Rockwell Automation 1756-NEX Nexus Module - Manual (Page 29)

About the NeXUS Network 3-3
Publication 1756-UM524B-EN-P - December 2008
Network Organization
Looking from the top down, a NeXUS network is viewed as a system of islands called
domains, interconnected via a wide area network. Each domain is uniquely identified by a
domain number (DMN), which ranges from 1 to 64. The domain number must be provided
in all ADP PDU headers. DMN 0 is reserved for the domain considered within the scope
of the ADP specification.
A domain is divided into data fields. A data field is an area within which a group of logical
nodes communicates with each other via multicast or peer-to-peer messages. A domain is
uniquely identified by a data field number (DFN) which ranges from 1 through 255 and
must be provided in all ADP PDU headers. One data field is configured per network or
sub-network address of the IP address.
Only nodes belonging to the same data field can communicate with each other. A node can
belong to more than one data field. Relative to a node, a data field can be local or remote
(for example, connected to the node via a router). Only local data fields are considered
within the scope of the ADP specification.
To support multicast communication, nodes within a data field are organized into
multicast groups. A node can be a member of more than one multicast group. A multicast
group is uniquely identified as a multicast group number, or MGN, which ranges from 1 to
255. The MGN must be provided in all multicast ADP PDU headers.
Each NeXUS node, also called a logical node, is uniquely identified by a logical node
number, or LNN, which ranges from 1 to 4095. The LNN must be provided in all ADP
PDU headers.
The user normally assigns and manages DFNs, LNNs, and MGNs. DMN, DFN, and LNN
form the source address (SA). DMN, DFN, and MGN form the destination address (DA)
of an ADP PDU header.