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Lecture 3 Middleware Fundamentals

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

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Lecture 3 Middleware Fundamentals

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  1. Wireless and Mobile Systems Design Lecture 3Middleware 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 Middleware Fundamentals 2

  3. 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. Middleware Fundamentals 3

  4. 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 Fundamentals 4

  5. 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 Application Programs API Middleware Operating Systemand Networking Services Middleware Fundamentals 5

  6. 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 Middleware Fundamentals 6

  7. 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 Middleware Fundamentals 7

  8. 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 Middleware Fundamentals 8

  9. 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 Middleware Fundamentals 9

  10. 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 Middleware Fundamentals 10

  11. 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 Middleware Fundamentals 11

  12. 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) Middleware Fundamentals 12

  13. Example “Mobile” Middleware (2) • Peer-to-peer and ad hoc model • Intel/Microsoft Universal Plug and Play (UPnP) • Jini/J2ME • Service Location Protocol (SLP) Middleware Fundamentals 13

  14. 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 WAP Wireless Middleware Fundamentals 14

  15. WAP – Programming Model encodedrequest • WAP gateway or proxy • Content encoders and decoders • Protocol gateways, e.g. for WAP protocols to HTTP and TCP/IP Client Gateway Server request WebBrowser Encoders Decoders HTTPServer wireless ProtocolGateways CGI,etc. encodedresponse response Middleware Fundamentals 15

  16. 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 Encoded Response (WML) Encoded request WAP Gateway Request (e.g., HTTP) Response (e.g., HTML) WebServer Middleware Fundamentals 16

  17. 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 Middleware Fundamentals 17

  18. 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) Middleware Fundamentals 18

  19. 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 Middleware Fundamentals 19

  20. J2ME Architecture (1) From S. Helal, “Pervasive Java,” IEEE Pervasive Computing, Vol. 1, No. 1, Jan.-March 2002, pp. 82-85. Middleware Fundamentals 20

  21. 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) Middleware Fundamentals 21

  22. 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 Middleware Fundamentals 22

  23. 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 Middleware Fundamentals 23

  24. 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 Middleware Fundamentals 24

  25. .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 just-in-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. Middleware Fundamentals 25

  26. .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. Middleware Fundamentals 26

  27. 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 CE • Caching • Synch Internet Internet Information Server (IIS) SQL Server Middleware Fundamentals 27

  28. .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 Applicationsdynamically deliveredto CLR-enabled devices Middleware Fundamentals 28

  29. .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 Middleware Fundamentals 29

  30. 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 Middleware Fundamentals 30

  31. 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 Middleware Fundamentals 31

  32. 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 Pocket PC User Interface Controls Middleware Fundamentals 32

  33. .NET CF and VS .NET • NET Compact Framework – add-in for Visual Studio .NET 2003 • Uses C# • Write managed .NET code Middleware Fundamentals 33

  34. Summary • Basics of middleware and unique requirements for wireless and mobile devices • Example middleware: WAP, J2ME, and .NET CF Middleware Fundamentals 34

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