Wireless Application Protocol

Outline

 Mobile applications
 How are mobile/wireless environments different?
 What is WAP?
 WAP Architecture
 WAE (WML/WMLScript)
 WTA Framework
 WAP Push Services
 WAP Protocol Stack
 Hype v/s Reality
 References and Resources
 Mobile Applications - 1

 Vehicles
– transmission of news, road condition etc
– ad-hoc network with near vehicles to prevent accidents

 Emergencies
– early transmission of patient data to the hospital
– ad-hoc network in case of earthquakes, cyclones
– military ...

 Traveling salesmen
– direct access to central customer files
– consistent databases for all agents
– mobile office
 Mobile Applications - 2

 Web access
– outdoor Internet access
– intelligent travel guide with up-to-date location dependent
information

 Information services
– push: stock quotes; pull: nearest cash ATM

 Disconnected operations
– file-system caching for off-line work
– mobile agents, e.g., shopping

 Entertainment
– games, etc
 Variability of the Mobile Environment

Mobility
• stationary
• nomadic (pedestrian speed)
• mobile (vehicular speed)
• roaming (mobile across networks)

Connectivity
• connected
Mobile Device Capability • semi-connected
• form factor (asymmetric)
• GUI • weakly connected
• multimedia • disconnected
• real-time multimedia
 World Wide Web and Mobility
HTTP/HTML have not been designed for mobile applications/devices
 HTTP 1.0 characteristics
– designed for large bandwidth, low delay
– stateless, client/server, request/response communication
– connection oriented, one connection per request
– TCP 3-way handshake, DNS lookup overheads
– big protocol headers, uncompressed content transfer
– primitive caching (often disabled, dynamic objects)
– security problems (using SSL/TLS with proxies)
 HTML characteristics
– designed for computers with “high” performance, color high-
resolution display, mouse, hard disk
– typically, web pages optimized for design, not for communication;
ignore end-system characteristics
 System Support for Mobile WWW
 Enhanced browsers
– client-aware support for mobility

 Proxies
– Client proxy: pre-fetching, caching, off-line use
– Network proxy: adaptive content transformation for connections
– Client and network proxy

 Enhanced servers
– server-aware support for mobility
– serve the content in multiple ways, depending on client capabilities

 New protocols/languages
– WAP/WML
 Wireless Application Protocol (WAP)

 Empowers mobile users with wireless devices to easily access and

interact with information and services.
 A “standard” created by wireless and Internet companies to enable
Internet access from a cellular phone

 wapforum.org:
– co-founded by Ericsson, Motorola, Nokia, Phone.com
– 450 members in 2000, comprise of Handset manufacturers, Wireless
service providers, ISPs, Software companies in the wireless industry
– Goals
• deliver Internet services to mobile devices
• enable applications to scale across a variety of transport options and
device types
• independence from wireless network standards
• GSM, CDMA IS-95, TDMA IS-136, 3G systems (UMTS, W-CDMA)
 WAP: Main Features

 Browser
– “Micro browser”, similar to existing web browsers
 Markup language
– Similar to HTML, adapted to mobile devices
 Script language
– Similar to Javascript, adapted to mobile devices
 Gateway
– Transition from wireless to wired world
 Server
– “Wap/Origin server”, similar to existing web servers
 Protocol layers
– Transport layer, security layer, session layer etc.
 Telephony application interface
– Access to telephony functions
Internet Model

HTML
HTTP
TLS/SSL
TCP/IP
 WAP Architecture

Client Web Server

WAP Gateway
WML

with WML-Script
WML Encoder CGI

WML Decks
WML- Scripts
WSP/WTP WMLScript
HTTP etc.
Script
Compiler
WTAI
Protocol Adapters Content
Etc.

Source: WAP Forum

 WAP Application Server

Client WAP Application Server

with WML-Script
WML WML Encoder

WML Decks
Application
WML- WSP/WTP WMLScript Logic
Script Compiler
WTAI Protocol Adapters Content
Etc.

