If the common period is smaller that 18,560 milliseconds the system will never keep up. We could try any number of additional combinations of clients, furnaces, and reading intervals and repeat the calculations. The performance results are summarized in Table 4-1 . For each of these fault scenarios we assume a rate of failure and a rate of repair. We can not simply add the downtimes as if these failures scenarios were independent.
Software failures can only occur when the hardware is operating.
We will consider two modes of operation for an attacker to distort the information sent by the server. In a MIM attack, the attacker uses a TCP intercept tool to modify the values of the temperatures during transmission. For an attempted intrusion to be successful, the intruder must then successfully apply the attack scenario with some probability of success P TCP . The only barrier is the length of the window of opportunity and the probability of success for the TCP intercept tool. To successfully spoof the server, there are three possible ways to succeed.