WAP Communication Protocol
2.2.4 WAP Communication Protocol
The proposal of WAP (Wireless Application Protocol) is based on the need of connecting mobile phones into the Internet. In June 1997, PHONE.COM, together with Nokia, Ericsson and Motorola, began to establish the WAP forum, the aim of which was to make a unified standard for the Internet business operated by
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mobile communication suppliers. In September 1997, WAP forum published the first WAP standard infrastructure. In the next May, WAP 1.0 was formally developed. Then version 1.1 was published in June 1999.
After the establishment of WAP forum, it has received wide attention. Now there are more than 200 companies that have become the members of the forum, including major telecom operators, equipment manufacturers and software providers. Since the members of the WAP forum represent 95% of the global mobile markets, the WAP regulations thus formulated have to enable equipments produced by different manufacturers to realize mutual inter-connection. Thus WAP is becoming a widely accepted standard for wireless network interconnection.
WAP has provided a set of open and unified technical platforms. It is easy for users to access and obtain, through mobile agents, information and services in a unified format, as illustrated in Fig. 2.6.
Figure 2.6 WAP infrastructure WAP defines a set of interfaces for both hardware and software. The mobile
agents and web servers that implement these interfaces will make it possible for us to receive and send e-mails, and even browse the Internet by using cell phones.
WAP supports mobile terminals, which have relatively weak CPU, small memory, limited power supply and input. As for the network, WAP also supports the existing networks, including GSM, CDMA and PHS. It also supports the third generation mobile communication system. However, compared with general network, the bandwidth of wireless network is always restricted. Considering these factors, WAP takes full advantage of the Internet, and makes certain modifications and simplification. That is, applications and network contents are represented in the standard data format; micro browsers similar to that of a PC are used, thereby enabling network surfing in standard communication mode.
WAP standard defines an application environment, which allows the designers to develop user interface independent of equipments and use the WMLScript to embed executables to mobile terminals. Actually, a micro browser is running at the mobile terminal, which resembles the browser used on PCs.
The WAP application environment in its general sense is an application development framework, which guarantees efficient development and application
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of WAP on different wireless communication networks. This framework is primarily based on the existing Internet technologies.
The structure of WAP application is similar to the Internet structure, and a typical WAP application has defined three kinds of entities:
(1) Mobile client with WAP user agent. Typical clients like WAP cell phones equal the PC in the Internet in that there is a micro browser running on their screens. The user can simply use selected keys to send WAP service request, and receive the response information wirelessly. WAP mobile terminal uses WML (Wireless Markup Language) to display text and image. WML is a language based on XML, primarily used to mark up the Internet information and user interface. WML enables the designer to define WAP application interface in a device-independent way.
(2) WAP agent It includes the protocol gateway, the transformation between WAP protocol
stack (WSP, WTP, WTLS and WDP) and the Internet protocol stack. Content Encoders and Decoders compress and encode the WAP data to reduce data flow and make full use of the wireless network bandwidth. Meanwhile, WAP adopts error correction technology to ensure that web surfing and data transmission will not be affected by the quality of the wireless communication.
(3) Data source servers, such as websites that supports WAP, the servers of which contain WAP applications coded by WMLScript. These applications can
be downloaded to the WAP client if needed, and uninstalled when not needed anymore.
WMLScript can supplement some restrictions of WML, such as inability to check the validity of user input. This enhances the browsing and representing functions of WML, allowing users’ operations to be more flexible and intelligent. At certain moments, WMLScript can process some warning messages on the mobile agent, thereby avoiding data transmission between mobile client and remote server, which reduces the cost of bandwidth.
The protocol stack of WAP is a hierarchically designed environment for the development of application system. Interface is defined for each layer, and is able to be used by the upper layer protocol and by other services or applications directly. WAP has borrowed the idea of the Internet protocol stack and made it simpler, which makes it more applicable in wireless environment.
(1) WSP (Wireless Session Protocol): The session layer protocol provides connection oriented, WTP-based session service or WDP-based, connectionless and reliable services.
(2) WTP (Wireless Transaction Protocol): Provides a light-weight and transaction- oriented service, which specializes to optimize and adapts to the design of mobile agent.
(3) WTLS (Wireless Transport Layer Security): SSL-based secure transmission protocol.
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(4) WDP (Wireless Datagram Protocol): Is a universal data transmission service supporting multiple networks, making WAE, WSP, WTP and WTLS in the upper layer independent of lower layer wireless network. Of course, the data transmitted and the nature of user interaction will surely influence the operator’s choice of the network to maximize the efficiency.
Apart from WAE and protocols, WAP standard also defines WTA (Wireless Telephony Applications), and therefore WAP can be used in the existing telecom operations, such as intelligent network. Using the user interface in the form of browser, mobile users can apply various operations without modifying mobile terminals. The WAP mobile agent uses WML and two kinds of WAP servers: WAP agent server and WTA server. WAP agent translates the WAP requests into www requests, thus mobile terminals can send www requests to web servers, WAP agent then translates the responses from web server into compressed binary WML data understandable to mobile terminals. If the web server supports WML format, WAP agent can get data directly from web server; if web database only supports html, then it can be transformed into WML via html filter, and then transmitted to web agent. WTA server can provide WAP users with various advanced intelligent network services.
WAP has created a business opportunity, which makes the existing or new businesses accessible to users at any moment, regardless of the location of the user. Since WAP is an open and unified technical standard and is independent of networks, it enables all mobile manufacturers to produce compatible products, and telecom ISPs can select products from a wide range. The whole telecom industry thus avoids redundant construction due to this universal standard.
WAP is commonly applied on WAP mobile terminals to connect directly to the Internet, receive and send e-mails or browse other information.
The biggest potential application of WAP is its combination with e-commerce to realize mobile e-commerce, such as real-time securities trading, mobile banking business, and mobile online shopping. In the near future, you may only need a WAP cell phone to manage all that you need carry with you a wallet, a telephone book, credit cards and mobiles to accomplish.