Wireless Application Protocol, or WAP, is a set of technologies developed by a consortium of mobile telephony equipment vendors that is designed to bring Web content to wireless handheld communication devices such as Personal Digital Assistants (PDAs) and mobile phones. These devices are too small to easily display or allow users to interact with regular Web content. Wireless Application Protocol (WAP) enables them to receive simplified versions of regular Web pages. Typical uses for WAP-enabled devices might be to access stock market information, perform online banking, access inventory and sales information for sales quotes, and exchange information with business partners.
Graphic W-13. Wireless Application Protocol (WAP).
WAP is part of the Mobile Station Application Execution Environment (MExE) initiative from the European Telecommunications Standards Institute (ETSI) and is currently being tested by companies such as Alcatel, Nokia, and APiON.
The WAP protocol stack lies within layers 4, 5, 6, and 7 of the Open Systems Interconnection (OSI) reference model for networking. For addressing and routing purposes, WAP uses the same layer 3 (network layer) protocol as TCP/IP, namely the Internet Protocol (IP). This allows WAP-enabled devices to request and receive Web content from the Internet by using the Hypertext Transfer Protocol (HTTP). However, instead of using the connection-oriented Transmission Control Protocol (TCP), WAP uses the connectionless User Datagram Protocol (UDP) for layer 4 (transport layer) session establishment because UDP has less overhead than TCP and is thus more suitable for the limited transmission capabilities of wireless handheld devices.
WAP uses the Wireless Transaction Protocol (WTP) instead of HTTP for its connectionless layer 7 (application layer) protocol. In addition, WAP-enabled devices can display only content that is formatted using Wireless Markup Language (WML), a simplified version of Hypertext Markup Language (HTML) for handheld wireless devices that includes limited display capabilities.
To request Web content from the Internet, a WAP-enabled device makes a WTP request to a WAP gateway, a device that stands between the WAP devices and Web sites. The WAP gateway services the WTP request in one of two ways:
WAP gateways can also be configured for other uses, such as collecting personal information from customers and recording traffic for billing purposes.
WAP is designed primarily to enable Web content to be delivered over wireless communication systems, which are characterized by low speed and variable delays. Caching can be implemented on wireless handheld devices to minimize the amount of information that needs to be downloaded, but memory limitations currently prevent this from being very effective. You can use TCP header compression to reduce headers to only 3 or 4 bytes to speed up standard TCP/IP connections with these devices in order to boost performance a bit. You can adjust the TCP retransmission parameters to compensate for the typical round-trip time of 100 milliseconds to several seconds when users move through cells in wireless communication networks. But the TCP window size negotiation algorithm to optimize TCP transmission generally works poorly in situations where the typical delay varies so frequently and greatly. You can use middleware between the WAP device and the application server to simplify and streamline the data being transferred. Nevertheless, WAP has growing support in the cellular industry, especially because it shifts vendors toward the role of content hosting and development, which is a lucrative add-on in light of falling cellular line charges.