Contemporary Control Systems BASrouter Application Guide - Manual (Page 7)

AG-BASRTB00-BD0 Page 7
Application Guide — BASrouters
C
ONTR LS O
®
CONTEMPORARY
Application #6 — BBMD server without Firewall
When attaching BACnet devices to IP networks it
is possible that the IP network has been sub-netted
through the use of IP routers such as the EIPR-E.
Most IP routers will not pass broadcast messages
which are crucial to BACnet’s operation. The solution
is to incorporate BACnet/IP Broadcast Management
Device (BBMD) functionality within the BACnet
internetwork.
The BBMD concept requires that a broadcast message
originating on one subnet be encapsulated into a
directed message and sent to all remote subnets since
these directed messages will pass through IP routers.
Once the encapsulated messages are received on
the remote subnets, a BBMD device will decode
the message and resend it on its local subnet as a
broadcast message. Therefore it would appear that
a BBMD device must be present on each subnet in
order to provide this encoding and decoding function.
However, this is not the case if all the BACnet/IP
devices support Foreign Device Registration (FDR). At
a minimum, one BBMD device is required to be located
on one of the subnets with FDR devices registering to
this one BBMD. This is what is shown in the example
with a BASrouter providing BBMD functionality while
allowing for foreign device registration. Notice that
connecting to a BACnet MS/TP network is an option.
Before the BASrouter can function as a BBMD it must be
configured. A BBMD setup page is accessed by clicking the
Advanced button on the BASrouter’s main web page. On
the Advanced screen, BBMD is enabled by checking a box.
There are two choices for the BBMD UDP port. Normally,
the primary BACnet/IP UDP is used, but an alternate port
can be chosen. An Accept FDR box (checked by default)
allows foreign devices to register with the BBMD. But if
BBMD is not enabled, FDR is ignored. You will need to
set the FDR device address to 192.168.2.2 in your PC
application and on the controllers on the 192.168.1.0 subnet.
The application controllers on the 192.168.2.0 subnet need
not register because the BBMD is on the same subnet.
Another button accesses the Broadcast Distribution Table
(BDT). On this table, the locations of up to five BBMDs
can be entered by specifying their IP addresses and subnet
masks. Note that all BBMDs must all be on the same
BACnet/IP internetwork as the BASrouter.
Finally, another button gives access to the Foreign Device
Table (FDT) which displays all the foreign devices that have
registered with the BBMD.
Not all IP Routers allow for their firewalls to be disabled
but this is a feature with the EIPR IP Router.
Although the BACnet/IP network is sub-netted, all
subnets are assigned the same network number — in
this example Network 1.
BACnet/IP Subnet 192.168.1.0/24
Network 1
BACnet/IP Subnet 192.168.2.0/24
Network 1
Optional BACnet MS/TP
EIPR IP Router
BASRT-B
BACnet
Router
(BBMD
Enabled)
EIPR IP Router (WAN Side) EIPR IP Router (LAN Side)