Echelon LNS - Manual (Page 166)

LNS Programmer's Guide 152
Network Design Time
When designing a network, you should seek to achieve the most reliable solution, with
the most economic use of network and device resources. In this discussion, which deals
specifically with optimizing connection usage, network resources can be thought of as
network variable selectors, group identifiers, and channel bandwidth. Address table
entries and alias table space are the critical device resources.
When a connection is made, LNS first ensures that it complies with the L ON W ORKS
connection rules:
1. Standard network variables within a connection must have the same type.
2. All network variables within a connection (including user-defined network
variables) must have the same length.
3. At least one network variable in a connection must be an input network variable
and at least one of them must be an output network variable.
These three rules are fundamental to L ON W ORKS networks, and all network variable
connections must comply with these rules. There are, however, some additional
constraints that apply to connections in to L
ON W ORKS networks. These constraints are:
4. Network variables within a connection must share one, and only one, network
variable selector, which must be unambiguous.
5. Multiple input and output network variables on a given device cannot share a
network variable selector. The same applies to non-polled network variables on
nodes earlier than firmware version 6, and to all polled output network variables.
6. Each network variable has one and only one network variable selector. In
addition, typically each network variable may have up to one address table entry
associated with it.
However, these final three constraints can be worked around with a planned approach,
as described in the following sections. Once LNS has approved the compliance of a
desired connection with these rules and constraints, it will implement the connection.
You can make sure your connections comply with the rules listed above by writing to the
properties of the ConnectDescTemplate assigned to the connection. Two key properties
are the AliasOptions and the BroadcastOptions properties. The following sections
describe how you can set these properties to maximize your network resources, while
complying with the rules and constraints introduced in this section.
Alias Options
The AliasOptions property determines how LNS will use network variable aliases in a
given connection. This property can be set to the default
lcaAliasForSelectorConflicts value, or to the lcaAliasForUnicasts value.
When set to the default lcaAliasForSelectorConflicts value, LNS will allocate one
or more input or output network variable aliases to overcome the selector conflicts that
are described in rules 4 to 6 above in an attempt to maintain all multicast connections.
The lcaAliasForUnicasts option will allow LNS to split a single multicast connection
into multiple unicast connections using one or more aliases to the primary output