Design of protocols in Timed CSP for highly reliable and available client-server system

In distributed environment, a client-server model is often used because of its easiness of implementation. The reliability of the server on the model determines the reliability of the whole system. By making a backup server, tolerance of server failure can be improved. This method, however, takes long recovery time because a recovery operation includes generally detecting failure, switching to the backup server, starting the server process, and re-executing services executed at failure. Thus, the method cannot be introduced to application area that have constraints on time. The authors aim to implement the highly reliable and the available client-server system which is able to recover failures very short time. In order to shorten recovery time, process level replication is employed. A server process has more than one copies of it on different hosts. Copies are kept its status as same status of the original process as possible. Thus, they can replace original process very fast when a failure occurs. Several protocols, such as updating status of copies and recovering from failures, must be specified in order to implement the proposed system. In this paper, protocols for updating copies and recovering from failures are described formally in Timed CSP, which is the one of process algebraic language, for defining them precisely.