Source: WAP Forum

 WAP Architecture

 Another look

Key Components
• Origin/Web Server
• WAP Gateway/Proxy
• WAP Protocol Stack
• Micro Browser
• WML/WML Script
• Transcoders
• WTA

Source: WAP Forum

 WAP: Network Elements

fixed network wireless network

HTML WML WAP Binary WML

Internet
filter proxy

HTML WML
HTML
filter/ Binary WML
WAP
web HTML proxy
server

WTA Binary WML

server
PSTN

Binary WML: binary file format for clients

Source: Schiller
 WAP Specifies

 Wireless Application Environment

– WML Microbrowser
– WMLScript Virtual Machine
– WMLScript Standard Library
– Wireless Telephony Application Interface (WTAI)
– WAP content types

 Wireless Protocol Stack

– Wireless Session Protocol (WSP)
– Wireless Transport Layer Security (WTLS)
– Wireless Transaction Protocol (WTP)
– Wireless Datagram Protocol (WDP)
– Wireless network interface definitions
 WAP Stack

Runs on top of WDP

Provided lightweight X-oriented service
• Unreliable 1-way request
MicroBrowser (WML,
• Reliable 1-way/2-way req./response
WMLScript, WTA, WTAI)

Lightweight SSL
Uses WIM/PKI-Cards

Datagram service on different

bearers
Convergence between bearer
services

Different Wireless Tech.

Source: WAP Forum

 WAP Stack
 WAE (Wireless Application Environment):
– Architecture: application model, browser, gateway, server
– WML: XML-Syntax, based on card stacks, variables, ...
– WTA: telephone services, such as call control, phone book etc.
 WSP (Wireless Session Protocol):
– Provides HTTP 1.1 functionality
– Supports session management, security, etc.
 WTP (Wireless Transaction Protocol):
– Provides reliable message transfer mechanisms
– Based on ideas from TCP/RPC
 WTLS (Wireless Transport Layer Security):
– Provides data integrity, privacy, authentication functions
– Based on ideas from TLS/SSL
 WDP (Wireless Datagram Protocol):
– Provides transport layer functions
– Based on ideas from UDP

Content encoding, optimized for low-bandwidth channels, simple devices

 WHY WAP?

 Wireless networks and phones

– have specific needs and requirements
– not addressed by existing Internet technologies
 WAP
– Enables any data transport
• TCP/IP, UDP/IP, GUTS (IS-135/6), SMS, or USSD.
– Optimizes the content and air-link protocols
– Utilizes plain Web HTTP 1.1 servers
• leverages existing development methodologies
• utilizes standard Internet markup language technology (XML)
• all WML content is accessed via HTTP 1.1 requests
– WML UI components map well onto existing mobile phone user interfaces
• no re-education of the end-users
• leveraging market penetration of mobile devices
– Several modular entities together form a fully compliant Internet entity
 Why is HTTP/HTML not enough?

Big pipe - small pipe syndrome

Internet Wireless network
<HTML> HTTP/HTML <WML>
<CARD> WAP
<HEAD>
<TITLE>NNN Interactive</TITLE> <DO TYPE="ACCEPT">
<META HTTP-EQUIV="Refresh" CONTENT="1800, <GO URL="/submit?Name=$N"/>
URL=/index.html"> </DO>
</HEAD> Enter name:
<BODY BGCOLOR="#FFFFFF" <INPUT TYPE="TEXT" KEY="N"/>
BACKGROUND="/images/9607/bgbar5.gif" LINK="#0A3990" </CARD>
ALINK="#FF0000" VLINK="#FF0000" TEXT="000000" </WML>
ONLOAD="if(parent.frames.length!=0)top.location='ht
tp://nnn.com';">
<A NAME="#top"></A>
<TABLE WIDTH=599 BORDER="0">
<TR ALIGN=LEFT>
<TD WIDTH=117 VALIGN=TOP ALIGN=LEFT>
Content encoding
<HTML> 010011
<HEAD> 010011
<TITLE 110110
>NNN 010011
Intera 011011
ctive< 011101
/TITLE 010010
> 011010
<META
HTTP-
EQUIV=
"Refre
sh"
CONTEN
T="180
0,
URL=/i
ndex.h
tml">
Source: WAP Forum
 WAP: “Killer” Applications
 Location-based services
– Real-time traffic reporting, Event/restaurant recommendation
 Enterprise solutions
– Email access, Database access, “global” intranet access
– Information updates “pushed” to WAP devices
 Financial services
– Banking, Bill-paying, Stock trading, Funds transfers
 Travel services
– Schedules and rescheduling, Reservations
 Gaming and Entertainment
– Online, real-time, multi-player games
– Downloadable horoscopes, cartoons, quotes, advice
 M-Commerce
– Shopping on the go
– Instant comparison shopping
– Location-based special offers and sales
 Wireless Application Environment (WAE)

