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Servers
DSA and firewalls
If there is a firewall in your DSA system other than the default Windows Firewall, you will
need to ensure that the necessary ports are opened in the firewall to enable DSA
communications between the DSA client and server nodes.
For information on DSA communication through a firewall and Windows security
enhancements, see the Network and Security Planning Guide.
About point data in a DSA system
DSA provides global access to point parameter data on all servers in the system. Each server
provides automatic dynamic caching of remote data for all of its clients, so that clients access
their local server for all data. In general, clients do not access remote servers directly.
However, some process data is accessed directly; for example, chart visualization via a
Process Detail display.
DSA data access works as follows:
1. When one of its clients requests data for a point that is not already in the local server's
database, the local server asks the servers in the system for the data owner of the point.
2. When the data owner is determined, the local server subscribes to the remote server
from which it obtained the data and automatically creates a cache reference (known as
a 'local cache point') in the local database.
3. While the subscription is in effect the data owner uses 'report by exception', only
sending data to the caching server when there is a change. When the data is no longer
referenced by any of its client Stations or applications, the subscribing server cancels
the subscription to the data owner. This subscription mechanism ensures maximum
efficiency both on the servers and over the network.
How DSA affects your total point count
The cached points created by DSA do not count against the licensed point count for a given
server. They do, however, count towards the total maximum number of points per server.
Note that you can reduce the number of DSA points on a server by disabling DSA
subscription to the system model and system alarms on a remote server. This setting is useful
if you are approaching the maximum number of points on a server in a DSA system. For
more information, see 'Configuring servers to subscribe to data and alarms' in the
'Configuring Distributed System Architecture' topic in the Station Configuration Guide.
You can check the current number of DSA points (and other types of unlicensed points) on
the Server License Details display. See 'Checking your Experion license' in the
'Configuration overview' topic in the Station Configuration Guide.
Honeywell 2017
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