GHT uses this property to detect and store events at the home node.
When a packet returns in perimeter mode to the node that originated the
perimeter traversal, the corresponding event is stored at that node.
301
Jinbao Li, Zhipeng Cai, and Jianzhong Li
d
A
Fig. 6. Find host node using perimeter mode [16].
GHT Robustness: Perimeter Refresh
However, this alone is not su?±cient, since events can be lost if the home node
fails. Furthermore, if new nodes are deployed, the definition of a home node
may change. To solve these problems, robustness of sensor networks is needed.
GHTs use a simple perimeter-refresh protocol to maintain the associations
with a set of given sensor nodes. The set of sensors are called home node
associations. Periodically, for a given event, a home node will send a message
destined to the corresponding location periodically. This refresh message will
traverse the perimeter around the specified location. As this message traverses
the perimeter, each node on the perimeter stores a local copy of the event.
Each node also associates a timer with the event. This timer is reset whenever
a subsequent refresh is received. If the timer expires, nodes use this as an
indication of the home node failure, and initiate a refresh message themselves.
In this manner, home node failures are detected, and the correct new home
node is discovered.
As the refresh message traverses the perimeter, it may encounter a new
node that is closer to the specified location.
Pages:
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485