Download poster - Distributed Object Computing

Wireless Access and
Terminal Mobility in CORBA
Dimple Kaul,
Arundhati Kogekar,
Stoyan Paunov
Background and Motivation
• What is Mobility Support? • Link Layer Mobility Support:
– Mobility Transparency for
clients
– Efficient hand-off
mechanisms
• Where is the Mobility
Support implemented?
– Link Layer
– Network Layer
– Middleware Layer
– 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?
Layer which resides
between applications and
underlying OS and network
protocols
– Scalable resource discovery
– Security and Authentication
– Interoperability between
heterogeneous nodes
– QoS Monitoring and Adaptation
– Location-Aware Optimizations
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.
Access
Bridge
Wireless
Access
Network
Mobile
server
Terminal Bridges
Home Location
Agent
Wireless
Access
Network
Access
Bridge
Fixed Network
Mobile
client
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
CORBA invocations
Object
Object
GIOP messages
GIOP
GTP
GTP adaptation layer
transport
Terminal ORB
GIOP
GTP
msgs
GTP
IIOP messages
IIOP
IIOP
TCP
TCP
GTP adaptation layer
transport
Access Bridge ORB
TCP byte stream
peer ORB
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.