This paper describes a group communication system called the timewheel group communication system
that has been designed for a timed asynchronous distributed system model. The timewheel group communi-
cation system consists of three protocols: a clock synchronization, an atomic broadcast protocol, and a group
membership protocol. All these protocols have been designed to be fail-aware in the sense that a process can
detect at any point in time whether any of its properties is violated. Although these protocol have been de-
signed to operate in an asynchronous distributed computing environment, they provide timeliness properties.
The timewheel group communication system provides nine group communication semantics that a user can
dynamically choose from while broadcasting an update. This system provides high throughput, fast delivery
and stability times, uses a small number of messages per update broadcast, and distributes evenly the process-
ing load among group members. The good overall performance is maintained in the absence of any failures
and normal update arrival rates, in the presence of communication or process failures, and under very fast or
very slow update arrival rates.