The Wireless Application Protocol (WAP) is a specification developed by the WAP Forum for sending and reading Internet content and messages on small wireless devices, such as cellular phones equipped with text displays. Common WAP-enabled information services are news, stock quotes, weather reports, flight schedules, and corporate announcements.

Special Web pages called “WAP portals” are specifically formatted to offer information and services. CNN and Reuters are among the content providers that offer news for delivery to cell phones, wireless personal digital assistants (PDAs), and handheld computers. Electronic commerce and e-mail are among the WAP-enabled services that can be accessed from these devices as well.

Typically, these devices will have very small screens, so content must be delivered in a “no frills” format. In addition, the bandwidth constraints of today’s cellular services mean that the content must be optimized for delivery to handheld devices. To get the information in this form, Web sites are built with a light version of the HyperText Markup Language (HTML) called the Wireless Markup Language (WML).

The strength of WAP is that it spans multiple air link standards and, in the true Internet tradition, allows content publishers and application developers to be unconcerned about the specific delivery mechanism. Like the Internet, the WAP architecture is defined primarily in terms of network protocols, content formats, and shared services. This approach leads to a flexible client-server architecture that can be implemented in a variety of ways but which also provides interoperability and portability at the network interfaces.

WAP solves the problem of using Internet standards such as HTML, HyperText Transfer Protocol (HTTP), TLS, and Transmission Control Protocol (TCP) over mobile networks. These protocols are inefficient, requiring large amounts of mainly text-based data to be sent. Web content written with HTML generally cannot be displayed in an effective way on the small-sized screens of pocket-sized mobile phones and pagers, and navigation around and between screens is not easy with one hand.

Furthermore, HTTP and TCP are not optimized for the intermittent coverage, long latencies, and limited bandwidth associated with wireless networks. HTTP sends its headers and commands in an inefficient text format instead of compressed binary format. Wireless services using these protocols are often slow, costly, and difficult to use. The TLS security standard, too, is problematic, since many messages need to be exchanged between client and server.

With wireless transmission latencies, this back-and-forth traffic flow results in a very slow response for the user. WAP has been optimized to solve all these problems. It makes use of binary transmission for greater compression of data and is optimized for long latency and low to medium bandwidth.

WAP sessions cope with intermittent coverage and can operate over a wide variety of wireless transports using the Internet Protocol (IP) where possible and other optimized protocols where IP is impossible. The WML used for WAP content makes optimal use of small screens, allows easy navigation with one hand without a full keyboard, and has built-in scalability from two-line text displays through to the full graphic screens on smart phones and communicators.

WAP Applications Environment

WAP applications are built within the Wireless Application Environment (WAE), which closely follows the Web content delivery model, but with the addition of gateway functions. Figure W-2 contrasts the conventional Web model with the WAE model. All content is specified in formats that are similar to the standard Internet formats and is transported using standard protocols on the Web while using an optimized HTTP-like protocol in the wireless domain (i.e., WAP).

The architecture is designed for the memory and CPU processing constraints that are found in mobile terminals. Support for low-bandwidth and high-latency networks is also included in the architecture as well. Where existing standards were not appropriate due to the unique requirements of small wireless devices, WAE has modified the standards without losing the benefits of Internet technology.

The major elements of the WAE model include:

• WAE user agents These client-side software components provide specific functionality to the end user. An example of a user agent is a browser that displays content downloaded from the Web. In this case, the user agent interprets network content referenced by a Uniform Resource Locator (URL). WAE includes user agents for the two primary standard content types: encoded WML and compiled WML Script.

• Content generators Applications or services on servers may take the form of Common Gateway Interface (CGI) scripts that produce standard content formats in response to requests from user agents in the mobile terminal. WAE does not specify any particular content generator, since many more are expected to become available in the future.

• Standard content encoding A well-defined content encoding, allowing a WAE user agent (e.g., a browser) to conveniently navigate Web content. Standard content encoding includes compressed encoding for WML, bytecode encoding for WMLScript, standard image formats, a multipart container format, and adopted business and calendar data formats (i.e., vCard and vCalendar).

• Wireless Telephony Application (WTA) This collection of telephony specific extensions provides call and feature control mechanisms, allowing users to access and interact with mobile telephones for phonebooks and calendar applications.

WMLScript is a lightweight procedural scripting language based on JavaScript. It enhances the standard browsing and presentation facilities of WMLwith behavioral capabilities. For example, an application programmer can use WMLScript to check the validity of user input before it is sent to the network server, provide users with access to device facilities and peripherals, and interact with the user without a round-trip to the network server (e.g., display an error message).

WAP 2.0

The latest version of the Wireless Application Protocol is WAP 2.0, which continues the convergence of WAP with the evolving Internet, merging the work of the WAP Forum, the World Wide Web Consortium (W3C), and the Internet Engineering Task Force (IETF) and enabling more rapid development of new mobile Internet applications.

New technologies of WAP 2.0 that will improve the user experience are data synchronization, multimedia messaging service (MMS), persistent storage interface, provisioning, and pictograms. Additionally, WTA, Push, and User Agent Profile (UAPROF) use more advanced features in WAP 2.0 than in previous versions.

• Data synchronization adopts the SyncML protocol to ensure a common solution framework with a multitude of devices. The SyncML messages are supported over both the Wireless Session Protocol (WSP) and the HTTP/1.1 protocols.

• Multimedia messaging service provides the framework to develop applications that support feature-rich messaging solutions, permitting delivery of varied types of content in order to tailor the user experience.

• Persistent storage interface provides a set of storage services that allows the user to organize, access, store, and retrieve data on wireless devices.

• Provisioning permits the network operator to manage the devices on its network with a common set of tools.

• Pictogram permits the use of a set of tiny images, allowing users to quickly convey concepts in a small amount of space while transcending traditional language boundaries.

• Wireless Telephony Application provides a range of advanced telephony services within the application environment, enabling a host of call handling functions such as making and answering calls, placing them on hold, and redirecting them even while performing data-centric tasks. The availability of these services enables operators to offer customers a unique user interface to control complex network features, such as call forwarding options.

• Push technology allows trusted application servers to proactively send personalized content to the end user, such as a sales offer for a product a person might be interested in buying, a new e-mail notification, or a locationdependent promotion. Push technology complements the traditional “pull” model of the Internet, where users request specific information from a Web site.

• User agent profile enables application servers to send the appropriate content to the user and to recognize the capabilities of devices, such as screen size and color, to maximize performance potential, bringing the user increased satisfaction.

WAP 2.0 is a next-generation specification that addresses the needs of all players in the wireless industry who plan on incorporating the platform-agnostic specification in their products and services to grow the wireless market by offering value-added features.

WAP is an open global specification that empowers mobile users with wireless devices to easily access and interact with information and services instantly. It is designed to work with most wireless networks, including Bluetooth, Infrared, CDPD, CDMA, GSM, PDC, PHS, TDMA, iDEN, DECT, and GRPS. It can be built to run on any operating system, including PalmOS, EPOC, Windows CE, FLEXOS, OS/9, and JavaOS. WAP offers the additional advantage of providing service interoperability between different device families.