Wireless Access and Terminal Mobility in CORBA Dimple Kaul, Arundhati Kogekar, Stoyan Paunov

Background and Motivation What is Mobility Support? –Mobility Transparency for clients –Efficient hand-off mechanisms Where is the Mobility Support implemented? –Link Layer –Network Layer –Middleware Layer Link Layer Mobility Support: –Restricted to single link technology, administrative domain and small area –Example: Mobile hosts on the same WLAN Network Layer Mobility Support: –Uses Mobile IP –May cause unacceptable delays –Does not support interoperability between multiple wireless protocols –Does not allow applications to exploit location information for optimization purposes –Does not address wireless protocols

Mobility Support at the Middleware Layer What are the advantages of using middleware? –Hide low-level details from application developers –Enables heterogeneous systems to communicate with each other –Provides QoS guarantees. Examples: Reliability, fault tolerance, load balancing Why provide mobility support at the middleware layer? –Scalable resource discovery –Security and Authentication –Interoperability between heterogeneous nodes –QoS Monitoring and Adaptation –Location-Aware Optimizations Layer which resides between applications and underlying OS and network protocols

Project Statement Implement the “Wireless Access and Terminal Mobility in CORBA” specification as an extension to The ACE ORB (TAO). Key Terms: –Common Object Request Broker Architecture (CORBA) CORBA is a specification for a set of interfaces which enables efficient and transparent client-server communication. –The ACE ORB (TAO): An implementation of CORBA, developed at University of California, Irvine, Washington University, St. Louis, and Vanderbilt University, Nashville.

Macro (Host) Mobility Home agent is important Does not address wireless protocols Hides all handoff events making location aware services difficult Object level Mobility Can have homeless terminals Addresses wireless protocols Mobile IPWireless CORBA

Wireless Access Network Mobile client Access Bridge Fixed Network Wireless Access Network Home Location Agent Access Bridge Mobile server Terminal Bridges

Mobility Architecture Home Domain: hosts the Home Location Agent of the terminal. Visited Domain: hosts one or more Access Bridges through which it provides ORB access to some mobile terminals. Terminal Domain: terminal device hosting an ORB and a Terminal Bridge through which its objects can communicate with objects in networks.

Key Components  Mobile IOR: Mobile re-locatable object reference  Home Location Agent: Keeps track of the current location of the mobile terminal  Access Bridge: The network side end-point of the GIOP tunnel. It encapsulates GIOP messages to the Terminal Bridge and de-capsulates the GIOP messages from the Terminal Bridge  Terminal Bridge: Terminal side end-point of the GIOP tunnel  GIOP tunnel:  It is a means to transmit GIOP messages between the Terminal Bridge and the Access Bridge  Only one GIOP tunnel between Terminal bridge & Access bridge  The abstract GIOP Tunneling Protocol (GTP) defines how GIOP messages are presented. It also specifies necessary control messages. Different types of concrete tunneling protocols like TCP, UDP and WAP can be specified. We have implemented only TCP tunneling protocol.

Implementation Specifics 1/2 Context: –Distributed objects exposing interfaces –Objects communicate and invoke operations via Interoperable Object References (IOR) –Standard communication protocol: GIOP/IIOP Goal –need standard way to discover and forward object requests to/from mobile objects Mechanisms –Mobile object forwards to Terminal Bridge –Terminal Bridge forwards to Access Bridge –Access Bridge forwards to non-mobile object –Bridges communicate via GIOP tunneling protocol –Provide recovery and hand-off support to enable terminal mobility

Protocol Stacks in GIOP Tunneling Terminal ORB Access Bridge ORB peer ORB GIOP GIOP messages TCP TCP byte stream IIOP IIOP messages GTP adaptation layer transport GTP GTP msgs Object CORBA invocations Object

Implementation Specifics 2/2 Implementation parts: –Implement the Mobile Interoperable Object References (MobileIORs) –Detect at the ORB level if a an object is mobile or not –Forward the GIOP messages to/from mobile objects to the Terminal Bridge –Implement the abstract GIOP Tunneling protocol between the Terminal Bridge and the Access Bridge and provide at least 1 concrete implementation –Forward GIOP messages within the fixed network once they arrive at the Access Bridge via the GIOP tunnel –Optionally implement the Home Location Agent –Optionally implement the hand-off support part of the GTP to enable terminals to migrate their GIOP tunnels to other Access Bridges and perform recovery operations. –Optionally integrate the mobility mechanisms with the Notification service to enable terminal movement tracking.