Wireless Application Protocol (WAP) is a technical standard for accessing
information over a mobile wireless network. A WAP browser is a web browser for
mobile devices such as mobile phones that uses the protocol.
Before the introduction of WAP, mobile service providers had limited opportunities to offer interactive data services, but needed interactivity to support Internet and Web applications such as:
Email by mobile phone
Tracking of stock-market prices
WAP incorporates a simple microbrowser, designed to work on the limited platforms of mobile handsets, with a central WAP gateway that performs the more processor-heavy operations. It defines a standard for data transmission to the handset, WDP (WAP datagram protocol), which is a variation of the internet standard transmission protocol, HTTP (Hypertext Transport Protocol), but redesigned for wireless network characteristics. WDP mostly differs from HTTP by stripping out much of the text information, replacing it with more efficient binary information for the low-bandwidth connection. The WAP data can be sent over any available network, be it the circuit-switched connection of TDMA (Time Division Multiple Access) IS-136 or packet-switched GPRS.
Added to this core transmission protocol are several scalable layers that can develop independently. The wireless transport layer security (WTLS) layer adds optional encryption facilities that enable secure transactions. WTP (WAP transaction protocol) adds transaction support, adding to the datagram service of WPD, while WSP (WAP session protocol) allows efficient data exchange between applications.
WAP also defines an application environment (WAE) that enables third-party developers to develop more advanced services and applications, along with the microbrowser used to access web pages on the handset itself.
To access internet content, the user's handset sends a request to the WAP gateway, which retrieves the information in either HTML (Hypertext Markup Language) or WML (Wireless Markup Language) from the host server. WML is a variation of HTML, designed specifically to enable viewing on the limited mobile terminal platform. If the information retrieved is in HTML, a filter in the gateway will attempt to convert it to WML. The information will then be transmitted to the handset over whatever network is available, using the transmission protocols described above.
In some cases, where HTML data is generated using a style sheet to convert XML data using an XSL processor, a WML style sheet can be added to the system to generate seamless information in the correct format for wireless viewing.
FUTURE OF WAP:
Because WAP is a protocol designed to work over any mobile network, its use will continue to increase as more sophisticated data transmission technologies are introduced (e.g. GPRS, EDGE (Extended Data for Global Evolution) and W-CDMA (Wideband-CDMA)). As the bandwidth available to mobile terminals and the quality of displays improve, WAP can be enhanced to provide as effective an internet viewing experience as is possible on fixed terminals.
The simplest way to think about a WAP gateway is that it is the system that WAP devices communicate directly with, and any content delivered to WAP devices via IP networks (like the Internet) must travel through these gateways on their way to those little, tiny screens.
The WAP gateway performs a host of duties, which we'll cover here in detail, but the most important is the protocol translations that are necessary to connect the TCP/IP-based world of the wired Internet with the WAP-based world of wireless mobile devices. Without something to perform this essential task, WAP simply wouldn't work.
A WAP gateway is a piece of software that usually resides on a dedicated Unix-type of server. Often the box itself will also be referred to as the gateway, but for the purposes of this article we will only be considering the software functionality of WAP gateways. There are also WAP gateways that can run on Windows-based systems, as well as combination content-server/gateway products, but the norm is to have a stand-alone Unix server running the gateway software
What does a Gateway Do:
A WAP Gateway plays many roles in the scheme of turning the WAP model into working services. A list of just some of the functions of a WAP gateway include the following:
implementation of the WAP stack
converting markup languages
compiling WMLScript programs
encoding WML into a binary bitstream
providing access control
domain name resolution services (DNS)
Clearly, these gateways can pack a lot of punch. There is a wide range of products available, with differing feature sets and price ranges (from free to big bucks) so we'll deal with the most commonly implemented and important features here.
Providing the software to maintain the WAP stack layers is a critical function of any WAP gateway, though they will not all implement the same layers. Gateways that support connectionless services will not need to implement the WTP layer, just as products that don't support secure services won't need to include the WTLS layer. A gateway that will be used for secure, connection-oriented services will need to implement WSP, WTP, WTLS, and WDP.
Converting between WAP's WSP and the Internet's HTTP is another central function of any WAP gateway. One of the main differences between WSP and HTTP is that WSP's headers are encoded in binary form, or "tokenized." For example, the token "Accept" from the HTTP/1.1 header becomes "0x80". This is a way for WAP to save on bandwidth by transmitting the bare minimum bits possible to represent a specific group of characters.
Some gateways also offer HTML to WML conversion, though this feature rarely results in functional WAP services. It is generally agreed that mobile applications should serve WML directly from the origin server, and that the code needs to be designed and tested separately from HTML implementations.
Encoding the WML content is another mandatory function of a gateway, and again it is done to save on the precious bandwidth of the wireless networks. By converting the WML to a binary, tokenized format, the amount of data sent over the wireless network is greatly diminished. The gateway also checks the WML for errors as part of this process, which is rigorous as WML is derived from XML and has strict syntax requirements.below image show the architecture of web getway..........