WAP: New Web Whopper.

TCP & IP are splitsville 

In the contest for dominion over the wireless Web, a new competitor is emerging, and it has already become the darling of mobile phone, handheld, and PDA OEMs. The Wireless Application Protocol, or WAP, has come on so strong and so suddenly that key companies in all major wireless device markets are lining up to participate. Many are hailing it as the revolutionary roaming access protocol that will bring the Web where it's destined to go: over the airwaves.

But what's truly exciting about WAP is its combination of new and existing Web technologies used in new ways to solve old problems, among them the performance and display limitations of handhelds, the shortcomings of HTML, and the wireless deficiencies of TCP/IP.

While WAP has been around for more than a year, technical hurdles--particularly the slow adoption of XML--a lack of WAP-enabled content, and a scarcity of devices have resulted in a low profile. But with the release of version 1.1 (July), which incorporates fixes and feedback from users and vendors, reliable WAP-enabled devices and data services are finally becoming available. In this discussion, we take a look at how the elegant WAP is designed, the technical problems it hopes to solve, how it will work, and how wireless users can benefit.

WAP Session

At its essence, WAP is simple: it is a new protocol developed to deliver Internet content to wireless, portable devices. However, the problems associated with this seemingly basic service are numerous. For one thing, wireless devices have strict power, processing, and display requirement which limit the kinds of information they can display--and the duration that they can display it.

Take just one basic example. Wireless communication is prone to service interruptions and lost data, which translates into dropped connections, static, or fade-out. HTTP and TCP are optimized for devices that are constantly connected and can send multiple, repeated requests for data. These protocols are not designed for the long latencies associated with wireless communications, nor are their transmissions optimized for low bandwidth (just try browsing on a slow modem over a noisy phone line).

Another problem is related to the display of Web content. Content on the Web is designed for one or two standard browser types. Because of their resource requirements (not to mention disk space demands), IE and Navigator won't run on small portable devices with limited memory and disk space. This means that wireless devices must use another browser type, which may have difficulty displaying information in the way it was designed to be shown: for example, in columns, as part of a table, or as a form element. And, even when graphic elements are not downloaded to save bandwidth, HTML and HTTP still use them for positioning elements on the page, meaning pages still take up lots of room. Data security is another problem: packets sent across the airwaves are particularly prone to theft; just ask anyone with a cell phone that's been cloned.

WAP offers solutions to these problems, as well as several others. According to WAP documentation, instead of sending uncompressed text strings, WAP sends data in compressed binary packets. Instead of using HTML, WAP uses a language called WML (Wireless Markup Language), which is based on XML and which allows data to be optimized for smaller displays, from two-line screens on pagers to the bigger, full-content screens used on some PDAs.

But not surprisingly, perhaps the biggest change is in data transport. While WAP uses IP as its transport layer, it also uses the User Datagram Protocol (UDP) instead of TCP, and it uses the new WTP (Wireless Transaction Protocol) at the transaction layer. WAP also includes a lightweight session re-establishment protocol which allows sessions to be interrupted and resumed without the overhead associated with initial session establishment.

WAP Around

UDP is a connectionless protocol which, like TCP, is layered on top of IP. But unlike TCP, which tightly controls the transmission of data (hence the "C" in TCP), UDP does not packetize messages at one end and then reassemble them at the other, the method which allows packets to take different routes across the Internet if necessary.

How is this UDP-based packetization scheme compatible with the Internet, a many-to-many network that allows packets to take different routes from the host to the client? And, further, because UDP doesn't provide sequencing of packets, normally the client application is responsible for reordering data, meaning that error processing and retransmission are also handled by the client, not the server. In a wireless world, where client-side processing is severely limited, this would seem to be a step backward. Because WAP clients are small and with limited processing resources, and because they are prone to disconnection, a new solution to both problems was necessary.

The true elegance behind WAP, in my opinion, provides the answers: the WAP Gateway. The WAP Gateway (also called the uplink server) acts as a proxy server between the traditional Internet network and the wireless client. Because this is only a single route from the proxy to the handheld device, packets don't need to travel over multiple routes, which reduces the overhead demanded by TCP as well as the number of packets sent.

