System Architecture Design

pSHIELDSystem Architecture DesignPU• Fault prevention, tolerance, diagnosis• Error detection, correction• Failure rate, failure mode4.1.2.2 The attributesDependability is a concept composed by the following basic attributes• Availability• Reliability• Safety• Confidentiality• Integrity• MaintainabilityThe description of the required goals of those attributes in terms of frequency, severity and duration offailure modes for a specific set of failure modes in a specific environment, is the dependability requirementof the system.Depending on the indented application of the system, those attributes contribute in different weights to thedependability requirement. Availability is always a prerequisite, but reliability, safety and confidentialitymay be required to a limited degree in certain applications.Integrity is a prerequisite for availability, reliability and safety but not always for confidentiality. Forexample, attacks via passive listening can lead to loss of confidentiality without threatening integrity.Security, although not included as a single attribute of dependability, can be described as the combinationof confidentiality, integrity and availability.There are also some secondary attributes, especially relevant to security, which can be defined when wedistinguish amongst various types of information• Accountability: availability and integrity of the identity of the person that performs an operation• Authenticity: integrity of the source and content of a message and other attributes of the messagesuch as time of emission• Non-repudiation: availability and integrity of the identity of the sender and receiver of a messageThe different weights that are put on those attributes directly affect the means that are to be used in orderto make the resulting system dependable. Most of the times, those attributes are also conflicting with eachother and several design trade-offs are required.4.1.2.3 The meansThe four main techniques utilized for the development of a dependable computing system are thefollowing• Fault prevention: It is attained by employing quality control during the design and implementationphases. For software, these include structured programming and modularization and forhardware, rigorous design rules. Physical faults are prevented through shielding, radiationhardening etc. Interaction faults are prevented through training and rigorous procedures.Malicious faults are prevented through the use of firewalls, intrusion detection systems and similardefences• Fault tolerance: Is the notion of delivering the correct service even during the presence of activefaults. This is achieved by error detection and system recovery in the forms of rollback,PUD2.3.2Issue 5 Page 52 of 122