Practical / Field Issues
|How does Segmentation affect you as a user ?If a
device has a large number of objects and a message is sent to read the
object list then it is possible that the response wont fit in a single
packet. If both the device and the requestor support segmentation then
there is no problem. If either side doesn’t support segmentation then 1)
You are out of luck or 2) The requestor must use a different method to
read the object list – for example, reading each object using its index
until it reaches an index number with no object.The CAS BACNet explorer
works like that – first it tries the most efficient method and then it
slowly downgrades itself to try and ensure the response will fit in a
How do you know if a device supports segmentation ?
You can read the vendor’s PIC (Protocol Implementation and Conformance) Statement or you can look at the device object’s properties.
How can you work around the segmentation issue ?
If you can configure the services your system uses to read data you have a fighting chance. Ensure you use read-property for a single property – avoiding read-property for all properties. If you have to use read-property-multiple then limit the list of properties to be read and avoid reading all using this service.