Wireless Application Protocol

Here's what happens when you access a Web site using a WAP-enabled device:

• 
  
  You turn on the device and open the minibrowser.
  
• 
  
  The device sends out a radio signal, searching for service.
  
• A connection is made with your service provider.
  
• You select a Web site that you wish to view.
  
• A request is sent to a gateway server using WAP.
  
• The gateway server retrieves the information via HTTP from the Web site.
  
• The gateway server encodes the HTTP data as WML.
  
• The WML-encoded data is sent to your device.
  
• You see the wireless Internet version of the Web page you selected.
  

To create wireless Internet content, a Web site creates special text-only or low-graphics versions of the site. The data is sent in HTTP form by a Web server to a WAP gateway. This system includes the WAP encoder, script compiler and protocol adapters to convert the HTTP information to WML. The gateway then sends the converted data to the WAP client on your wireless device.

What happens between the gateway and the client relies on features of different parts of the WAP protocol stack. Let's take a look at each part of the stack:

WAP protocol stack

Wireless Markup Language

WAP uses Wireless Markup Language (WML), which includes the Handheld Device Markup Language (HDML) developed by Phone.com.

WML can also trace its roots to eXtensible Markup Language (XML). A markup language is a way of adding information to your content that tells the device receiving the content what to do with it. The best known markup language is Hypertext Markup Language (HTML). Unlike HTML, WML is considered a meta language. Basically, this means that in addition to providing predefined tags, WML lets you design your own markup language components. WAP also allows the use of standard Internet protocols such as UDP, IP and XML.

There are three main reasons why wireless Internet needs the Wireless Application Protocol:

• Transfer speed
• Size and readability
• Navigation

Most cell phones and Web-enabled PDAs have data transfer rates of 14.4 Kbps or less. Compare this to a typical 56 Kbps modem, a cable modem or a DSL connection. Most Web pages today are full of graphics that would take an unbearably long time to download at 14.4 Kbps. Wireless Internet content is typically text-based in order to solve this problem.