Lecture9 Wap

Lecture 9: Wireless Application Protocol Dr. Reynold Cheng

This lecture is based on the textbook “W. Stallings, Wireless Communications and Networks, Prentice Hall, 2005” and the slides (prepared by Tom Fronckowiak) and figures provided at the Web site of the textbook.

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Class Objectives Last lecture we examined Mobile IP, a standard that provides application-level support for wireless networking.  This time we studied another standard, known as the Wireless Application Protocol (WAP). 

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Wireless environment is different



Low bandwidth, high latency, unpredictable availability and stability Tiny display screens Limited input functions Limited battery life

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WAP is designed to deal with these challenges

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 

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Wireless Application Protocol (WAP)  

An open standard developed by the WAP Forum The WAP Forum is established by Ericsson, Motorola, Nokia and Phone.com  >100

 

members now

The current version is 2.0 Reference: http://www.openmobilealliance.org/tech/affiliates/wap/wapindex.html

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Wireless Application Protocol (WAP) 

Open standard providing mobile users of wireless terminals access to telephony and information services  Wireless

terminals include wireless phones, pagers and personal digital assistants (PDAs)  Designed to work with all wireless network technologies such as GSM, CDMA, and TDMA  Based on existing Internet standards such as IP, XML, HTML, and HTTP  Includes security facilities 5

WAP Programming Model WAP

HTTP

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Uses of the WAP Gateway   

Acts as a proxy server for wireless domain Caches frequently requested information Provides services that offload the limited capabilities of the mobile terminals  DNS

services, conversion between WAP stack and WWW stack (HTTP + TCP/IP)

 

Encodes Web info to more compact form Decodes compacted form into standard Web communication conventions

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WAP Infrastructure

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WAP Protocol Stack

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Web vs. WAP Web

WAP

HTML

WML

JavaScript

WMLScript

HTTP

WSP

TCP

WTP

SSL/TLS

WTLS

IP

WDP 10

Wireless Markup Language (WML)

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Wireless Markup Language (WML) Features 



Text and image support – formatting and layout commands Deck/card organizational metaphor – WML documents subdivided into cards, which specify one or more units of interaction A

WML deck is similar to an HTML page (identified by URL)



Support for navigation among cards and decks – includes provisions for event handling; used for navigation or executing scripts

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Example WML <wml>

Hello WAP World.

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WML Tags

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WMLScript

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WMLScript Scripting language for defining script-type programs in a user device with limited processing power and memory  WMLScript capabilities: 

 Check

validity of user input before it is sent  Access device facilities and peripherals  Interact with user without introducing round trips to origin server 16

WMLScript 

WMLScript features:  JavaScript-based

scripting language

 Procedural

logic  Event-based  Compiled implementation 

Can be complied down to a more efficient bytecode that is transported to the client

 Integrated 

into WAE

Fully integrated with the WML browser

 Efficient

extensible library support 17

WMLScript Statements

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Wireless Application Environment (WAE)

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Wireless Application Environment (WAE)  

WAE specifies an application framework for wireless devices WAE elements:  WAE

User agents – software that executes in the wireless device (e.g., browser)  Content generators – applications that produce standard content formats in response to requests from user agents in the mobile terminal  Standard content encoding – defined to allow a WAE user agent to navigate Web content  Wireless telephony applications (WTA) – collection of telephony-specific extensions for call and feature control mechanisms

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WAE Client Components

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Wireless Session Protocol (WSP)

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Wireless Session Protocol (WSP) Transaction-oriented protocol based on the concept of a request and a reply  Provides applications with interface for two session services: 

 Connection-oriented

session service – operates above reliable transport protocol WTP  Connectionless session service – operates above unreliable transport protocol WDP 23

Connection-mode WSP Services     

Establish reliable session from client to server and release Agree on common level of protocol functionality using capability negotiation Exchange content between client and server using compact encoding Suspend and resume a session Push content from server to client in an unsynchronized manner 24

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WSP Transaction Types      

Session establishment – client WSP user requests session with server WSP user Session termination – client WSP user initiates termination Session suspend and resume – initiated with suspend and resume requests Transaction – exchange of data between a client and server Nonconfirmed data push – used to send unsolicited information from server to client Confirmed data push – server receives delivery confirmation from client

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WSP Service Primitive: Successful session establishment      

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SA – Server Address CA – Client Address CH – Client Header RQ – Requested Capabilities SH – Server Header NC – Negotiated Capabilities

The WSP provider may modify RQ if the requested capabilities are higher than it can offer Thus, S-Connect.ind may be different from S-Connect.req 27

