User Manual

System overview
Communication principles
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● 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.
Client/Server
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.