Westermo LR-11 - Manual (Page 9)

Data routed to the fibre network will be transmitted onto both F/O links. All data
received by a LR-11 unit on either Rx1 or Rx2 is transmitted to the router module and
will be transmitted over the corresponding TP network if accepted by the router algo-
rithm. The received data on Rx1 or Rx2 will also be forwarded by the opposite trans-
mitter, Tx2 or Tx1. The units at the endpoints does not need to forward data on both
fibre links, and thus only one fibre link is required (PP version).
The bus topology provides a possibility for all L ON W ORKS ® ‚ nodes to send and receive
data to and from all TP segments.
3.3 Ring topology
Another possibility with the LR-11 units is to use it in a fibre optic ring topology. The
ring topology requires one dedicated LR-11 unit (ring master) to stop all messages on
the fibre ring, thus preventing message looping.
With ring topology, a built-in redundancy scheme offers communication fault tolerance.
If a fault is detected on one of the fibre links, the data flow will automatically be re-con-
figured to make a new communication path that reaches all units in the ring. The time to
set-up the new communication path could take up to 4ms. Any data that is transmitted
during that time is lost and needs to be resent. The LR-11 can handle a fault on one fibre
or a fibre pair and still be able to communicate. The LR-11 unit has two alarm outputs
for fault detection, one for each fibre link.
The redundancy scheme requires the fibre optic links to be connected as follow:
F/O Link 1: Tx2 " Rx1 " Tx2 " Rx1 " Tx2 etc.
F/O Link 2: Tx1 " Rx2 " Tx1 " Rx2 " Tx1 etc.
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