PNNI Signaling Protocol
93
Alternate Routing
and Crankback
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 signal will
crankback to a point where an alternate route exists and will open the
rest of the channel in that direction. Figure 32 shows the same signal
with a bad connection between two switches.
Figure 32
Signal Failure in a Hierarchical Network
The signal between nodes B.2.1 and B.2.2 has failed. B.2.1 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 fist node that has an
alternate route, so that an alternate route can be chosen. Figure 33
shows the crankback path.
X
X
C.1.1
C.1.2
A.3.2
A.3.1
A.1.3
A.1.1
A.1.2
A.2.2
A.2.1
A.2.3
B.1.1
B.1.3
B.1.4
B.1.2
B.2.2
B.2.1
B.2.3
Peer Group Leader
Source
Destination
Chosen Path to Take
Physical Link
Place Where Signal Failed
Summary of Contents for CoreBuilder 7000
Page 12: ......
Page 30: ...30 CHAPTER 1 ATM NETWORK BASICS...
Page 32: ...32 CHAPTER 1 ATM NETWORK BASICS...
Page 34: ...34 CHAPTER 1 ATM NETWORK BASICS Figure 8 LANE Network over WAN...
Page 96: ...96 CHAPTER 4 PRIVATE NETWORK TO NETWORK INTERFACE PNNI VERSION 1 0...
Page 184: ...184 CHAPTER 7 LAN EMULATION VERSIONS 1 0 AND 2 0...
Page 206: ...206 CHAPTER 9 DEVICE MANAGEMENT...
Page 222: ...222 APPENDIX A TECHNICAL SUPPORT...
Page 234: ...234 APPENDIX B PROTOCOLS AND INTERFACES...
Page 238: ...238 APPENDIX C COREBUILDER 7000 FAMILY ATM SWITCH SPECIFICATIONS...
Page 242: ...242 APPENDIX D SAFETY INFORMATION...