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					Service Invocation and Roaming
    in Pervasive Computing
         Environments

            Masters Seminar

          Presenter: Alvin Chin
     Supervisor: Kostas Kontogiannis
     Software Engineering Group, E&CE,
            University of Waterloo
          achin@swen.uwaterloo.ca
         kostas@swen.uwaterloo.ca
          Friday, June 27, 2003
 Service Invocation and Roaming in                   2
 Pervasive Computing Environments
  Agenda
  1.    Introduction
  2.    Problem with pervasive computing today
  3.    How to perform service discovery
  4.    Roaming
  5.    System architecture
  6.    Using mRoam
  7.    Related work
  8.    Conclusions
  9.    Future work
  10.   References
  11.   Discussion
MASc Seminar           Alvin Chin          June 27, 2003
 Service Invocation and Roaming in                                     3
 Pervasive Computing Environments
  1. Introduction
  •   What is pervasive computing?
  •   Mark Weiser summed it best:

      Conceive a new way of thinking about computers, one
      that takes into account the human world and allows
      the computers themselves to vanish into the
      background
      [1] Mark Weiser, The Computer for the 21st Century, Scientific
      American, 1991.




MASc Seminar                 Alvin Chin                June 27, 2003
 Service Invocation and Roaming in                           4
 Pervasive Computing Environments
  2. Problem with pervasive computing today
  •   Different devices, different operating systems, different
      user interfaces
  •   Have to learn how to do same task on different
      devices (eg. cell phone, Palm PDA, Pocket PC)
  •   Wireless networks are unreliable and slower than
      wired LANs (limited bandwidth)
  •   Devices and users are not stationary, devices and
      networks prone to failure and disconnection

         A new paradigm is needed to address
                     these issues

MASc Seminar              Alvin Chin            June 27, 2003
 Service Invocation and Roaming in                           5
 Pervasive Computing Environments
  2. Problem with pervasive computing today
  How can we achieve the vision of pervasive computing?
  •   Service driven paradigm
  •   Service invocation – users access services on any
      device depending on profile and privileges
  •   Service roaming – users continue service when
      moving from one location to another without
      interruption, or access services at specific locales
      Computing environment is adapted to user mobility,
         complexity is insulated from the user and
       becomes blended into the human environment

MASc Seminar              Alvin Chin            June 27, 2003
 Service Invocation and Roaming in                         6
 Pervasive Computing Environments

  3. How to perform service discovery
  •   Service advertisement, service registration and service
      discovery
  •   Many technologies supporting this: UPnP, Jini,
      Salutation, SLP, UDDI, Bluetooth SDP

      Requirements: simple, low overhead, flexible
      service protocol

  •   We choose UDDI and web services



MASc Seminar             Alvin Chin            June 27, 2003
 Service Invocation and Roaming in                            7
 Pervasive Computing Environments

  3. How to perform service discovery
  Service-oriented architecture (SOA)

                            Service
                            provider


                Publish                   Bind



                               Find
                Service                  Service
                broker                  requester




MASc Seminar              Alvin Chin                June 27, 2003
 Service Invocation and Roaming in                      8
 Pervasive Computing Environments

  4. Roaming
  •   Ability to move from one coverage area to another
      without any interruption in service or loss in
      connectivity
  •   Much research and products for roaming capabilities
      on wireless devices are being done
  •   No complete integrated solution is available
  •   Idea: to support cellular-like roaming on devices
      between any wireless network (3G, Bluetooth, 802.11)
  •   Perform data transactions seamlessly



MASc Seminar            Alvin Chin           June 27, 2003
 Service Invocation and Roaming in                                       9
 Pervasive Computing Environments

  4. Roaming
  •   How to achieve roaming?
      Ø   Many different methods each operating at different OSI layer
      Ø   Physical radio layer
      Ø   Network layer
      Ø   Application layer
  •   Physical radio layer
      Ø   Measure signal strength from access point to device
      Ø   Vertical handoff [3]
      Ø   Disadvantages: access point has to initiate polling and
          constantly send beacon signal, unique to different wireless
          technologies

MASc Seminar                   Alvin Chin                June 27, 2003
 Service Invocation and Roaming in                                   10
 Pervasive Computing Environments

