P1253297647ZGPne

1
TU/e
Service Discovery Mechanisms Two
case studies
Control point
UPnP
Device
Terminal Domain
wireless CORBA
Host
Service Discovery Mechanisms two case studies /
IC2002
2
TU/e
Software Architectures for
interoperability
Application
Application
network manager
network manager
(a) Middleware bases on API, network issues are
kept away
Application
Application
specific protocols
specific protocols
transport layer
transport layer
(b) Aspects of the protocol and of the
underlying network technology carry
through into the application.
Service Discovery Mechanisms two case studies /
IC2002
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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 /
IC2002
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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.
advertising
searching
Device 1
Control point 1
Internet
searching
advertising
Device 2
Control 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 /
IC2002
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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 /
IC2002
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Service Discovery in UPnP(3)
A remote UIClient controls a TVDevice
UIClient
TVDevice
UPnP
API for Control point
API for Device
Java Virtual Machine
Java Virtual Machine
Operating system
Operating system
IP
IP Network
IP Network

• UIClient and TVDevice use SSDP to discover each
  other.
• UIClient retrieves the TVDevice description and
  get a list of
• associated services.
• UIClient retrieves the service descriptions of
  interesting services.
• UIClient starts interacting with TVDevice.

Service Discovery Mechanisms two case studies /
IC2002
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Service Discovery in CORBA(1)
CORBA uses a centralized Naming or Trading
Service to locate the services available on the
network.
register
access
Access Bridge
Shop 1
Cient 1
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 /
IC2002
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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 /
IC2002
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Service Discovery in CORBA(3)
A remote UIClient controls a TVDevice
Remote UI
UIClient
TVDevice
GIOP
ORB
ORB
Operating system
Operating system
IP
IP Network
IP Network

• UIClient and TVDevice use Naming service
  todiscover each other.
• UIClient subscribes to the TVDevice and get an
  initial
• user interface description
• User performs actions through the user interface
  renderedby UIClient
• TVDevice handles requests from UIClient and
  returns updates for the user interface.

Service Discovery Mechanisms two case studies /
IC2002
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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 /
IC2002