Doppler: Internet Radar

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Introduced Doppler, an internal project for mapping and measuring the network between users and Facebook. Doppler uses a lightweight JavaScript probe appended to a sample of page hits to perform continuous, large-scale network experiments (50 million per day). It measures end-to-end DNS latency by timing unique hostname requests and packet RTT by timing cached requests. The collected data is geolocated and rolled up by country and autonomous system number to identify network issues. Doppler is also used to evaluate TCP optimizations, hardware, and measure effective bandwidth. Future work includes mobile support, SSL, and IPv6, and using Doppler data for DNS-based global server load balancing.