BECKHOFF DK9222-0411-0038 - Manual (Page 3)

I/O
I/O, Building Automation
Application Note DK9222-0411-0038
3.1 Network structure
A LonWorks network is divided into the domain, subnet and nodes. There may be a maximum of 255 subnets (subnetworks) in
the domain – a subnet in turn may consist of a maximum of 127 nodes (LON nodes). Additionally, a domain may consist of a
maximum 32385 LON nodes, i.e. LON devices. Several domains can be connected if necessary. In principle, however, only nodes
within a domain can communicate directly with one another. Each node in a network has a unique logical address, which is
divided into these three hierarchical levels: Domain ID, Subnet ID and Node ID.
max. 63 nodes max. 63 nodes
repeater router
max. 127 nodes + 1 repeater
subnet
router
router
repeater router
max. 255 subnets per domain, each with 127 nodes = 32385 devices
Fig. 1 Structure of LON networks
Components such as routers, bridges and repeaters are used for the construction of LON networks.
Repeaters are physical amplifiers with no processing function. They are used to achieve greater transmission distances and/or
to extend the maximum permissible number of nodes of 64 nodes per 2-wire segment when using FTT-10-transceivers.
Routers are devices with several bus connections, which are used to interconnect several subnetworks. Telegrams received on
one side are normally transmitted again on the other side by the router – and vice versa, of course. The router can also perform
the function of a filter, a pathfinder or a post distributor.
4. Communication
LON nodes communicate directly with one another on the basis of the LonTalk ® protocol, without going through a central
control unit. Data exchange takes place by means of SNVTs: they form the logical interface between two nodes. SNVTs consist
of three sections: unit, range of values and resolution, which must be configured identically in both nodes for unambiguous
interpretation of the data.
New Automation Technology Beckhoff 3
For application notes see disclaimer on the last page