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Ppt On Agreement Protocol In Distributed System

Introduction – Processes/sites in distributed systems are often competing and cooperating to achieve a common goal. Mutual trust/agreement is in high demand. In distributed databases, data managers may be forced to decide whether to transfer or cancel the transaction – If there is no error, it is easy to reach an agreement. However, in the event of a failure, processes must exchange values with other processes and transmit the values obtained by others several times in order to isolate the effects of a faulty processor. Contract protocols help to reach an agreement in the event of an error. Solution for the Bizantin Agreement Problem – First defined and solved by lamport. Source transmits its initial value to all other processors. Processors send their values to other processors and pass on the values they receive to others. During execution, defective processors can be scrambled by sending conflicting values. However, if faulty processors dominate in number, they can prevent defective processors from reaching a deal.

No defective processor should exceed certain limits. Pease has shown that in a fully connected network, it is impossible to reach an agreement if the number of defective processors exceeds “m” (n-1)/3. n – number of processors Authentication VS Messages not authenticated – Authenticated messages: -Also called signed message – The processor can`t falsify/modify a received message – The processor can verify the authenticity of the message – It`s easier to reach an agreement in this case – Unathentified Messages: -Also known as oral message – Processor can falsify/modify a message received and claims to have received it by others – The processor cannot confirm the authenticity of the message. AGREEMENT PROTOCOLS Chapter 8. Processes/locations in distributed systems are often competing and cooperating to achieve a common goal. Mutual trust/agreement is in high demand. Performance aspects of contractual protocols – The following measures are used: Time: No need for tricks to reach an agreement – Message traffic: the number of messages exchanged to reach an agreement. Memory overload: the amount of information that needs to be stored in processors while the protocol is running. Classification of agreement problems cont… – For all of the problems mentioned above, all non-defective transformers must reach an agreement – For Byzantine and consensual problems, the agreement is fixed on a single value – In the problem of interactive maintenance, the agreement is on a number of common values.

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