The Fdt Manager is the default view. Using it you can manually enter foreign devices if they are incapable of self-registration. Manually entered foreign devices are not purged from the FDT table.

In a case of an IP subnet, where only a few (or perhaps just one) BACnet/IP device exists, a local BBMD may be considered excessive for BACnet broadcast message support. An alternative for that subnet is for each BACnet/IP device to register as a foreign device with a particular BBMD on a remote subnet. Once registered, the driver adds the device to that BBMD’s FDT (Foreign Device Table). It then becomes that BBMD’s responsibility to deliver global BACnet broadcast messages to the remote device.

Because this scheme is sometimes used for BACnet/IP devices that are not permanent, it was designed with a mandatory registration lifetime feature. When any BACnet/IP device registers as a foreign device with a BBMD, it must specify its Time To Live value, in seconds. It is then expected to re-register within this period, otherwise the BBMD removes (purges) it from its FDT. This prevents unnecessary broadcast delivery attempts to part-time participants.

The FDT in any BBMD reflects the current list of its registered foreign devices, along with each device’s Time To Live value and calculated purge time. If the host station is configured as a BBMD, you can see all entries in its FDT.

Figure 40.   Foreign Device Table properties

You access these properties by expanding Config > Drivers > BacnetNetwork > Bacnet Comm > Network > Ip Port > Link, right-click Foreign Device Table and click Views > AX Property Sheet.