State machine replication (SMR) is a replication technique that ensures fault tolerance by duplicating a service. Geographical SMR can enhance its robustness against disasters by distributing replicas in separate geographical locations. Several geographical SMR protocols have been proposed in the literature, each of which tailored to specific requirements; for example, protocols designed to meet the requirement of latency reduction by either sacrificing a part of their fault tolerance or limiting the content of responses to clients. However, this diversity complicates the decision-making process for selecting the best protocol for a particular service. In this study, we introduce a latency estimation model for these SMR protocols based on the communication patterns of the protocols and perform simulations for various cases. Based on the simulation results and an experimental evaluation, we present five selection guidelines for geographical SMR protocols based on their log management policy, distances between replicas, number of replicas, frequency of slow paths, and client distribution. These selection guidelines enable determining the best geographical SMR protocol for each situation.

翻译：状态机复制（SMR）是一种通过复制服务来确保容错的复制技术。地理SMR通过在独立的地理位置分布副本来增强其抗灾能力。文献中已提出了多种地理SMR协议，每种协议都针对特定需求进行了定制；例如，某些协议旨在通过牺牲部分容错能力或限制对客户端的响应内容来满足降低延迟的要求。然而，这种多样性使得为特定服务选择最佳协议的决策过程变得复杂。在本研究中，我们基于这些协议的通信模式，引入了一种延迟估计模型，并针对各种情况进行了模拟。基于模拟结果和实验评估，我们提出了基于日志管理策略、副本间距离、副本数量、慢路径频率和客户端分布的五项地理SMR协议选择指南。这些选择指南能够为每种情况确定最佳的地理SMR协议。