Before presenting the WAP programming model, we briefl y discuss the WWW model that is the basis for the WAP model.
The WWW Model
The Internet WWW architecture provides a fl exible and powerful programming model. Applications and content are presented in standard data formats, and are browsed by
applications known as web browsers. The web browser is a network application, i.e., it sends requests for named data objects to a network server and the network server responds with encoded data using the standard formats.
The WWW standards specify several mechanisms necessary to build a general-purpose
application environment which includes:
● Standard naming model. All servers and content on the WWW are named with an Internet-standard Uniform Resource Locator ( URL ).
● Content typing. All content on the WWW is given a specific type, thereby allowing web browsers to correctly process the content based on its type.
● Standard protocols. Standard networking protocols allow any web browser to communicate with any web server. The most commonly used protocol on the WWW
is the HTTP. This infrastructure allows users to easily reach a large number of thirdparty
applications and content services. It also allows application developers to easily create applications and content services for a large community of clients.
The WWW protocols defi ne three classes of servers:
1. Origin server: The server on which a given resource (content) resides or is to be created.
2. Proxy: An intermediary program that acts as both a server and a client for the purpose of making requests on behalf of other clients. The proxy typically resides between clients and servers that have no means of direct communication (e.g., across a firewall). Requests are ither serviced by a proxy program or passed on with possible translation to other servers. A proxy must implement both the client and the server requirements of WWW specifications.
3. Gateway: A server which acts as an intermediary for some other server. Unlike a proxy, a gateway receives requests as if it were the origin server for the requested resource. The requesting client may not be aware that it is communicating with a gateway.
The WAP Model
The WAP programming model is similar to the WWW programming model. This provides several benefits to the application developer community, including a familiar programming model, a proven architecture, and the ability to leverage existing tools (e.g.,
web servers, XML tools, etc.). Optimization and extensions have been made in order to match the characteristics of the wireless environment. Wherever possible, existing standards have been adopted or have been used as the starting point for the WAP technology.
WAP content and applications are specified in a set of well-known content formats based on WWW content formats. Content is transported using a set of standard communication
protocols based on WWW communication protocols. A microbrowser in the wireless terminal coordinates the user interface and is analogous to a standard web browser. WAP defines a set of standard components that enable communication between mobile terminals and network servers, including:
● Standard naming model : WWW-standard URLs are used to identify WAP content on origin servers. WWW-standard URLs are used to identify local resources in a device (e.g., call control functions).
● Content typing : All WAP content is given a specifi c type consistent with WWW typing. This allows WAP user agents to correctly process the content based on its type.
● Standard content formats : WAP content formats are based on WWW technology
and include display markup, calendar information, electronic business card objects,
images, and scripting language.
● Standard protocols : WAP communication protocols enable the communication of
browser requests from the mobile terminal to the network web server. The WAP
content types and protocols have been optimized for mass market, hand-held wireless
devices. WAP utilizes proxy technology to connect between the wireless domain and
The WAP proxy typically comprises the following functionality:
● Protocol gateway : The protocol gateway translates requests from the WAP protocol stack to the WWW protocol stack (HTTP and TCP/IP).
● Content encoders and decoders : The content encoders translate WAP content into compact encoded formats to reduce the size of data over the network. This infrastructure ensures that mobile terminal users can browse a wide variety of WAP content and applications, and that the application author is able to build content services and applications that run on a large base of mobile devices. The WAP proxy allows content and applications to be hosted on standard WWW servers and to be developed using proven WWW technologies such as cell global identity (CGI) scripting. While the nominal use of WAP includes a web server, WAP proxy, and WAP client, WAP architecture can easily support other confi gurations. It is possible to create an origin server that includes WAP proxy functionality. Such a server might be used to facilitate end-to-end security solutions, or applications that require better access control or a guarantee of responsiveness.
Source of Information : Elsevier Wireless Networking Complete 2010
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