Technical data

Fieldbus Communication • 211
BACnet/IP
WAGO-I/O-SYSTEM 750
BACnet/IP Controller
4.2.1.6 BACnet in the Network
There are 2 possibilities for sending reports over networks that are based on
the Internet protocol (IP)
• IP Message Tunneling
• BACnet/IP
4.2.1.6.1 IP Message Tunneling
Devices that do not communicate over BACnet/IP or that do not use the inter-
faces specified by the BACnet Standard for communication need a BACnet
Tunneling Router (BTRs). Since the functioning is described in Annex H of
the Standard, these routers are also called "Annex H routers".
IP tunneling between the different communication technologies takes place
over routing tables with a combination of BACnet network numbers and IP
addresses.
Sending a report from one device A to a device B requires the BACnet Proto-
col Annex H router in both local networks (see Fig. 4-2).
The Annex H router for network 1 transfers the BACnet message to a UDP
(User Datagram Protocol) frame and transmits the message over standard IP
links, or over the Internet to the Annex H router in network 2.
This unpacks the incoming data packet and sends the report over the BACnet
Protocol to the target device B.
IP
router
IP
router
Internet
Annex H router
BACnet device
BACnet device
BACnet device
Annex H router
BACnet device
BACnet device
BACnet device
Network 1
Network 2
A
B
Fig. 4-2: Communication over an Annex-H router G083009e
The advantage of this type of communication via BTRs is the economical de-
livery costs. Also, the BACnet devices do not have to be IP-capable. BTRs are
frequently used in existing BACnet networks that have a link to IP networks,
to an intranet or to the Internet.
A disadvantage of this method is the high data traffic on the line, for each re-
port is sent twice over the network - once as a BACnet and once as an IP re-
port.