User Manual

Network architecture
BACnet architecture (MLN & ALN)
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Domain ID : The domain ID is the highest unit in the LonWorks addressing
system. Data can only be exchanged within a domain. A gateway is required for
inter-domain communication. The domain ID can be 0, 1, 3 or 6 octets in length.
A domain can consist of up to 255 subnets.
Subnet ID : The subnet is a logical collection of up to 127 nodes within a
domain. The bus traffic within a subnet can be kept local by using BACnet
routers. Subnets must never be defined across a router.
Node ID : Unique identifier within the subnet. Each node can be addressed
uniquely within a domain by the subnet ID and the node ID.
Group ID : The group address is a type of addressing. The group address is not
used in BACnet.
On the ALN, the following rules apply to Desigo:
Designation Values/Range Description
Domain ID 0x49h (73) The default length of the domain ID is one octet and the default value
is 0x49h (73).
Subnet ID 1…255 The subnet ID is a consecutive number that starts with one. The
subnet ID is incremented by one when a subnet is full (no free node
IDs).
Node ID 1…100 This range is for automation stations (PXC), system controllers (PXC...)
and system devices (BACnet routers).
101…120 Operator units and Desigo CC are assigned to this range.
121…127 Temporary operator units and tools (XWP/ABT) look for a free node ID
in this range.
IP data link layer
An additional layer, the BACnet Virtual Link Layer (BVLL), is used for BACnet
over IP. This layer transmits broadcast messages across IP routers.
Below the BVLL, BACnet relies on UDP (User Datagram Protocol). Unlike TCP
(Transmission Control Protocol), UDP supports broadcast messages. The
connection monitoring (carried out by TCP) is resolved in the Application Layer.
All media, such as ethernet, are available if supported by IP as physical layers.
For detailed information on the IPv6 data link layer, see
Ethernet, TCP/IP,
MS/TP and BACnet basics
(CM110666).
The IP address of stationary and temporary operator units can be set
automatically via DHCP (Dynamic Host Configuration Protocol) provided that
there is a DHCP server in the network. The use of DHCP is not recommended
with automation stations and BACnet routers. DHCPv6 is currently not
supported for IPv6.
DHCP is not allowed for devices using integrated BBMD functionality.
The IP addresses must be agreed upon with the IT department.
Application Layer
Network Layer
PTPIPLonTalk MSTP
IP addresses