Network Programming: WAP architecture & WAP services

Wireless Application Protocol -

The Wireless Application Protocol (WAP) is a worldwide standard for the delivery and presentation of wireless information to mobile phones and other wireless devices. The idea behind WAP is simple: simplify the delivery of Internet content to wireless devices by delivering a comprehensive, Internet-based, wireless specification. The WAP Forum released the first version of WAP in 1998. Since then, it has been widely adopted by wireless phone manufacturers, wireless carriers, and application developers worldwide. Many industry analysts estimate that 90 percent of mobile phones sold over the next few years will be WAP-enabled.

WAP architecture
WAP services

Fig3. WAP Architecture

1. WAP Architecture

i. It provides a scalable and extensible environment for application development of mobile
ii. This is achieved using layered design of protocol stack. The layers resemble the layers of OSI model.
iii. Each layer is accessible by layers above as well as by other services and applications through a set of well defined interface.
iv. External applications may access session, transaction, security and transport layers directly.

2. Wireless Application Environment

i. WAE is the uppermost layer in the WAP stack. It is general purpose environment based on combination of WWW and mobile telephony technologies.
ii. Its primary objective is to achieve interoperable environment that allows operators and service providers to build applications that can reach wide variety of wireless platforms.
iii. It uses URL and URI for addressing. Language used is WML and WML script. WML script can be used for validation of user input.

3. Wireless Telephony Application

i. WTA provides a means to create telephony services using WAP. It uses WTA Interface (WTAI) which can be evoked from WML and for WML script.
ii. The Repository makes it possible to store WTA services in device which can be accessed without accessing the network. The access can be based on any event like call disconnect, call answer etc.
iii. Sometimes, there can be notification to user based on which WTA services are accessed by users. The notification is called WTA service indication.

4. Wireless Session Protocol.

i. WSP provides reliable, organized exchange of content between client and server.
ii. The core of WSP design is binary form of HTTP. All methods defined by HTTP 1.1 are supported.
iii. Capability negotiation is used to agree on common level of protocol functionality as well as to agree on a set of extended request methods so that full compatibility to HTTP applications can be retained.
iv. An idle session can be suspended to free network resources and can be resumed without overload of full-blown session establishment.
v. WSP also supports asynchronous requests. Hence, multiple requests will improve utilization of air time.

5. Wireless Transaction Protocol

i. WTP is defined as light-weight transaction-oriented protocol suitable for implementation in thin clients.
ii. Each transaction has unique identifiers, acknowledgements, duplicates removal and retransmission.
iii. Class 1 and Class 2 enable user to confirm every received message, however, in class 0, there is no acknowledgement.
iv. WTP has no security mechanisms and no explicit connection set-up or tear-down phases.

6. Wireless Transport Layer Security

i. WTLS is security protocol based on industry standard transport layer security (TLS). It provides transport layer security between a WAP client and the WAP Gateway/ Proxy.
ii. The goals of WTLS are data integrity, privacy, authentication, Denial-of-service protection.
iii. It has features like datagram support, optimized handshake and dynamic key refreshing.

7. Wireless Datagram Protocol

i. WDP provides application addressing by port numbers, optional segmentation and reassembly, optional error detection.
ii. It supports simultaneous communication instances from higher layer over a single underlying WDP bearer service. The port number identifies higher level entity above WDP.
iii. The adaptation layer of WDP maps WDP functions directly on to a bearer based on its specific characteristics.
iv. On the GSM SMS, datagram functionality is provided by WDP.

8. Optimal WAP Bearers

i. The WAP is designed to operate over a variety of different service like SMS,’ Circuit Switched Data (CSD)’, GPRS,’ Unstructured Supplementary Services Data(USSD)’.

2. WAP services

In addition to a new protocol stack, WAP 2.x introduced many other new features and services. These new features expand the capabilities of wireless devices and allow developers to create more useful applications and services. The following is a summary of the features of interest:

WAP Push. WAP Push enables enterprises to initiate the sending of information on the server using a push proxy. This capability was introduced in WAP 1.2, but has been enhanced in WAP 2.x. Applications that require updates based on external information are particularly suited for using WAP Push. Examples include various forms of messaging applications, stock updates, airline departure and arrival updates, and traffic information. Before WAP Push was introduced, the wireless user was required to poll the server for updated information, wasting both time and bandwidth.
User Agent Profile (UAProf). The UAProf enables a server to obtain information about the client making the request. In WAP 2.x, it is based on the Composite Capabilities/Preference Profiles (CC/PP) specification as defined by the W3C. It works by sending information in the request object, allowing wireless servers to adapt the information being sent according to the client device making the request.
External Functionality Interface (EFI). This allows the WAP applications within the WAE to communicate with external applications, enabling other applications to extend the capabilities of WAP applications, similar to plug-ins for desktop browsers.
Wireless Telephony Application (WTA). The WTA allows WAP applications to control various telephony applications, such as making calls, answering calls, putting calls on hold, or forwarding them. It allows WAP WTA-enabled cell phones to have integrated voice and data services.
Persistent storage interface. WAP 2.x introduces a new storage service with a well-defined interface to store data locally on the device. The interface defines ways to organize, access, store, and retrieve data.
Data synchronization. For data synchronization, WAP 2.x has adopted the SyncML solution. As outlined in Chapter 10, "Enterprise Integration through Synchronization," SyncML provides an XML-based protocol for synchronizing data over both WSP and HTTP.
Multimedia Messaging Service (MMS). MMS is the framework for rich-content messaging. Going beyond what is possible for SMS, MMS can be used to transmit multimedia content such as pictures and videos. In addition, it can work with WAP Push and UAProf to send messages adapted specifically for the target client device.