To eliminate the need for increased processing and packet reordering in the client, the WAP Gateway is also responsible for stepping in and translating requests from the WAP protocol stack to TCP, and vice versa (See Fig). Thus, it is the WAP Gateway that encodes packets and compresses them on their way to WAP-enabled devices, and hence handles much of the processing overhead.

This clever scheme also serves another purpose: it allows developers of WAP content to use standard Web technologies like CGI and to host their content on standard Web servers. The WAP Gateways can also cache frequently requested data and can store user-defined criteria that allows Web content to be personalized. Further, carriers can designate more than one uplink server, allowing the phone to connect to various gateways, depending on the nature of the data sent in the request.

WAP also introduces an innovative way for users of handheld devices to view Web page content. Because HTML pages are often long documents that require scrolling, WML displays documents and content in ways that make them more accessible to mobile users on small devices. One such method is via a "card" metaphor, which basically breaks pages into single-screen views that can be accessed and reordered (or shuffled) like file-cards, using a scroll button on the handheld device. This process allows pages to be navigated with the touch of a single button, rather than by scrolling and manipulating graphical page elements like navbars and menus. Another method is the translation of links into elements that can be easily selected and activated through a number pad, but without the use of a keyboard or mouse. A traditional 12-key phone keypad can be used to enter alphanumeric characters as dictated by the application.

WAP utilizes a new programming language known as WMLScript which is similar to JavaScript. WMLScript, however, does not assume that a QWERTY keyboard and mouse are available for user input. Standard HTTP 1.1 headers are used for communication between the WAP Gateway and Web servers, and WML developers can use standard development tools and methods--including ASP, Perl and CGI--to create WML content. They also can use a single URL for HTML and WML content using browser detection--or separate URLs can be created. While it is possible to translate HTML to WML on-the-fly, this is not recommended--at least not yet.

WAP also provides security for packets traveling through the ether. WTLS, or Wireless Transport Layer Security, is the WAP security service and is based on SSL and TLS. WTLS provides encryption, data integrity (through MACs), and public-key and symmetric-based authentication.

WAPid Deployment?

One of the keys to the likely success of WAP is its carrier and OS independence. Like HTTP and HTML, WAP and WML can operate over virtually any network architecture, including but not limited to GSM, CDPD, and TDMA, and over any OS. Of course, universal wireless connectivity means international connectivity, and there are efforts afoot to unify the global cellular network which will impact WAP adoption rates. Most promising is the ITU's IMT-2000 standard (International Mobile Telephone 2000). This proposal seeks to unify wireless technology, spur interoperability, and combine the Internet and telephone networks.

The front-runner in this next-generation cellular race is currently Wideband Code Division Multiple Access (WCDMA) technology, which will support WAP. Earlier this year, cellular giants Ericsson and Qualcomm settled their various differences and patent spats over CDMA and both companies have agreed to support the standard. Version 1.1 of the WAP standard supports CDMA SMS (Short Messaging Service), which is expected to spur WML-based service offerings. Further, the WAP Forum, an industry trade consortium, has asked The Open Group to develop a test suite to support a WAP certification program, which hopes to ensure interoperability among WAP clients and servers.

"One of the main things we have been working on in the WAP Forum is global roaming," says Greg Williams, Board Chairman. "However, there are both technical and business issues that need to be worked out." Williams says that while the technical difficulties are significant, the business aspects of global roaming--in particular billing and provisioning between carriers--are proving thorny indeed. "Basically, there needs to be more international cooperation among carriers," he says. Because it is Internet-based, WAP can be used on any bearer network with the proper infrastructure in place. Williams predicts that we will see devices that support multi-air interfaces sometime in the second half of next year.

Still, a number of WAP initiatives are now under way. While many WML-based services are currently available only in Europe and Asia, several agreements for the U.S. market have been announced. Sprint and Nokia will offer PCS-based WAP service to Nokia phones, and Nextel and Motorola have announced a similar agreement.

Airline reservation giant Sabre has partnered with IBM and Nokia on a WAP travel booking service, and there is now a WAP-based Web portal for SMS-enabled PCS phone users (www.web2pcs.com). The site offers free WML-based news and information, including stock quotes, sports scores, and headlines. Another site, Infinite Technologies' Mailandnews.com, delivers email to WAP-enabled devices for free. WAP Forum officials note, however, that products and services standardized on WAP 1.1 probably won't be available until the end of the year.