Network

The Gizmo platform relies on a lot of IP communications to move data from one place to another. This data comprises location information for robot assignments, control data for various systems, and status information reported back to centralized logging and metrics collection systems. In order to maintain a uniform approach, all of these systems communicate over one or more IP networks.

During field initializations, a special local subnet is used to communicate between the FMS and the Scoring Box which provides core IP services to the network. This is done since during setup the layer 2 network topology will be changed, and the normal IP addresses the system would use are not yet available. Once the core FMS network is up, field boxes, the FMS server, and scoring boxes receive IPs in the 100.64.0.0/24 subnet. While this subnet is not intended for local assignment, instead being part of the CG-NAT allocation (RFC6598). We select this range and the adjacent subnet for bootstrapping (100.64.0.1/24) due to the extremely small chance in a collission between this range and the range in a host venue, which would render normal NAT services impossible to deliver. There is no risk to sitting this range behind an external CGN as the intermediate NAT will prevent each side from seeing the conflicting range.

Gizmo communications happen on networks which include the team number. The team numbers all reside within the RFC1918 space in the 10/8 Class A block. This space was chosen to allow for up to 9999 teams to be identified in a single network without additional considerations. Future work would include migrating the Gizmo network to IPv6 space in order to permit an even higher limit to number allocations.

Team subnets are allocated by taking the team number, padding to 4 digits, then splitting the first and second 2-digit groups into the second and third octets of the address. For example, team number 4 would be represented as 0004, then assigned IP space in 10.0.4.0/24. Note that duplicate zeros are collapsed prior to allocation. While technically not necessary, this normalization makes addresses easier to parse and reason about. Lets look at another example. Team number 1729 is already 4 digits in length, so we partition the number and allocate 10.17.29.0/24 for this team's use.

These networks are managed by the FMS's Scoring Box which resides at the first address in each block and provides DNS as well as DHCP services. In the case that the FMS is unavailable, the Driver's Station runs a reduced functionality DHCP server that can assign addresses in its local subnet only.

Wireless Networks

The Gizmo is designed to function as part of a mobile robotics platform, and as such needs to support wireless communications. While a variety of wireless standards exist, we use 802.11n wireless networking in the 2.4Ghz channel space. This ensures a good balance between range, overhead, and interworking with other wireless users.

By operating according to the 802.11n standard we support the most permissive interworking profile, and can down-clock to support any lower mode, ensuring that the Gizmo poses no risk to any other nearby fixed or mobile networks following North American standards. Interworking profiles are how this is achieved, and the Gizmo supports the highest profiles currently available for the 2.4Ghz bands.

While the flexibility of the 802.11n standard allows the use of any SSID and security combination, for consistency the Gizmo makes use of specific patterns. Since no human needs to join the point-to-point control network the SSID is formatted as a 64 character hexadecimal sequence. This sequence is randomly generated and is the maximum length that SSIDs are permitted to be. Similarly, WPA2-PSK authentication with TKIP encryption is used to secure the channel against unauthorized users. The gizmo utilities generate 64 character random hexadecimal strings to use for these keys.

FMS Network

Based on the information above, we can now fully detail the FMS network. The network is comprised of 2 broad components. First, the internal network on which the FMS workstation, the scoring box, and all field boxes reside is formed. This network resides in the 100.64.0.0/24 space, and is the only network from which certain control actions can be taken. It operates on VLAN ID 1 using standard 802.1q tagging for ports facing internal devices.

Team networks are assigned to VLANs with numerically increasing IDs starting at 500. While this technically limits the number of teams that could compete in a single event to just 3,596 it is considered an acceptable tradeoff given that no venue exists which can comfortably host that many teams. Prior to each match, the team location mapping is consulted to determine which field and quadrant each team will be assigned to, and the relevant networks are made available on those radios and access ports. This sophisticated automation is managed by the FMS workstation, and is completely passive once changes are synced.