------+

- `IP Address/Domain Name`

  The IPv4/IPv6 address or domain name of the backend server.

- `Port`

  The port of the backend server and local port of terminal.

  The format of this field is `Server Port` or `Server Port|Local Port`.

  If the format of this field is 'Server Port', it means that the port number of backend server is 'Server Port' and the terminal will use the automatically assigned port number for data transmission and reception.

  If the format of this field is 'Server Port|Local Port', then 'Server Port' represents the port number of the backend server and 'Local Port' represents the port number of the terminal. The terminal will use the 'Local Port' as the local port for data transmission and reception.

- `Mode`

  - **0** - Long-term.

    Once the terminal successfully connects to this backup backend server,
    it will continue to connect to it until the connection clearly cannot be continued.

  - **1** - Short-term.

    Each time the terminal is disconnected from the backup backend server,
    it first attempts to connect to the primary backend server (configured with the :ref:`AT@BSS <headlabel-refx-cmd-bss>` command),
    and only attempts to connect to this backup backend server if it fails.