Specifications

Functional Description
RADring
Installation & Operation Manual
2-38 Elementary Bridge Modules Functional Description 3/11/98 12:33
Cable Break Protection
In addition to the fault tolerance of the TFC/2 redundant link, cable break
protection is provided on each link. The cable break protection function
automatically detects breaks in the fiber-optic cable and loops the main path
to the back-up path, in order to maintain ring continuity. This is illustrated in
the diagram above, which indicates what happens on the fiber-optic
segment when one of the cable fibers breaks or is accidentally disconnected
at an optical patch panel.
Should the fiber connected to the RX connector of site A break, the TFC
detects the loss of the optical signal and carries out the following actions:
1. Loops the main path to the back-up path. This ensures that the TFC
returns a regenerated ring signal.
2. Sends a fault pattern on the TX fiber. The TFC at site B detects this
pattern and loops the main path to the backup path.
These two actions maintain ring continuity in case of a break in the
fiber-optic segment.
To notify the user that a fault condition exists, the two TFCs provide fault
indication as follows:
•
At the receiving TFC, the FLT indicator lights continuously to indicate that
the receive light is missing.
•
At the transmitting TFC, the FLT indicator flashes to indicate that the
transmit fiber is disconnected.
The cable break detection operates even when the Token Ring network is
inactive, e.g. when all the stations are deinserted and there is no ring signal.
In the case of cable break protection for the TFC/2 with redundant
fiber-optic channel, switch both modules to the redundant channel (without
activating the backup path of the ring signal).
Protection In Case of Power Loss
In case of power loss, the TFC automatically loops the main path to the
back-up path.
When the cable break protection is enabled and the optical input signal is
lost, the TFC at the far end will also detect the loss and will perform looping
to the back-up path.
Compatibility Rules for Cable Break Protection
As outlined above, all the TFC modules include cable break protection.
Always enable cable break protection at both ends of the link, unless a
compatibility problem exists. This implies that cable break protection should
always be enabled when operating two TFCs in the same link.