Scalable layered membership service for group communications in WANs

Abstract

Group Communication System (GCS) is an important building block for reliable, fault-tolerant distributed applications. This is useful especially when processes geographically span over large networks like the Internet. Despite its usefulness, when GCS operate over multiple WANs, GCS needs to cope with frequent membership changes due to highly variable and unpredictable latency in WANs. Most membership management schemes used in the existing systems are LAN-oriented group membership services. They are not suitable if exchanging messages among member processes becomes expensive in terms of process computation or network load, which is common in WANs. There are a few GCSs supporting a group membership service for WANs, the schemes also cope with heavy computation and do not scale when they spans over multiple WANs. In this thesis we propose a new scheme that improves the scalability of a group membership service for WANs by exploiting dedicated membership servers configured into multiple layers and reaching global agreement on the view through layered servers. It improves the scalability of a process group of N member process from O($N^2$) to O($N^3$) with three layers. Computer simulation verifies that the proposed scheme requires much smaller number of messages for reaching an agreement and does that much quicker. In addition, the proposed scheme prevents applications from being blocked until reaching the final view agreement when the applications permit temporary inconsistency.