Echelon LNS DDE Server - Manual (Page 56)

acknowledgements are not an indicator of reliable delivery should the LNS DDE
Server and attached client applications not be running.
• If a network variable that is already connected to another device is monitored
using bound updates, a group is created on the host. If unsuccessful in a creating
a bound connection, the LNS DDE Server will automatically revert to polling the
network variable. No errors or warnings are generated if the connection is
not successful.
• Each time a network variable is bound, the lifetime of the rewritable non-volatile
memory on the device is decreased. If you use the Bound Updates Persistent
option, this is not much of an issue. In most systems this is the desired option
when using bound updates.
• Using bound acknowledged updates to the LNS DDE Server may produce uneven
update rates under high traffic conditions due to resource limits on the host
interface. For periods of 4 to 7 seconds or more, several devices may be blocked
from updating the LNS DDE Server. Limit the number of bound connections for
consistent update performance. The resource limits are less of an issue when
using Unacknowledged service.
Unacknowledged bound updates cannot be used with network variables already
using Acknowledged service.
• Shutting down the LNS DDE Server for a network with many bound connections
to the host will take a long time while the LNS DDE Server is deleting all of
these connections. Limit the number of bound connections to the host to improve
shut down performance, or use the
Bound Updates Persistent option to eliminate
this issue.
For these reasons, the use of polled updates is typically recommended. If bound
updates are used, the following guidelines should be followed:
• Use Unacknowleged (or Repeated) service. This will avoid a system saturation
with retries in the event that the PC running the LNS DDE Server is turned off,
crashes, or becomes disconnected. If an acknowledged connection connects the
network variable to another device, the connection must first be defined to use
Unacknowledged (or Repeated) service.
• Explicity bind (i.e. establish a connection between the device network variable
and network variable on the host) any network variables to be updated with
bound updates using an LNS installation tool such as the LonMaker Integration
Tool. The LNS DDE Server will automatically use bound updates for network
variables that are explicitly bound. If you explicitly bind a network variable
to the host using an LNS installation tool, do not turn on bound
monitoring for that network variable using the Network Configuration
dialog or the –b option.
• Use alias connections when binding a network variable to both the host and
another network variable. This prevents creating a new group on the host for
every network variable. Devices without alias tables allocated do not support this
type of connection.
3-24 Using the LNS DDE Server