The Internet Encyclopedia (Volume 3)

P1: IML

Cassel WL040/Bidgoli-Vol III-Ch-65 September 15, 2003 8:52 Char Count= 0

806 WIRELESSAPPLICATIONPROTOCOL(WAP)

of the visitor. Although there are location-specific services,

such as yellow pages, most Web-based information is rel-

atively static. A mobile user has different needs than a

stationary browser. A mobile user might want to know

what the traffic is just ahead or how to get from here

to there. By combining the other features of the mobile

device with a GPS system (or mobile positioning system

“MPS” technology), an application could address those

questions. When a mobile user asks for information about

nearby restaurants, the response needs to be organized for

effective viewing on the small screen and must accom-

modate the limitations of imperfect connections. When a

mobile user queries his or her bank balance before mak-

ing a purchase, strong encryption must protect the data

transferred without unduly impacting the amount of time

required to get the answer.

One class of applications geared specifically to mobile

users is localized data push. Assuming the user gives per-

mission for such intrusion, a store may broadcast notice

of a sale or even a special offer to a mobile device user

who happens to be driving or walking nearby. Thus, the

information obtained will be offered by a company or or-

ganization to attract the attention of a potential customer

and entice him or her with coupons or other offers.

Designing applications for the mobile device user

requires criteria different from those for designing Web-

based applications that will be accessed through large-

screen devices with high-speed, reliable connections.

Income for the service provider is likely to be in the form of

a charge for the amount of information delivered rather

than advertising revenue. That means that the informa-

tion presented to the user must be efficiently designed

and delivered. The small screen size of most mobile de-

vices requires consideration in designing the information

presentation. Having to scroll both horizontally and ver-

tically to see the content of a message is difficult with

devices typically held and controlled by one hand. User

responses must be obtained without the use of a full key-

board and often without an effective pointing device. The

design challenges are significant.

Standards

WAP must deal with two sets of constraints: limitations

of wireless data networks and limitations of the handheld

devices used to send and receive data. When compared to

landline networks, wireless data networks, regardless of

the technology used, are characterized by

less bandwidth,

more latency,

less connection stability, and

inconsistent availability.

Compared to desktop or even full-featured portable com-

puters, handheld wireless devices are characterized by

small screens,

limited input options,

less memory, and

less powerful CPUs.

Figure 1: The WAP protocol stack (Wireless Application

Protocol Forum, Ltd., 2002).©c 2002 Wireless Application

Protocol Forum, Ltd. Reprinted with permission.

Although technology will improve the situation, some

characteristics will remain. Screen sizes will be small be-

cause an important feature of these devices is their small

size and light weight. Battery life restrictions will limit

CPU and memory size. WAP is a set of standards designed

with these restrictions in mind. The WAP protocol stack is

similar to the ISO OSI Reference Model (ISO/IEC, 1994)

for the upper layers. Layers below the network layer are

implied in the bearer protocols. Figure 1 shows the pro-

tocol stack with the WAP standards in place.

Wireless Application Environment

WAE is a framework for the development of applications

that can be accessed from many types of wireless de-

vices from a variety of manufacturers (Wireless Appli-

cation Environment Specification, 2002). The goal is a

structure in which operators and service providers can

build their products with confidence of interoperability

with a wide variety of devices and applications. WAE in-

cludes XHTML mobile profile [HTMLMP], WML, WCSS,

WMLScript, WBXML, vCARD, and vCalendar. Each of

these is summarized briefly below:

XHTML mobile profile W3C is migrating HTML to

XHTML, making it an XML application, and at the

same time making it modular. Applications can be built

using just the modules that are appropriate for the

target devices. Starting with module XHTML Basic,

XHTML mobile profile adds extensions suitable for the

mobile devices.

WMLThe wireless markup language, an XML-based

markup language designed for use on devices charac-

terized by low-bandwidth connections, limited mem-

ory and restricted CPU capacity, small screen, and lim-

ited user input interfaces.

WCSSThe wireless cascading style sheet. Cascading style

sheets are used in Web development to control dis-

play without sacrificing device independence. WCSS

is specified for the features of small mobile devices.

WMLScript A scripting language, roughly similar to

JavaScript, designed to run on small mobile devices.

WBXMLA compact binary representation of XML docu-

ments intended to reduce the size of the files for trans-

mission without losing semantic information.