 Goals
– device and network independent application environment
– for low-bandwidth, wireless devices
– considerations of slow links, limited memory, low computing power,
small display, simple user interface (compared to desktops)
– integrated Internet/WWW programming model
– high interoperability
 WAE Components

 Architecture
– Application model, Microbrowser, Gateway, Server
 User Agents
– WML/WTA/Others
– content formats: vCard, vCalendar, Wireless Bitmap, WML, ...
 WML
– XML-Syntax, based on card stacks, variables, ...
 WMLScript
– procedural, loops, conditions, ... (similar to JavaScript)
 WTA
– telephone services, such as call control, text messages, phone
book, ... (accessible from WML/WMLScript)
 Proxy (Method/Push)
 WAE: Logical Model

Origin Servers Gateway Client

response encoded WTA

web Method proxy
with response user agent
server
content with
content

Push proxy WML

other content
user agent
server push encoded
content push
content
encoders other
& WAE
decoders user agents
request encoded
request
 WAP Microbrowser

 Optimized for wireless devices

 Minimal RAM, ROM, Display, CPU and keys
 Provides consistent service UI across devices
 Provides Internet compatibility
 Enables wide array of available content and
applications
 WML: Wireless Markup Language

 Tag-based browsing language:

– Screen management (text, images)
– Data input (text, selection lists, etc.)
Content (XML)
– Hyperlinks & navigation support
 Takes into account limited display,
navigation capabilities of devices
 XML-based language XSL Processor
– describes only intent of interaction
in an abstract manner WML Stylesheet HTML StyleSheet
– presentation depends upon device
capabilities
WML Browsers HTTP Browser
 Cards and Decks
– document consists of many cards
– User interactions are split into cards
– Explicit navigation between cards
– cards are grouped to decks
– deck is similar to HTML page, unit
of content transmission
 Events, variables and state mgmt
 WML
 The basic unit is a card. Cards are grouped together into Decks Document ~
Deck (unit of transfer)
 All decks must contain
– Document prologue
• XML & document type declaration
– <WML> element
• Must contain one or more cards

WML File Structure

<?xml version="1.0"?>
<!DOCTYPE WML PUBLIC "-//WAPFORUM//DTD WML 1.0//EN"
"http://www.wapforum.org/DTD/wml.xml">

<WML>
...
</WML>
 WML Example

<WML>
<CARD>
<DO TYPE=“ACCEPT”>
Navigatio <GO URL=“#eCard”/>
Card
</DO
n Welcome!
</CARD>
<CARD NAME=“eCard”>
<DO TYPE=“ACCEPT”>
Variables <GO URL=“/submit?N=$(N)&S=$(S)”/> Deck
</DO>
Enter name: <INPUT KEY=“N”/>
Choose speed:
<SELECT KEY=“S”>
Input <OPTION VALUE=“0”>Fast</OPTION>
Elements <OPTION VALUE=“1”>Slow</OPTION>
<SELECT>
</CARD>
</WML>
 Handling User Input

 Select lists
– Choose from a list of options

 Input fields
– Enter a string of text or numbers

 KEY variables
– Set by SELECT and INPUT elements
– How user input is passed to other cards and the application server

Source: WAP Forum

 The SELECT Element

 Display a list of options

– Each option may set the KEY variable and/or bind a task to the
ACCEPT key
– TITLE= dynamically sets the label string
– MULTIPLE=“TRUE”: Allows user to pick multiple items

<CARD>
<DO TYPE="ACCEPT" LABEL="View"> Forecast
<GO URL="getcity.cgi?location=$city"/> 1 Berlin
</DO> 2 Rome
Forecast 3>New City
<SELECT KEY="city"> ____________
<OPTION VALUE="ber">Berlin</OPTION> Find
<OPTION VALUE="rom">Rome</OPTION>
<OPTION TITLE="Find" ONCLICK="find.cgi">New City</OPTION>
</SELECT>
</CARD>

