Wireless Application Protocol

One

fine day, Mr dotcom millionaire is roaming around in his Mercedes. Suddenly, he

remembers he has to buy a fast laser printer for his new office and luckily,

there’s a computer peripherals shop nearby. But before buying one, he wants to

go through the printer reviews on PC Quest Website. However, he doesn’t have a

PC or a notebook, a modem or a phone line in his car. What he always carries

along is his small metal brown-colored cellphone. Does he give up saying "I

can’t get connected"? For the dotcom millionaire’s of this world, who

want to connect to the Net from anywhere and everywhere, welcome to the

unconnected world–welcome to the world of WAP.

Before you misinterpret what we’ve said above, by

unconnected world we don’t mean a world that isn’t connected. We mean that

there are no wires or cables, but you’re still connected. Interesting? Read on

for more on how this is happening around the world, with the help of this

exciting technology–in fact, a protocol (set of rules)–to access computer

networks, especially the Internet, through your mobile or cellphone. It’s

called WAP, short for Wireless Application Protocol.

WAP

is meant to provide services to all small devices–cellphones, pagers, PDAs,

etc–that you can carry along comfortably. It’s meant primarily to access the

information highway–that is, the Internet–through devices with low and

inadequate resources like slow CPUs, less RAM, small displays, and low bandwidth

and connection stability. The protocol builds upon existing wireless networks,

like mobile or cellphone networks, and also provides some enhancements, like

better user interface, to their standard services.

Let’s contrast HTTP with WAP to understand how you can

browse a WAP-enabled Website.

WAP defines a protocol stack which has a layered design

similar to OSI network layers. It defines a Wireless Application Layer (WAL),

Wireless Session Layer (WSL), Wireless Transaction Layer (WTL), Wireless

Transport Security Layer (WTSL) and Wireless Datagram Protocol (WDP).

WML (Wireless Markup Language) is to WAP what HTML is to the

Web. If you’re familiar with HTML, you’ll find the WML syntax very similar.

WML pages are designed such that they can be viewed comfortably on small

displays. So, a wireless device seeks for a WML page from a Web server, to be

displayed on an embedded microbrowser, very much like your browser seeking for

an HTML page. The difference is that the wireless device uses an additional

intermediary called the WAP proxy.

A WAP transaction with a Web server

The figure depicts a simple transaction that requests a WML

page through a mobile phone.

The mobile phone user; keys in a URL in the microbrowser in

his cellphone, say www.foo.com/foo.wml or www.foo.com/foo.html and connects to

his mobile service provider. The request is encoded for transmission across the

wireless network and is sent to a WAP proxy, which is most likely installed at

the service provider’s site. The WAP proxy constructs a standard HTTP request

and contacts the Web server addressed. The Web server sends the requested WML or

HTML page to the WAP proxy. If the page is a WML page, the WAP proxy encodes it

for the cellphone network you’re using, and simply forwards it to the

microbrowser running on the WAP phone. If it’s a non-WAP page, say an HTML

page, the WAP proxy applies a filter to translate it to a WAP page, encodes it,

and delivers it to the microbrowser.

Non-Internet services

As explained above, a WAP proxy acts as an intermediary

between your WAP phone and a remote Web server on the Internet. But that isn’t

the only thing that you can access using WAP. Your mobile service provider could

use WAP to make available additional services–including virtual private

networks to your office network, from your cellphone. This is done using WTA

(Wireless Telephony Application) servers. Here, the wireless device (your

cellphone) connects directly to the WTA server, which is usually installed at

the mobile service provider’s site. The WTA server may provide some standard

as well as service provider specific services. For example, a WAP-phone user

could maintain an address book on the WTA server. The WTA server can also be

used to maintain a private database accessible to all cellphone users from a

subscriber company, etc. Enhanced security would be an obvious feature in a WTA

server.

WAP for users

As a user, you get a whole range of customized, up-to-date

services when on the move. For instance, you could check your cash position at

your bank before committing to deals. Or, you could track your stock portfolio

when on the move. You could even buy or bid for products on a WAP-enabled

Website. WAP implements a security layer called Wireless Transport Layer

Security, which is based on SSL (Secure Socket Layer), for enabling secure

transactions. Not only that, you could also view your e-mail inbox, while on the

move, or use WAP-enabled search engines to search for anything and everything.

Moreover with WAP’s push technology, you can be notified of events like

changes in airline schedules, by your service provider or a Website.

WAP for developers

WML is based on XML (eXtensible Markup Language) and supports

both text and images. A simple static WML page which displays "PCQ Labs, No

hype, only unbiased truth" on your device’s display would be:

    "http://www.wapforum.org/DTD/wml_1.1.xml">






    

        PCQ Labs, no hype, only unbiased

truth    

Here, the first two lines are the XML declaration and

Document Type Definition (DTD). The is coupled with and

is similar to the tag in HTML. It’s called deck header. In WML,

the smallest unit sent to a WAP-enabled device is called a deck. A deck in turn

consists of cards, which are displayed one at a time, since the display area is

small. The above example is thus a simple WML deck. This deck contains a single

card enclosed within . The

tags

are similar to the HTML

tag and the message to be displayed is written

within them.

WMLScript is a scripting language similar to JavaScript for

client-side scripting. The first use of such scripting is validation at the

client side. The example below illustrates how WMLScript can be used for

checking whether the ID the user enters is of the prescribed length or not. The

actual script is in a separate file named script.wmls, which is called from

scripttest.wml.

scripttest.wml

1.1//EN" "http://www.wapforum.org/DTD/wml_1.1. xml">

Enter ID (5 digits):

name="ID"/>

You entered: $(ID)

You entered an incorrect ID

________________________________

script.wmls

extern function validate (ID)

{

if (String.length(ID) != 5)

WMLBrowser.go("scripttest.wml#



error");

else

WMLBrowser.go("scripttest.wml#



Sok");

};

The file scripttest provides the user with an input text field (similar to

Form text element)

When the user enters the ID, the ID is passed to a function validate() of the

script.wmls as

The function validate( ) is defined as an external function,

in the file script. wmls, using the keyword extern. This function employs an

if-else construct to check whether the ID supplied is of the correct length. If

not, it tells the microbrowser to show the card with ID "error" of the

scripttest deck, else the card with ID "ok" of the scripttest deck is

shown. To accomplish this, the library function WMLBrowser.go( ) is used.

Since a WML page can reside on a normal Web server,

server-side scripting languages like Perl, C, PHP, Java Servlets, etc, can be

used to deliver dynamic content to WAP devices. You must configure your Web

server to understand WML and WMLScript MIME types as:

MIME type : text/vnd.wap.wml

File Extension : wml

MIME type: text/vnd.wap.wmlscript

File Extension : wmls

The WAP future

WAP as of now delivers only text, but is expected to become

more versatile in the future. Currently, WAP is restricted by bandwidth and

hardware constraints. As these constraints get removed, WAP is expected to

deliver much more than it can today. And don’t be surprised if by that time

WAP undergoes metamorphosis, into something totally different and beautiful–a

butterfly