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[KB296]Network station performance

Tags: Multistation, Networking

Communication interfaces
14 years ago
By RM
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Applies to:

PcVue all versions.
While the basic content of this article remains valid, details may have changed since it was written.
Summary:

Bandwidth use in network station configuration and optimization.
Details:

Part 1: Bandwidth use

Each variable exchanged between a server and a client station, uses 70 or 150 bytes. For detailed information you can examine the send flow counters and receive flow counters in the audit files.

See in audit files the following counters:

  • LAN send bloc
  • LAN Send msg
  • LAN Send byte
  • LAN Rcv bloc
  • LAN Rcv msg
  • LAN Rcv byte

For example, if there are 1000 register variables which are changing each second the average bandwidth is 70kbytes/s for each client.

This result must by multiplied by the number of clients in case of multiple clients in the architecture.

At Start up: the bandwidth is about 150 bytes between server and client, the subscription is made by block of 500 variables, so 500 x 150 bytes = 75kbytes/s. This information must be sent in less than 20 second in order to not time out. The second block of variables is sent then the server receives information about the first block sent.

In nominal mode: the size of message (value refresh) by variable is 70 bytes.

Part 2: Optimization 

1st Try: 48200 external variables (OPC) with 12000 alarms, 5300 internal variables with 1217 variables in external coming from the association

Start up time: 6 minutes

For a client station to start quicker, you can untick Permanent Scan For Mimics in the Variable section of the Configuration/General Operation dialog.

In that case, register variable subscription is made on demand each time a mimic is opened. Note that Alarm variables are always subscribed at startup.

The same job has to be done for each variable.

Start up time is then only 3 minutes and 10 seconds.

2nd Try with more variables to load: 90000 variables with 20000 variables in alarms, .82000 variables are external, with the 20000 alarms

The setting of the first try is kept (no permanent scan for mimics).

Start up time is between 3 minutes and 50 seconds and 4 minutes et 10 seconds.

Note that the setting Permanent Scan For Mimics is not taken into account for variables that are configured as alarms, archived (trend or logs), used in expressions or used in SCADA Basic/VBA.

Created on: 17 Dec 2010 Last update: 13 May 2024