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2. BACnet Services
Services provide some commands to save or control information and some functions to
achieve the purpose of monitoring and control. Namely, one BACnet device receive certain
information or command to complete specific work from other BACnet device so the two
devices need to support the same service to complete communication. To complete the
exchange of these service messages, these communication requirements are specified in
the communication protocol of application layer by BACnet. Thus, services are parts of the
communication protocol data unit (PDU) in the application layer and build the
communication modes via the relationship of Server – Client. Client will send the message
of service requirements to Server and Server needs to respond to Client to execute this
service. Refer to the following figure.
Client
Request
All BACnet devices have the application programs to manage the requirements of device
motion and executing services. Take work station for example, the application program
needs to keep the display value of every input so it requires sending the service request to
the object of other device to update the display value of input. The application program of
the device needs to respond to the service requirements. Refer to the following figure.
Send
Request for PDU
Receive
Respond to PDU
BACnet Device
Object
Object
Application
Program
Object
Object
Receive
Send
Request for
Service
Respond to
Service
Service Reply?
App 3-19
Server
Respond
Service request
Read property
Network
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