lecture 3 middleware fundamentals wireless and mobile systems design

Lecture 3Middleware Fundamentals

Wireless and Mobile Systems Design

Middleware Fundamentals 2

Lecture Objectives

● Understand the role of middleware● Understand the unique requirements of wireless and

mobile applications that middleware should address● Understand mobile computational models and

functionality supported by various middleware platforms


Resources

● S. Helal, “Pervasive Java,” IEEE Pervasive Computing, Vol. 1, No. 1, Jan.-March 2002, pp. 82-85.

● S. Helal, “Pervasive Java, Part II,” IEEE Pervasive Computing, Vol. 1, No. 2, April-May 2002, pp. 85-89.

● C. Neable, “The .NET Compact Framework,” IEEE Pervasive Computing, Vol. 1, No. 4, Oct.-Dec. 2002, pp. 84-87.

● A. Tripath, “Challenges in designing next-generation middleware systems,” Communications on the ACM, Vol. 45, No. 6, June 2002, pp. 39-42.

● Open Mobile Alliance, http://www.openmobilealliance.org/, 2003.


Agenda

● Overview of middleware● Middleware for wireless and mobile wireless

applications● Example mobile middleware

■ Wireless Access Protocol (WAP)■ Java 2 Micro-Edition (J2ME)■ Microsoft .NET Compact Framework (.NET CF)


Middleware (1)

● Middleware is a somewhat overloaded term● Generally speaking, middleware provides software

services for application programs above the basic operating system and networking services

● Accessed via an application program interface (API), but more than an API

Operating Systemand Networking Services

Middleware

Application ProgramsAPI


Middleware (2)

● Goal is to simplify development effort and increase application functionality and robustness■ Allow code to run across different platforms■ Provide higher level abstractions of services

● Example functions■ Messaging■ Distributed object management■ Directory services■ Location services■ User-defined and composite data types■ Remote procedure calls (RPC)■ Alternate communication abstractions


Role of Middleware

● Middleware is a layer between the operating system and applications that provides a set of services

● Middleware presents an abstract interface to the application that provides the application developer with a uniform view of lower-level operating systems and networks

● In wireless mobile environments, middleware must be flexible to enable adaptation to changes in…■ the underlying operating systems and networks, and■ application requirements


Wireless and Mobile Applications (1)

● “Resource-poor” mobile devices■ Limited memory and buffer space (typically no disk)■ Small screen■ Low processing capabilities■ Limited battery life

● Location of a mobile device may change frequently due to mobility■ Relative to network and other services■ Relative to other hosts


Wireless and Mobile Applications (2)

● Capacity of the wireless channel is limited and may vary

● Communication is often unreliable■ Short-term “fades” – high bit errors■ Long-term disconnects – disconnected operationForced or

voluntary disconnection

● Disconnected operation (read/write) requires system support■ Data caching■ Pre-fetching■ Integration


Desirable Middleware Functionality (1)

● Optimization – data compression● Transformation – data format transformation to suit

various device specifications■ HTML pages to WML (for WAP 1.0 devices) and vice versa■ SOAP/XML for web services

○ From XML to xHTML (for WAP 2.0 and future i-mode devices)

○ From XML to cHTML (for existing i-mode phone devices)

● Support for security and privacy● Support for mobility

■ Location transparency (ad hoc communication) versus awareness


Desirable Middleware Functionality (2)

● Support for service discovery● Support for disconnected operation● Context-aware adaptability

■ Status of the host device, the user, the surrounding environment, and the interactions between the host device and other devices

■ Essential for pervasive (ubiquitous) computing

● Platform independence■ Same program can be run on a wide variety of devices and

platforms


Example “Mobile” Middleware (1)

● Client-server model■ Wireless Application Protocol (WAP)■ Web services

○ Server Microsoft’s Mobile Internet Toolkit (MIT)

○ Client Microsoft’s eMbedded Visual Toolkit (eVT) Microsoft’s .NET Compact Framework (.NET CF) Sun’s Java 2 Micro Edition (J2ME)


Example “Mobile” Middleware (2)

● Peer-to-peer and ad hoc model■ Intel/Microsoft Universal Plug and Play (UPnP)■ Jini/J2ME■ Service Location Protocol (SLP)


WAP – Objectives

● Enable wireless terminals, especially digital cellular phones, to access Internet content and advanced data services

● Specify a protocol that will work across differing global wireless network systems

● Enable creation of content and applications that scale across different networks and devices

● Where possible, use and extend existing standards and technologies

WAPInternet Wireless


WAP – Programming Model

● WAP gateway or proxy■ Content encoders and decoders■ Protocol gateways, e.g. for WAP protocols to HTTP and

TCP/IP

Client

WebBrowser

Server

HTTPServer

CGI,etc.

Gateway

EncodersDecoders

encodedrequest

encodedresponse

request

responseProtocol

Gateways

wireless


WAP and Wireless Web Access (1)

● Data transformation■ WAP gateway performs data

transformation between WML (or XHTML) and HTML

● Data compression■ Technique are used for dealing

with images and other graphics

● Adaptability■ User profile and device

characteristics are stored in the WAP gateway

WebServer

WAP Gateway

Encodedrequest

Request(e.g., HTTP)

Response(e.g., HTML)

EncodedResponse(WML)


WAP and Wireless Web Access (2)

● Security■ Secure Enterprise Proxy (SEP) using 128-bit encryption in

WAP 1.2

● Service discovery and mobility support■ WAP’s “walled garden” – WAP gateways are provided by ISP

such as AOL


J2ME – Java for Hand-Held Devices (1)

● Platform independence■ The same byte-code Java

application can be downloaded and executed by all Java-enabled devices○ For example, a MIDlet created

based on the MIDP API■ Pre-verification at compile time to

verify if an application can run with J2ME’s Kilobyte Virtual Machine (KVM)

Byte-code JavaApplications

(e.g., MIDlets)


J2ME – Java for Hand-Held Devices (2)

● Data compression■ A MIDlet application comes with a Java Application

Descriptor (JAD) metafile containing instructions for uncompressing the application in compressed Java Archive (JAR) format

● Security■ Java Card technology using public key■ A downloaded Java program must have a legal digital

signature to execute

● Service discovery■ JINI based on Java service objects


J2ME Architecture (1)

From S. Helal, “Pervasive Java,” IEEE Pervasive Computing, Vol. 1, No. 1, Jan.-March 2002, pp. 82-85.


