The major role of wireless middleware is bridging enterprise applications
that are running on wired networks with WLAN and mobile WAN transports.
Middleware can take the form of a gateway or a software development tool, or it
can be included in the offerings of a wireless application service provider.
Figure
shows a Wireless
Application Protocol (WAP) middleware example. The Wireless Markup Language
(WML) is a language similar to HTML, which has been optimized for wireless. It
is based on the Extensible Markup Language (XML). WAP is covered in the next
section.
There are different approaches to accomplishing this bridging role, and
different functions that can be provided by the various solutions. Not all
vendor products will perform all of the functions. Some of these functions
include the following:
-
Data and header compression – Compressing data minimizes the payload
sent over wireless links, which boosts bandwidth efficiency. This can be
particularly important to user response times.
-
Recovery from breaks in transmissions – Transmission interruptions
are caused by poor coverage or interference. Some middleware can detect when a
transmission has been interrupted. The middleware will enable the session to
resume from the breakoff point when the session is reestablished. Some
middleware will queue messages, to protect users who may become disconnected
from the network. Then, when the user reconnects, the messages will be
forwarded to the mobile device of that user.
-
Packet consolidation – Some middleware will combine smaller data
packets into a single, larger packet for transmission over the wireless
network. This can help lower transmission service costs of usage-based mobile
WAN services that charge users by the packet.
The Cisco CTE 1400 Series Content Transformation Engine is another
middleware solution. The CTE 1400 transforms existing enterprise content for
display and interaction on small-screen mobile devices and IP phones. When a
device makes a connection request, the CTE transforms the content to suit the
device, using a transformation rule as shown in Figure
. The
source data is left unchanged.