  4. Roaming
  •   Network layer
      Ø Signalling protocol for roaming
      Ø Disadvantages: requires change to existing network
        infrastructure, idea of home and foreign agents (as in MobileIP)

  •   Application layer
      Ø Use middleware software to detect client roaming from one
        location to another
      Ø Advantages: does not require change to existing network
        infrastructure, no need to change design of access point or use
        polling



MASc Seminar                  Alvin Chin               June 27, 2003
 Service Invocation and Roaming in                                     11
 Pervasive Computing Environments

  5. System architecture
  •   Out of all the roaming methods, application roaming is
      most flexible
  •   We select that in our architecture
  •   Introduce middleware proxy
      Ø Performs logic needed to perform roaming
      Ø Brokers client requests and server responses
      Ø Insulates client disconnections, crashes and migrations from
        backend server




MASc Seminar                 Alvin Chin               June 27, 2003
 Service Invocation and Roaming in                                       12
 Pervasive Computing Environments
  5. System architecture



     Handheld                                                   Server
      device     Wireless                              Corporate
                 Network                              Wired Network

                                       mRoam



   Laptop computer
                                                                Server



                            High level architecture


MASc Seminar                  Alvin Chin                   June 27, 2003
 Service Invocation and Roaming in                                                          13
 Pervasive Computing Environments
   5. System architecture
                               SOAP Service operation call


                      SOAP Service operation response        Service
                                                             discovery     UDDI
           Service                                           lookup
                                                                          registry
           request
                                                                           UDDI       Web Services
                                                                          registry



           Service                                                         UDDI
          response                                                        registry




 Mobile      Wireless Front-end      Service   Service Distributed                   Back-end
 client    access point Content      roaming invocation directory of                 enterprise
                                   framework framework services                       services

                          Detailed deployment architecture


MASc Seminar                       Alvin Chin                            June 27, 2003
 Service Invocation and Roaming in                                     14
 Pervasive Computing Environments

  5. System architecture
  •       Mobile client
      •     Mobile device with wireless interface and HTTP web browser
      •     User can select services & execute operations on that service

  •       Wireless access point
      •     Connects mobile client over wireless network to wired network
      •     Associated with location

  •       Front-end content
      •     Receives HTTP requests, processes them, retrieves HTTP
            responses, formats them, and delivers to clients

MASc Seminar                    Alvin Chin                June 27, 2003
 Service Invocation and Roaming in                                                       15
 Pervasive Computing Environments

  5. System architecture
  •      Front-end content
                           service request

                                        login                               service request/
                         Login                            Dispatcher        response
               login    Process                            Process
                                                                                     Service
      Mobile                        logout      session                find location Roaming
      client                                    mgmt        display    & proxy      Framework
               logout   Logout                  Session               Content
                        Process                 Manager               Pages


                           service response



MASc Seminar                        Alvin Chin                           June 27, 2003
 Service Invocation and Roaming in                                    16
 Pervasive Computing Environments

  5. System architecture
  •       Service roaming framework
      •    Provides seamless invocation and interaction of services
           without any interruptions
      •    Disruptions are:
           Ø network & client disconnections
           Ø client crashes
           Ø location changes and migrations




MASc Seminar                     Alvin Chin              June 27, 2003
 Service Invocation and Roaming in                                                  17
 Pervasive Computing Environments

   5. System architecture
   •     Service roaming framework
                                              translate
       service request                           req /
       service response         Proxy    proxy resp Service
                  find proxy   Manager proxy           Translator
                                                       proxy   SIF
                                                                                Service
Front-end           DPC
                                   DPU                 resp    request        Invocation
 Content find      Manager
                                                                              Framework
           loc &                               proxy     Proxy
           proxy                Proxy proxy req
                    DPC                                  Server          SIF
                               Manager proxy
                                                                         response

                                   DPU




MASc Seminar                       Alvin Chin                     June 27, 2003
 Service Invocation and Roaming in                                      18
 Pervasive Computing Environments

  5. System architecture
  •       Service invocation framework
      •    Processes client service requests from service roaming
           framework and discovers available services satisfying that
           request
      •    Based on previous Masters student’s thesis




MASc Seminar                   Alvin Chin                June 27, 2003
 Service Invocation and Roaming in                                                     19
 Pervasive Computing Environments