J2ME Architecture (2)

● Profile layer■ Minimum set of APIs available for the specified underlying

configuration

● Configuration layer■ Defines a minimum set of JVM features and core Java class

libraries available on a particular category of devices

● JVM layer■ Virtual machine layer (bottom layer)


J2ME/MIDP Runtime on a PocketPC

● Sun Microsystems has released JVM with MIDP for PalmOS PDAs, but is not continuing development of JVM for PocketPC

● J2ME can be run on a PocketPC■ Jeode JVM provides Personal

Java 1.2 support. ■ me4se emulates MIDP devices

using Personal Java

PocketPC

Jeode JVM(Personal Java)

ME4SE(J2ME emulator)

J2ME applications(MIDP)


Microsoft’s .NET CF (1)

● .NET Compact Framework (.NET CF) is part of Microsoft’s larger .NET Framework■ Targets PocketPC, WindowsCE, Windows Mobile, etc.

● .NET CF is based on Microsoft’s Common Language Infrastructure (CLI) standard ■ Source code and complied binaries in Microsoft Intermediate

Language (MSIL) can run across CLI-based heterogeneous devices

■ Microsoft’s Common Language Runtime (CLR), like Sun’s JVM, has the objective of platform independence


Microsoft’s .NET CF (2)

● .NET CF allows small form-factor devices to easily access remote (server) data using the Internet standard protocols■ XML-based Simple Object Access Protocol (SOAP)■ Web Service Description Language (WSDL)■ XML web services are central to Microsoft’s .NET framework


.NET Component Framework (1)

C. Neable, “The .NET Compact Framework,” IEEE Pervasive Computing, Vol. 1, No. 4, Oct.-Dec. 2002, pp. 84-87.

Platform adaptation layer (PAL) tailored for a specific platform

CLR runs MSIL and uses a just-in-time (JIT) compiler to convert MSIL to native code

CLI-compliant base class libraries provide building block functionality for all applications (basic file I/O, networking, XML handling)


.NET Component Framework (2)

C. Neable, “The .NET Compact Framework,” IEEE Pervasive Computing, Vol. 1, No. 4, Oct.-Dec. 2002, pp. 84-87.

Available to applications in .NET CF

Windows forms library XML web services ADO.NET (for remote

data-access)


Mobile Data Access in .NET CF

● Active Data Object (ADO) .NET■ Mobile applications can access

Microsoft SQL Server 2000 on remote servers or access a SQL Server CE locally on the device

● Disconnected mode support■ SQL Server CE lets applications cache

large volumes of data (tens of megabytes), read, and update in disconnected mode

● SQL Server CE provides synchronization mechanisms for changes made upon reconnection

SQL Server

Internet Information Server (IIS)

Internet

SQL Server CE

• Caching• Synch


.NET CF Functionality (1)

● Platform independence■ The same .NET MSIL-code

application can be downloaded and executed by CLR enabled devices

● Optimization■ Proxy protocols can be

designed to optimize performance using techniques such as forms differencing

MSIL-code.NET Applications

dynamically deliveredto CLR-enabled devices


.NET CF Functionality (2)

● Data Transformation■ XML transformed automatically to HTML, XHTML, cHTML, or

WML (at the server end)

● Disconnected operations■ Data caching, pre-fetching, and synchronization available

using Microsoft SQL Server 2000 on the remote server and SQL CE on the local device


PocketPC User Interface Design (1)

● User Interface design constraints■ A small, portrait-oriented, touch-sensitive screen■ User input with an input panel and the stylus (pointer)

○ Single-tap opens an item○ A tap and hold displays a pop-up menu or a tip

● Normally no “Close” button is necessary■ PocketPC automatically closes idle applications as more

memory is needed

● Normally no “Save” button is necessary■ PocketPC relies on application’s “autosave” to retain user

data


PocketPC User Interface Design (2)

● System-level and navigation actions at the top of the screen■ Start Menu■ Navigation Bar (top)

● Application-level and editing actions at the bottom of the screen■ Menu bar (also called

command bar)■ Input Panel Button


Pocket PC User Interface Controls

● Buttons● Check boxes● Option buttons● Command bars● Tool bars● ToolTips● Menus● Pop-up menus● Message boxes● Property sheets● Tabs● Text boxes● List boxes

● Combo boxes● Up/Down controls● Date/Time pickers● MonthCal controls● List views● Header controls● Tree views● Group Line Separators● Scroll bars● Sliders● Status bars● Progress bars


.NET CF and VS .NET

● NET Compact Framework – add-in for Visual Studio .NET 2003

● Uses C#● Write managed .NET code


Summary

● Basics of middleware and unique requirements for wireless and mobile devices

● Example middleware: WAP, J2ME, and .NET CF

lecture 3 middleware fundamentals wireless and mobile systems design

Documents

role of middleware middleware

set of services middleware

generation middleware

various middleware platforms

mobile applications

wireless mobile environments

mobile systems design

wireless channel