Group communication support for distributed collaboration systems

The Collaborative Computing Transport Layer (CCTL) is a communication substrate consisting of a suite of multiparty protocols, providing varying service qualities among process groups. CCTL explicitly supports distributed collaborative and multimedia applications. CCTL is based on a two-level group hierarchy. Logical interconnections among entities, called channels, define an efficient and light-weight group mechanism. Channels support a variety of service qualities such as reliability and message ordering. Related channels can also be combined to form sessions, heavy-weight groups which provide a default atomic multicast service. CCTL supports membership protocols tailored to the quality of service offered by a channel, including a relaxed form of virtual synchrony. In this paper, we present three membership protocols and compare and relate our implementations to alternatives. Our two-level architecture allows simple and efficient implementation of the membership protocols.