A WAP Primer

WAP was the buzzword at the GSM World Congress and Wireless 2000, and for good reason: An open, industry-standard platform is key to making wireless data live up to its promise.

The explosion in connectivity is astounding. Growth rates have surpassed predictions in almost every area: IP connections, e-mail, wireless phones, messaging, data traffic and voice traffic on wired systems. In the process, the concept of distance is vanishing: We routinely call across the country without thinking much beyond dialing an area code.

This revolution wouldn't be possible without standards and their authors: unseen, diligent committees working in organizations such as the Internet Engineering Task Force, the World Wide Web Consortium (W3C) and the WAP Forum. Although it's easy to appreciate the power at our fingertips when accessing the expansive world of content and applications via our desktop computers, it's not readily apparent that this ability wouldn't be possible without a family of standards, including HTTP, IP and TCP. The ambiguity of the acronyms understates the power of their purpose.

In June 1997, three of the largest cellular-phone manufacturers, Ericsson, Motorola and Nokia, and a hitherto unknown start-up, Unwired Planet (now Phone.com), formed the WAP Forum, an open, not-for-profit body that would create standards allowing small, consumer-class wireless devices to access the Internet anywhere, anytime. Since then, infrastructure vendors, device manufacturers, wireless-service providers, content suppliers and applications vendors have met and sculpted the various forum committees as wireless-Internet convergence began attracting consumer and investor interest.

Why WAP?
Constructing a wireless protocol is similar to constructing a wired protocol. Although the forum had to make assumptions about limited CPU power, short battery life and small displays, it hasn't described any reference platforms. The protocol seeks to enable any wireless device, be it a cellular phone, interactive pager or wireless PDA.

By comparison, for example, when Microsoft launched Windows CE, it defined the end-user device's minimum features, such as number of buttons on the side and the ability to accommodate pen-based data entry. Although this approach makes rolling out applications initially faster because developers know what they have available, in the long term, it constricts innovation with respect to devices for special purposes or those really tiny or really large.

In all of these devices, cost is critical: Adding just $1 to the cost of the materials that make up a phone might push the retail price outside the affordability range of a million potential subscribers. WAP devices are limited in the sense that they don't have the luxury of accommodating large code space to run applications, unwieldy kernels and expansive displays. Developing applications "in the small" is given new meaning on a WAP device.

Usability is a key driver in developing WAP applications. If an application isn't user-friendly, consumers won't use it. The problem snowballs from there: Take-up rates will be poor, and the critical mass of usage won't be achieved because people won't spread the word about all the benefits of their wireless devices.

Personal salience also is important: Information needs to be relevant and important to the person using it. Applications need to be useful or just plain fun, as is the case with gaming and entertainment. The wireless Internet can't be the Internet of busy signals, cryptic error messages and missing links. Experience shows that users expect simplicity and ease-of-use: They won't carry a manual with their wireless devices.

A Peek Under the Hood
The technology behind WAP offers developers a rich environment that's comparable to the wired Web. WAP is built on a programming model that's based on the existing wired-Web programming model. WAP is a world of request/response transactions with far-flung servers.

In terms of a markup language, WAP strives to be XML-conforming, and the WAP Forum continues to forge relationships with wired-Web bodies such as the W3C. Like wired-Web protocols, wireless markup language (WML) makes few assumptions about the end-user device. This approach lets developers construct applications for a variety of devices. Small units of execution are needed because they're moved wirelessly and with limited available bandwidth. WML also has an associated scripting language, WMLScript, designed to add computational capabilities to WML.

Bandwidth conservation is crucial in wireless. WAP provides a protocol stack designed to minimize bandwidth requirements while offering secure connections over a variety of transport protocols. Developers also have a framework for wireless-telephony applications (WTA) so that WML applications can interact and integrate with telephone applications. Examples include address-book synchronization, message management and call management.

The WAP architecture is straightforward and looks similar to the pervasive International Standards Organization network model.

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Application Layer — WAE
Session Layer — WSP
Transaction Layer — WTP
Security Layer — WTLS
Transport Layer — WDP
Bearer Layer — Includes CDMa, GSM, ReFlex and TDMA

Figure 1. Although the WAP protocol stack looks like most protocol stacks, it has many attributes necessary for use in a wireless environment.

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The WAP application environment (WAE) is the topmost layer and the one that application developers are most interested in. This layer holds general device specifications, WML and WMLScript programming languages, the WTA telephony application programming interfaces, and defines content formats, including graphics and personal-information-management (PIM) information.

The wireless session protocol (WSP) in the session layer is a tokenized version of HTTP 1.1 designed specifically for limited bandwidth and longer latency applications while still allowing guaranteed delivery and "push" content.

The transaction layer encompasses the wireless transaction protocol (WTP), which limits the overhead of packet sequencing. It supports a variety of message types, including non-guaranteed 1-way requests, guaranteed 1-way requests and guaranteed 2-way request/response transactions used with a browser.

The security layer supports wireless transport layer security (WTLS), a protocol based on standard TLS, formerly known as secure sockets. WAP's lowest level contains the wireless datagram protocol (WDP), which provides a consistent interface between various over-the-air protocols, including CDMA, CDPD, GSM, ReFlex and TDMA.

With all the attention and excitement in the wireless market today, it's inevitable that the dynamic, innovative developer community that's forming within the wireless industry will exceed all our expectations. They'll create exciting and compelling applications that will continue to drive the massive growth we've already seen. Empowering those developers and enabling those applications will be the unsung heroes: the people working the WAP Forum's committees, subcommittees and expert groups.

Yuzdepski (jyuzde01@sprintspectrum.com) is Sprint PCS vice president of product management and development, and a member of the WAP Forum board of directors.