Mixnet networks deliberately induce additional latency to communications to provide anonymity. Recent developments have allowed mixnets to reduce their latency from hours to seconds while maintaining the same level of anonymity. As a result, real-time communications are now possible on mixnets. There has been limited research on how users tolerate different levels of delay, and it is unclear what latency levels mixnet operators should choose. Previous studies about latency do not apply to these 'mid-latency' mixnet scenarios. Our paper contributes the first measurement of users' tolerance to real-time applications under mixnet delay. We design a text-based collaborative quiz system to test user response to latency where participants complete a set of question tasks in collaboration with a simulated second user. Different levels of latency are added, analogous to a modern mixnet system. We show that average delay parameters of 1s and 4s maintain usability, a mean delay of 7s shows some difficulty and a mean delay of 10s is detrimental to user experience. Using these delay parameters, mixnet operators can ensure that most types of real-time communication applications are usable. Mixnets thus can balance usability and anonymity without compromising either.

翻译：混合网络通过刻意引入额外通信延迟来提供匿名性。近期发展使得混合网络在保持同等匿名水平的同时，能将延迟从数小时降低至秒级，从而实现了实时通信在混合网络上的应用。目前关于用户对不同延迟水平的容忍度研究有限，混合网络运营商应选择何种延迟水平尚不明确。先前关于延迟的研究并不适用于这种"中延迟"混合网络场景。本文首次测量了用户在混合网络延迟下对实时应用的容忍度：我们设计了一个基于文本的协作问答系统，通过参与者与模拟第二用户协作完成问题任务来测试用户对延迟的反应。系统添加了与现代混合网络系统相对应的不同延迟水平。实验表明：平均延迟参数为1秒和4秒时系统保持可用性，7秒平均延迟开始显现操作困难，10秒平均延迟则对用户体验产生损害。基于这些延迟参数，混合网络运营商可确保大多数类型的实时通信应用保持可用。混合网络由此能在可用性与匿名性之间取得平衡，而无需牺牲任一特性。