tem may make between all acceptable forms of service Service probabilities that define the chances that each service state satisfies the criteria of dependability CHAPTER 5 NETWORK ROADMAP EVOLUTION Disruption tolerance: This could primarily arise from environmental challenges that are intrinsic to communication networks. There could be a wide variety of disruptions affecting components of the network, as in: Problems with channel connectivity Issues related to mobility Latency figures that cannot be predicted Rapidly changing environment factors Aspects of energy management in the end-user devices, which could mean issues with low energy levels Traffic tolerance: Primarily relates to dynamically injected traffic load into the system: This could be a related to unexpected but valid events like a surge of people arriving at some location due to some valid reason (arrival of a celebrity, attending a ball game, etc.) It could also be a result of attacks initiated by people or systems with malicious intent, like a distributed denial of service (DDoS) attack. Trustworthiness. Contributes a counter set of disciplines related to aspects of the network that can be measured when it is subjected to challenges. Properties related to trustworthiness give a measure of the resilience indicator of the network, including: Dependability: A discipline that tries to quantify the extent to which a network can be relied upon to provide a service. This includes the factors of availability and reliability, which can be defined based on the following failure and repair-related measures: Mean time to failure (MTTF) is the expected value of the failure density function or a measure of how soon the next failure could occur. Mean time to repair (MTTR) is the expected value of the repair density function or a measure of how soon the system recovers from the failure. Mean time between failures (MTBF) is the sum of MTTR and MTTF, as in the time from failure to repair to the occurrence of the next failure. Availability: Defined as the probabili