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FAQ.md

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Frequently Asked Questions

This file contains a collection of frequently asked questions and additional background information.

Why can't I connect to my local device simulator?

BACnet uses unicast and broadcast UDP telegrams on a single port to communicate with other devices. This makes it impossible to run two BACnet stacks on the same machine without taking a detour. The most promising way is either to rely on something like Docker an use it's internal network (e.g. see docker-compose.yml) or use a secondary IP for your local machine.

I receive the error ERR_TIMEOUT. What does this mean?

The error type ERR_TIMEOUT is created by Node BACstack itself, if no answer has been received from a target device in the defined timeout window. This can have a variety of root-causes like issues on the remote device itself (e.g. communication disabled), network issues (e.g. wrong network topology), wrong communication parameters (e.g. wrong port) or ignored limitations (stack doesn't support routing). Some tips regarding debugging such issues are described in this document.

I receive the error BacnetError - Class: X - Code: Y. What does this mean?

The two error types BacnetError and BacnetAbort are application level errors and are returned by a BACnet remote device in case of a failure. Both error types also contain the reason for the failure, which can be interpreted like:

Error: BacnetError - Class: [X] - Code: [Y]
[X] => In `lib/enum.js` see `ErrorClass`.
[Y] => In `lib/enum.js` see `ErrorCode`.

Error: BacnetAbort - Reason: [Z]
[Z] => In `lib/enum.js` see `RejectReason`.

We therefore can encode the example Error: BacnetError - Class: 2 - Code: 32 to Error: BacnetError - Class: PROPERTY - Code: UNKNOWN_PROPERTY, meaning the property we tried to read or modify doesn't exist.

What is the easiest way to debug failing operations?

A good way to start debugging all sort of failures, is to cross-check the attempted function with another BACnet tool, such as one of the many freely available BACnet browsers. This verifies, if the attempted function itself works with the target device and rules-out other issues like connectivity.

This stack also has internal debug messages, which can be enabled with export DEBUG=bacstack. It will print all sorts of internals to the console, which can be used to get an idea, if or why messages are getting dropped.

Another powerful tool to not only identify network issues, but also verify sent and received messages is Wireshark. It comes with inbuilt BACnet analysis tooling, which can help to make all BACnet telegrams visible and also checks if they comply to the BACnet standard.

Where can I get more information / examples on undocumented functions?

Beneath the rendered documentation itself, a good starting point for even more examples are the compliance tests. They use the stack via it's public interface and test a wide variety of scenarios. The tests are splitted into individual files per function and can be found in test/compliance/.