Wireless Application Protocol (WAP) provides
a standard for the presentation and delivery of wireless information
and telephony services on mobile phones and other mobile terminals.
It was fully specified in 1997 using many of the existing standards
from telephony manufacturers, such as Ericsson, Nokia or Motorola
(who joined the WAP Forum). This group has since defined global
wireless protocol specifications, based on existing Internet standards
such as XML and IP, for all wireless networks. It has the following
- Integrate Internet content and advanced data services for wireless
phones and other wireless terminals.
- Define a global wireless protocol specification which supports
existing wireless network technologies.
- Define and extend existing standards.
- Support the creation of content and applications that can be
scaled across a wide range of wireless networks and devices types.
WAP has a similar architecture to the global Internet. Like the
HTTP protocol, WAP uses the concept of a browser, which is included
inside the mobile phone. This delivers the content and is adapted
to support the special environment with a mobile phone. The main
differ-ence between common WWW technology and WAP is a gateway
(sometimes called proxy), which bridges the GSM network and Internet.
Mobile devices are typically grouped into three main classifications:
- Mobile phones.
- PDA (Personal Data Assistant).
- HPC (Hand-held PC).
As these devices typically have limited resources, in terms of
memory, processing power and graphical displays, the browser supports
two types of simplified mark-up languages: WML and WMLScript Given
that the terminals have small resources (CPU or memory). Typically
the micro browser is either initially installed or, with a PDA
and HPC, can downloaded on the terminal. The mobile client is
an important key element in the WAP environment as it allows interacting
directly with the user and keeps the data transferred confidential.
An important part of the WAP framework is the link between the
WML content server and the GSM operator. This is illustrated in
Figure 1. The WML page typical resides on a standard WWW server.
This makes it easy to setup WML pages.
When mobile terminal makes a request for a page, the request
is sent through the GSM network to a gateway. This then transforms
the request into a standard HTTP request, and passes it onto the
content server (in the same way that a normal HTTP request would).
The gateway is thus responsible for checking the integrity of
the content format, for its WML content, and to compress the data
before to send it back to the mobile terminal.
The gateway thus makes the WAP device look like any other WWW-access
device. It can thus use most of the standard protocols, such as
HTTP and SSL, and standard WWW servers.
Figure 1: WAP architecture
WAP uses a layer approach to its protocols.
" Wireless Application Environment (WAE).
" Wireless Session Protocol (WSP). This layer defines the
services which can be used by the micro browser. There are two
main modes: connected or non-connected. WSP is mainly responsible
for data confirmation.
" Wireless Transaction Protocol (WTP). This layer is transaction
oriented, and has the following functions: transaction services
classes; asynchronous transaction; and con-catenation and acknowledgement
" Wireless Transport Layer Security (WTLS). This is based
on SSL (Secure Sockets Layer). It is designed to support networks
with limited bandwidth, and provides the following functions:
data integrity; private channel; and authentication.
" Wireless Datagram Protocol (WDP). This is responsible for
the transport process be-tween a mobile terminal and the gateway.
It is independent from the speed of data transfer, so that it
can support any type of network, such as SMS, GSM, and GPRS. Its
main function is to provide the upper layers with a network independent
access to a network.