December 12, 2000, 3:46 PM — Components of a successful wireless LAN implementation involve more than just
compliant radio cards and access points. To complete a system, you also need
application connectivity software with which end-user devices can communicate with
application software or databases located on a centralized server.
The common forms of connectivity software that implementers use to connect wireless
clients are terminal emulation, direct database connectivity, and wireless middleware.
Let's take a look at each of these alternatives.
Terminal emulation software runs on an end-user device, which then operates as a
terminal and communicates directly with application software running on a host-based
system. For example, VT220 terminal emulation communicates with applications running on
a Unix host and 5250 terminal emulation works with AS/400-based systems.
Terminal emulation software's advantage is its low initial cost. Keep in mind,
though, that wireless systems using terminal emulation may not be able to maintain
continuous connections with legacy applications, which have timeouts set for the more
reliable wired networks. (Timeouts automatically disconnect a communications session if
they don't sense activity within a given time period.) As a result, corporate MIS folks
may spend a lot of time responding to end-user complaints of dropped connections and
the associated issues of incomplete data transactions. Thus, implementing terminal
emulation can have a significant deleterious effect on long-term support costs.
Direct database connectivity encompasses application software running on a client
that interfaces over TCP/IP directly with a database located on a server. With this
configuration, the software on the end-user device provides all application
functionality. This provides flexibility when developing applications, because the
programmer has complete control over what functions are implemented and is not
constrained by the legacy applications on the host. Direct database connections are
often the best approach if you need a lot of flexibility in writing the application
A problem, however, is that the direct database approach relies on TCP/IP, which is
not well suited for traversing a wireless network. TCP/IP uses a significant amount of
bandwidth overhead when re-establishing connections after a break, and supports the
transmission of packets with relatively large headers.