Wireless CORBA

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

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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

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Example IDL

• interface Account
• void deposit(in unsigned long amount)
• void withdraw(in unsigned long amount)
• long balance()

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Example client

• CORBAObject_var
• obj orb-gtstring_to_object( uri )
• Account_var
• account Account_narrow( obj )
• ...
• if (account-gtbalance() lt 100)
• account-gtdeposit( 500 )
• else
• account-gtwithdraw( 100 )

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Example server (1)

• class Account_impl virtual public POA_Account
• ...
• CORBALong _current_balance
• ...
• void deposit( CORBAULong amount)
• _current_balance amount
• ...
• CORBALong balance()
• return _current_balance

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Example server (2)

• // orb, poa and mgr setup
• Account_impl
• servant new Account_impl()
• PortableServerObjectId_var
• oid poa-gtactivate_object(servant)
• // construct object uri
• mgr-gtactivate()
• orb-gtrun()

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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

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Implementation Layer
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Interoperability Layer
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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//)

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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

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MobileIP

• IETF solution (RFC 2002)
• Addresses macro-mobility
• home-office, office-travel
• Requires an activehome agent

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Wireless CORBA

• Issues
• MobileIP
• Architecture
• Mobile IORs
• Handoff Access Recovery

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Wireless CORBA - Issues

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

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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.

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Architecture
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Architecture

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

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Architecture

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

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Architecture

• Similar to the Access Bridge
• Does not provide forwarding
• Generates mobility events
• Does not list services

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Architecture

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

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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

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Mobile IOR usage
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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

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Message Forwarding

• Old access bridges forward open connections

GIOP
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Network Initiated Handoff
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Test Case

• ITEA Project Vivian
• Common platform for mobile phones
• CORBA for distributed middleware
• SOAP as alternative

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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)

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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