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					TU/e Service Discovery Mechanisms:
                                             Two case studies


                                     Control                UPnP
                                                                      Device
                                     point



                                   Terminal                wireless   Host
                                   Domain                  CORBA




Service Discovery Mechanisms: two case studies / IC’2002
TU/e                        Software Architectures for
                                 interoperability
                                         Application                         Application


                                           network                             network
                                           manager                             manager


                                      (a) Middleware bases on API, network issues are kept away


                                         Application                        Application


                                           specific                           specific
                                           protocols                          protocols

                                           transport                          transport
                                           layer                              layer


                                      (b) Aspects of the protocol and of the underlying network technology
                                          carry through into the application.
Service Discovery Mechanisms: two case studies / IC’2002
TU/e                            Service recognition

                          •A service can range from the unstructured use of
                           a device to the structured control of well-defined
                           functions.

                          •How the service is made available:
                                - Via the driver provided by the device
                                - Via the interface definition document (XML)
                                - Rely on standardized protocols

                          •Service discovery mechanisms can be classified:
                                 - Centralized
                                 - Distributed


Service Discovery Mechanisms: two case studies / IC’2002
TU/e                      Service Discovery in UPnP(1)
                         The Universal Plug and Play Protocol (UPnP)
                         uses the Simple Service Discovery Protocol (SSDP) to
                         locate the service in IP networks.

                                                 searching              advertising
                                                                                        Device 1
                                 Control
                                 point 1

                                                             Internet

                                               searching                 advertising


                                  Control                                              Device 2
                                  point 2

                                     •Both searching and advertising use HTTP Multicast.
                                     •The response uses HTTP Unicast.
                                     •UPnP targets to home-networking environments.
Service Discovery Mechanisms: two case studies / IC’2002
TU/e                      Service Discovery in UPnP(2)

              UPnP uses the context-based mechanism to make the
              control point understand about the device and its services:

                     - At the device side, the device and its services are
                        specified in XML files.

                     - After processing SSDP, the control point downloads
                        these files, parse them to fully understand the device.




Service Discovery Mechanisms: two case studies / IC’2002
TU/e                      Service Discovery in UPnP(3)
                                  A remote UIClient controls a TVDevice
                                         UIClient                            TVDevice


                                       API for             UPnP               API for
                                       Control point                          Device


                                       Java Virtual                         Java Virtual
                                       Machine                              Machine


                                       Operating                            Operating
                                       system                               system


                                                            IP
                                        IP Network                          IP Network



                                  1.   UIClient and TVDevice use SSDP to discover each other.
                                  2.   UIClient retrieves the TVDevice description and get a list of
                                       associated services.
                                  3.   UIClient retrieves the service descriptions of interesting services.
                                  4.   UIClient starts interacting with TVDevice.
Service Discovery Mechanisms: two case studies / IC’2002
TU/e Service Discovery in CORBA(1)
                         CORBA uses a centralized Naming or Trading Service
                         to locate the services available on the network.

                                                 access                  register
                                                           Access                    Shop 1
                                 Cient 1                   Bridge


                                                              Internet
                                                           Access
                                                           Bridge
                                               access                     register

                                                                                     Shop 2
                                  Client 2


                                     •Services are registered at a Naming Service
                                     •Clients discover services by accessing a Naming Service
                                     •Each Access Bridge can contain its own Naming Service
                                     •Wireless CORBA targets the mobile phone environment

Service Discovery Mechanisms: two case studies / IC’2002
TU/e Service Discovery in CORBA(2)
                      CORBA uses pre-defined API interfaces to allow clients
                      to access services that use supported interfaces:

                                 • Each service uses a certain API interface
                                 • Clients support a limited set of API interfaces
                                 • API interfaces are not extensible

                                 Problem: this does not scale well

                                 Solution: protocol on top of CORBA
                                 Example: Remote User Interface protocol



Service Discovery Mechanisms: two case studies / IC’2002
TU/e Service Discovery ina TVDevice (3)
          A remote UIClient controls
                                     CORBA
                                                           Remote UI
                                          UIClient                           TVDevice


                                                            GIOP
                                            ORB                               ORB


                                         Operating                         Operating
                                         system                            system


                                                             IP
                                         IP Network                        IP Network



                                    1.     UIClient and TVDevice use Naming service to
                                           discover each other.
                                    2.     UIClient subscribes to the TVDevice and get an initial
                                           user interface description
                                    3.     User performs actions through the user interface rendered
                                           by UIClient
                                    4.     TVDevice handles requests from UIClient and returns
                                           updates for the user interface.
Service Discovery Mechanisms: two case studies / IC’2002
TU/e                                         Conclusion
             •UPnP and wireless CORBA use clearly different models for
                    service discovery. Wireless CORBA belongs to (a) and
                    UPnP belongs to (b) – slide 2.
             •UPnP uses HTTP Multicast – a distributed method.
             •Wireless CORBA relies on the infrastructure available within
                    it to publish services, like the use of naming service
                    – a centralized method..
             •Scalability in both technologies is limited. In UPnP because of
                    the restriction of the multicasting protocol. In wireless
                    CORBA this is due to the limitation of API interfaces.
             •For wireless CORBA, it is unclear how services are easily
                    discovered on other terminals that are nearby.



Service Discovery Mechanisms: two case studies / IC’2002

				
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