Distributed applications are realized by cooperation of multiple processes which manipulate data objects like databases. Objects in the systems are replicated to make the systems fault-tolerant. We discuss a system where read and write request messages are issued to replicas in a quorum-based scheme. In this paper, a quorum-based (QB) ordered (QBO) relation among request messages is defined to make the replicas consistent. We discuss a group protocol which supports a group of replicas with the QBO delivery of request messages.