Connect User Computer
=====================

After the Remote mode for RDK is enabled and entered, a connection between the user computer and the robot can be established following steps below.

Choose a LAN port
------------------

.. figure:: /_static/control_box_panel.png
   :width: 100.0%
   :align: center
   :figclass: align-center   

The robot's control box has 3 LAN ports open to the user, namely User Port 1, User Port 2, and General Port. The default IPv4 method used by these ports are different:

+--------------+---------------------+-----------------------+
| LAN port     | Default IPv4 method | Default robot address |
+==============+=====================+=======================+
| User Port 1  | Static              | 192.168.2.100         |
+--------------+---------------------+-----------------------+
| User Port 2  | Automatic (DHCP)    | Dynamically assigned  |
+--------------+---------------------+-----------------------+
| General Port | DHCP server (DHCPD) | 192.168.100.1         |
+--------------+---------------------+-----------------------+

The user computer's Ethernet connection should be configured differently based on the IPv4 method of the LAN port it connects to:

- If using static: connect the user computer directly to User Port 1, then configure the user computer to also use static IPv4. Set the address to ``192.168.2.xxx`` and netmask to ``255.255.255.0``, leave gateway empty.
- If using automatic: connect both the user computer and User Port 2 to the same network router, then configure the user computer to use automatic IPv4. The robot and the user computer will obtain different addresses under the same subnet from the router.
- If using DHCP server: connect the user computer directly to General Port, then configure the user computer to use automatic IPv4. The DHCP server in the robot will assign an address to the user computer.

Update MTU setting
-------------------

For a direct device-to-device Ethernet connection, the MTU (Maximum Transmission Unit) setting on both devices must be the same, otherwise only the small packets can be transmitted and the large packets will be dropped. However, if the connection is going through a router, the MTU mismatch will be handled automatically by the router and having the same MTU is optional.

In our case, the following connection methods require the user computer to have the same MTU setting (MTU = 1500) as the robot:

1. Direct port-to-port connection with static IPv4 configuration, e.g. default setting of User Port 1.
2. Direct port-to-port connection with DHCP server configuration, e.g. default setting of General Port.

To view the current MTU setting of the Ethernet interface on the user computer::

      ip link show <interface_name>

Look for the keyword "mtu" followed by a number. If you see "mtu 1500", then the user computer's MTU is already the same as the robot. Otherwise, the MTU needs to be updated to 1500. To change the setting temporarily (reset after reboot)::

      sudo ip link set dev <interface_name> mtu 1500

To change the setting permanently:

1. In a Terminal, run ``nmtui`` to open the NetworkManager GUI.
2. Select "Edit a connection" and choose the Ethernet interface.
3. Expand "ETHERNET" and find the "MTU" field, then type in 1500.
4. Save the change by selecting <OK>.
5. Restart the connection for the new MTU to take effect.

Verify the MTU setting is successfully changed::

      ip link show <interface_name>

Configure firewall
-------------------

If the user computer has an active firewall, one of the two options below must be done to allow the RDK program to establish connection with the robot:

- Temporarily disable the firewall if the computer is in a safe network environment or disconnected from the Internet; OR
- Add the RDK program's executable to the firewall's whitelist.

Check connection
-------------------

If everything works, the user computer should be able to ping the robot::
   
      ping <robot_ip>

The robot's IP address is determined by the aforementioned IPv4 method.

.. note:: The *time* value from the ping command denotes the round trip latency. Please make sure this latency complies with the requirement listed in :doc:`system_requirements`.