Alternate Routing And Crankback - 3Com CoreBuilder 7000 Operation Manual

Alternate Routing
and Crankback
A.1.1 A.1.2
A.1.3
A.1.5
A.1.6
Source
Destination
connection is established and the data is sent. These connections are
permanent because they are established administratively, rather than on a
demand basis. If the signal is to be established by demand, it is known as
a soft PVC or soft PVCC.
Occasionally, after the decision has been made by the switch to open a
channel in a certain direction, the link may fail or the attributes may
change. When the switch detects this change, it does not close the
connection and send a disconnect message. Instead it hops backwards,
or cranksback. In crankback, hops are decreased. The switch will
crankback to a point where an alternate route exists and will open the
rest of the channel in that direction. If, the network is a flat network,
crankback will be done to the source. Figure 28 shows the same signal
with a bad connection between two switches.
A.1.4
A.1.8
A.2.1
A.1.7
A .2 .2
A.2.3
Figure 28 Sending a Signal with a Failed Link
PNNI Signaling Protocol
A.2.0
A.1.9
A.2.5
A.2.4
Place Where Link Failed
Chosen Path to Take
Physical Link
89
A.2.7
A.2.6