The Web Service Stack on Symbian OS

The Web Service Stack on Symbian OS

Marco Aiello VITALab --- TUWien (A) & DIT --- Universita’ di Trento (I) [email protected]

Summary • The Web Service Stack • WS-Notification • Application to the case study – WS-Notification Server – WS-Notification on Symbian OS – Implementation on the Nokia 6600 series

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Layers Applications, services

Middleware

Operating system Platform Computer and network hardware © Aiello 2005

ISO Open Systems Interconnection model Message received

Message sent Layers Application Presentation Session Transport Network Data link Physical Sender

Communication medium

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Recipient

OSI protocol summary Layer Application Presentation Session Transport Network Data link Physical

Description Protocols that are designed to meet the communication requirements of specific applications, often defining the interface to a service. Protocols at this level transmit data in a network representation that is independent of the representations used in individual computers, which may differ. Encryption is also performed in this layer, if required. At this level reliability and adaptation are performed, such as detection of failures and automatic recovery. This is the lowest level at which messages (rather than packets) are handled. Messages are addressed to communication ports attached to processes, Protocols in this layer may be connection-oriented or connectionless. Transfers data packets between computers in a specific network. In a WAN or an internetwork this involves the generation of a route passing through routers. In a single LAN no routing is required. Responsible for transmission of packets between nodes that are directly connected by a physical link. In a WAN transmission is between pairs of routers or between routers and hosts. In a LAN it is between any pair of hosts. The circuits and hardware that drive the network. It transmits sequences of binary data by analogue signalling, using amplitude or frequency modulation of electrical signals (on cable circuits), light signals (on fibre optic circuits) or other electromagnetic signals (on radio and microwave circuits). © Aiello 2005

Examples HTTP,FTP , SMTP, CORBA IIOP Secure Sockets (SSL),CORBA Data Rep.

TCP, UDP IP, ATM virtual circuits Ethernet MAC, ATM cell transfer, PPP Ethernet base- band signalling, ISDN

Middleware • Middleware: software layer which abstracts from network hardware, computing hardware, operating systems, programming languages and different implementations providing a uniform computational model • Examples, CORBA, Java RMI, DCOM, … • Middleware provides API to enable the communication of processes as a result of application requests relying on the transport layer © Aiello 2005

Middleware ISO/OSI

Applications, services RMI and RPC request-reply protocol

7 Middleware

6

marshalling and external data representation UDP and TCP

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4

Web Service • Web Services are a form of middlewere in which the abstraction from the implementation is even greater • Web Services are a family of XML-based languages for describing, publishing and binding loosely-coupled applications over the Internet © Aiello 2005

Definition (W3C) • Web service: a software applicatgion indentified by a URI, whose interfaces and bindings are capable of being defined, described and discovered as XML artifacts. A web service supports direct interactions with other software agents using XML-based messages exchanged via Internet-based protocols. © Aiello 2005

Web Service stack

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SOAP • Message format for one way communication • A set of conventions for RPC interaction pattern for client and servers • A set of rules for processing the messages (errors) • Description on how to transport the messages on top of HTTP, SMTP, etc. © Aiello 2005

QoS • A number of protocols for describing nonfunctional properties of services including: – Security – Transactionality – Poilicies

• And for defining Service Level Agreements

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WSDL • An interface definition language relaying on a type system • Abstract part: – types, messages, operations, porttypes

• Concrete part: – Bindings servics and ports

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UDDI • A business registry for the publication and discovery of services • Composed of – White pages: name listings – Yellow pages: taxonomy based – Green pages: technical details

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An example: Google’s web services • Google offers the possibility of performing 1000 queries per day via its freely available web services

GoogleSearch.wsdl

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SOAP Request 00000000000000000000000000000000 shrdlu winograd maclisp teletype 0 10 true false latin1 latin1

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But what’s behind a service? • http://www.mturk.com/

AWSMechanicalTurkRequester.wsdl

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BPEL • For the definition of processes, both abstract and executable • Roles of parties involved in the message exchange in the process • Port types that must be supported • Orchestration context • Correlation of information defining how messages can be routed to correct composition instances • State based system © Aiello 2005

Publish and Subscribe • For mobile devices and pervasive computing, process execution and orchestration are not the only coordination means • Asynchrnous event publishing and subscription mechanisms are paramount!

