A system model represents aspects of a system and its environment. There are many different types of models, as there a variety of purposes for which they are built.
This tutorial provides an explanation of three important and complementary ways in
which the design of distributed systems can usefully be described and discussed:
and their interconnectivity, without details of specific technologies.
communication tasks performed by its computational elements; the computational
elements being individual computers or aggregates of them supported by appropriate
network interconnections. Client-server and peer-to-peer are two of the most
commonly used forms of architectural model for distributed systems.
individual issues faced by most distributed systems.
.
There is no global time in a distributed system, so the clocks on different computers do
not necessarily give the same time as one another. All communication between processes
is achieved by means of messages. Message communication over a computer network
can be affected by delays, can suffer from a variety of failures and is vulnerable to security
attacks. These issues are addressed by three models:
• The interaction model deals with performance and with the difficulty of setting time
limits in a distributed system, for example for message delivery.
• The failure model attempts to give a precise specification of the faults that can be
exhibited by processes and communication channels. It defines reliable
communication and correct processes.
• The security model discusses the possible threats to processes and communication
channels. It introduces the concept of a secure channel, which is secure against
those threats.
This tutorial provides an explanation of three important and complementary ways in
which the design of distributed systems can usefully be described and discussed:
1. Physical models
consider the types of computers and devices that constitute a systemand their interconnectivity, without details of specific technologies.
2. Architectural models
describe a system in terms of the computational andcommunication tasks performed by its computational elements; the computational
elements being individual computers or aggregates of them supported by appropriate
network interconnections. Client-server and peer-to-peer are two of the most
commonly used forms of architectural model for distributed systems.
3. Fundamental models
take an abstract perspective in order to describe solutions toindividual issues faced by most distributed systems.
.
There is no global time in a distributed system, so the clocks on different computers do
not necessarily give the same time as one another. All communication between processes
is achieved by means of messages. Message communication over a computer network
can be affected by delays, can suffer from a variety of failures and is vulnerable to security
attacks. These issues are addressed by three models:
• The interaction model deals with performance and with the difficulty of setting time
limits in a distributed system, for example for message delivery.
• The failure model attempts to give a precise specification of the faults that can be
exhibited by processes and communication channels. It defines reliable
communication and correct processes.
• The security model discusses the possible threats to processes and communication
channels. It introduces the concept of a secure channel, which is secure against
those threats.
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