ty that a service provided by the system or network will be operational and hence can be represented as a ratio of MTTF over MTBF. Reliability: This is more related to continuity of service, whereas availability is more about a network being available to initiate a service. Reliability is defined as the probability of a system continuing to be in service over a defined time period. Maintainability: The ability of the system to undergo repairs and changes to continue to remain functional. Safety: The reliability of the system being dependable during times of crippling failures. Integrity: This is factored into dependability in terms of the system being able to maintain its state of operations and being consistent with respect to it services. CHAPTER 5 NETWORK ROADMAP EVOLUTION Security: This is characterized by the ability of a network or system to maintain and implement authorization and authentication policies consistently. Security is the backbone of network correctness and operation in the sense that failures in security can drastically impact other factors due to wrong access being granted to agent provocateurs and saboteurs. Factors influencing security include: Authentication under security pertains to ensuring that any user of the system is indeed the same user as being claimed. Authorization pertains to making sure the users are only able to perform or access services from the network they are authorized to do SO. Auditability pertains to ensuring that all access to the system, including success and failure, valid and invalid, authorized and unauthorized, are audited in a consistent manner and available for future review. Performability: Covers aspects of the system governing the specifications of services to be offered by the system, including the QoS aspects. Performability directly affects overall effectiveness of the network and would mostly be covered by key performance indicators, as described in Chapter 1. In addition to these factors, the complexity of the system under analysis, in terms of the la