Source: WAP Forum

 The INPUT Element
 Prompts user to enter a string of text
– DEFAULT=key_value; Default KEY variable (displayed to user)
– FORMAT=format_specifier; If omitted, free-form entry is allowed
– EMPTYOK="TRUE“; Browser will accept null input
– TYPE="PASSWORD“; Special entry mode handled by the browser
– MAXLENGTH=number; Maximum number of allowed characters

Soc. Security:

<CARD> 287-33- _
<DO TYPE="ACCEPT"> ____________
<GO URL="?get=person" NUM
METHOD="POST" POSTDATA="userid=$ssn"/>
</DO> Soc. Security:
Soc Security:
<INPUT KEY="ssn" FORMAT="NNN\-NN\-NNNN"/> 287-33- 7629
</CARD> ____________
OK

Source: WAP Forum

 WML Content Formats

 Common interchange formats, for interoperability

 Formats:
– Business cards: IMC vCard standard
– Calendar: IMC vCalendar standard
– Images: WBMP (Wireless BitMaP)
– Compiled WML, WMLScript
 Newly defined formats:
– WML text and tokenized format
– WMLScript text and bytecode format
– WBMP image format
 Binary format for size reduction
– Bytecodes/tokens for common values and operators
– Compressed headers
– Data compression (e.g. images)
 General-purpose transport compression can still be applied
 Displaying Images

 Insert app images or local icons within display text

– 1-bit BMP format
 Images are ignored by non-bitmapped devices
– Check HTTP_ACCEPT for “image/bmp”

<CARD>
<DO TYPE="ACCEPT">
<GO URL="#c2"/>
</DO>
Continue <IMG LOCALSRC="righthand"
ALT="forward..."/>
</CARD>

<CARD NAME="c2">
<IMG SRC="../images/logo.wbmp"
ALT="Unwired Planet"/>
<BR/>Welcome!
</CARD>

Source: WAP Forum

 WML (other features)

 Setting card styles to create forms

 Using variables to cache user data
 Using card intrinsic events to trigger transparent tasks
 Using timers
 Securing WML decks
 Bookmarking decks
 WMLScript

 Complement to WML
– Derived from JavaScript™
 Provides general scripting capabilities
– Procedural logic, loops, conditionals, etc.
– Optimized for small-memory, small-cpu devices

 Features
– local user interaction, validity check of user input
– access to device facilities (phone call, address book etc.)
– extensions to the device software
• configure device, download new functionality after deployment

 Bytecode-based virtual machine

– Stack-oriented design, ROM-able
– Designed for simple, low-impact implementation
 WMLScript compiler resides in the network
 WMLScript Libraries

 Lang - VM constants, general-purpose math functionality,

etc.
 String - string processing functions
 URL - URL processing
 Browser - WML browser interface
 Dialog - simple user interface
 Float - floating point functions
 WMLScript Example

function currencyConvertor(currency, exchRate) {

Functions return currency*exchangeRate;
}

function myDay(sunShines) {
Variables var myDay;
if (sunShines) {
myDay = “Good”;
Programming } else {
Constructs myDay = “Not so good”;
};
return myDay;
}

Source: WAP Forum

 Wireless Telephony Application (WTA)

 Collection of telephony specific extensions

– designed primarily for network operators

 Example
– calling a number (WML)
wtai://wp/mc;07216086415
– calling a number (WMLScript)
WTAPublic.makeCall("07216086415");

 Implementation
– Extension of basic WAE application model
– Extensions added to standard WML/WMLScript browser
– Exposes additional API (WTAI)
 WTA Features
 Extension of basic WAE application model
– network model for interaction
• client requests to server
• event signaling: server can push content to the client
– event handling
• table indicating how to react on certain events from the network
• client may now be able to handle unknown events
– telephony functions
• some application on the client may access telephony functions
 WTAI includes:
– Call control
– Network text messaging
– Phone book interface
– Event processing
 Security model: segregation
– Separate WTA browser
– Separate WTA port
 WTA Example (WML)

Placing an outgoing call with WTAI:

