Moreover, if mobility is available, sensors
are even harder to trace than others. Thus how to facilitate location service
in a distributed way is not a trivial task.
Location service includes two major tasks. First is the location update or
location registration, where nodes periodically disseminate their up-to-date
position information. Second is the destination search. The current location
of a node can be obtained from some servers when communication to that
node is initiated. There exist many interesting issues in the management of
location information for these nodes which is similar to many mobile networks
[7], [8]:
238
1) Frequency of location updates. There are basically three alternatives,
namely time-based, movement-based and distance-based strategies to determine
update intervals [9].
2) Information organization. There are several distributed strategies for
hierarchical organization of location information proposed in [10], [11].
3) Information update and retrieval. There can be multiple location servers
in the networks. It is the tradeo?® between performance of the write/read
quorum and the system overhead.
4) Load balance of servers. In distributed database architecture, some location
servers may be overloaded with location updates and query requests
while other servers are relatively idle. We should distribute those servers, balance
the load, and make full use of those available resources to prolong the
life of networks.
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