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The Domotic Web Service Stack WS-Notification

Coordination

WSDL, WS-Policy, UDDI

Service Description

WS-Agreement, WS-QoS, WS-Security

Quality of Service

SOAP device dependent Bluetooth

HTTP WiFi

GPRS

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Transport and Encoding Network

Home outgoing connection

Web Service Stack Implementators as server

Home open network

Web Service Stack Implementators as clients

Device connections

Devices and Actuators © Aiello 2005

WS-Notification • Topic based publish and subscribe mechanism • Includes three specifications: – WS-Base Notification • WS interfaces for point to point communication, operations and message structure

– WS-Brokered Notification • WS interfaces for broker

– WS-Topics • Tree structure, metadata and subscription expression © Aiello 2005

Known implementations • Used in the Globus Toolkit for notification in GRIDs (no broker server implemented) • WS-Messenger (WSMG) at Indiana University, an open source prototype • Zanoni’s implementation at Univ. of Trento for the Domotic scenario

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The use of WS-Notification for the case study • A WS server connected to the sensors • A number of WS clients: – – – –

Java implementation for Palm OS C++ implementation for 60SDK C++ implementation for UIQ (in preparation) .Net implementation for Windows Mobile (in preparation)

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The Server Listens for registrations and sensor events Socket info; ServerSocket ss = new ServerSocket(Property.listeningPort); while (true){ info = ss.accept(); RegisterSubscriptionNotifyThread registerSubscriptionNotifyThread=new RegisterSubscriptionNotifyThread (info,eventSubscriptionTree); registerSubscriptionNotifyThread.start(); } © Aiello 2005

The client’s registration Registration and port on which client is listening for events hostName:port

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The client’s registration Selecting a topic and an expiration for the registration “esns:eventPath” xmlDate © Aiello 2005

WS-Topic LISTING ONE

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Registrations LISTING TWO © Aiello 2005

Implementing the Symbian client

Thanks to Michele Iannotta for the code http://dit.unitn.it/~aiellom/tesi/iannottaCodice.zip © Aiello 2005

Application architecture

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Active Objects CHomeSEngine creates the socket server session creates and connects the socket for server communication manages feedback from socket reader and socket writers informs the UI of visualization tasks

CSocketsReader sends asynchronous requests for reading from the socket server reports data or communication errors to the CHomeSEngine through the MEngineNotifier interface

CSocketsWriter sends asynchronous requests for writing on the socket server reports data or communication errors to the CHomeSEngine through the MEngineNotifier interface © Aiello 2005

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CHomeSEngine

HomeSEngine.cpp

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CSocketReader

SocketsReader.cpp

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CSocketWriter

SocketsWriter.cpp

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An example

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Home outgoing connection

Web Service Stack Implementators as P2P on the home open network

Device connections

Devices and Actuators © Aiello 2005

Discussion • We have implemented the web service stack on a symbian mobile device in the context of a domotic application • But the techniques is general • Symbian is suitable given the attention in resource management, in particular, battery, memory, processing time active objects and leaves © Aiello 2005

Discussion • We should build the WS Stack on Symbian for any P2P application • The important issues are: – XML processing – Portability – Smart use of active objects

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Discussion • Disadvantages of this approach are in the high cost of message exchange: – XML messages are heavy to parse – XML messages may be unecessarly big

The price to pay for interoperability?

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Discussion • Other possibility for using the WS stack on a mobile device are: – Java (e.g. for Palm OS) • http://java.sun.com/products/wsa/

– .Net (e.g. for iMate poketPC) • http://msdn.microsoft.com/library/default.asp?url=/library/enus/dnppcgen/html/devsmartphone.asp • http://msdn.microsoft.com/library/default.asp?url=/library/enus/dnnetcomp/html/compactfxtechart.asp

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