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Real Time & Multimedia Lab
Mobile Computing Middleware A Peek into Jini, UPnP and OSGI
Saad Liaquat Kiani
RTMM Lab
Saad Liaquat Kiani
Kyung Hee University
1
Real Time & Multimedia Lab
Mobile Computing
• Mobile, computing means that the computing device is
not continuously connected to the base or central
network.
• Mobile devices include PDAs, laptop computers, and
many of today’s cell phones (aptly called "smart
phones").
• These products may communicate with a base location
with or without a wireless connection.
– An example of a wireless mobile application is using a
modem-equipped PDA to receive text messages via satellite
technology.
Saad Liaquat Kiani
Kyung Hee University
2
Real Time & Multimedia Lab
Types of Mobile Devices
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A categorization of five different types of mobile devices:
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Laptops are typically used and supported in the same way as desktop PCs.
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They are undergoing rapid evolution and are being brought into organizations in the same way the earliest
PCs were.
Smart phones that allow users to
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Many organizations have replaced desktops with their portable cousins as the workforce has grown
increasingly mobile.
PDAs are the least planned-for and supported devices.
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Laptop computers
PDAs and handheld PCs
Pagers
Smart phones and cellular phones
Task devices, such as bar code scanners
access phone calls,
two-way radio transmissions
paging and data transmissions
Pagers
Task devices such as the parcel tracking devices used by Federal Express (FedEx) and the United
Parcel Service (UPS)
Saad Liaquat Kiani
Kyung Hee University
3
Real Time & Multimedia Lab
Types of Mobile users
• Three types of mobile users:
Percentage of Workforce
– Telecommuters who work away
from the office but connect
directly to the office from a
remote location.
– Casual telecommuters and other
workers who work a few days
per month outside the office.
– Predominantly mobile
employees
Mobility
Saad Liaquat Kiani
Kyung Hee University
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Real Time & Multimedia Lab
Distributed Middleware
•
Middleware is an enabling layer of software that resides between the application
program and the networked layer of heterogeneous platforms and protocols.
– It decouples applications from any dependencies on the plumbing layer that consists of
heterogeneous operating systems, hardware platforms and communication protocols
•
Most distributed applications and services were designed with the assumption that the
terminals were powerful, stationary and connected to fixed networks.
– Conventional middleware technologies thus have focused on masking out the problems of
heterogeneity and distribution to facilitate the development of distributed systems.
– They allow the application developers to focus on application functionality rather than on
dealing explicitly with distribution issues. Different middleware systems such as CORBA,
DCOM and Java RMI have proved their suitability for standard client-server applications.
•
However, under the highly variable computing environment conditions that
characterize mobile platforms, it is believed that existing traditional middleware
systems are not capable of providing adequate support for the mobile wireless
computing environment.
– There is a great demand for designing modern middleware systems that can support new
requirements imposed by mobility.
Saad Liaquat Kiani
Kyung Hee University
5
Real Time & Multimedia Lab
Why separate middleware for mobile computing ?
• There are at least three common factors that affect the design of the middleware
infrastructure required for mobile computing:
– mobile devices
– network connection
– mobility
• Mobile devices vary from one to another in term of resource availability
– Devices like laptops can offer fast CPUs and large amount of RAM and disk space
while others like pocket PCs and phones usually have scarce resources.
– It is either impossible or too expensive to augment the resource availability
• Hence, middleware should be designed to achieve optimal resource utilization.
• Network connection in mobile scenarios is characterized by
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limited bandwidth
high error rate
higher cost
frequent disconnections due to
• power limitations
• available spectrum
• Mobility
Saad Liaquat Kiani
Kyung Hee University
6
Real Time & Multimedia Lab
Why separate middleware for mobile
computing ?
• Physical host mobility can greatly affect network
connection
– Mobile clients may interact with different types of networks,
services, and security policies as they move from one area to
another.
• This requires applications to behave differently to cope with dynamic
changes of the environment parameters.
• Due to these limitations, conventional middleware
technologies designed for fixed distributed systems are
not prepared to support mobile systems.