<WML>
<CARD>
<DO TYPE=“ACCEPT”>
WTAI Call <GO URL=“wtai:cc/mc;$(N)”/>
</DO>
Enter phone number:
Input Element
<INPUT TYPE=“TEXT” KEY=“N”/>
</CARD>
</WML>

Source: WAP Forum

 WTA Example (WMLScript)

Placing an outgoing call with WTAI:

function checkNumber(N) {
if (Lang.isInt(N))
WTAI Call WTAI.makeCall(N);
else
Dialog.alert(“Bad phone number”);
}

Source: WAP Forum

 WTA Logical Architecture
other telephone networks
WTA Origin Server
Client
WML
Scripts mobile WTA
WTA & WML network user agent
server
WML
decks WAE
WAP Gateway services
WTA
services
encoders
&
network operator decoders
trusted domain other WTA
servers

third party
firewall
origin servers

Source: Schiller
WTA Framework Components

Source: Heijden
 WTA User Agent

 WTA User Agent

– WML User agent with extended functionality
– can access mobile device’s telephony functions through WTAI
– can store WTA service content persistently in a repository
– handles events originating in the mobile network

 WTA User Agent Context

– Abstraction of execution space
– Holds current parameters, navigation history, state of user agent
– Similar to activation record in a process address space

 Uses connection-mode and connectionless services offered by WSP

 Specific, secure WDP ports on the WAP gateway
 WTA Events and Repository
 WTA Events
– Network notifies device of event (such as incoming call)
– WTA events map to device’s native events
– WTA services are aware of and able to act on these events
– example: incoming call indication, call cleared, call connected
 WTA Repository
– local store for content related to WTA services (minimize network traffic)
– Channels: define the service
• content format defining a WTA service stored in repository
• XML document specifying eventid, title, abstract, and resources that
implement a service
– Resources: execution scripts for a service
• could be WML decks, WML Scripts, WBMP images..
• downloaded from WTA server and stored in repository before service is
referenced
– Server can also initiate download of a channel
WTA Channels and Resources

Source: Heijden
 WTA Interface (public)

 WTA Interface
– generic, high-level interface to mobile’s telephony functions
– setting up phone calls, reading and writing entries in phonebook..

 Public WTAI
– for third party WML content providers
– restricted set of telephony functions available to any WAE User Agent
– library functions
• make call: allows application to setup call to a valid tel number
• send DTMF tones: send DTMF tones through the setup call
– user notified to grant permission for service execution
– cannot be triggered by network events
– example: Yellow pages service with “make call” feature
 WTA Interface (network)
 Network Common WTAI
– WTA service provider is in operator’s domain
– all WTAI features are accessible, including the interface to WTA events
– library functions
• Voice-call control: setup call, accept, release, send DTMF tones
• Network text: send text, read text, remove text (SMS)
• Phonebook: write, read, remove phonebook entry
• Call logs: last dialed numbers, missed calls, received calls
• Miscellaneous: terminate WTA user agent, protect context
– user can give blanket permission to invoke a function
– example: Voice mail service

 Network Specific WTAI

– specific to type of bearer network
– example:
• GSM: call reject, call hold, call transfer, join multiparty, send USSD
 WTA Event Handling
 Event occurrence
– WTA user agent could be executing and expecting the event
– WTA user agent could be executing and a different event occurs
– No service is executing
 Event handling
– channel for each event defines the content to be processed upon reception
of that event
 Event binding
– association of an event with the corresponding handler (channel)
– Global binding:
• channel corresponding to the event is stored in the repository
• event causes execution of resources defined by the channel
• example: voice mail service
– Temporary binding:
• resources to be executed are defined by the already executing service
• example: yellow pages lookup and call establishment
Event Handling (no service in execution)

Source: Heijden
 Event Handling (service already execution)

1: Temporary binding exists

2. No temporary binding and context is protected
3: No temporary binding and context is not protected
Source: Heijden
 WTA: Voice mail Example

