Echelon LonWorks Router - Manual (Page 23)

1 to channel B, then the same message could be forwarded by router 2 back to
channel A, starting an endless loop of forwarded messages.
Channel A
Router 1 Router 2
Channel B
Figure 6. Looping Topology
The LonTalk protocol does not support topologies where loops can occur.
However, looping topologies can be desirable for the following reasons:
• Increased Reliability. Redundant routers can increase system reliability
by providing multiple paths between two channels.
• Support for Open Media. Open media (such as radio frequency [RF]
communications) might require redundant routers with overlapping
coverage to ensure complete coverage of an area.
You can use configured routers (see Configured Router) to support looping
topologies by configuring the routers to prevent message loops. For example, the
topology in Figure 6 can be supported if both routers are configured to forward
all messages addressed to subnets on channel B from channel A; and all
messages addressed to subnets on channel A from channel B. Any groups with
members on both channels can only be forwarded by one of the two routers.
Network management tools, such as OpenLNS CT, can automatically set up the
forwarding tables for configured redundant routers.
Power Line Routers
A looping topology can be inadvertently created when using power line (PL)
media. Passive coupling between different phases of a power line system can
cause packets transmitted on one phase to be received by devices installed on
another phase. A loop can be formed when active coupling provided by a router is
combined with passive coupling. Figure 7 shows an example looping topology
with a power line router.
L ON W ORKS Router User’s Guide 13