User Manual

Network architecture
BACnet architecture (MLN & ALN)
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Designation Description
IP address IP address of the BBMD.
UDP port UDP port number of the BBMD.
Broadcast mask If the BBMD is to be addressed via direct broadcast (one-hop distribution) the subnet mask of
the BBMD must be specified. Since not all IP routers support this mechanism, direct
broadcasts are not supported by default. Two-hop-distribution is always possible. The
broadcast mask is then 255.255.255.255.
Not required for IPv6.
Foreign device
A foreign device is a (remote) BACnet device in a remote IP segment. It registers with a BBMD in order to
send or receive broadcast messages. Registration with a BBMD involves making an entry in its Foreign
Device Table (FDT). The registration must be renewed at regular intervals.
The foreign device does not send broadcast messages, but passes them as unicast messages to the BBMD
for distribution. The BBMD in turn passes incoming broadcast messages as unicast messages to the
foreign devices in its FDT.
In the Desigo system, Desigo CC, XWP/ABT, and PXM30/40/50-E can be operated as foreign devices. IPv6
does not support foreign devices
Examples from the Desigo topology
● IP Segment 1: Desigo CC 1 does not have to be configured as a foreign device, because this IP segment
contains a BBMD.
● IP Segment 2: Desigo CC 3 does not have to be configured as foreign device, because this IP segment
contains a BBMD.
● IP Segment 3: This segment only contains Desigo CC 2. To enable Desigo CC 2 to receive and send
broadcast messages, it must register with a BBMD as a foreign device. It does not matter with which
BBMD it registers.
Foreign device parameters
If a BACnet device operates as a foreign device, the IP address and UDP port number of the BBMD must
be specified.
Designation Description
IP Address of BBMD IP address of the BBMD with which the foreign device registers.
UDP Port of BBMD UDP port number of the BBMD with which the foreign device is registered. The default is
0xBAC0.
The recording interval (Time-To-Live) for Desigo products is set at 300 seconds (= 5 minutes).
PTP data link layer
The PTP Data Link Layer is used for remote management over the telephone line. Unlike LonTalk and IP,
PTP does not allow the creation of a network. The PTP connection is always between two half routers, and
between two different BACnet networks. Several BACnet networks may be located at each end of the PTP
connection. Only one active communication line can exist between any two BACnet networks or between
any BACnet devices.
The half-router function is implemented in Desigo CC, XWP/ABT and PX.
PTP connections are only possible between Desigo CC, XWP/ABT und PX. PTP connections between PXs
are not permitted.
PX devices which can be reached via PTP always belong to a separate site. With reference to the topology
at the beginning of the chapter, the site named Baar must not be combined with the sites named Zug or
Cham. Several PXs per site can be used as half routers. When establishing a communication, the best-
Application Layer
Network Layer
PTPIPLonTalk MSTP