WTA client WTA server mobile network voice mail server

incoming voice
indicate new voice message message
generate
push deck new deck
display deck;
user selects request

wait for call translate

play requested voice message

setup call
call indication setup call

accept call
accept call accept call
voice connection

Source: Schiller
 WAP Push Services
 Web push
– Scheduled pull by client (browser)
• example: Active Channels
– no real-time alerting/response
• example: stock quotes
 Wireless push
– accomplished by using the network itself
• example: SMS
– limited to simple text, cannot be used as starting point for service
• example: if SMS contains news, user cannot request specific news
item
 WAP push
– Network supported push of WML content
• example: Alerts or service indications
– Pre-caching of data (channels/resources)
WAP Push Framework

Source: Heijden
 Push Access Protocol

 Based on request/response model

 Push initiator is the client
 Push proxy is the server
 Initiator uses HTTP POST to send push message to proxy
 Initiator sends control information as an XML document,
and content for mobile (as WML)
 Proxy sends XML entity in response indicating submission
status
 Initiator can
– cancel previous push
– query status of push
– query status/capabilities of device
 Push Proxy Gateway

 WAP stack (communication with mobile device)

 TCP/IP stack (communication with Internet push initiator)
 Proxy layer does
– control information parsing
– content transformation
– session management
– client capabilities
– store and forward
– prioritization
– address resolution
– management function
 Over the Air (OTA) Protocol

 Extends WSP with push-specific functionality

 Application ID uniquely identifies a particular application
in the client (referenced as a URI)
 Connection-oriented mode
– client informs proxy of application IDs in a session
 Connectionless mode
– well known ports, one for secure and other for non-secure push
 Session Initiation Application (SIA)
– unconfirmed push from proxy to client
– request to create a session for a specific user agent and bearer
 WAE Summary

 WML
– analogous to HTML (optimized for wireless)
– event based, microbrowser user agent
 WMLScript
– analogous to JavaScript
– features of compiler in the network
 WTA
– WTAI: different access rights for different applications/agents
– WTA User Agent (analogy with operating systems)
• Context – Activation Record
• Channel – Interrupt Handler
• Resource – Shared routines invoked by interrupt handlers
• Repository – Library of interrupt handlers
– feature of dynamically pushing the interrupt handler before the event
 Push
– no analogy in Internet
 WAP Gateway Summary

 Encoders
– translate between binary (WML) and text (HTML/WML)
 Filters
– transcoding between WML (wireless) and HTML (wired)
 Method Proxy
– similar to standard proxy services
– WAP stack on wireless interface and TCP/IP stack on Internet interface
 Push Proxy
– Push Access Protocol with Internet Push Initiator (Web Server)
– Over the Air Protocol with mobile device (and WAP Push Initiator)
– Performs necessary filtering, translation etc.
 WAP Servers Summary
 Origin Server
– Web server with HTML/WML contents
– Runs TCP/IP stack, needs PAP protocol for push, no end-to-end
security
 WAP Server
– Serves WML content
– Runs WAP stack, uses OTA protocol for push, end-to-end security
possible
 WTA Server
– Specialized for telephony applications (runs WAP stack, uses push
extensively)
– Client initiated (make call “hyperlink” from a Yellow pages
service)
– Server intiated (incoming call from a Voice mail service)
 WAP: Protocol Stack

Internet A-SAP WAP

HTML, Java Application Layer (WAE) additional services

and applications
S-SAP
Session Layer (WSP)
HTTP TR-SAP
Transaction Layer (WTP)
SEC-SAP
SSL/TLS Security Layer (WTLS)
T-SAP

TCP/IP, Transport Layer (WDP) WCMP

UDP/IP,
media Bearers (GSM, CDPD, ...)

WAE comprises WML (Wireless Markup Language), WML Script, WTAI etc.

Source: Schiller
 WDP: Wireless Datagram Protocol
 Goals
– create a worldwide interoperable transport system by adapting WDP to the
different underlying technologies
– transmission services, such as SMS in GSM might change, new services
can replace the old ones

 WDP
– Transport layer protocol within the WAP architecture
– uses the Service Primitive
• T-UnitData.req .ind
– uses transport mechanisms of different bearer technologies
– offers a common interface for higher layer protocols
– allows for transparent communication despite different technologies
– addressing uses port numbers
– WDP over IP is UDP/IP
 Service, Protocol, and Bearer Example

