Specifications

Page 11–2
FOCUS System Manual
With this option, there is a pair of standby, or
backup, fibers connecting every two nodes in the
system. If the link between any two nodes, or
substations, goes down, the signal is automatically
rerouted around the loop in the opposite direction,
using the backup fiber pair. Switching time is less
than one frame (i.e., less than 125 µs).
Figure 11–3. FOCUS Network with Four-Fiber
Dual Counter Rotating Ring.
This is a non-revertive system with no preference
for using the primary or standby fibers. This
option provides the most benefit when an alterna-
tive fiber path is available for the standby fibers.
Although this approach uses more fibers, it is the
surest and most reliable form of backup.
11.2.2 Four-Fiber Hot Standby
Another reliable backup transmission path option
is the four-fiber hot standby, also known as the
four-fiber-dual-counter-rotating ring. Figure 11-3
shows a sample system configuration using the
four-fiber hot-standby option. This option uses
two pairs of fibers between all adjacent nodes.
One of the fiber pairs serves as the main commu-
nication path, and the other pair serves as a hot
standby or redundant path shared by all nodes in
the loop.
A break in the primary path between two nodes
initiates rerouting of all 24/30 channels through
the standby fiber pair. The rerouted signal travels
in the opposite direction around the ring to the
node at the opposite side of the break. This
procedure reliably re-connects all channels
affected by the break. When the normal path has
been restored, the signals are automatically
returned to the main fibers.
Unlike traditional path-switched schemes, the
line-switched four-fiber hot standby option lets
you use the full T1 bandwidth between each
adjacent station. The system provides fast service
restoration with complete reconfiguration in less
Figure 11–2. FOCUS Network with Hot Standby.