Download ECE/CS 4984: Lecture 1

Wireless and Mobile Systems Design
Lecture 3
Middleware Fundamentals
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
Middleware Fundamentals
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Resources
● S. Helal, “Pervasive Java,” IEEE Pervasive
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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.
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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)
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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
API
Application Programs
Middleware
Operating System
and Networking Services
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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
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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
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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
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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
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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
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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
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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)
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Example “Mobile” Middleware (2)
● Peer-to-peer and ad hoc model
■ Intel/Microsoft Universal Plug and Play (UPnP)
■ Jini/J2ME
■ Service Location Protocol (SLP)
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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
Internet
Middleware Fundamentals
WAP
Wireless
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WAP – Programming Model
Client
encoded
request
Web
Browser
Gateway
request
Server
Encoders
Decoders
HTTP
Server
Protocol
encoded
Gateways response
response
CGI,
etc.
wireless
● WAP gateway or proxy
■ Content encoders and decoders
■ Protocol gateways, e.g. for WAP protocols to HTTP and
TCP/IP
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WAP and Wireless Web Access (1)
● Data transformation
■ WAP gateway performs data
transformation between WML (or
XHTML) and HTML
Encoded
request
● Data compression
■ Technique are used for dealing with
images and other graphics
● Adaptability
■ User profile and device
characteristics are stored in the
WAP gateway
Middleware Fundamentals
Encoded
Response
(WML)
WAP Gateway
Request
(e.g., HTTP)
Response
(e.g., HTML)
Web
Server
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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
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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
Byte-code Java
○ For example, a MIDlet created
Applications
based on the MIDP API
(e.g., MIDlets)
■ Pre-verification at compile time to
verify if an application can run with
J2ME’s Kilobyte Virtual Machine
(KVM)
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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
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J2ME Architecture (1)
From S. Helal, “Pervasive Java,” IEEE Pervasive Computing, Vol. 1, No. 1, Jan.-March 2002, pp. 82-85.
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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)
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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
J2ME applications
(MIDP)
ME4SE
(J2ME emulator)
Jeode JVM
(Personal Java)
PocketPC
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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
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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
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.NET Component Framework (1)

CLI-compliant base class
libraries provide building block
functionality for all applications
(basic file I/O, networking, XML
handling)

CLR runs MSIL and uses a justin-time (JIT) compiler to convert
MSIL to native code

Platform adaptation layer (PAL)
tailored for a specific platform
C. Neable, “The .NET Compact Framework,” IEEE Pervasive Computing, Vol. 1, No. 4, Oct.-Dec. 2002, pp. 84-87.
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.NET Component Framework (2)
 Available
to applications in
.NET CF
 Windows forms library
 XML web services
 ADO.NET (for remote
data-access)
C. Neable, “The .NET Compact Framework,” IEEE Pervasive Computing, Vol. 1, No. 4, Oct.-Dec. 2002, pp. 84-87.
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Mobile Data Access in .NET CF
SQL Server CE
• Caching
• Synch
Internet
Internet
Information
Server (IIS)
SQL Server
Middleware Fundamentals
● 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
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.NET CF Functionality (1)
● Platform independence
■ The same .NET MSIL-code
application can be downloaded
and executed by CLR enabled
devices
MSIL-code
.NET Applications
dynamically delivered
to CLR-enabled devices
● Optimization
■ Proxy protocols can be
designed to optimize
performance using techniques
such as forms differencing
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.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
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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
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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
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Pocket PC User Interface Controls
● Buttons
● Combo boxes
● Check boxes
● Up/Down controls
● Option buttons
● Date/Time pickers
● Command bars
● MonthCal controls
● Tool bars
● List views
● ToolTips
● Header controls
● Menus
● Tree views
● Pop-up menus
● Group Line Separators
● Message boxes
● Scroll bars
● Property sheets
● Sliders
● Tabs
● Status bars
● Text boxes
● Progress bars
● List boxes
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.NET CF and VS .NET
● NET Compact Framework – add-in for Visual Studio
.NET 2003
● Uses C#
● Write managed .NET code
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Summary
● Basics of middleware and unique requirements for
wireless and mobile devices
● Example middleware: WAP, J2ME, and .NET CF
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