This feature was introduced in adsb_hub 2.3 to demonstrate ADS-B capabilities in RealADSB iOS app. Since data is coming from 3rd party web site with delays it's not a replacement for good antenna and ADS-B receiver. Also it's ONLY intended for personal learning or/and entertainment. When adsb_exchange input is in use you shouldn't expose adsb_hub ports to the Internet.
adsb_hub can be started with command line java -jar adsb_hub.jar exchange.json > 1.log &
Line 2> adsb_exchange - calls ADS-B Exchange to get latest traffic in area specified by following parameters: latitude, longitude, radius in miles.
interval in seconds is used to specify how often get updated traffic data from ADS-B Exchange, default is 10 seconds and value can't be less than 3 secnonds.
mlat_color parameter can be used to override default color of MLAT traffic in RealADSB iOS app, format is #RRGGBB.
Line 3> bonjour - exposes TCP/IP port used by RealADSB iOS app.