BACnet Proxy Agent

Introduction

Communication with BACnet device on a network happens via a single virtual BACnet device. Previous versions of Volttron used one virtual device per device on the network. This only worked in a limited number of circumstances. (This problem is fixed in the legacy sMap drivers in Volttron 3.0 only) In the new driver architecture we have a separate agent specifically for communicating with BACnet devices and managing the virtual BACnet device.

Configuration

The agent configuration sets up the virtual BACnet device.

{
    "vip_identity": "platform.bacnet_proxy",
    "device_address": "10.0.2.15",
    "max_apdu_length": 1024,
    "object_id": 599,
    "object_name": "Volttron BACnet driver",
    "vendor_id": 15,
    "segmentation_supported": "segmentedBoth"
}

• vip_identity - The VIP identity of the agent. Defaults to "platform.bacnet_proxy". This should only be changed if multiple Proxies need to be run for communication with multiple BACnet networks. See below.

BACnet device settings

• device_address - Address bound to the network port over which BACnet communication will happen on the computer running VOLTTRON. This is NOT the address of any target device. See notes about device addressing below.

These settings determine the capabilities of the virtual BACnet device. BACnet communication happens at the lowest common denominator between two devices. For instance if the BACnet proxy supports segmentation and the target device does not communication will happen without segmentation support and will be subject to those limitations. Consequently there is little reason to change the default settings outside of the max_apdu_length (the default is not the largest possible value).

• max_apdu_length - (From bacpypes documentation) BACnet works on lots of different types of networks, from high speed Ethernet to “slower” and “cheaper” ARCNET or MS/TP (a serial bus protocol used for a field bus defined by BACnet). For devices to exchange messages they have to know the maximum size message the device can handle. (End BACpypes docs)

This setting determines the largest APDU accepted by the BACnet virtual device. Valid options are 50, 128, 206, 480, 1024, and 1476. Defaults to 1024.(Optional)

• object_id - ID of the Device object of the virtual bacnet device. Defaults to 599. (Optional)
• object_name - Name of the object. Defaults to "Volttron BACnet driver". (Optional)
• vendor_id - Vendor ID of the virtual bacnet device. Defaults to 15. (Optional)
• segmentation_supported - (From bacpypes documentation) A vast majority of BACnet communications traffic fits in one message, but there can be times when larger messages are convinient and more efficient. Segmentation allows larger messages to be broken up into segemnts and spliced back together. It is not unusual for “low power” field equipment to not support segmentation. (End BACpypes docs)

Possible setting are segmentedBoth (default), segmentedTransmit, segmentedReceive, or noSegmentation (Optional)

Device addressing

In some cases it will be needed to specify the subnet mask of the virtual device or a different port number to listen on. The full format of the address is ADDRESS/SUBNET_MASK:PORT. For instance if you need to specify a subnet mask of 255.255.255.0 and the IP address bound to the network port is 192.168.1.2 you would use the address

192.168.1.2/24

If your BACnet network is on a different port (47809) besides the default (47808) you would use the address

192.168.1.2:47809

If you need to do both

192.168.1.2/24:47809

Communicating with multiple BACnet networks

If two BACnet devices are connected to different ports they are considered to be on different BACnet networks. In order to communicate with both devices you will need to run one BACnet Proxy Agent per network. Each proxy will need to be bound to different ports appropriate to each BACnet network and will need a different VIP identity specified. When configuring drivers you will need to specify which proxy to use by specifying the VIP identity.

For example a proxy connected to the default BACnet network

{
    "vip_identity": "platform.bacnet_proxy_1",
    "device_address": "192.168.1.2/24"
}

and another on port 47809

{
    "vip_identity": "platform.bacnet_proxy_2",
    "device_address": "192.168.1.2/24:47809"
}

a device one the first network

{
    "driver_config": {"device_address": "1002:12",
                      "proxy_address": "platform.bacnet_proxy_1" },
    "campus": "campus",
    "building": "building",
    "unit": "bacnet1",
    "driver_type": "bacnet",
    "registry_config":"/home/kyle/configs/bacnet.csv",
    "interval": 60,
    "timezone": "UTC",
    "heart_beat_point": "Heartbeat"
}

and a device on the second network

{
    "driver_config": {"device_address": "12000:5",
                      "proxy_address": "platform.bacnet_proxy_2" },
    "campus": "campus",
    "building": "building",
    "unit": "bacnet2",
    "driver_type": "bacnet",
    "registry_config":"/home/kyle/configs/bacnet.csv",
    "interval": 60,
    "timezone": "UTC",
    "heart_beat_point": "Heartbeat"
}

Notice that both configs use the same registry configuration (/home/kyle/configs/bacnet.csv). This is perfectly fine as long as the registry configuration is appropriate for both devices.