WAP INTERNAL STRUCTURE
Introduction
Wireless Application Protocol (WAP)
is a communications protocol that formats Web data for transmission over
wireless Internet connections, letting you surf with a mobile phone or other
wireless device. If access to e-mail and the Web is critical to your mental and
fiscal well-being, you need to know about the Wireless Application Protocol.
Using a wireless Web service and a mobile phone, pager, or other wireless
device that supports WAP, you can tap into the Web from almost anywhere,
vendors claim. Faster wireless Internet access and an increasing number of Web
sites that support WAP mean that wireless Web surfing could be the wave of the
future. WAP specification enables development of applications that can
offer services like e-mail, web browsing, on-line shopping, on-line banking,
on-line ticketing, stock quotes, etc., to an end user on his or her mobile
phone.
WAP INTERNAL
STRUCTURE
The
basic construction of WAP architecture can be explained using the following model.
The order of the independent levels – which are a hierarchy - has the advantage
that the system is very flexible and can be scaled up or down. Because of the
different levels – or stacks - this is called the "WAP Stack", which
is divided into 5 different levels.
- Application Layer: Wireless Application Environment (WAE).
- Session Layer: Wireless Session Protocol (WSP).
- Transaction Layer: Wireless Transaction Protocol (WTP).
- Security Layer: Wireless Transport Layer Security (WTLS).
- Transport Layer: Wireless Datagram Protocol (WDP).
WAP INTERNAL
STRUCTURE
Application Layer
(WAE and WTA)
The environment for wireless
applications (Wireless Application Environment WAE) and the application for
wireless phones (Wireless Telephony Application WTA) are the highest layer in
the hierarchy of WAP architechture. These two are the main interface to the
client device, which gives and controls the description language, the script
language of any application and the specifics of the telephony. WAE and WTA
have only a few easy functions on the client device, like the maintenance of a
history list, for example.
WAE
The Wireless Application
Environment (WAE) is the top most level in the Wireless Application Protocol
(WAP) suite, which combines both the WWW and Mobile Telephony technologies. WAE
provides the operators and service providers an interoperable environment on
which they can build applications and services for handheld client devices. WAE
includes the micro-browser that contains functionality for using not only WML
and WML Script , but also Wireless Telephony Application, namely WTA and WTAI
-- telephony services and programming interfaces as well as content formats
including well-defined data formats, images, phone book records and calendar
information.
Session Layer
(Wireless Session Protocol WSP)
The Wireless Session Protocol (WSP)
has all the specifications for a session. It is the interface between the
application layer and the transfer layer and delivers all functions that are
needed for wireless connections.
A session mainly consists of 3 phases:
- · Start of the session,
- · Transfering information back and forth
- · End of the session.
Additionally, a session can be
interrupted and started again (from the point where it was interrupted.)
WSP
The Session layer protocol family
in the WAP architecture is called the Wireless Session Protocol, WSP. WSP
provides the upper-level application layer of WAP with a consistent interface
for two session services. The first is a connection-mode service that operates
above a transaction layer protocol WTP, and the second is a connectionless
service that operates above a secure or non-secure datagram transport service.
The Wireless Session Protocols
currently offer services most suited for browsing applications. WSP provides
HTTP 1.1 functionality (it is a binary form of HTTP) and incorporates new
features such as long-lived sessions, a common facility for data push,
capability negotiation and session suspend/resume. The protocols in the WSP
family are optimized for low-bandwidth bearer networks with relatively long
latency. Requests and responses can include both headers and data. WSP provides
push and pull data transfer WSP functions on the transaction and datagram
services.
Messages can be in connection mode
or connectionless. Connection mode messages are carried over WTP. In this case
the protocol consists of WTP protocol messages with WSP PDUs as their data.
Connectionless messages consist only of the WSP PDUs.