WSP Service Primitive: Session Termination      

RC – Code for cause of disconnection RS – Redirect Security RA – Redirect Address EH – Error Header EB – Error Body If RC indicates the cause for disconnection is the client being redirected to a new server, RS and RA will be needed

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WSP Service Primitive: Suspend and Resume

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SA – Server Address CA – Client Address 29

WSP Service Primitive: Transaction Operation

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CI – Client Transaction ID M – Method RU – Request URI

    

RH – Request Header RB – Request Body SI – Server Transaction ID S – Status AH – Acknowledge Headers 30

WSP Service Primitive: Push

    

PH – Push Header PB – Push Body SI – Server Transaction ID CI – Client Transaction ID AH – Acknowledgment Headers 31

Wireless Transaction Protocol (WTP)

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Wireless Transaction Protocol (WTP)  

Lightweight protocol suitable for "thin" clients and over low-bandwidth wireless links WTP features  Three

classes of transaction service  Optional user-to-user reliability: WTP user triggers confirmation of each received message  Optional out-of-band data on acknowledgments  PDU concatenation and delayed acknowledgment to reduce the number of messages sent  Asynchronous transactions 33

WTP Transaction Classes Class 0: Unreliable invoke message with no result message  Class 1: Reliable invoke message with no result message  Class 2: Unreliable invoke message with one reliable result message 

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WTP PDU Types      

Invoke PDU – used to convey a request from an initiator to a responder ACK PDU – used to acknowledge an Invoke or Result PDU Result PDU – used to convey response of the server to the client Abort PDU – used to abort a transaction Segmented invoke PDU and segmented result PDU – used for segmentation and reassembly Negative acknowledgment PDU – used to indicate that some packets did not arrive 35

Examples of WTP Operation

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WSP-WTP Timing Diagram (example)

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Wireless Transport Layer Security (WTLS)

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Wireless Transport Layer Security (WTLS) Features 

  

Data integrity – ensures that data sent between client and gateway are not modified, using message authentication Privacy – ensures that the data cannot be read by a third party, using encryption Authentication – establishes authentication of the two parties, using digital certificates Denial-of-service protection – detects and rejects messages that are replayed or not successfully verified 39

WTLS Protocol Stack 

WTLS consists of two layers of protocols  WTLS

Record Protocol – provides basic security services to various higher-layer protocols  Higher-layer protocols: The Handshake Protocol  The Change Cipher Spec Protocol  The Alert Protocol 

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WTLS Protocol Stack Change encryption algorithm, cryptographic attributes etc.

Provides alert messages to peer entity

Upper Layer Lower Layer

•Allow server and client to authenticate each other •Negotiate encryption, authorization algorithms, keys to be used to protect data •Provide parameters for WTLS Record Protocol

provides basic security services to various higherlayer protocols 41

WTLS Record Protocol Operation

(Message authentication code)

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WTLS Record Format

Question: How to set crytographic attributes?

Answer: Handshaking Protocol

(0: No comparison, MAC protection, or encryption used) 43

WTLS Protocol Stack Change encryption algorithm, cryptographic attributes etc.

Provides alert messages to peer entity

Higher Layer Lower Layer

•Allow server and client to authenticate each other •Negotiate encryption, authorization algorithms, keys to be used to protect data •Provide parameters for WTLS Record Protocol

provides basic security services to various higherlayer protocols 44

Phases of the Handshake Protocol Exchange 

Used before application data is transmitted



First phase – initiates a logical connection and establish security capabilities (e.g., which cyrotgraphic and comparison algorithm) Second phase – used for server authentication and key exchange Third phase – used for client authentication and key exchange Forth phase – completes the setting up of a secure connection

  

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WTLS Handshake Protocol Action

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Wireless Datagram Protocol (WDP)

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Wireless Datagram Protocol (WDP) 





Used to adapt higher-layer WAP protocol to the communication mechanism (called the bearer) used between mobile node and WAP gateway WDP hides details of the various bearer networks from the other layers of WAP Adaptation may include:  Partitioning

data into segments of appropriate size for the

bearer  Interfacing with the bearer network 48

Wireless Control Message Protocol (WCMP) 

 



Performs the same support function for WDP as ICMP does for IP Used in environments that don’t provide ICMP Used by wireless nodes and WAP gateways to report errors encountered in processing WDP datagrams Also used for informational and diagnostic purposes

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Conclusions 

WAP may be considered as a light-weight version of TCP/IP to support mobile devices A

simplifed layering protocol  Support heterogeneity through the negotiation mechanism of “capabilities” 

Even with wider bandwidth (e.g., 3G), WAP will still be useful due to other limitation, e.g., user input, display, and processing power

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