Empirical Comparison of Block Relay Protocols

—Block relay protocols play a key role in the perfor- mance and security of public blockchains. As a result, several such protocols have been deployed in the context of Bitcoin and its variants ( e.g., legacy, compact block relay and Graphene ) in an attempt to reduce bandwidth utilization. However, the relative performance of these protocols in realistic networking conditions ( e.g., with nodes churning - joining and leaving the network) is still not known. This paper aims to fill this key knowledge gap using an experimental testbed of twelve full nodes connected to the Bitcoin Cash blockchain. With the aid of novel logging tools, we contrast the performance of these three protocols, in realistic scenarios, with respect to communication, delay, and block decoding success. Our main findings are that Graphene generally performs the best when nodes remain connected, boasting an average propagation delay of 190 ms ( i.e., 29% lower than compact block and 80% lower than the legacy protocol). However, when nodes churn at a high rate, compact blocks may perform better. Through a careful temporal analysis, we identify some root causes of the protocol inefficiencies, together with potential mitigation. We have made our measurement framework and experimental logs publicly available to the broader research community.