Installation guide

90 Estimating Network Performance
890 USE 100 00
3.15 Estimating Throughput (W ith Peer Cop)
3.15.1 Estimating Total Communication Time
With Peer Cop communication, data can be sent to specific nodes
during token passes. Nodes using Peer Cop can transmit Specific
Output data to one or more destinations. The destination nodes can be
set to receive Specific Input data from selected sources.
If the sending and receiving nodes have scan times that are
significantly shorter than the network’s token rotation time, data can
sent from a source node, and a response received back to that node,
within a total communication time that is a fraction of the token
rotation time. An example is shown below.
The total communication time between Specific Output and Specific
Input in a controller can be estimated using the following formula
(times in ms):
One scan time, sending controller
Specific output time, sending controller+
% of token rotation time, sending node to receiving node+
Specific input time, receiving controller+
One scan time, receiving controller+
Total communication time between specific output and specific input
Percent of token rotation time is the portion of the network’s total token
rotation time that elapses between the sending node’s release of the
token and the receiving node’s release of the token. Figure 38 shows a
network at the start of a Peer Cop transaction between two controllers.
In Figure 38, Controller A has the token, with Peer Cop Specific Output
traffic for Controller B. Two other nodes exist in the network’s address
sequence between Controllers A and B.
CONTROLLER
A
CONTROLLER
B
MODBUS PLUS NETWORK
NEXT
NODE
NEXT
NODE
Figure 38 Example: Estimating Peer Cop Performance