Fault Tolerance Chapter 7 Fault Tolerance Chapter 7 Basic Concepts Notes | EduRev

: Fault Tolerance Chapter 7 Fault Tolerance Chapter 7 Basic Concepts Notes | EduRev

 Page 1


Fault Tolerance 
Chapter 7 
Page 2


Fault Tolerance 
Chapter 7 
Basic Concepts 
Dependability Includes 
 
• Availability 
• Reliability 
• Safety 
• Maintainability 
Page 3


Fault Tolerance 
Chapter 7 
Basic Concepts 
Dependability Includes 
 
• Availability 
• Reliability 
• Safety 
• Maintainability 
Failure Models 
Different types of failures. 
Type of failure Description 
Crash failure A server halts, but is working correctly until it halts 
Omission failure 
     Receive omission 
     Send omission 
A server fails to respond to incoming requests 
A server fails to receive incoming messages 
A server fails to send messages 
Timing failure A server's response lies outside the specified time interval 
Response failure 
     Value failure 
     State transition failure 
The server's response is incorrect 
The value of the response is wrong 
The server deviates from the correct flow of control 
Arbitrary failure A server may produce arbitrary responses at arbitrary times 
Page 4


Fault Tolerance 
Chapter 7 
Basic Concepts 
Dependability Includes 
 
• Availability 
• Reliability 
• Safety 
• Maintainability 
Failure Models 
Different types of failures. 
Type of failure Description 
Crash failure A server halts, but is working correctly until it halts 
Omission failure 
     Receive omission 
     Send omission 
A server fails to respond to incoming requests 
A server fails to receive incoming messages 
A server fails to send messages 
Timing failure A server's response lies outside the specified time interval 
Response failure 
     Value failure 
     State transition failure 
The server's response is incorrect 
The value of the response is wrong 
The server deviates from the correct flow of control 
Arbitrary failure A server may produce arbitrary responses at arbitrary times 
Failure Masking by Redundancy 
Triple modular redundancy. 
Page 5


Fault Tolerance 
Chapter 7 
Basic Concepts 
Dependability Includes 
 
• Availability 
• Reliability 
• Safety 
• Maintainability 
Failure Models 
Different types of failures. 
Type of failure Description 
Crash failure A server halts, but is working correctly until it halts 
Omission failure 
     Receive omission 
     Send omission 
A server fails to respond to incoming requests 
A server fails to receive incoming messages 
A server fails to send messages 
Timing failure A server's response lies outside the specified time interval 
Response failure 
     Value failure 
     State transition failure 
The server's response is incorrect 
The value of the response is wrong 
The server deviates from the correct flow of control 
Arbitrary failure A server may produce arbitrary responses at arbitrary times 
Failure Masking by Redundancy 
Triple modular redundancy. 
Flat Groups versus Hierarchical Groups 
a) Communication in a flat group. 
b) Communication in a simple hierarchical group 
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