Wireless Application Protocol

WAP History

In the mid-1990s it was generally felt, following the recent explosion in the popularity of the WWW and increasing popularity of mobile telephones in Europe, that the next market to open up would be that of information services on wireless networks. The major players in the European mobile telecommunications market set about developing their own protocols to enable them to offer value added services to these networks. It quickly became obvious that by developing competing protocols these companies were not only duplicating effort, but also harming their chances of any of the protocols achieving success in the market. It was realised that a single standard protocol, like that developed for digital mobile telephony (the Global System for Mobile Communications, GSM) would rally companies and customers around the new technology and would ensure that growth in the industry would not be stunted by rival operators using different systems (as had happened with the US digital mobile market).

Following a period of intense development and negotiations, a varied group of companies decided to formalise their relationship and founded the Wireless Application Protocol Forum. This co-operative released WAP 1.0 in 1997 and European network operators were quick to announce their support, in the knowledge that, as far as the provision of online wireless applications was concerned, WAP was for the moment, the only game in town.

WAP Features

WAP is best thought of as a bringing together of various protocols in order to allow for efficient, fast, flexible and secure use of the wireless communications network. Among its important features are:

• No Licence
  The most important feature of WAP is that you do not need to sign conditions or pay a fee to use it. The companies that are behind WAP, who are responsible for approximately 75 per cent of the world's mobile phone market, hope that this will allow the protocol to flourish in the same way as another set of licence-free protocols: TCP/IP (the Internet protocols).
• Hardware Independence
  Like HTTP and HTML (the standards that are the basis for the WWW), WAP does not make presumptions about the kind of devices that may make use of it. It is equally usable on mobile phones, two-way radios, pagers and personal data organisers.
• Operating System Independence
  Again like HTTP and HTML, WAP will work on any operating system that has a correct implementation of the underlying layers of communication protocols. It will work on platforms ranging from giant systems like Microsoft Windows 2000 and Sun Solaris to minimalist offerings such as Palm OS and Microsoft Windows CE.
• Use of Existing Standards and Protocols
  WAP is built on the proven Internet communications protocols TCP and HTTP, which allows an easy migration path for network operators and application developers. WAP also tries to use existing standards rather than create proprietary solutions: this is why it adopted eXtensible Markup Language (XML) as the basis for its own language, Wireless Markup Language.
• Optimal Use of Bandwidth
  Because wireless data communication is so slow compared to fixed-line communications, WAP must try to squeeze as much data as possible over the low bandwidth available to it, which it does by, for instance, compiling WML pages instead of sending them in raw form.

Wireless Markup Language (WML)

WML was designed specifically to cater for narrow-band devices, such as mobile phones, and transmission across WAP-based networks. It is a subset of eXtensible Markup Language (XML) so it inherits many of the XML commands and document tags. WML is transmitted in compressed form as binary data so as to make the most efficient use of the low bandwidth allocated to it. The language must also make optimum use of limited display size and simple user input. Up until recently it was desirable for mobile phones to be compact and simple to use, but with the advent of WAP technology there is an increasing need for greater diversity in user interaction. It is assumed that any WAP device will have 2 buttons for navigating up and down through text and 2 for selection or activation purposes.

As with most areas of the WAP protocol, WML was created as a compromise between the already existing markup languages being produced by various interested parties. It primarily used the protocol developed by a US company called Unwired Planet (now known as Phone.com), which was called Handheld Device Markup Language (HDML), but also drew inspiration from the European offerings of the time: Ericsson's Intelligent Terminal Transfer Protocol (ITTP) and Nokia's Tagged Text Markup Language (TTML).

The basic unit of WML is the card, which specifies a single interaction between the user agent (or "WAP browser") and the user. Cards are grouped together into decks. A deck is the smallest unit of WML that a web server can send to a user agent. When a user agent receives a deck, it typically activates the first card in the deck, though it can be directed to any particular card in the deck. This is congruent to visiting a Web site on a computer-based browser and downloading all pages in that site without explicitly opening them all. It is possible to move from one card to another within the same deck or to move to another deck, but in changing decks new data must be retrieved from the WAP server.