WAP Over GSM Circuit-Switched

WAP
Mobile
Proxy/Server

WAE WAE Apps on

Other Servers
WSP WSP
IWF ISP/RAS
WTP WTP
UDP UDP
IP IP IP

PPP PPP

CSD-RF CSD- PSTN PSTN Subnetwork Subnetwork

RF Circuit Circuit

RAS - Remote Access Server

IWF - InterWorking Function

Source: WAP Forum

 Service, Protocol, and Bearer Example
WAP Over GSM Short Message Service
WAP
Mobile Proxy/Server
WAE WAE Apps on
other servers
WSP WSP

WTP SMSC WTP

WDP WDP

SMS SMS WDP Tunnel WDP Tunnel

Protocol Protocol
Subnetwork Subnetwork

under development
Source: WAP Forum
 WTLS:Wireless Transport Layer Security

 Goals
– Provide mechanisms for secure transfer of content, for applications
needing privacy, identification, message integrity and non-repudiation
– Provide support for protection against denial-of-service attacks

 WTLS
– is based on the TLS/SSL (Transport Layer Security) protocol
– optimized for low-bandwidth communication channels
– provides
• privacy (encryption)
• data integrity (MACs)
• authentication (public-key and symmetric)
– Employs special adapted mechanisms for wireless usage
• Long lived secure sessions
• Optimised handshake procedures
• Provides simple data reliability for operation over datagram bearers
 WTLS Internal Architecture

Transaction Protocol (WTP)

Handshake Alert Application Change Cipher

WTLS Protocol Protocol Protocol Spec Protocol

Record Protocol
Record protocol

Datagram Protocol (WDP/UDP)

Bearer networks

Source: WAP Forum

 WTP: Wireless Transaction Protocol
 Goals
– different transaction services that enable applications to select reliability,
efficiency levels
– low memory requirements, suited to simple devices (< 10kbyte )
– efficiency for wireless transmission
 WTP
– supports peer-to-peer, client/server and multicast applications
– efficient for wireless transmission
– support for different communication scenarios
– class 0: unreliable message transfer
• unconfirmed Invoke message with no Result message
• a datagram that can be sent within the context of an existing Session
– class 1: reliable message transfer without result message
• confirmed Invoke message with no Result message
• used for data push, where no response from the destination is expected
– class 2: reliable message transfer with exactly one reliable result message
• confirmed Invoke message with one confirmed Result message
• a single request produces a single reply
 WTP Services and Protocols
 WTP (Transaction)
– provides reliable data transfer based on request/reply paradigm
• no explicit connection setup or tear down
• optimized setup (data carried in first packet of protocol exchange)
• seeks to reduce 3-way handshake on initial request
– supports
• header compression
• segmentation /re-assembly
• retransmission of lost packets
• selective-retransmission
• port number addressing (UDP ports numbers)
• flow control
– message oriented (not stream)
– supports an Abort function for outstanding requests
– supports concatenation of PDUs
– supports User acknowledgement or Stack acknowledgement option
• acks may be forced from the WTP user (upper layer)
• default is stack ack
 WSP - Wireless Session Protocol

 Goals
– HTTP 1.1 functionality
• Request/reply, content type negotiation, ...
– support of client/server transactions, push technology
– key management, authentication, Internet security services

 WSP Services
– provides shared state between client and server, optimizes content transfer
– session management (establish, release, suspend, resume)
– efficient capability negotiation
– content encoding
– push

 WSP/B (Browsing)
– HTTP/1.1 functionality - but binary encoded
– exchange of session headers
– push and pull data transfer
– asynchronous requests
 HTTP 1.1 and WSP
 HTTP 1.1
– extensible request/reply methods
– extensible request/reply headers
– content typing
– composite objects
– asynchronous requests
 WSP enhancements beyond HTTP
– binary header encoding
– session headers
– confirmed and non-confirmed data push
– capability negotiation
– suspend and resume
– fully asynchronous requests
– connectionless service
 Why Not HTTP?
– encoding not compact enough, inefficient capability negotiation
– no push facility
 WSP Overview

