Echelon LNS - Manual (Page 88)

LNS Programmer's Guide 74
LNS Network Installation Scenarios
To understand what is required to install L
ON
W
ORKS
devices on a L
ON
W
ORKS
network,
you should consider the types of control systems that L ON W ORKS networks replace.
Many conventional control systems use wiring harnesses or point-to-point wires. In these
systems, the wiring between devices serves two purposes when the devices are installed.
It physically interconnects the devices, and it determines which control signals should be
sent to which device. Once attached to the wire, the behavior and interaction among the
devices is completely defined.
Other control systems use a master-slave architecture, and require DIP switches or dials
on each device to specify the device’s address. The device addresses are predefined and
based on the control algorithm in the master. When these devices are installed, the
master polls each address, and the appropriate device responds. Such systems are
usually limited to a small number of devices, and changes to system behavior usually
require resetting the DIP switches on each device, and modifying the master control
software.
A L ON W ORKS network consists of intelligent devices called nodes or application devices
that are connected by one or more communications media. Application devices
communicate with one another using the L ON W ORKS protocol (also referred to as the
LonTalk protocol). Each intelligent device on the network, e.g. a programmable
thermostat in a building control system, is a L
ON W ORKS application device. The devices
communicate with one another across a shared communications medium, such as a
twisted pair cable, a power line circuit, or an RF link. Figure 5.1 shows the wiring
difference between a conventional system and a L ON W ORKS network.
Figure 5.1 Wire Reduction in a L ON W ORKS Network
The devices on a L ON W ORKS network contain objects that respond to a variety of inputs,
and produce desired outputs. Although the function of a given device may be quite
simple, the interaction among devices allows L ON W ORKS networks to perform complex
tasks. A benefit of L ON W ORKS networks is that a small number of common device types
can perform a broad spectrum of different functions, depending on how they are
configured and logically connected.
In a L
ON
W
ORKS
network, devices share their physical media (e.g. twisted-pair wire or a
power line circuit), which eliminates the redundant point-to-point wiring found in
conventional control systems. Without point-to-point wiring (e.g. a light switch wired to a
lamp) the physical attachment no longer uniquely identifies a device. In a L
ON W ORKS
network, the physical attachment only provides a path for devices to send and receive
messages. It does not tell the devices which other devices they should send data to.
Therefore, in addition to physically attaching the devices to the network, you also need to
perform the following tasks when installing a L ON W ORKS network:
• Assign a network address to each device. A network address identifies
which application device a L ON W ORKS messages should be sent to, just as
a postal address identifies which house a letter should be delivered to. A