LoRa Gateway Bridge is a service which abstracts the packet-forwarder UDP protocol into JSON over MQTT. The package-forwarder software is running on most gateways and its purpose is to communicate with the LoRa chipset.
Because LoRa Gateway Bridge publishes the content of the UDP packets as JSON over MQTT, it becomes trivial to monitor the data that is sent and received by each gateway.
As each LoRa Gateway Bridge subscribes to the topics related to the gateways that are connected to the instance, the MQTT broker will handle the routing of which (downlink) frame must be sent to which LoRa Gateway Bridge instance.
By running the LoRa Gateway Bridge on the gateway itself, it is possible to use MQTT over TLS, meaning the transport between the gateway and server(s) is secure.