The switching system provides lifeline network service such as telephony service, and isrequired to serve more than 99.999% time of a year. Typical network service requires tobe performed as real time; the call control should be performed within deadline. Thereforeswitching system of PSTN (Public Switched Telephone Networks) had been developed byusing specialized hardware and software in order to satisfy service availability and realtime capability.Though, the cost of the specialized switching system is high, the most of the specializedswitching system is aging, and hard to obtain the repair parts. Consequently, the demandof replace aging specialized switching system by using cost effective COTS (Commercialoff-the-shelf) such as Intel Architecture computer, is so high. However, it is difficult to satisfythe requirements of the switching system by just applying COTS system. Especially,availability and real time capability are missing on COTS system.In this paper, I propose the approaches that improve availability and real time capabilityof COTS system, using Intel x86-64 CPU SMP machine and Linux, in order to satisfyrequirements of the switching system.First, I propose the live patching approach that enables dynamic modification of processand kernel without restarting. The proposed approach enables to fix the software withoutrestarting, within deadline, and without disrupting real time service.Then I propose the priority control of disk IO that reduces the maximum response timeof high-priority write system call. The adoption of COTS components causes the callprocessing to record transaction log to hard disk drive, and that recording increase in theservice response time. The proposed approach reduces bottlenecks of write mechanism inthe kernel.The proposed approaches enable to adopt COTS system to switching system. Theapproaches are not only for switching system but also for the system which use COTSsystem and improve the availability and the real time capability.