Page 127 - DCAP311_DCAP607_WIRELESS_NETWORKS

Unit 7: Wireless LAN

the connectivity issues associated with wireless, such as throughput and latency. Another Notes
disadvantage is the requirement for software installation on field computers, which can
add to maintenance and support.
Another approach is to use Citrix MetaFrame* (combined with Microsoft Terminal Server),
where applications run on an application server at a central location, and mobile nodes
operate as terminals (thin clients). The utility has already deployed Citrix MetaFrame to
support dial-up users. The advantage of this approach is that installing and maintaining
mobile computers is simplified because they only need the Citrix client software to access
multiple applications. The disadvantage is that Citrix MetaFrame has some significant
limitations when operating over wide area wireless connections. We learn about these
limitations in the next section when we look at test results.

The third approach is to use wireless middleware (specialized software installed on a
mobile computer and on a centralized server that acts as an intermediary between client
applications and server processes) to optimize communications. The utility has looked
at wireless middleware designed specifically for MAXIMO, as well as general purpose
middleware that optimizes IP communications over wireless links. The advantage of
wireless middleware is it allows applications to run with much better response times and
much greater reliability, however, it increases complexity and adds cost.
Figure 3: Wireless Middleware Adds a Mobile Server that Handles
Transactions on Behalf of the Mobile Client

Because wireless coverage is not always available everywhere the workers spend time, an
approach also considered was Oracle Lite where workers can download a subset of the
database they need, operate on it locally during the day, and then synchronize at the end
of the day. This approach reduces the demand for wireless connectivity, but it is not as
flexible as the other approaches where field workers remain in constant communications
during the day and can respond quickly to changing circumstances.
By using a flexible computing platform such as Windows 95 on a laptop, the utility realized
it could also consider a mix of approaches. Perhaps one application would work best in its
native form, and another would work best using a thin-client approach. This indeed was
the case as we see next.

Test Results
Whereas architecting different wireless approaches on paper may be an entertaining
diversion, it is difficult to predict how the approaches will actually perform until tested
in the real world. The utility has tested the architectures discussed earlier with results that
did not always match expectations. For instance, the utility expected that an IP-based client
would perform reasonably well over a wireless IP connection. This was the case for certain
Contd...

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