PRO WAP,: With WML, WMLScript, ASP, JSP, XML, XSLT, WTA, Push and VoiceXML (Programmer to programmer) - Softcover

Über die Autorin bzw. den Autor

Charles Arehart Charlie Arehart is a veteran information systems developer, educator, and industry analyst with nearly 20 years experience. His company, SysteManage, is a web application development firm now focusing on wireless applications.

Nirmal Chidambaram Nirmal Chidambaram works for Geologik Software and his main area of interest is in developing Multi-Modal interfaces. He is also currently developing GeoXML, a XML vocabulary for representation of geological data.

Shashikiran Guruprasad Shashikiran Guruprasad is currently working with Silicon Automation Systems in Bangalore, India and has been involved in the development of Nortel Networks' GSM/GPRS products for more than two years now.

Alex Homer Alex Homer is a software consultant and developer, who lives and works in the idyllic surroundings of Derbyshire UK. His company, Stonebroom Software, specializes in office integration and Internet-related development, and produces a range of vertical application software.

Ric Howell Ric Howell is Chief Technology Officer for Concise Ltd, a London-based business and software consultancy serving Financial, Insurance and Banking markets. He provides consultancy for clients on enterprise IT Architecture and the utilization of technology in meeting corporate strategy.

Stephan Kasippillai Stephan is a senior management consultant and has been following developments in the world of mobile computing and wireless technology for several years. His role as Principal Consultant with the Concise Group involves the conception, development and deployment of leading edge wireless solutions for the Investment Banking and Asset Management industries.

Rob Machin Rob Machin graduated from Durham University in 1994 with a First in Mathematics and Philosophy. Since then he has discarded Fermat and Sartre, and become a specialist in mobile commerce, n-tier systems architecture and new technologies, developing object-oriented software using both Smalltalk and Java. He is currently working as a Technical Consultant with the Concise Group Ltd.

Tom Myers Tom has a BA (cum laude), St. John's College, Santa Fe, New Mexico ("Great Books'' program), 1975 and a PhD in computer science from the University of Pennsylvania, 1980. He taught computer science at the University of Delaware and Colgate before becoming a full-time consultant and software developer.

Alexander Nakhimovsky Alexander Nakhimovsky received an MA in mathematics from Leningrad University in 1972 and a PhD in general linguistics from Cornell in 1978, with a graduate minor in computer science. He taught general and Slavic linguistics at Cornell and SUNY Oswego before joining Colgate's computer science department in 1985.

Luca Passani Luca is an Italian IT-professional who lives in Oslo, Norway. He has extensive experience with client-side and server-side scripting in web technologies. Over the past year he has been working extensively with WAP.

Chris Pedley Chris joined a software company based in Oxfordshire last year undertaking a year's industrial placement as part of a degree in Computer Science from the University of York. His first task at the company was to look at the new technology of WAP, which proved to be very relevant to many business areas of the company. Since then, he has worked on WAP solutions for a variety of different purposes ranging from banking information to healthcare solutions.

Richard Taylor Richard Taylor is the co-founder of Poqit.com, a WAP development consultancy and content conversion specialist. Prior to this, Richard has coded and project-managed his way through every computing fad since 1982, and has worked in the object-oriented field for the past 8 years.

Marco Toschi Marco is an Italian engineer who has been working for two and a half years in Oslo as a consultant for Consafe Infotech, an international consultancy company based in Sweden. During the last two years, he has been developing Internet and mobile solutions for Scandinavian telecom operators and companies using the latest technologies available, such as Java, WAP and GPRS.

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In the preceding chapters, we have discussed various aspects of WAP that enable content to be delivered to a wireless device, but only when the user of such a device requests or "pulls" the content from the network. In other words, the content is constantly present in the network, but the user only gets to view it if they request it, for example by using a browsing application on the mobile device.

However, when we look at real-life applications, we realize that there is a lot of information that is useful to a user, but which a user does not see because they do not know when it is available or when there is a change in the status of the information. Such information ideally needs to be "pushed" to the user either at predefined intervals or when certain events occur that would then make the information useful to the user. Some examples of possible push situations are arrival of new emails, stock market information, multi-user game updates, and so on.