WML Tags

A tag is a language element descriptor. A tag describes an element and contains an element type name and a unique identifier. A tag could also include attributes describing other properties. WML consists of content surrounded by formatting tags, each enclosed in a pair of angle brackets, < and >.

WML Elements

Elements specify all markup and structural information for a WML deck. Elements may contain a start tag, content, other elements, and an end tag. Elements have one of two structures:

The main categories of tag elements are:

• Deck and Cards
• Events
• Tasks
• Variables
• User Input
• Anchors, Images, and Timers
• Text Formatting

WML Structure

A valid WML deck is a valid XML document and therefore must contain an XML declaration and a document type declaration (in this case for WAP 1.1) as follows:

<?xml version="1.0"?>
<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN"
"http://www.wapforum.org/DTD/wml_1.1.xml">

A WML deck begins and ends with the wml element, while all other elements lie between these start and end tags:

<wml>
...all other elements...
</wml>

The following is a simple WML deck containing a single card.

<?xml version="1.0"?>
<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN"
"http://www.wapforum.org/DTD/wml_1.1.xml">
<wml>
	<card id="First_Card" title="My First Card">
		<p>
			This is just normally displayed text.
		</p>
	</card>
</wml>

The following is a line-by-line explanation of this example:

• 1. The first line specifies the XML version number.
• 2. The second line specifies the SGML public document identifier.
• 3. The third line specifies the location of the WML document type definition (DTD). The DTD can be located in the network, or you can store it locally to make accessing it faster.
• 4. The fourth line defines the header of the WML deck. All WML decks must begin with a <wml> tag and end with a </wml> tag.
• 5-9. The following lines define a card containing a start and an end tag and text to be displayed to the user.
• 10. The last line is the deck footer. The user agent treats everything between the deck header and the deck footer as a single WML deck.

WAP Problems

Like all new technologies WAP has suffered from some problems, though only time will tell whether they are fundamental flaws in the protocol or merely teething problems:

• Marketing
  Marketed in many places as the "Wireless Web" and the "Mobile Internet", WAP found it hard to live up to the hype generated. Customers used to full-colour WWW sites with pictures and sound on a large screen were unimpressed by small black text on a tiny screen.
• Immature Development Environments
  Early on in its life there was a lack of tools for application developers and content providers to test their work on. This meant that they were reduced to testing pages by actually signing up to a network operator's WAP service: a very costly activity and laborious process. Now many development kits, emulators and WAP browsers are available for various desktop platforms so that developers can adopt a more traditional approach to writing and testing.
• Hardware and Software Problems
  It seems as though, in a rush to get to market, or as a result of the previous problem, mistakes were made both in the hardware and software of leading brand-name WAP products. For content developers the lack of a uniform browser implementation was frustrating, as it was difficult to build pages that performed the same on all phones. For some customers regular software crashes (often necessitating a battery replacement to resume normal use) in a leading WAP phone, tainted the new technology and led to network operators refusing to distribute that particular phone.
• Lack of Cookie Support
  The WAP protocol currently fails to allow cookies (which are commonly used on WWW sites to maintain state between sessions) to be used. This means that the personalisation of WAP services based on user profiles is made more difficult. This problem is due to be rectified in WAP 1.2.
• Monochrome Displays
  Although WAP does support the use of colour, the failure of mobile phone manufacturers to take advantage of this so far means that a user's WAP experience is entirely based in two colours. Hardware support for colour would mean that basic pictures, and therefore advertising, could be displayed.
• Upgrades
  Upgrades, which will be crucial to the future of WAP, are not a pleasant experience from the user's point of view. For instance, in order to avail of the improvements in WAP 1.2 (due in late 2000), many phones will have to have their ROM chips updated, while some phones will even need replacement.
• Network
  Although WAP does not prescribe any particular underlying network (despite attempts to do so by US GSM operators trying to prevent rival D-AMPS operators from using WAP), in Europe, WAP's potential success was hampered by the underlying network. This is because the GSM network in Europe is still a circuit-switched network, and so WAP users there must dial up their WAP service and wait to connect. Also, because a circuit-switched network has no means of measuring data transfer amounts, users must be charged for time spent online, which is not conducive to encouraging m-commerce.