    5. System architecture
    •   Service invocation framework


                                                    invoke                   Invoke
            SIF             fwd           SOAP       ECA                     service
  Service   req             req    Servlet req SOAP script           ECA          Distributed
                   HTTP
 Roaming                           Request         Request           Rule          Directory
                   Server
Framework                         Dispatcher      Dispatcher        Engine        of Services
             SIF            resp               SOAP        ECA                 get
            resp                                resp       script            service
                                                           resp




MASc Seminar                           Alvin Chin                      June 27, 2003
 Service Invocation and Roaming in                                         20
 Pervasive Computing Environments

  5. System architecture
  •       Distributed directory of services
      •     Yellow pages catalog of back-end enterprise services exposed
            as web services
  •       Back-end enterprise services
      •     Services available in the enterprise such as e-mail, billing and
            scheduling




MASc Seminar                     Alvin Chin                 June 27, 2003
  Service Invocation and Roaming in                                         21
  Pervasive Computing Environments

     5. System architecture
     •    Distributed directory of services

                            UDDI
                           registry                          invoke
                                                   Web
          invoke service                                     service
                                      register   Service 1
   Service lookup service             service                          Back-end
 Invocation             UDDI                       Web                 Enterprise
Framework service reg registry                   Service 2     get      Services
                                                             service
                 get
               service                             Web
                            UDDI
                           registry              Service N




MASc Seminar                             Alvin Chin          June 27, 2003
 Service Invocation and Roaming in                                                              22
 Pervasive Computing Environments

  5. System architecture
  •       Roaming
                                                      Login process

                      1           3                                     7

                                          2       8       9
                              4                                     9

                                                          Service roaming        7
      1   3   4   5           5                             framework                   9



                          6
                                      4       5       8         9
       Location 1:                                                             Location 2:
                                                      Service invocation
      GPRS network                                                          Bluetooth network
                                                         framework



MASc Seminar                              Alvin Chin                           June 27, 2003
 Service Invocation and Roaming in                                              23
 Pervasive Computing Environments

  5. System Architecture
  •    Roaming
  1.   Mobile device logs into network using HTTP browser with username,
       password and location
  2.   Recovery and roaming proxy determines this is new session, create new
       proxy instance
  3.   Mobile device gets URL to perform service search
  4.   Client creates query to find service in location 1, obtain proxy instance,
       forward to ECA rule engine to make UDDI request, get UDDI response
       with service, return URL to service page to client




MASc Seminar                      Alvin Chin                    June 27, 2003
 Service Invocation and Roaming in                                          24
 Pervasive Computing Environments

  5. System Architecture
  •    Roaming
  5.   Client invokes service operation, forward from proxy to ECA rule engine
       to invoke SOAP request to web service, get SOAP response, proxy
       queues response, send response from proxy back to client
  •    Continue accessing services
  6.   Client now moves from GRPS network outside to Bluetooth network
       indoors, get network disconnection
  •    Client connects to Bluetooth network in Location 2




MASc Seminar                    Alvin Chin                   June 27, 2003
 Service Invocation and Roaming in                                                  25
 Pervasive Computing Environments

  5. System Architecture
  •    Roaming
  7.   Log back in to network. Login Process determines client has existing
       session, location changed from Location 1 to Location 2, updates
       location to Location 2 and locates proxy instance associated with client
       as well as last accessed service.
  8.   Send service authorization request to determine whether interrupted
       service still available to use in Location 2, find out client can use this
       service
  9.   Service authorized, send back last response sent from proxy before
       roaming to client
  •    Client has been successfully handed over to Location 2


MASc Seminar                       Alvin Chin                     June 27, 2003
 Service Invocation and Roaming in                                        26
 Pervasive Computing Environments

  6. Using mRoam
  •       Issuing queries
      •     Perform service query
           Ø Search for all services in this location
           Ø Query for a specific service (local or nonlocal)

      •     Select service
           Ø From list of service(s) above, select appropriate service

      •     Invoke service
           Ø From service, select service operation




MASc Seminar                       Alvin Chin                   June 27, 2003
 Service Invocation and Roaming in                                       27
 Pervasive Computing Environments

