Database Reference
In-Depth Information
Mobile
Unit
Mobile
Unit
Mobile
Unit
Fixed
host
Wireless Cell
Support
Station
Fixed
host
Fixed
host
Support
Station
Fixed
host
Support
Station
Support
Station
Fixed
host
W
ireless
C
e
ll
W
ireless
C
ell
Mobile
Unit
Mobile
Unit
Mobile
Unit
Mobile
Unit
Mobile
U
nit
Mobile
U
nit
Figure 20-26
Mobile computing architecture.
Wired network
Connects a set of fixed hosts and support stations (base stations).
Communication
Support stations and fixed hosts are reachable over the
wired network. Mobile hosts and support stations communicate through wireless
connections.
Downlink
Used for sending data from a support station to a mobile unit.
Uplink
Used for sending data from a mobile unit to a support station.
Mobility domain
The entire domain in which a mobile unit can move.
Cell
A part of the mobility domain where wireless connectivity with the control-
ling support station is possible.
Movements
Mobile units move from cell to cell. When a mobile unit moves from
one cell to another, a handoff procedure transfers connectivity with the mobile unit
from one cell to another.
Access contiguity
Guarantees that movement from cell to cell will not affect data
access.
Mobile Database Considerations
As you can observe, the database considera-
tions for mobile computing relate many different issues not present in centralized
or even distributed databases. Note the following considerations.
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