1-2
Introduction
Routers are used to:
•
Extend the limits of a single channel.
A router may be used to add a channel to a
L
ON
W
ORKS
network to support additional nodes or extend the maximum channel
length. Multiple routers may be added, depending on the capacity or distance
needed.
•
Interface different communication media, or bit rates, in a L
O N
W
ORKS
network.
For example, it may be desirable to trade data rate for distance on portions of the
network, or to use a 1.25Mbps backbone twisted pair channel to connect several
78kbps free topology and link power channels. Alternatively, it may be desirable
to use power line for a portion of the network where the nodes are subject to
frequent physical relocation, or if cable installation is difficult. In all of these
cases, a router must be used to connect the dissimilar L
ON
W
ORKS
channels.
•
Enhance the reliability of the L
O N
W
ORKS
network.
The two channels connected
to a router are physically isolated, so a failure on one channel does not affect the
other. For example, in an industrial control network, isolation among connected
cells may be desirable to prevent a failure in a single cell from bringing down
multiple cells. This would be achieved by dedicating channels to individual cells
and isolating them from one another with routers.
•
Improve overall network performance.
Routers can be used to isolate traffic
within subsystems. For example, in a cluster of industrial cells, most of the
communications may be with nodes within cells rather than across cells. Use of
intelligent routers across cells will avoid forwarding messages addressed to nodes
within a cell, thus increasing the capacity and decreasing the response time of
the overall network.
The use of routers across channels is transparent to the application programs within
nodes. Thus, application development can be done independently, without knowledge
of the workings of the routers. Routers need to be taken into account only when
determining the network image of a node. If a node is moved from one channel to
another, only the network image must be changed. Network images are managed by a
network services tool such as the LonManager
®
LonMaker
®
Installation Tool.
L
ON
W
ORKS
routers are offered in a variety of options so that they can be tailored for
specific uses. Options include the following:
•
Integration
. Router components are available for embedding in OEM products. An
RTR-10 router and two transceiver modules, one to handle each of two channels
connected by the router, may be mounted on a motherboard, along with a power
supply and two network connectors. This sub-assembly constitutes a custom router.
It can be packaged in an enclosure to meet unique form factor and environmental
requirements. Depending on the application, the package may contain a single
router sub-assembly, or may include other application-specific hardware. See
figure 1.2 for a block diagram of a router based on the RTR-10 router. Multiple
routers may be packaged together for some applications, e.g., a backbone
connecting multiple channels.