Specifications

Optimizing Performance
EIO0000000051 6/2010 107
Remote Device Connections and RPI
For the purpose of this example, it is assumed that the remote devices require the
following numbers of CIP connections, and are configured for the stated requested
packet interval (RPI) settings:
For the purposes of this example, it is also assumed that all connections are bi-
directional.
I/O Scanner Calculations
The Ethernet communication module, acting as local I/O scanner, must be able to
handle the implicit messaging load contributed by all of the remote devices. Your
task is to:
1 estimate the implicit messaging load and bandwidth contributed by each remote
device
2 sum the load and bandwidth values for each remote device
3 compare the total load and bandwidth against the maximum implicit messaging
capacity of the local I/O scanner
Recall that the implicit messaging load calculation formula for a single remote device
is:
Load = (number of packets per connection) x (number of connections) / RPI
Because all connections are assumed to be bi-directional, the number of packets
per connection value is always 2. Consequently, the estimated implicit messaging
load contributed by each device, and the total implicit messaging load the local I/O
scanner must handle can be estimated as follows:
Load:
Device CIP I/O Connections RPI Setting I/O Packet Size
I/O Adapter (A) 5 20 ms 8000 bits
I/O Adapter (B) 2 30 ms 4096 bits
I/O Drive (C) 2 30 ms 8000 bits
I/O Scanner (D) 2 50 ms 8000 bits
Device Number of
packets per
connection
X Number of
connections
÷RPI =Load
I/O Adapter (A) 2 X 5 ÷ 20 ms = 500 pps
I/O Adapter (B) 2 X 2 ÷ 30 ms = 134 pps
I/O Drive (C) 2 X 2 ÷ 30 ms = 134 pps
I/O Scanner (D) 2 X 2 ÷ 50 ms = 80 pps