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Parameters in BNCS associate a human readable datapoint with display and data rules and map them to underlying infodriver storage slots.  Traditionally in BNCS, parameters have been defined in a Device Type - an XML file that lists all of the controllable datapoints of a given device.  One or more instances of that device are then defined referencing the device type definition to create the physical incarnations of a device.  Instances can also contain other, child instances, so that a complex device can be defined.  For example, an audio mixer might define three device types representing mono inputs, stereo inputs and outputs.  The composite mixer instance would then reference child instances, one for each input and one for each output building up a multi-level hierarchy that models the physical device.  All of this information is presented in various XML files that form the BNCS system configuration.

 

More details of the traditional approach to Device Types and instances can be found in the BNCS documentation.

 

One significant limitation of the traditional approach to device modelling found in previous versions of BNCS, however, is that it is highly static.  Changing the configuration required updating the various XML files and then restarting the affected parts of the system to load the new configuration.  While this approach is still supported, modern broadcast systems are much more dynamic in nature with software defined devices able to remodel themselves, and hence their control parameters, into an almost infinite number of shapes.  Device virtualisation also means that, while the device type model of a device may be pre-definable, the instances of that device available for control may be highly dynamic.

 

To help solve the issue of a constantly changing system, the latest versions of BNCS have added the concepts of dynamic devices where the devices and their controllable parameters can be added or removed arbitrarily by the driver based on the discovered devices and their configuration.  These dynamic capabilities rely on the use of an NMOS IS-04 Registry to allow other parts of the BNCS system and, potentially, external systems to discover and control devices.

 

This chapter will focus on creating and interacting with Parameters without focusing too much on the NMOS aspects which will be discussed in a subsequent section.