WAP is an open international standard for application layer network communications in a wireless communication environment. Its main use is to enable access to the Internet (HTTP) from a mobile phone or PDA.
A WAP browser provides all of the basic services of a computer based web browser but simplified to operate within the restrictions of a mobile phone, such as its smaller view screen. WAP sites are websites written in, or dynamically converted to, WML (Wireless Markup Language) and accessed via the WAP browser.
Before the introduction of WAP, service providers had extremely limited opportunities to offer interactive data services. Interactive data applications are required to support now commonplace activities such as:
- Email by mobile phone
- Tracking of stock market prices
- Sports results
- News headlines
- Music downloads
The Japanese i-mode system is another major competing wireless data protocol.
Protocol design lessons from WAP
The original WAP was a simple platform for access to web-like WML services and e-mail using mobile phones in Europe and the SE Asian regions and continues today with a considerable user base. The later versions of WAP were primarily for the United States region and was designed for a different requirement - to enable full web XHTML access using mobile devices with a higher specification and cost, and with a higher degree of software complexity.
There has been considerable discussion about whether the WAP protocol design was appropriate. Some have suggested that the bandwidth-sparing simple interface of Gopher would be a better match for mobile phones and Personal digital assistants (PDAs).
The initial design of WAP was specifically aimed at protocol independence across a range of different protocols (SMS, IP over PPP over a circuit switched bearer, IP over GPRS, etc). This has led to a protocol considerably more complex than an approach directly over IP might have caused.
Most controversial, especially for many from the IP side, was the design of WAP over IP. WAP's transmission layer protocol, WTP, uses its own retransmission mechanisms over UDP to attempt to solve the problem of inadequacy using TCP over high packet loss networks.
The Wireless Application Protocol is a standard developed by the WAP Forum, a group founded by Nokia, Ericsson, Phone.com (formerly Unwired Planet), and Motorola. The WAP Forum’s membership roster now includes computer industry heavyweights such as Microsoft, Oracle, IBM, and Intel along with several hundred other companies. According to the WAP Forum, the goals of WAP are to be:
- Independent of wireless network standard.
- Open to all.
- Proposed to the appropriate standards bodies.
- Scalable across transport options.
- Scalable across device types.
- Extensible over time to new networks and transports.
As part of the Forum’s goals, WAP will also be accessible to (but not limited to) the following:
- GSM-900, GSM-1800, GSM-1900
- CDMA IS-95
- TDMA IS-136
- 3G systems - IMT-2000, UMTS, W-CDMA, Wideband IS-95
WAP defines a communications protocol as well as an application environment. In essence, it is a standardized technology for cross-platform, distributed computing. Sound similar to the World Wide Web? If you think so, you’re on the right track! WAP is very similar to the combination of HTML and HTTP except that it adds in one very important feature: optimization for low-bandwidth, low-memory, and low-display capability environments. These types of environments include PDAs, wireless phones, pagers, and virtually any other communications device.
The remainder of this overview will concentrate on presenting WAP from a software developer’s perspective so that other software developer’s can be quickly brought up to speed. Other documents on this site go into much greater detail on development specifics including in-depth reviews and demonstrations using a variety of vendor packages.
How Does It Work?
A WAP request is routed through a WAP gateway which acts as an intermediary between the “bearer” used by the client (GSM, CDMA, TDMA, etc.) and the computing network that the WAP gateway resides on (TCP/IP in most cases). The gateway then processes the request, retrieves contents or calls CGI scripts, Java servlets, or some other dynamic mechanism, then formats data for return to the client. This data is formatted as WML (Wireless Markup Language), a markup language based directly on XML. Once the WML has been prepared (known as a deck), the gateway then sends the completed request back (in binary form due to bandwidth restrictions) to the client for display and/or processing. The client retrieves the first card off of the deck and displays it on the monitor.
The deck of cards metaphor is designed specifically to take advantage of small display areas on handheld devices. Instead of continually requesting and retrieving cards (the WAP equivalent of HTML pages), each client request results in the retrieval of a deck of one or more cards. The client device can employ logic via embedded WMLScript (the WAP equivalent of client-side JavaScript) for intelligently processing these cards and the resultant user inputs.
To sum up, the client makes a request. This request is received by a WAP gateway that then processes the request and formulates a reply using WML. When ready, the WML is sent back to the client for display. As mentioned earlier, this is very similar in concept to the standard stateless HTTP transaction involving client Web browsers.
