WWW Programming Model

WWW Model The Internet WWW architecture provides a flexible 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 content formats. – All web browsers support a set of standard content formats. – These include (HTML), JavaScript scripting language (ECMAScript, JavaScript), and a large number of other formats. 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 third party 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 define 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. - It resides between clients and servers that have no means of direct communication (e.g., across a firewall). - Requests are either 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 Internet Model:

Here WWW client request a resource stored on a web server. On the Internet standard communication protocols, like HTTP and Transmission Control Protocol/Internet Protocol (TCP/IP) are used. The content available at the web server may be static or dynamic. Static content is produced once and not changed or updated very often; for example, a company presentation. Dynamic content is needed when the information provided by the service changes more often; for example, timetables, news, stock quotes, and account information. Technologies such as Active Server Pages (ASP), Common Gateway Interface (CGI), and Servlets allow content to be generated dynamically.

The WAP Model The WAP programming model is similar to the WWW programming model. Purpose of WAP: To enable easy, fast delivery of relevant information and services to mobile users. Type of devices that use WAP: Handheld digital wireless devices such as mobile phones, pagers, two-way radios, smart phones and communicators -- from low-end to high-end. WAP works with most Wireless networks such as: CDPD, CDMA, GSM, PDC, PHS, TDMA, FLEX, ReFLEX, iDEN, TETRA, DECT, DataTAC, Mobitex.

The WAP Model WAP Gateway/Proxy is the entity that connects the wireless domain with the Internet. The request that is sent from the wireless client to the WAP Gateway/Proxy uses the Wireless Session Protocol (WSP). A mark-up language – It has been adapted to develop optimized WAP applications to save valuable bandwidth in the wireless network, it can be encoded into a compact binary format.

How WAP Model Works? The user selects an option on their mobile device that has a URL with Wireless Markup language (WML) content assigned to it. The phone sends the URL request via the phone network to a WAP gateway using the binary encoded WAP protocol. The gateway translates this WAP request into a conventional HTTP request for the specified URL and sends it on to the Internet. The appropriate Web server picks up the HTTP request. The server processes the request just as it would any other request. If the URL refers to a static WML file, the server delivers it. If a CGI script is requested, it is processed and the content returned as usual.

How WAP Model Works? The Web server adds the HTTP header to the WML content and returns it to the gateway. The WAP gateway compiles the WML into binary form. The gateway then sends the WML response back to the phone. The phone receives the WML via the WAP protocol. The micro-browser processes the WML and displays the content on the screen.

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 WWW.

Disadvantages: Small screens: For web phones, there's an incredibly small viewing area; palmtops are barely better. Speed of access: All devices have slow access. Limited or fragmented availability: Wireless web access is sporadic in many areas and entirely unavailable in other areas. Price: Many technology limitations are being addressed by higher-end devices and services. Lack of user habit: It takes some patience and overcoming the learning curve to get the hang of it -- connecting, putting in an address, typing. Users just aren't used to the idea and protocol yet.