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How do two devices that are not on the same LAN communicate

  • Hello, everyone, now I have a problem. When two bacnet devices are not in the same LAN, how can two devices communicate through IP and port

  • I'm no Bacnet wizz here, Phil or someone will be able to likely help you more. But when it comes networks I know that if you set up static routing you can definitely incorporate other networks into the mix provided there is a default route/path back.

  • @mattfox I would like to ask how to set up a static route, is there an example to look at?

  • Fox may be right that you could get it to work by configuring the networks to at least appear as one network for the sake of BACnet broadcasts and whatnot, but the BACnet way of going about it is to have a BBMDs on the networks which you are going to link together.

    If you only need one device to be joining another established network, that can be done by registering as a foreign device with the BBMD on the network.

  • Sorry I'm late to the party. Routing can be configured depending on your network topology and the hardware you are using. When I was working with Cisco gear, you can set up a static route to forward all data from an interface to another network, or from one network to another.
    Follow Phil's advice first. If still no luck we can help you with your network convergence issue after.

  • Thank you very much for your help. I still have a question. Is BBMD hardware or software?

  • Hardware, it's neat little black box unit that handles cross network comms, have a google and you'll quickly see what Phil means.

  • Thank you for your reply. But can BBMD be software?

  • Yep, I should have said hardware or software 'black box solution', I merely relayed the first thing that came up in Google, sorry about that. I am unable to recommend a provider here so you'll likely have to refer to whomever supplied you with your current bacnet devices.
    I'm not sure of your system set up. There appears to be an open source application available. Not sure how well it works though. All I can say from here is good luck!

  • There are definitely devices whose sole function is to serve as a BBMD. There is some limited support in the IpNetwork class for behaving as a BBMD, but I believe there are limitations on the BBMD functionality supported (but I'm not 100% on that).

  • Thanks a lot team.
    I got a follow up question.

    Let's say we have a remote device on a different LAN / subnet, without a BBMD, the broadcast messages are not reaching the other subnet. A static route is already setup such that the remote device can be pinged from the local device.

    If we already have the instance number of that remote device, can we skip the "RemoteDeviceDiscoverer" process, and add the remote device manually (not cached in local device yet) ?

  • Purely as a BACnet4J question, I would suspect you could add the remote device to the LocalDevice's remoteDeviceCache manually, though this means you are working around a failure to comply with the BACnet spec in doing so, so there may be other problems down the road to solve.