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

In distributed environment, a client-sewer model is often used because of its easiness of implementation. The reliability of the sewer on the model determines the reliability of the whole system. By making a backup sewer tolerance of sewer failure can he improved. This method, however, rakes long recovery time because a recovery operation includes generally detecting failure, switching to the backup server, starting the sewer process, and re-executing services executed at failure. Thus, the method cannot be introduced to application area that have constraints an time. The authors aim to implement the highly reliable and the available client-sewer 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 tile 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.