The general structure of the WSP
PDU is as follows:
1 bite1 bite
|
|
TID/PIDPDU Type
|
Type Specific Contents
|
TID/PID
Transaction ID or Push ID. The TID field is used to associate requests with replies in the connectionless session service. The presence of the TID is conditional. It is included in the connectionless WSP PDUs, and is not included in the connection-mode PDUs. In connectionless WSP, the TID is passed to and from the session user as the "Transaction Id" or "Push Id" parameters of the session primitive
Transaction ID or Push ID. The TID field is used to associate requests with replies in the connectionless session service. The presence of the TID is conditional. It is included in the connectionless WSP PDUs, and is not included in the connection-mode PDUs. In connectionless WSP, the TID is passed to and from the session user as the "Transaction Id" or "Push Id" parameters of the session primitive
PDU Type
The Type field specifies the type and function of the PDU. The type numbers for the various PDUs are defined below. The rest of the PDU is type-specific information, referred to as the contents.
The Type field specifies the type and function of the PDU. The type numbers for the various PDUs are defined below. The rest of the PDU is type-specific information, referred to as the contents.
Number
|
Name Assigned
|
0x00
|
Reserved
|
0x01
|
Connect
|
0x02
|
ConnectReply
|
0x03
|
Redirect
|
0x04
|
Reply
|
0x05
|
Disconnect
|
0x06
|
Push
|
0x07
|
ConfirmedPush
|
0x08
|
Suspend
|
0x09
|
Resume
|
0x10–0x3
|
FUnassigned
|
0x40
|
Get
|
0x41
|
Options (Get PDU)
|
0x42
|
Head (Get PDU)
|
0x43
|
Delete (Get PDU)
|
0x44
|
Trace (Get PDU)
|
0x45-0x4
|
FUnassigned (Get PDU)
|
0x50-0x5
|
FExtended Method (Get PDU)
|
0x60
|
Post
|
0x61
|
Put (Post PDU)
|
0x62–0x6
|
FUnassigned (Post PDU)
|
0x70-0x7
|
FExtended Method (Post PDU)
|
Transaction Layer
(Wireless Transaction Protocol WTP)
The specifications for the transfer
layer are in the Wireless Transaction Protocol (WTP). Like the User Datagramm
Protocol (UDP), the WTP runs at the head of the datagramm service. Both the UDP
and the WTP are a part of the standard application from the TCP/IP to make the
simplified protocol compatible to mobile terminals. WTP supports chaining
together protocol data and the delayed response to reduce the number of
transmissions. The protocol tries to optimize user interaction in order that
information can be received when needed.
WTP
The Wireless Transaction Protocol
provides the services necessary for interactive browsing applications. During a
browsing session the client requests information from a server and the server
responds with the information. This is referred to as a transaction. WTP runs
on a datagram service and possible a security service.
Advantages of WTP include:
- Improved reliability over datagram services
- Imported efficiency over connection oriented services
- As a message oriented protocol, it is designed for services oriented towards transactions.
Main features:
- 3 kinds of transaction services.
- Class 0: Unreliable invoke messages with no result messages
- Class 1: Reliable invoke messages with no result messages
- Class 2: Reliable invoke messages with exactly one reliable result message.
- Reliability achieved by using unique transaction identifiers, acknowledgements, duplicate removal; and retransmissions.
- No explicit set up or tear down phases.
- Optional user-to-user reliability.
- Optionally the last acknowledgement of the transaction may contain out-of-band information.
- Concatenation may be used to convey multiple PDUs in one service data unit of the datagram transport.
- The basic unit of interchange is an entire message, not a stream of bytes.
- Mechanisms are provided to minimize the number of transactions replayed as a result of duplicate packets.
- Abort of outstanding transactions.
- For reliable invoke messages, both success and failure reported.
- Asynchronous transactions allowed.
Wireless Transport Layer Security WTLS
The Wireless Transport Layer
Security (WTLS) is a optional layer or stack which consists of description
devices. A secure transmission is crucial for certain applications such as
e-commerce or WAP-banking and is a standard in these days. Furthermore WTLS
contains a check for data integrity, user authentification and gateway
security.
