#85 Foreign Device with Non BBMD Mode in BACnet Server

[Prasad Kulkarni]

A) How long should a BACnet server device wait for a response to a "Register-Foreign-Device" (RFD) request? Wait time of 1 Sec, 3 Sec etc.
In case. If there is no BBMD response, what should be the 'Foreign Device' behaviour ?

B) If there is no response from BBMD and BACnet Foreign device wants to retry the registration process again. How will it handled?

1. Do we need to 'Reinit Device Service' (e.g. Warm start) request to the device?    
2. Do we need to implement retry logic code without restarting the device?

C) In case if successfully registration with the BBMD, how does the device decide whether to send the RFD request repeatedly or once?

Case 1 - BACnet Foreign device is temporarily needed (may be two hours) in the network. 
Register with BBMD, Do the required work and when our subscription lifetime in BBMD is over our device will be automatically disconnected from BBMD as device didn't resend the RFD request. In this case, we assume that device will continue as 'Foreign' device and will continue to response to any request from its peer device in same network as long as it is connected in network

Case 2 - BACnet Foreign device need to be on network more that 18+ hours (Max limit value 65535 for Subscription Lifetime)
Register with BBMD, Continue with required work on network. Now device need to maintain its entry in FDT table of connected BBMD, so it has to initiate the registration process again with BBMD before expiry of subscription lifetime.
We understood from the code that, Maintenance time is expire will resend the Foreign Device Registration Messages. Is Maintenance time mandatory ? because if Maintenance time is continuously taking care of re-registration, then what is the significance of Subscription Lifetime?

D) Subscription Lifetime value of BACnet Foreign device is expired and hence it has been removed from FDT table of connected BBMD device.
Now what will be the status of BACnet Foreign device's 'Network Port Object'? Will it be in 'Fault' state? We assume that device will continue as 'Foreign' device and will continue to response to any request from its peer device in same network as long as it is connected in network.

E) 'Delete-Foreign-Device-Table-Entry Message'
As per the BACnet specification it is clear that this message is 'for BBMD' device. But who will initiate this message?

F) Is it necessary to have 'FD_BBMD_Address' and 'Subscription Lifetime' properties 'Writable' via BACnet interface?

[Anonymous]