Cellular network performance is often viewed as primarily dominated by
the radio technology. However, middleboxes such as DNS resolvers and
omnipresent performance-enhancing proxies in the IP core of the
operators' mobile networks can significantly impair a user's access
despite being designed for the contrary. In addition, common roaming
and network sharing agreements between mobile operators to extend
their network coverage at minimum deployment cost — as well as
innovative business models such as Mobile Virtual Network Operators
(MVNOs) — can increase the complexity of cellular networks while
potentially degrading the performance standards expected by mobile
users and complicating their trust decisions.

Using the Android version of ICSI's popular network troubleshooting
service Netalyzr, our team has characterized the properties and
performance of DNS resolvers and proxies present in the cellular
networks of more than 260 operators worldwide, based on measurements
collected by the Netalyzr Android app from the edge of the network.
Our analysis reveals unexpected business relationships, including
third-party service providers, as well as remarkable differences in
network properties even within a single operator due to roaming
agreements.  We also find significant performance degradation in basic
network operations such as DNS lookups due to inefficient network
deployments. In addition to that, the talk describes some of the
technical and research challenges that our team encountered while
implementing Netalyzr for Android: from HCI considerations to platform
limitations.