WTLS
Wireless Transport Layer Security
is a protocol based on the TLS protocol. It is used with the WAP transport
protocols and has been optimised for use over narrow-band communication
channels. The WTLs layer is above the transport protocol layer. The required
security layer of the protocol determines whether it is used or not. It
provides a secure transport service interface that preserves the transport
service interface below; additionally it provides an interface for managing
secure connections. WTLS aims to provide privacy, data integrity and
authentication between two communication applications. Among its features are
datagram support, optimised handshaking and dynamic key refreshing. It is
optimised for low-bandwidth bearer networks with relatively long latency.
The WTLS Record Protocol is a
layered protocol. The Record Protocol takes messages to be transmitted,
optionally compresses the data, applies a MAC, encrypts, and transmits the
result. Received data is decrypted, verified, and decompressed, then delivered
to higher-level clients. Four record protocol clients are described in the WTLS
standard; the change cipher spec protocol, the handshake protocol, the alert
protocol and the application data protocol. If a WTLS implementation receives a
record type it does not understand, it ignores it. Several records can be
concatenated into one transport SDU. For example, several handshake messages
can be transmitted in one transport SDU. This is particularly useful with packet-oriented
transports such as GSM short messages.
Handshake
protocols |
Alert Protocol
|
Application
Protocol |
Change Cipher
Spec Protocol |
Record protocol
|
•
Features:
–
Data integrity
–
Privacy
–
Authentication
–
Denial-of-service protection
Transport Layer
(Wireless Datagram Protocol WDP)
The Wireless Datagram Protocol
(WDP) represents the transfer or transmission layer and is also the interface
of the network layer to all the above stacks/layers. With the help of WDP the
transmission layer can be assimilated to the specifications of a network
operator. This means that WAP is completely independent from any network
operator. The transmission of SMS, USSD, CSD, CDPD, IS-136 packet data and GPRS
is supported. The Wireless Control Message Protocol (WCMP) is an optional addition
to WAP, which will inform users about occurred errors.
WDP
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.
•
The WAP datagram
protocol (WDP) is the Transport layer that sends and receives messages via any
available bearer network, including SMS, USSD, CSD, CDPD, IS–136 packet data,
and GPRS.
•
Operates
above the data capable bearer services supported by various network types.
•
Provides a
common interface to the upper layer protocols and hence they function
independent of the underlying wireless network.
Transport Bearer
Interfaces
WAP supports dial-up networking
using IP and Point-to-Point Protocol (PPP) as the bearer interface underneath
WDP. It also supports Short Message Service (SMS) and General Packet Radio
System (GPRS). SMS passes text and binary data between digital phones. GPRS is
a relatively new technology that implements faster, "always-on" connections
for wireless devices; GPRS actually runs on top of IP.
Conclusion
Each of these layers provides a well-defined interface to the layer
above it. This means that the internal workings of any layer are transparent or
invisible to the layers above it. The layered architecture allows other
applications and services to utilise the features provided by the WAP-stack as
well. This makes it possible to use the WAP-stack for services and applications
that currently are not specified by WAP.
The primary focus
of WAP technology is to create a global wireless Internet by bringing services
offered by Internet to mobile phone users. WAP has been designed to benefit
wireless subscribers, handset vendors, network operators and service providers.
Subscribers get access to a wide range of services available on Internet from
their mobile phones and other wireless interoperable open standard, which is
handset vendor independent.
References
- · Advanced Programming Language (630501) By Dr.Qadri Hamarsheh
- · www.tutorialspoint.com/wap/wap_architecture.htm
- · www.radcom.com
- · www.javvin.com/protocolWAP.html
Thanks for sharing internal structure of WAP. It is useful to everyone who don't know the structure of WAP
ReplyDeleteIts useful for me thank u
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