Contemporary Control Systems BASrouter Application Guide - Manual (Page 4)

AG-BASRTB00-BD0 Page 4
Application Guide — BASrouters
C
ONTR LS O
®
CONTEMPORARY
Application #3 — Tunnelling over BACnet/IP
In a tunnelling application, a lower speed technology
uses a high speed technology to pass data between
two lower speed segments without any change in the
end-to-end protocol. With this approach, minimal
understanding of the high speed protocol is required.
In this example, two BACnet MS/TP networks located
in separate buildings need to be connected together
but no fieldbus wiring exists between the two buildings.
Instead, it is desired to utilize the buildings’ existing
Ethernet cabling. This can be accomplished with
the use of two BASrouters. The result is three cable
segments each requiring a unique BACnet network
number. This solution is not limited to just two MS/TP
segments. Additional segments each with a BASrouter
can be added together through the use of an Ethernet
switch. Once the data is tunnelled onto Ethernet,
advantage can be taken of all the Ethernet connectivity
products that are available. For example, the cabling
between buildings could be fibre optics thereby
providing the ultimate in electrical isolation.
Using a high-speed BACnet/IP tunnel for two low-speed
networks is acceptable but the inverse of using two high
speed networks using a low speed MS/TP tunnel is
not. With a low-speed tunnel like MS/TP, the maximum
message size is still too short for the longer sized
messages of BACnet/IP. This should be avoided.
Router 1
Configuration
Router 2
Configuration
BACnet MS/TP Network 1 BACnet MS/TP Network 2
BACnet/IP Network 3
Router 1 Router 2