ABSTRACT
Availability, performance and reliability of computer systems have become issues of critical importance in the area of computer systems and networks. Special focus has been paid in providing higher levels of service availability in cases such as communication networks, VoIP and website services, in order to make service attractive to users or clients (Koutras & Platis 2007), (Kravets et al. 1998), (Xiao et al. 2004).
