WAP Architecture - Part III

The WAP Model

The WAP programming model (Figure 2) is the WWW programming model with a few enhancements. Adopting theWWW programming model provides several benefits to the application developer community, including a familiarprogramming model, a proven architecture, and the ability to leverage existing tools (e.g., Web servers, XML tools,etc.). Optimisations 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 WAPtechnology.

The most significant enhancements WAP has added to the programming model are:

· Push

· Telephony Support (WTA)





The classical request-response mechanism is commonly referred to as pull to contrast it with the push mechanism.

WAP content and applications are specified in a set of well-known content formats based on the familiar WWW contentformats. Content is transported using a set of standard communication protocols based on the WWW communicationprotocols. The WAP microbrowser in the wireless terminal co-ordinates the user-interface and is analogous to astandard 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. WWWstandardURIs are used to identify local resources in a device, e.g. call control functions.

· Content typing – All WAP content is given a specific type consistent with WWW typing. This allows WAP useragents 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 communication protocols – WAP communication protocols enable the communication of browserrequests from the mobile terminal to the network web server.

The WAP content types and protocols have been optimised for mass market, hand-held wireless devices.


Feature/Performance-Enhancing Proxies

WAP utilises proxy technology to optimise and enhance the connection between the wireless domain and the WWW.

The WAP proxy may provide a variety of functions, including:

· Protocol Gateway – The protocol gateway translates requests from a wireless protocol stack (e.g., the WAP 1.xstack—WSP, WTP, WTLS, and WDP) to the WWW protocols (HTTP and TCP/IP). The gateway also performsDNS lookups of the servers named by the client in the request URLs.

· Content Encoders and Decoders – The content encoders can be used to translate WAP content into a compactformat that allows for better utilisation of the underlying link due to its reduced size.

· User Agent Profile Management – User agent profiles describing client capabilities and personal preferences[UAProf] are composed and presented to the applications.

· Caching Proxy – A caching proxy can improve perceived performance and network utilisation by maintaining acache of frequently accessed resources.

This infrastructure ensures that mobile terminal users can access a wide variety of Internet content and applications, andthat application authors are able to build content services and applications that run on a large base of mobile terminals.

The WAP proxy allows content and applications to be hosted on standard WWW servers and to be developed usingproven WWW technologies such as CGI scripting.

While the nominal use of WAP will include a web server, WAP proxy and WAP client, the WAP architecture can quiteeasily support other configurations.