Unlike the Internet, the push model for WAP has been well defined as a complete framework for delivering content to a user in an asynchronous manner without the user being required to request the information. This was done for the first time in the WAP 1.2 specifications. The definition should make implementations of push standardized and independent of vendor. Also in comparison to the Internet, where the users can be away from their computers for substantial periods, WAP content is targeted towards personal devices that users usually have with them. Therefore, it makes a lot more sense to have a standardized push model in WAP; it is more likely to succeed than its counterpart on the Internet. In addition, the perhaps expected rivalry between mechanisms like e-mail and push is not there. In fact, the WAP push model assumes the arrival of e-mails would be notified to the user using push, so that they could then make a decision on whether to download it.

As a matter of fact, push services already exist in mobile phone networks, using the well-known Short Message Service (SMS) and the Cell-Broadcast mechanism in GSM networks. Many users already have dozens of messages sent to their mobile phones, which information on key news items, scores from a sports game or that a new message has arrived in the user's voice mailbox. There is, however, a very important element missing in all these services; the service is not interactive.

For example, currently if you receive notification that you have a voicemail, you still need to dial the number that gives you access to your voicemail separately. No interactive mechanisms exist that offers you a menu of choices to act upon your voicemail in an interactive manner as soon as the notification has arrived.

Consider another example, where you have registered with your online investment broker to provide you with short messages as soon as a certain stock price crosses a threshold (defined by you). On receiving the information, if you choose to buy or sell the particular stock, you will need to separately communicate with your broker to place the order, as would be the case in SMS. On the other hand, if this whole transaction was defined using WAP push technologies, it could be combined with a menu option to follow a link to a site where you can buy or sell stock.

It is therefore important to make a distinction between (1) SMS and Cell-Broadcast services that have already been widely deployed to push pager-like text messages to users, and (2) WAP based push services that use SMS or Cell-Broadcast as the bearer to transmit packets over the wireless network. In this case, SMS or Cell-Broadcast can become a viable WAP bearer that would not only use existing network infrastructure but also provide the required interactive behavior that characterizes WAP based push.

Push services in wireless networks offer a definite advantage over their Internet counterpart, which is, location based push content. Because we can discover the users location, it opens up an opportunity to provide local content and information. For example, tourist or hotel information specific to a particular geographical area can be pushed to wireless device users in that area. This is clearly impossible in Internet based push.

We'll now take a closer look at the framework that defines the new push technologies. Within this framework, the protocols used by the origin server that initiates the push of content are separated from the protocols used in the WAP domain. This is achieved by placing an intermediary known as the Push Proxy Gateway (PPG) between the push origin server known as the Push Initiator (PI) and the WAP client on the wireless device. Note that it is possible to draw similarities between the WAP pull model that we have seen in the previous chapters and the push framework. The most obvious similarity is that, both models use an intermediary, and mostly for similar reasons.

The Push Access Protocol (PAP), used between the PI and the PPG, is designed to work on top of one of the application level protocols, like HTTP or SMTP on the Internet. In other words, PAP is tunneled over a commonly available application layer protocol on the Internet. In this chapter, we will assume that a HTTP POST mechanism is used for tunneling PAP messages. However, this doesn t mean that a PPG implementer cannot devise a way to use SMTP. The specifications only suggest some mechanisms for the tunneling and an implementer could always use a different mechanism and still be standards compliant.

The Push Over-the-Air (OTA) protocol, on the other hand, which is used between the PPG and the wireless device, is implemented on top of the WSP layer of the WAP stack of protocols.

The Push Proxy Gateway (PPG) has to implement the entire WAP protocol stack, in addition to the above two push specific protocols, PAP and push OTA. It therefore makes sense to have push functionality as a component or add-on for a WAP gateway.

Many of the protocols, as well as some of the content, in the push framework are applications of XML. For example, PAP is an XML language. It is therefore reasonably easy for PPG and PI implementers to implement most of their functionality, because XML parser libraries are very commonly and freely available.

We will look at the protocols used in the push framework in some detail later in this chapter.