1. Wireless CORBA Richard Verhoeven

2. Content Quick Introduction to CORBA Wireless & Mobile Wireless CORBA Test Case Conclusions

3. What is CORBA? Common Object Request Broker Architecture Distributed object-oriented middleware –Network abstraction of object location –Independent of programming language, platform or operating system Set of open standards defined by the OMG –interface definition language (IDL) –interoperability standards (GIOP, IIOP) –collection of services

4. How does it work? Write the interface definition in IDL Use the ORB-specific IDL compiler to generate client stubs and server skeletons Use the stubs in the client application Fill the skeletons with the server implementation Compile everything

5. Example: IDL interface Account { void deposit(in unsigned long amount); void withdraw(in unsigned long amount); long balance(); };

6. Example: client CORBA::Object_var obj = orb->string_to_object( uri ); Account_var account = Account::_narrow( obj );... if (account->balance() < 100) { account->deposit( 500 ); } else { account->withdraw( 100 ); }

7. Example: server (1) class Account_impl : virtual public POA_Account {... CORBA::Long _current_balance;... void deposit( CORBA::ULong amount) { _current_balance += amount; };... CORBA::Long balance() { return _current_balance; }; }

8. Example: server (2) … // orb, poa and mgr setup Account_impl* servant = new Account_impl(); PortableServer::ObjectId_var oid = poa->activate_object(servant); … // construct object uri mgr->activate(); orb->run();

9. In more detail ORB interface allows generic configuration settings and ORB startup Portable Object Adaptor provides a server with common service features Support for dynamic and static method invocation Interceptors allow extra services

10. Implementation Layer

11. Interoperability Layer

12. Locating a server Object references are standardised (IOR) With a naming service: Client & server use the same naming service Server publishes an IOR at the naming service Client queries the naming service for IORs Or: Exchange the IOR as a string Use a CORBA URL ( corbaloc:// )

13. Sizes of ORBs

14. Interoperability Timing

15. Wireless & Mobile Wireless protocols InfraRed, BlueTooth, 802.11b, GSM, GPRS, UMTS Wireless issues packet loss, network congestion, packet cost Mobile issues hand-off, roaming, address changes Location based services wireless range, position & direction detection

16. MobileIP IETF solution (RFC 2002) Addresses macro-mobility home-office, office-travel Requires an active home agent

17. Wireless CORBA Issues MobileIP Architecture Mobile IORs Handoff & Access Recovery

18. Wireless CORBA - Issues CORBA relies on fixed end-points for connections Nomadic computing Wireless transport issues Mobility transparency Handoff Backwards compatible

19. Why not MobileIP? It only addresses macro-mobility, not the movement between small cells The home agent is too important It does not address wireless protocols It hides all handoff events, thus making location-aware services difficult.

20. Architecture

21. Redirects requests for services on the terminal Keeps track of the current access bridge

22. Architecture Encapsulates, forwards or ignores incoming GIOP messages Decapsulates and forwards messages from the GIOP tunnel Generates mobility events Lists available services

23. Architecture Similar to the Access Bridge Does not provide forwarding Generates mobility events Does not list services

24. Architecture Abstract transport-independent tunnel for GIOP messages Concrete tunnels for TCP/IP, UDP/IP and WAP. Protocol requires reliable and ordered delivery

25. Mobile IORs Contain a special Mobile Terminal Profile Use the Access Bridge or Home Location Agent in the IIOP profile Have a limited lifetime if no Home Location Agent is used Work backwards compatible

26. Mobile IOR usage

27. Handoff & Access Recovery Network initiated handoff –started by an external application –optional to support make-before-break Terminal initiated handoff –terminal discovered a new Access Bridge –make-before-break is required Access recovery

28. Handoff Issues The Home Location Agent is informed Old Access Bridges are informed to allow forwarding of open connection Mobility events are generated in the visited domain and the terminal domain

29. Message Forwarding Old access bridges forward open connections

30. Network Initiated Handoff

31. Test Case ITEA Project “Vivian” Common platform for mobile phones CORBA for distributed middleware SOAP as alternative

32. Test Case Mobile device (Psion Revo) Java virtual machine Java ORB XML sax parser Remote User Interface Protocol Conclusion: it works reasonable (Wireless CORBA not used yet)

33. Conclusions Wireless CORBA addresses wireless & mobility, not low resource constraints. CORBA works on a mobile device, but it requires lots of resources Handoff notification breaks the layered network model