Installation guide

94 Estimating Network Performance
890 USE 100 00
3.17 Estimating Latency for a Small Network
Here is an example for estimating drop-out latency in a small network
of programmable controller nodes. Peer Cop transfer of Specific Input
and Specific Output data is used.
The network is structured as follows:
V 10 nodes, Programmable Controllers addressed 2 ... 11
V Node 2 has an output of 2 registers to each of the other nine nodes
(a total of 2 * 9 = 18 registers)
V Nodes 3 ... 11 each will input 2 registers and output 2 registers
V Scan time of each controller is 10 ms
Normal Transaction Time
The example shows the normal response time for a transaction from
node 11 to node 2, which is processed by node 2 and then returned to
node 11. A similar transaction is shown between nodes 9 and 2.
Abnormal Transaction Time Due to Node Dropout
The example shows the abnormal time for the same two transactions in
the case of node 10 dropping out while node 11 holds the token.
The example includes the calculation of the following times:
Times Calculated
V The token transmission time (the time required for any node to
transmit its data during the token pass)
V The token rotation time
V The NDOL
(L)
and NDOL
(H)
times
V The normal response times (minimum and maximum) for
communication between two nodes before a drop-out occurs
V The abnormal response times (minimum and maximum) between
the same two nodes with the latency interval included.