12 Performance Considerations
TAC Xenta 555, Supplement Manual
TAC AB, Oct 2006
04-00054-01-en
As a performance example, consider a Xenta 555 ARCNET or NCP net-
work with three web clients showing three web pages (two alarm pages
and one values page with 50 signals).
The Xenta 555 configuration comprises a total of 480 signals:
•
100 alarm signals set with a scan time of four seconds.
•
300 logs at a logging interval of one hour.
•
30 connection objects at a period of 10 seconds.
•
50 point signals on a values page with a fixed refresh time of 10
seconds.
In this network, the signals will arrive in the alarm pages typically
within 60 seconds. Connection objects and signals in values pages will
update within 60 seconds.
The Xenta 555 polling algorithm computes the optimum poll rate for
each signal, therefore if the sum of the poll frequencies exceeds the
available bandwidth at any particular time, the lower frequency polls
will be delayed. This has the effect of spreading the polls out over the
available bandwidth and therefore optimizing performance.
Signals on graphics pages and values pages are only polled when the
page is being displayed in a web browser, however when a signal is
required for logging, alarming or for a connection object, the signals are
continuously polled at the configured poll time.
12.3
Web Page Updates
In addition to MicroNet network updates, web pages are updated at reg-
ularly intervals and this should be considered when analyzing the over-
all performance; ten seconds should be considered typical for a web
page update.
However, polling performance is affected by the number of web clients
and the number of web pages. If each web client simultaneously
requests a different web page, each with a set of signals not currently
being polled (for example, alarms), then the number of polled signals
will increase substantially and therefore slow down the rate of web page
updates. For this reason it is recommended that the number of web cli-
ents is restricted to three for a typical Xenta 555 network as described
in the example given earlier.
!
Tip
Connection objects should be kept to a minimum because each con-
nection comprises a read signal and a write signal (that is, two opera-
tions).
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