Figure 11-15 Communication Load As A Function Of The Response Time (Basic Profile) - Siemens SIMATIC S7-400H System Manual

Communication
11.7 Communication performance

Figure 11-15 Communication load as a function of the response time (basic profile)

Standard and fault-tolerant systems
What we have said so far applies to standard and fault-tolerant systems. Since communication
performance in standard systems is clearly higher than that of redundant H systems,
saturation point will seldom be reached in today's plants.
In contrast, fault-tolerant systems always require synchronization to maintain parallel
operation. This increases block execution times and reduces communication performance,
This means that performance limits are reached earlier. If the redundant fault-tolerant system
is not operating at its performance limits, the performance benchmark compared to the
standard system will be lower by the factor 2 to 3.
Which variables influence communication load?
The communication load is affected by the following variables:
● Number of connections/connected OCM systems
● Number of tags, or number of tags in pictures displayed on OPs or using WinCC
● Communication type (OCM, S7 communication, S7 message functions, S5-compatible
● The configured maximum cycle time extension as a result of communication load
The sections below show the factors that influence communication performance.
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System Manual, 09/2007, A5E00267695-03
S7-400H