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JoelBender / bacpypes

BACpypes provides a BACnet application layer and network layer written in Python for daemons, scripting, and graphical interfaces.
MIT License
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[QUESTION] How to identity MSTP Devices #435

Open WeiTangLau opened 3 years ago

WeiTangLau commented 3 years ago

I am looking for docs regarding identifying MSTP Devices hidden behind an IP Device (could be a router), but I couldn't find any. Furthermore, I found an extension to add MSTP support. Does this mean that MSTP is not supported by this library? If not, how can I identity the MSTP device?

Thanks in advance!

JoelBender commented 3 years ago

For BACnet devices that are Revision 17 or later and support the Network Port Object then you can find out by looking in the Network_Type property (Clause 12.56.8), in BACpypes that would be the networkType property name. The value is one of the enumerations of a BACnetNetworkType, in BACpypes that is the NetworkType class. An MS/TP device will probably only have one network port object, so it should be easy to find. If the IP-to-MS/TP router supports network port objects, you should be able to find it that way as well.

Most of the time a single octet address is probably an MS/TP or ARCNET address and there is no way to distinguish them from each other. If you send an Initialize-Routing-Table to a router, you will get some port information, but most of the time you won't get anything very useful.

The misty project adds MS/TP support for directly connected serial port devices and isn't needed for talking through a router.

WeiTangLau commented 3 years ago

Hi! Thanks for your response. My current setup is MSTP -> Router -> Laptop. I do have a router like the case you mentioned. However, I am actually using a third party software that uses this library. As such, I do not have much flexibility. The developer told me that they actually uses this under the hood. Is this sufficient or has to do what you mentioned above?

JoelBender commented 3 years ago

You are correct. The router is going to have two ports, each will have a unique network number. Let's assume that the IPv4 network is BACnet network 10 and the MS/TP network has BACnet network 20. Your laptop will be on network 10 and you will be sending messages to the IP address of the router asking it to forward the message to some device on network 20.

First try running the WhoIsRouter.py sample application and enter wirtn * which means "send out a local broadcast on this network to all of the routers and have them respond with the list of attached networks." You should see a message from the router saying "I am router to network 20."

Now try running the WhoIsIAm.py application and enter whois *:* which means "send out a global broadcast message to every BACnet node and have them respond with an I-Am message. You should see at least one from a device on the MS/TP network, the address will look like 20:13 which in BACpypes means "address 13 on network 20."

All of the rest of you read and write property requests should be sent to 20:13 and the router will take care of shuffling the packets between networks.