Desigo uses open communications to connect various technical building systems based on open and standardized data interfaces:
- BACnet is used from room automation to the management level
- KNX®, DALI, EnOcean® and LonWorks® are used in room automation and decentralized secondary processes
- M-bus, Modbus, OPC, MS/TP, and other interfaces are used for connecting third-party devices and systems
BACnet (Building Automation and Control Networks) is a communications protocol for building automation and control networks. BACnet ensures the interoperability between devices from different manufacturers.
Each BACnet device has a VendorID to identify the manufacturer. The VendorID for the Siemens BACnet system devices is 7.
BACnet over Ethernet/IP
Applications on the management level can interact via standard IT network services concurrently to BACnet services.
Desigo supports BACnet/IPv4 and BACnet/IPv6 (via PXG3.M/L router). IPv6 to IPv4 is NOT compatible. The parallel operation of IPv4 and IPv6 is possible with the use of a PXG3.L/M BACnet router.
The performance of the network depends on the following criteria:
- Number of devices on the bus
- Segmentation of the topology via routers (for LonTalk bus)
- Number of simultaneously active clients
- Peer-to-peer communication resulting from distributed PX applications
- Other communications services using the same transmission medium, where, e.g., office communication on a separate VLAN share the same IP trunk
- Application download on the network
Due to these factors, which can vary widely from project to project, it is not possible to make any generalized statements about network performance. If the specified product quantities are adhered to, performance is adequate.
If the network performance is not satisfactory, the following actions may help:
- Use the same automation station for items of equipment with frequent process interaction.
- Divide the network into segments via BACnet router and an Ethernet/IP backbone.
- Isolate the automation station from the network when downloading an application.
BACnet and IP network structuring
BACnet supports various application services which are transmitted to all BACnet devices (broadcasts). Global broadcasts are blocked by the IP router. BACnet solves this problem by using a BACnet Broadcast Management Device which ensures that IP broadcasts only appear in one IP segment. The logical BBMD functionality can be configured in every BACnet router and in every PX automation station with BACnet/IP. One BBMD can be configured per BACnet/IP port. Devices with BBMD must have a static IP address.
BACnet over MS/TP
MS/TP stands for Master Slave / Token Passing. Each device on the link is considered the master when it has the token. If it does not have immediate need to use the token, it passes the token along to the next device. All devices on the link which do not currently have the token are regarded as slaves, and listen to any messages the current master may have for it. As all devices take turns being master, the link is effectively peer-to-peer.
Use of other network technologies
IP networks (besides the other technologies mentioned above) provide the network infrastructure Desigo devices are connected to. In case a Desigo installation is spatially distributed (e.g., several buildings on a campus, multiple branches in a country) the connection of these local IP networks (LANs) normally is done using a Wide Area Network (WAN) or a point-to-point transmission line. These can be based on non-IP technologies but typically are transparent for IP traffic. In this way, all the BACnet devices connected via an IP network can communicate with each other.
A BACnet device can assume two different roles within a system, the role as a server and the role as a client. These roles are defined as follows:
- Client: A system or device which uses another device via a BACnet service (service request) for a specific purpose. The client (e.g., Desigo CC, operator unit) requests a service from a server.
- Server: A system or device which responds to a given service request. The server (e.g., PXC automation station, Desigo room automation station) performs a service for a client.
Most system devices in Desigo can act either as a client or as a server, but they normally each carry out their more typical role. An automation station is normally a BACnet server, which supplies process data to other system devices. The automation station can also act as a client, when it, e.g., subscribes to a process value from another automation station.
BACnet standard device profile
The BACnet standard defines several device profiles that simplify to judge (and test) a device's capabilities against a specified function set. Desigo always tries to work with such profiles and prove their fulfillment by independent test laboratories and respective BTL logos and BACnet certificates.
- The PXC3 and DXR2 room automation stations comply with the B-ASC standard device profile.
- The PXC automation stations comply with the B-BC standard device profile.
- The Desigo CC management platform complies with the B-AWS standard device profile.
For a complete list with additional details, see BACnet Protocol Implementation Conformance Statement (PICS) (CM110665) and the products page of the BIG-EU website (https://www.big-eu.org).
Desigo complies with the AMEV guideline BACnet 2011 Version 1.2 with the following profiles:
- Desigo CC: AMEV profile MOU-B
- Desigo PX: AMEV profile AS-B
Desigo room automation
BACnet is used to exchange information between PX automation stations and DXR2 and PXC3 room automations stations and the management platform.
The Desigo RXB room automation range communicates via KNX S-Mode (EIB).
Restrictions for LonWorks
A LonWorks network cannot be segmented with LonWorks routers, as the message length for BACnet is 228 bytes for performance reasons. Commercially available LonWorks routers do not have sufficiently large buffers for this length. No other media (power lines, infrared, etc.) can be used either.
For performance reasons, we do not recommend the operation of LonWorks and BACnet devices on the same LonTalk cable.