Echelon LNS - Manual (Page 173)

LNS Programmer's Guide 159
these pools can typically be overcome by allowing other types of resources to be
consumed.
For example, group IDs can be saved by using network variable aliases, and vice versa.
Preferring aliases over group addressing, for example, can also impact the third resource:
such a change might not only change the total number of address table entries required,
but can also redistribute these address tables entries differently among the devices that
participate in the connection.
Predictive Strategies
The previous section described ways to deal with resource shortages as they occur.
However, it is best to avoid such a shortage and the related repair work by planning
ahead. System integrators should establish an understanding of the characteristics of the
current connection scenario and of probable extensions to that scenario, and create
connections based on such analysis.
In most cases, the system integrator should know what other connections are to be
created in the future. This should include detailed knowledge about a particular number
of future connections, as well as an understanding of the characteristics of the complete
connection scenario.
For example, consider an office building. The building might consist of any number of
floors with several rooms on each floor. Most inner-room networks will be very similar (a
light, a switch, a thermostat, etc), and most connections will operate within the local
room. On the other hand, a small number of connections will affect many devices in many
rooms, such as the intruder or smoke alarming systems, the sun position sensor, etc.
Such a network might be best divided into a few building-wide segments, and a number
of very similar, if not identical, subsystems separated from the backbone and building-
wide segments by router devices. Thus, network traffic local to a room can be concealed
within that room. Also, because subnets cannot span routers, each room (or small
number of rooms) will have a local subnet, which allows inner-room connections to use
repeated messaging service and subnet broadcast addressing. This will preserve group
IDs for use with the building-wide segments.
The strategy detailed in the following flow chart avoids the use of group connections,
instead using subnet broadcast addressing for multicasts whenever possible. This
strategy is a generalization of the building control example.