Installation guide

96 Estimating Network Performance
890 USE 100 00
3.18 Estimating Latency for a Large Network
Here is an example for estimating drop-out latency in a large network
of programmable controller nodes. Peer Cop transfer of Specific Input
and Specific Output data is used.
The network is structured as follows:
V 32 nodes, Programmable Controllers addressed 2 ... 33
V Nodes 2 and 3 act as Masters, each controlling 15 nodes which act
as Slaves
V Each Master sends a total of 480 words—32 words to each of its
Slave nodes
V Each Slave sends 32 words to its respective Master
V Scan time of each Master controller is 30 ms; scan time of each
Slave is 15 ms
Normal Transaction Time
The example shows the normal response time for a transaction from
node 31 to its Master node, which is processed by the Master node and
then returned to node 31. The example also shows a similar
transaction between nodes 33 and its Master node.
Abnormal Transaction Time Due to Node Dropout
The example shows the abnormal time for the same two transactions in
the case of node 32 dropping out while node 33 holds the token.
Times Calculated
The example includes the calculation of the following times:
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