Page 128 - DCAP311_DCAP607_WIRELESS_NETWORKS

Wireless Networks

Notes applications but not for others, which performed better using a different approach. Testing
emphasized three scenarios:
Given the slower speed of wireless connections, what are the issues when starting (and
restarting) sessions and applications?
How do applications perform once started, under normal operating conditions?

What happens when a connection is lost due to driving outside a coverage area or to strong
interference?
Interestingly, every application and every software approach performed somewhat
differently under the three different test scenarios.
Here are the various configurations and how they performed.
Remote IP-based Clients
The first configuration tested was with remote clients, specifically MAXIMO and Web
browser clients installed on laptops using TCP/IP communications. The version of
GroupWise used at the time did not provide a TCP/IP client, so GroupWise could not be
tested using this configuration.
Because both Metricom Ricochet and CDPD are based on IP, the applications operate in
the same fashion as if installed on LAN-based workstations using TCP/IP protocol stacks.
What is different, of course, is the slower speed of wireless connections. Also, the mobile
nodes are not necessarily always in wireless coverage. The first comprehensive series
of tests used the Metricom Ricochet network. Compared to CDPD, Ricochet has higher
average throughput but it does not support seamless hand-offs between base stations. This
means that active applications may lose their connections when the vehicle drives out of
range of the original base station.

In looking at the first test scenario (how applications started), Web applications experienced
no problems. But MAXIMO would sometimes require more than five minutes during the
logon process. Subsequent research revealed that because MAXIMO is an Oracle database
application, large data dictionaries are downloaded at startup. This is clearly not acceptable
in a field environment. Fortunately, it is possible to cache local versions of these dictionaries
on a local hard disk. Such up-front synchronization is common to many applications and
is often a performance issue for wireless communications.
Once connected (the second test scenario), the Web client performed acceptably as long
as the content was more textual than graphical. MAXIMO, in contrast, ran extremely
slowly. Opening new modules (e.g., the inventory module or the work-order module)
within MAXIMO would take 60 to 90 seconds. Once a module opens, a screen update
(such as looking at a new order) would take about 30 seconds. It is easy to understand
why operations were so slow. Oracle transactions, based on SQL, involve a considerable
amount of back-and-forth traffic. The slow screen updates make a remote MAXIMO client
practically unusable. However, users entering text in either application posed no problems.
The last operating scenario examined the effect of lost connections. The Web client was
highly tolerant of intermittent connections, which was expected since HTML applications
are stateless; each page entails a new TCP connection. With MAXIMO running, a dropped
connection would generate an error message for transactions in process and result in the
module closing; but the overall session is maintained. If no transactions were in progress,
MAXIMO readily tolerated the underlying connection being lost and regained.
Citrix MetaFrame

The second software scenario tested was the thin-client approach using Citrix MetaFrame.
Starting a remote MetaFrame session over a wireless connection took about 60 seconds.
Contd...

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