Echelon LNS DDE Server - Manual (Page 55)

The network topology, type of network interface, and LNS DDE Server host PC
performance will all affect the maximum number of points that can be polled per
second. In early tests of the LNS DDE Server, version 2.1, a 600 MHz PC on a
L
ON
W
ORKS
/IP channel connected to six TP/XF-1250 channels was able to poll over
600 points per second. Adjust polling intervals to ensure that you do not exceed the
maximum throughput of your configuration. For example, a network variable in a
sensor that monitors outside air temperature probably doesn’t need to be polled more
than once every 3 minutes. It is important to limit the polling demand to allow for
temporary demand spikes, and allow bandwidth for timely delivery of outgoing
updates.
You can override the default polling interval for an individual network variable with
the -i switch.
Refresh Rate (1/10 sec)
This setting specifies the default refresh rate that the LNS DDE Server will use
when reading configuration properties. Unlike network variables, configuration
properties are not read directly from a device. Instead they are retrieved from the
LNS Server database. A value in the database may change due to an update by
another LNS application.
Specify a value in tenths of a second. For example, a value of 100 specifies that the
LNS DDE Server will refresh its configuration property values every 10 seconds.
This value can generate significant network traffic when running remotely. Set this
option to 0 to receive a one time only update.
This setting also applies to system, device, and LONMARK object properties. The
default refresh rate is 600 (60 seconds).
Use Bound Updates
When enabled, this setting causes a network variable to be created on the local PC,
which is then bound to the network variable on the device to be monitored. A
network variable is not created if the network variable to be monitored is already
bound to the local PC. This occurs for every output network variable that is
monitored.
Using bound updates will eliminate the need for polling for changes; this can be
useful for network variables that change very infrequently but require immediate
host notification when they do change (for example, network variables which indicate
alarms). However, there are several drawbacks:
• When extensively using bound network variable updates, and using
Acknowledged service, the network may quickly become saturated with retries if
the PC that the LNS DDE Server runs on is disconnected from the network or
experiences a fatal software exception. You can avoid this problem by using
Unacknowledged or Repeated service. As long as the PC has power, the Network
Interface will generate acknoledgements to a bound update. However, the
LNS DDE Server User's Guide 3-23