Installation guide
104 Estimating Network Performance
890 USE 100 00
3.21.4 Security Considerations in Node Addressing
Modbus Plus nodes can be addressed within the range 1 ... 64 decimal.
For security purposes, consider limiting the range to between 2 and 64
(you probably will not require all 64 addresses on a single network).
In nonnetworked applications, many users have traditionally attached
to a local controller by identifying it as device 1. If a person tried to do
this with a controller operating in its bridge mode, a remote controller
at node address 1 could be attached and possibly started, stopped, or
programmed. Avoiding the use of address 1 prevents inadvertent
attaches by persons who may be unfamiliar with a controller’s bridge
mode.
3.21.5 Selecting Node Addresses for Best Throughput
Consider assigning network node addresses to the various devices in a
manner that supports efficient message handling. If your network
consists of multiple nodes with heavy traffic occurring at one node, your
choice of node addressing can affect the token rotation time and data
rate.
For example, consider a network of 12 nodes, with an average token
rotation time of 100 ms. The nodes are addressed from 2 ... 13, with no
gaps in the address sequence. In the application, nodes 2 and 3 are
initiating many transactions to node 4. As the token passes to node 4,
that node might not have had enough time to scan and process all of its
message traffic. Node 4 might have to wait for a later rotation of the
token in order to send its data responses to the initiating nodes.
By assigning a higher node address to the receiving node, for example
address 12, the device can use the time during which the token is
passing through the other nodes to process its traffic. By the time the
token arrives, a data response can be ready.
The time saved in each transaction is the difference between the time
for a full rotation (nodes 2, 3, 4 ... 13, 2, 3, 4) and the time for a partial
rotation (nodes 2, 3 ... 12).