Wireless Access Points
A wireless access point is a device that connects a wireless (usually Wi-Fi) local network to a wired (usually Ethernet) network.
Wireless Application Protocol
The Wireless Application Protocol was defined to support content delivery to mobile devices over wireless networks. Central to the design of WAP was a network stack based on the OSI model. WAP implemented several new networking protocols that perform functions similar to but separate from the well-known Web protocols HTTP, TCP, and SSL. WAP included the concepts of browsers, servers, URLs, and network gateways. WAP browsers were built for small mobile devices such as cell phones, pagers, and PDAs. Instead of developing content in HTML and JavaScript, WAP developers used WML and WMLScript. Being constrained on both mobile network speeds and processing power of the devices, WAP supported only a small subset of the usages of a PC. Typical applications of these technologies were news feeds, stock quotes, and messaging. While a decent number of WAP-enabled devices existed in the market from 1999 through the mid-2000s, it did not take long for the technology to become obsolete with the rapid technological improvements in mobile networking and smartphones.
The WAP Model
The WAP model consists of five layers in a stack, from top to bottom: Application, Session, Transaction, Security, and Transport. WAP’s application layer is the Wireless Application Environment (WAE). WAE directly supports WAP application development with Wireless Markup Language (WML) instead of HTML and WMLScript instead of JavaScript. WAE also includes the Wireless Telephony Application Interface (WTAI, or WTA for short) that provides a programming interface to telephones for initiating calls, sending text messages, and other networking capabilities. WAP’s session layer is the Wireless Session Protocol (WSP). WSP is the equivalent to HTTP for WAP browsers. WAP involves browsers and servers just like the Web, but HTTP was not a practical choice for WAP because of its relative inefficiency on the wire. WSP conserves precious bandwidth on wireless links; in particular, WSP works with relatively compact binary data where HTTP works mainly with text data. Wireless Transaction Protocol (WTP) provides transaction-level services for both reliable and unreliable transports. It prevents duplicate copies of packets from being received by a destination, and it supports retransmission, if necessary, in cases where packets are dropped. In this respect, WTP is analogous to TCP. However, WTP also differs from TCP. WTP is essentially a pared-down TCP that squeezes some extra performance from the network. Wireless Transaction Layer Security (WTLS) provides authentication and encryption functionality analogous to Secure Sockets Layer (SSL) in Web networking. Like SSL, WTLS is optional and used only when the content server requires it. Wireless Datagram Protocol (WDP) implements an abstraction layer to lower-level network protocols; it performs functions similar to UDP. WDP is the bottom layer of the WAP stack, but it does not implement physical or data link capability. To build a complete network service, the WAP stack must be implemented on some low-level legacy interface not technically part of the model. These interfaces, called “bearer services” or “bearers,” can be IP-based or non-IP based.
