Zero-rating, the practice of not billing data traffic that belongs to certain applications, has become popular within the mobile ecosystem around the globe. There is an ongoing debate whether mobile operators should be allowed to differentiate traffic or whether net neutrality regulations should prevent this. Despite the importance of this issue, we know little about the technical aspects of zero-rating offers since the implementation is kept secret by mobile operators and therefore is opaque to end-users and regulatory agencies. This work aims to independently audit classification practices used for zero-rating of four popular applications at seven different mobile operators in the EU. We execute and evaluate more than 300 controlled experiments within domestic and internationally roamed environments and identify potentially problematic behavior at almost all investigated operators. With this study, we hope to increase transparency around the current practices and inform future decisions and policies.

翻译：零费率（即不对特定应用的流量计费）已在全球移动生态系统中日益普及。关于移动运营商是否应允许流量差异化，或网络中立法规是否应加以禁止的争论仍在持续。尽管这一问题至关重要，但由于移动运营商对实现细节保密，导致终端用户和监管机构对其技术层面知之甚少。本研究旨在对欧盟七家移动运营商针对四款流行应用的零费率分类实践进行独立审计。我们在国内及国际漫游环境下执行并评估了300余次受控实验，发现几乎所有被调查运营商均存在潜在违规行为。通过本研究，我们期望提升当前实践的透明度，并为未来决策与政策制定提供参考依据。