User Manual

Network architecture
BACnet architecture (MLN & ALN)
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networks are automatically created, which must be connected to the PXG3 BACnet router. Multiple BACnet
internetworks can be created on an IP segment by using different UDP port numbers.
Desigo establishes PTP connections only between operator units and a network. Operator units duplicate a
virtual network since PTP connections demand a network at both ends.
Desigo CC does not use PTP.
Segment
Large networks are structured, that is, divided into several (logical) network segments for reasons of
security, performance, size and (limited) address range of network devices. The segments must then be
connected to routers of the corresponding transport protocol (e.g., LonWorks router, IP router).
In most cases it is not necessary to divide a BACnet/LonTalk network into several LonWorks segments
(ALN). However, if it does prove necessary, it is not possible to use a LonWorks router, because this limits
the length of the data packets. An L-switch (Loytec) can be used as a router on the ALN.
BACnet MS/TP networks cannot be segmented, because there are no associated routers.
With BACnet/IP some IP segments may be connected by IP routers. Since the IP router prevents
broadcasting, the connection must be activated with the BACnet Broadcast Management Device (BBMD).
Physical segment
Physically, (cable) networks cannot be expanded as desired. Depending on electrical transmission
properties and the data link layer based on it, repeaters must be added at specific cable lengths to amplify
the signal. This divides the network into multiple, physical segments. A repeater does not impact the
transmission protocol; it merely electrically connects two physical networks.
Dividing up the network into several physical segments may be necessary in LonWorks technology.
The physical segments are connected with physical or logical repeaters. Due to the limited buffer size of
logical repeaters, only physical repeaters may be used on the ALN. Only one physical repeater may be
located between any two nodes.
MS/TP is transmitted on a two-wire cable as per EIA-485/RS-485*. The length of the physical segment can
be max. 1,200 m and can be extended with EIA-485 repeaters.
*TIA standard (Telecommunications Industry Association): TIA-485-A Electrical Characteristics of
Generators and Receivers for Use in Balanced Digital Multipoint Systems (ANSI/TIA/EIA-485-A-98)
(R2003)
Desigo site
A site is an independent and self-contained logical entity within the building automation and control
system. This type of structuring is not defined by BACnet, and is therefore largely independent of the
BACnet network topology. The BACnet devices bound to a site can therefore be placed anywhere within a
BACnet internetwork. A site cannot extend across a PTP connection. Communication occurs only within the
site, but data can be exchanged with any device on the BACnet internetwork.
Only automation stations (PXC/PXC3) and LonWorks system controllers (PXC...D+PXX-L11/12)) are
assigned to the sites, by special structuring of the Device ID and Device Name. These products are
considered third-party devices for the purposes of a site.
Protocol layer model
Desigo supports:
● BACnet/IP
● BACnet/LonTalk (LonWorks technology)
● BACnet/PTP
● BACnet MS/TP
● BACnet/IPv6 (only via PXG3 BACnet router)