 Header Encoding
– compact binary encoding of headers, content type identifiers and other
well-known textual or structured values
– reduces the data actually sent over the network
 Capabilities (are defined for):
– message size, client and server
– protocol options: Confirmed Push Facility, Push Facility, Session Suspend
Facility, Acknowledgement headers
– maximum outstanding requests
– extended methods
– header code pages
 Suspend and Resume
– server knows when client can accept a push
– multi-bearer devices
– dynamic addressing
– allows the release of underlying bearer resources
 WSP Sessions

 Session Context and Push

– push can take advantage of session headers
– server knows when client can accept a push

 Connection-mode
– long-lived communication, benefits of the session state, reliability

 Connectionless-mode
– stateless applications, no session creation overhead, no reliability
overhead
 WSP/B session establishment
client server
S-SAP S-SAP
S-Connect.req
(SA, CA, CH, RC) S-Connect.ind
(SA, CA, CH, RC)
S-Connect.res
(SH, NC)
S-Connect.cnf
(SH, NC)

CH: Client Header

WTP Class 2
RC: Requested Capabilities
transaction
SH: Server Header
NC: Negotiated Capabilities

Source: Schiller
 WSP/B session suspend/resume
client server
S-SAP S-SAP

S-Suspend.req S-Suspend.ind
S-Suspend.ind (R)
(R) WTP Class 0
transaction
R: Reason for disconnection
S-Resume.req
(SA, CA)
~ ~
S-Resume.ind
(SA, CA)
S-Resume.res
S-Resume.cnf
WTP Class 2
transaction

Source: Schiller
 WSP/B session termination

client server
S-SAP S-SAP
S-Disconnect.req
(R) S-Disconnect.ind
S-Disconnect.ind (R)
(R) WTP Class 0
transaction

Source: Schiller
 WAP Stack Summary

 WDP
– functionality similar to UDP in IP networks
 WTLS
– functionality similar to SSL/TLS (optimized for wireless)
 WTP
– Class 0: analogous to UDP
– Class 1: analogous to TCP (without connection setup overheads)
– Class 2: analogous to RPC (optimized for wireless)
– features of “user acknowledgement”, “hold on”
 WSP
– WSP/B: analogous to http 1.1 (add features of suspend/resume)
– method: analogous to RPC/RMI
– features of asynchronous invocations, push (confirmed/unconfirmed)
 WAP: Ongoing Work
 WDP
– Tunnel to support WAP where no (end-to-end) IP bearer available
 WTLS
– support for end-to-end security (extending WTLS endpoint beyond WAP
Gateway)
– interoperable between WAP and Internet (public key infrastructure)
– integrating Smart Cards for security functions
 WTP
– efficient transport over wireless links (wireless TCP)
– bearer selection/switching
– quality of service definitions
 WSP
– quality of service parameters
– multicast data, multimedia support
 WAE
– User agent profiles: personalize for device characteristics, preferences etc
– Push architecture, asynchronous applications
– Billing
 WAP: Hype vs Reality

 Low-bandwidth wireless links

– tcp/ip over wireless can also address these problems
– encoding in http can also reduce data transfer on wireless links
 Limited device capabilities
– Microbrowser is appropriate to address this problem
– WTAI features are not present in tcp/ip domain

 Challenges in WAP
– adapting to applications rich in content and interaction
– service guarantees
– interface design and usability

 Other approaches for WWW access through mobiles

– i-Mode (from NTT DoCoMo)
– WAP is a TRAP (http://www.freeprotocols.org/wapTrap)
The ADVANTAGES that WAP can offer over these other
methods are the following:
•open standard, vendor independent
•network-standard independent
•transport mechanism–optimized for wireless data
bearers
•application downloaded from the server, enabling
fast service creation and introduction, as opposed to
embedded software
 DISADVANTAGES of WAP

• Small screens: For web phones, there's an incredibly small viewing area;
palmtops are barely better.
• Speed of access: All devices have slow access.
• Limited or fragmented availability: Wireless web access is sporadic in
many areas and entirely unavailable in other areas.
• Price: Many technology limitations are being addressed by higher-end
devices and services. But the entry price for a good wireless web palmtop
with decent display, keyboard, and speed is easily $700 to $900, not
including monthly access.
• Lack of user habit: It takes some patience and overcoming the learning
curve to get the hang of it -- connecting, putting in an address, typing.
Users just aren't used to the idea and protocol yet.
•