Hardware Reliability and Bathtub Curve

Bathtub Curve Phases

• The infant mortality phase is characterized by a high initial failure rate.
• The primary cause of failures during the infant mortality phase is defects in materials or manufacturing.

Constant Failure Rate Phase

• The constant failure rate phase is characterized by a constant failure rate.

Wear-Out Phase

• The primary cause of failures during the wear-out phase is deterioration due to aging.

Non-Phases of the Bathtub Curve

• There is no "random failure phase" in the bathtub curve.

Exception Handling

• Exception handling is a type of forward error recovery mechanism.

Software Quality Models

• ISO 9000 is not a software quality model.
• McCall model and Boehm model are software quality models.

Reliability

• MTTF stands for Mean Time To Failure.
• Reliability is defined as the ability of a system to perform its required functions under stated conditions for a specified period of time.
• Reliability and failure intensity are inversely related.

CMM Model

• CMM (Capability Maturity Model) is a technique to improve the software process.

Security

• Configuration management policies and processes define how to record and process proposed system changes.
• An independent relationship must not exist between the attribute that can be measured and the external quality attribute.
• Social engineering is when accredited users of a system are fooled into giving away secret information.
• It is difficult to protect against social engineering in large organizations because of their hierarchical structure and size.

Estimation

• Project size is an important factor that can affect the accuracy and efficacy of estimates.
• Software scope describes the data and control to be processed.
• Facilitated Application Specification Techniques (FAST) is a team-oriented approach to requirements gathering.

Application and Infrastructure Security Engineering

• Application security engineering is the responsibility of system designers who design security into the system.
• Infrastructure security engineering is the responsibility of system managers or administrators who configure the existing infrastructure software.

Diversity in Distributed Systems

• Diverse technologies provide protection against common vulnerabilities in different elements of the distributed system.
• Distributing assets so that attacks on one element do not disable the entire system enhances availability.

Survivability Strategies

• Resistance involves built-in mechanisms to resist attacks.
• Recognition involves recognizing that an attack is underway.
• Recovery involves built-in features to support recovery and resume normal system service quickly after a successful attack.

Software Reuse

• Software reuse is not recommended in certain circumstances, including:
  • If the business status of the code provider is dubious.
  • In critical applications where source code is not available.
  • In small systems where the costs of reuse are comparable to the savings.
  • In systems where performance is a critical requirement.

COTS Risks

• Risks that can arise when systems are constructed using COTS include:
  • Vendor risks (e.g., failure of vendor to provide support).
  • Product risks (e.g., incompatibility with other systems).

Reliability and Safety

• A reliable system can still be unsafe, and vice versa.
• It is practically impossible to validate reliability specifications when these are expressed in terms of a very small number of failures over the total lifetime of a system.