The WAE defines the application environment, which operates on
the mobile device, largely in terms of services and content
formats.
The architecture of the WAE presumes the existence of user
agents for interpreting the content referenced by a URL. User
agents are required for handling two types of content: the
microbrowser for rendering the WML and the virtual machine for
execution of the WMLScript. WMLScript also includes a number of
standard libraries that provide native implementations of common
functions. The specification itself does not mandate a specific
implementation or specify any particular user agent.
The WAE provides support for a number of standard content types,
including vCard and vCalendar, for communicating
phonebook and calendar information between applications, and
WBMP, which is a wireless bitmap format.
The Wireless Telephony API provides a mechanism to interact with
the device itself and with services and facilities that may be
available on the operators network, for example, the ability to
access the phone book on a mobile phone.
Wireless Session Protocol
The WSP is responsible for managing the session between the
mobile device and the server, and it provides a generalized session
management capability. This includes the ability to suspend and
resume sessions, which is an important feature of WAP, because
connections may be dropped and need reconnecting at a later point
in time to continue the session from where it was left off. We have
all experienced poor quality reception with mobile phones,
connections that drop in mid-sentence, and the classic situation of
driving down the road and out of the reception area of the cell. It
also provides support for long-lived sessions.
The capability of mobile devices varies significantly, so it
follows that the server cannot treat all devices the same way. Part
of the session setup process is the negotiation of the nature of
the session and the capability of both the participants.
WSP supports both connection-oriented and connectionless
sessions, where the connectionless session does not have the
overhead of session setup and tear down. Connection-oriented
sessions run over WTP, while connectionless sessions use WDP
directly.
The encoding and decoding of content is also handled at this
level.
Wireless Session Protocol/Browsing
The browsing extensions to WSP add features that are suited to
the way that the protocol is likely to be used - browsing WAP
sites. The semantics are based on HTTP 1.1. It includes features
such as the transmission of session and content headers and the
encoding of those headers to make them more efficient for
over-the-air-transmission. The content headers (also called Accept
headers) define the character sets, language and the user agent
profile, which defines the characteristics of the device. The user
agent profile information must be passed through to the origin
server.
It also provides some push capabilities, which are part
of the push framework of WAP 1.2. Three levels of push capability
are defined: confirmed push within a session context, non-confirmed
push within a session, and non-confirmed push without a session.
There is also support for asynchronous requests.
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