TU/e Service Discovery Mechanisms: two case studies / IC2002 Service Discovery Mechanisms: Two case studies Control point Device UPnP Terminal Domain Host wireless CORBA

TU/e Service Discovery Mechanisms: two case studies / IC2002 Software Architectures for interoperability Application network manager Application network manager Application specific protocols transport layer Application specific protocols transport layer (a) Middleware bases on API, network issues are kept away (b) Aspects of the protocol and of the underlying network technology carry through into the application.

TU/e Service Discovery Mechanisms: two case studies / IC2002 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

TU/e Service Discovery Mechanisms: two case studies / IC2002 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. Internet Control point 1 Control point 2 Device 1 Device 2 searching advertising Both searching and advertising use HTTP Multicast. The response uses HTTP Unicast. UPnP targets to home-networking environments.

TU/e Service Discovery Mechanisms: two case studies / IC2002 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.

TU/e Service Discovery Mechanisms: two case studies / IC2002 Service Discovery in UPnP (3) A remote UIClient controls a TVDevice API for Control point UIClient Java Virtual Machine Operating system IP Network API for Device TVDevice Java Virtual Machine Operating system IP Network UPnP IP 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.

TU/e Service Discovery Mechanisms: two case studies / IC2002 Service Discovery in CORBA (1) CORBA uses a centralized Naming or Trading Service to locate the services available on the network. 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 Internet Cient 1 Client 2 Shop 1 Shop 2 access register Access Bridge Access Bridge

TU/e Service Discovery Mechanisms: two case studies / IC2002 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

TU/e Service Discovery Mechanisms: two case studies / IC2002 Service Discovery in CORBA (3) A remote UIClient controls a TVDevice ORB UIClient Operating system IP Network ORB TVDevice Operating system IP Network GIOP IP 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. Remote UI

TU/e Service Discovery Mechanisms: two case studies / IC2002 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.