Reading BACnet in a lab is trivial. Reading BACnet across a real building estate is war. And the distance between the two is everything the vendor slides never talk about.
Here's what's waiting for you in the field. Segmented networks, where devices can't see each other without help. BBMD having to cross subnets — configured by someone who left the company five years ago. NAT in the middle. Hostile VLANs, set up by an IT team that (rightly) doesn't want strange traffic on its network. Point names with no documentation at all — "AHU3_ZN_T", and guess what it is. And "open protocols" with vendor lock-in hidden underneath the openness.
We've walked into 200-building portfolios without a single network diagram. The problem, again, was never the protocol. BACnet is documented, it's a standard, it behaves. The problem is the human and historical chaos it lives in.
So the hard part — and the boring part where most of the engineering lives — is discovery that survives this: auto-discovery that holds up against BBMD, NAT and VLANs without breaking, and mapping the points to a tagging convention (Haystack, BRICK, or the client's) so "AHU3_ZN_T" comes to mean something. Without it, you have data; you don't have information.
The honest caveat: sometimes the equipment really is dead, or proprietary and closed, and there's a piece you genuinely have to replace. When that's the case, we tell you — instead of pretending a gateway solves everything. But it's the exception. In the overwhelming majority of buildings, the nervous system is already there and works. What it's missing is a brain that can hear it through the noise.