By Request Combinations

There should be a series of interactions between a DoH client and resolver. For instance, the DoH resolver's IP address should be resolved first, followed by establishing a TCP connection, completing a TLS handshake, and finally sending a DoH query to the DoH resolver.

Many details in this process depend significantly on three factors: browsers, DoH resolvers, and HTTP methods. We defined the combination of these options as the 'request combination' and measured its effects on DoH downgrades.

We conducted a thorough analysis of the code bases of two major browsers, Chromium and Firefox*. Based on this analysis, we defined a total of twelve unique DoH request combinations as listed below.

* Safari is intentionally excluded; DoH is supported by MacOS but not by the browser itself.

You can find the downgrade rates for each country based on request combinations below, categorized by continents. Each X-axis represents request types in consecutive order.