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The coordination layer offers communication through a message broker and a data transmission via https. This is illustrated in the below figure. In general communication is initiated and actions are coordinated via the message broker, while the actual transmission of data is done via data transmission.

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There are no intelligence in the Coordination Layer and it is the clients that are responsible for choices that involves intelligence e.g. in chooing an alternative pillar for request of data (according to Service Level Agreement).

Message Broker

Communication

Start communication via Topic

All communication via the Coordination layer starts via a Topic that is send to all. It is up to the individual subscribers to determine whether it is a message that concerns them, for example a Get message does only concern the pillars involved in a certain service level agreement.

Atomic operations

Operation must be as atomic and simple as possible. this serves to give simplicity, and to get as little overlap between different operations as possible.

Using Get as example

The Get operation can begin by asking pillars who will be the fastes, or it can start by actually sending a get message for a specific default pillar.

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• there may be a heavy load of messages that all substribers must go through in order to find the ones interesting for themselves.

Bus software

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Software

Independence

In the design we need to ensure that we as independent of the software chosen as possible. If special features are used, e.g. for optimisation, then the design must be flexible enough to skip use of the special features at a later stage.

Data Transmission

Use of tokens

Tokens are used to til designation of where the data can be put to or downloaded from.