  6. Using mRoam
  •       Client disconnection or crash
      •     After connection, user logs back into same location
      •     Continue existing session
      •     Retrieve back last saved service response from proxy
      •     Disconnection
           Ø Previous session still intact

      •     Crash
           Ø Previous session lost, create new session and reload from
             previous stored session in database



MASc Seminar                       Alvin Chin               June 27, 2003
 Service Invocation and Roaming in                                                28
 Pervasive Computing Environments

  6. Using mRoam
  •       Client roaming
      •    Log into new location
      •    Continue existing session
      •    Client migration protocol
      •    Check last saved client query
           Ø If location-sensitive, previous response invalid for this location
           Ø Resend query but for this new location
           Ø If location-independent, just get last saved response
      •    Return updated service response



MASc Seminar                       Alvin Chin                    June 27, 2003
 Service Invocation and Roaming in                            29
 Pervasive Computing Environments

  7. Related Work
  •   Recovery-based proxy [5], [6]
  •   MobileIP and extensions to MobileIP [4], [8]
  •   Directory enabled solution for internet roaming using
      RADIUS and LDAP [6]
  •   Software assisted handover [7]




MASc Seminar             Alvin Chin            June 27, 2003
 Service Invocation and Roaming in                        30
 Pervasive Computing Environments

  8. Conclusions
  •   Pervasive computing requires ubiquitous access to
      services
  •   Need platform to distribute these services
  •   Cell phone has become pervasive
  •   Mobile data devices have not reached that level
  •   Should follow successful model of cellular phone
      networks
  •   Application roaming can help enable pervasive
      computing



MASc Seminar            Alvin Chin           June 27, 2003
 Service Invocation and Roaming in                        31
 Pervasive Computing Environments

  9. Future Work
  •   Add semantic search of services on mobile devices
      using DAML-S, add DAML-S and ontologies to extend
      UDDI for semantic web
  •   RADIUS and LDAP for storage of user profile, user
      authentication and authorization (enterprise network)




MASc Seminar             Alvin Chin            June 27, 2003
 Service Invocation and Roaming in                                          32
 Pervasive Computing Environments
  10. References
  [1] Mark Weiser. The Computer for the 21st Century. IEEE
      Pervasive Computing, Vol. 1, No. 1, January-March 2002, pp. 18-25.
  [2] Scott Weller. Web Services Qualification. IBM developerWorks,
      http://www-106.ibm.com/developerworks/library/ws-qual/, April 2002.
  [3] Mark Stemm and Randy H. Katz. Vertical Handoffs in Wireless Overlay
      Networks. Computer Science Division, Department of Electrical
      Engineering and Computer Science, University of California at Berkeley.
  [4] Theodore B. Zahariadis, Konstantinos G. Vaxevanakis, Christos P.
      Tsantilas, and Nikolaos A. Zervos. Global Roaming in Next-Generation
      Networks. IEEE Communications Magazine, February 2002, pp. 145-
      151.


MASc Seminar                   Alvin Chin                  June 27, 2003
 Service Invocation and Roaming in                                          33
 Pervasive Computing Environments
  10. References
  [5] B.Yao and W.K.Fuchs. Proxy-based Recovery for Applications on
      Wireless Hand-held Devices. In Proceedings of the 19 th IEEE
      Symposium on Reliable Distributed Systems, pp. 2-10, October 2000.

  [6] Cecilia Corbi, Giuseppe Sisto. A Directory Enabled Solution for Internet
      Roaming. In Proceedings of the IEEE International Symposium on
      Computers and Communications. 1999. pp. 39-45

  [7] Edmond Sung and Arkady Zaslavsky. Software Assisted Handover of
      Mobile Clients in Heterogeneous Wireless Computing Environments. 4th
      Asia-Pacific Software Engineering and International Computer Science
      Conference, Hong Kong, December 1997. pp. 527-528.

  [8] Charles E. Perkins. Mobile Networking Through Mobile IP.
      http://www.computer.org/internet/v2n1/perkins.htm

MASc Seminar                    Alvin Chin                  June 27, 2003
 Service Invocation and Roaming in            34
 Pervasive Computing Environments
  11. Discussion

                   Any questions?




MASc Seminar         Alvin Chin     June 27, 2003

				
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