Allen-Bradley PLC-5 MAP/OSI, Руководство пользователя, Страница: 14 / 135

Chapter 1
Overview of the MAP Communication
Environment
1-6
Figure 1.7
Vendors Must Map Their Devices to the VMD Model
VMD
Model
MMS
Device
Mapping a device to the VMD
establishes it as a virtual device
on the network.
The mapping concept.
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This mapping of a device to the VMD model establishes a device as a
virtual device on the MAP network, allowing it to be accessed by other
virtual devices through the use of MMS services. Note that the VMD
model theoretically exists within an MMS device.
The MMS Abstract Object Models
MMS also defines a series of abstract object models that describe the
externally visible behavior associated with a particular MMS service or
group of services. The concept of object models is entirely abstract within
the MMS specification, but represents real resources within a system. This
results in a standard external view of all MMS devices that make system
resources available, but allows each MMS device to implement the model
in a manner that is appropriate for the system (figure 1.8).