3Com CoreBuilder 7000 Operation Manual page 90

90 C 4: P
HAPTER RIVATE
A.1.1
A.1.2
A.1.3
A.1.5
A.1.6
Source
Destination
Crankback Path
N - -N I
ETWORK TO ETWORK NTERFACE
The signal between nodes A.2.3 and A.2.2 has failed. A.2.3 will send a
PTSE message that will be flooded to all nodes in the network. At the
same time, it will crankback the signal to the source, so that an alternate
route can be chosen. Figure 29 shows the crankback path.
A.1.4
A.1.8
A.1.7
A.2.3
Figure 29 Crankback Path Back to the Source
In Figure 29, the signal cranked back 6 hops. These hops are decreased
from the hop counter. Node A.1.1 will choose a new path and update its
topology database.
The new topology database information is transmitted as a PTSE message
as described previously. After the topology databases are updated, an
alternate route is chosen. Figure 30 shows the path that node A.1.1 has
chosen after crankback. The alternate route is established and the data is
sent.
(PNNI) V 1.0
ERSION
A.2.0
A.1.9
A.2.5
A.2.1
A.2.2
A.2.4
X
Place Where Link Failed
Chosen Path to Take
Physical Link
A.2.7
A.2.6