20
16-PORT TYPE 3 MAU
3.1.2 B
ACKUP
P
ATH
In a normal configuration, there is an unused pair of wires in the twisted-pair
cable used in the network. This extra pair of wires, used with a backup circuit
inside the MAUs, is called the backup path.
Main Path
Backup Path
MAU 3
Attaching
Devices
Ring Out
Looped
Back
Ring In
Looped
Back
MAU 1
MAU 2
Figure 3-2. Backup path.
The backup path is designed to enable the network to continue to operate
while a problem such as a faulty cable or MAU is being repaired.
For example, if a breakdown occurs in the cable between MAU 1 and MAU
2 as in Figure 9, the rest of the ring will remain in operation if the backup
path is used. Note that when the backup path is used, it becomes part of the
main ring and its length must be included in the main ring length. In most
situations, the network should be designed to allow the backup path to be
used. The backup path is automatically used by the MAU when no connector
is inserted in Ring In or Ring Out ports.