– They target a static execution platform where the host
location is fixed, the network bandwidth does not fluctuate,
and services are well defined
Saad Liaquat Kiani
Kyung Hee University
7
Real Time & Multimedia Lab
Mobile Computing: Reference Technologies
• The remaining of the presentation will briefly
describe 3 middleware technologies that can aid
mobile devices in utilizing existing network
infrastructure and resources
– UPnP
– Jini (Java RMI)
– OSGI
Saad Liaquat Kiani
Kyung Hee University
8
Real Time & Multimedia Lab
Universal Plug and Play
• Universal Plug and Play (UPnP) is a standard software architecture for peerto-peer network connectivity of intelligent appliances, wireless devices, and
PCs.
• A device can dynamically
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join a network
obtain an IP address
convey its capabilities
discover other devices
learn the capabilities of other devices.
• A UPnP enabled device can control remote devices, and transfer data to and
from remote devices.
• Devices can subscribe to events that may occur as state variables change.
– Subscription to events allows a distributed device to react to remote events
• e.g., when a track stops playing, start playing the next track.
• A device can leave a network smoothly and automatically without leaving any
unwanted state behind.
Saad Liaquat Kiani
Kyung Hee University
9
Real Time & Multimedia Lab
UPnP
• UPnP leverages Internet technologies
• Internet Protocol (IP) [TCP, UDP]
• HTTP
• XML.
• Like the Internet, UPnP is based on wire protocols that
are expressed in XML, and communicated via HTTP
• IP internetworking is a strong choice for UPnP because
– its proven ability to span different physical media
– to enable real world multiple-vendor interoperation
– to achieve synergy with the Internet and many home and
office intranets.
Saad Liaquat Kiani
Kyung Hee University
10
Real Time & Multimedia Lab
UPnP
• UPnP devices can be implemented using any
programming language, and on any operating
system.
• UPnP does not specify or constrain the design
of an API for applications running on control
points;
– OS vendors may create APIs that suit their
customers' needs.
Saad Liaquat Kiani
Kyung Hee University
11
Real Time & Multimedia Lab
UPnP Coordination in a NutShell
• Announcing presence
– Use SSDP and Directory service proxies (optional)
• Discovering other devices
– Listen to SSDP multicast channel directly or contact a directory service
proxy.
• Describing capabilities
– XML description of the device is made available at a specified URL
• Self configuration
– This is primarily DHCP or AutoIP, and multicast DNS.
– Auto configuration seems to be the strongest feature of UPnP as yet.
• Invoking Services
• Transports: TCP/IP and proxies to other transports
Saad Liaquat Kiani
Kyung Hee University
12
Real Time & Multimedia Lab
UPnP Example
• You wake at 6 a.m. to a view of the mountains
and a current ski report:
– snow is falling and the powder is piling up.
– You send an alert via your alarm clock to your
children's alarm clocks and the coffeepot.
– The coffee starts brewing, you hear the patter of
steps upstairs as the kids get out of bed, and soon
you're all off to an early start to the mountains for a
day of skiing.
Saad Liaquat Kiani
Kyung Hee University
13
Real Time & Multimedia Lab
Jini
• Motivation
• Enable devices / services enter and leave the network without
requiring explicit reconfiguration
• Jini is a Java based distributed computing
environment, that offers “network plug and play”
• Allows devices to dynamically establish communication to share and
exchange services across a network
• Simplifies interactions with a network and connections between
devices anytime anywhere.
• Enables devices to plug together to form an impromptu community-a
community put together without any planning, installation or human
intervention.
Saad Liaquat Kiani
Kyung Hee University
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Real Time & Multimedia Lab
Jini operations
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Lookup service  The Service Registry
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supports searching for services that meet certain criteria,
e.g. those that have a particular Java type
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Services  Devices or Software
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Service Object  Contains the Java programming
language interface for the service. Contains methods
that users and clients will invoke to execute the service
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A Device hosting a service registers with the Lookup
service to announce its presence
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A Client wishing to use a particular service, asks the
Lookup service for contact information about the service
to be used
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The process of finding a Lookup service, either by client
or device/service is called Discovery
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The process of registering a device/service with a Lookup
service is called Join
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The process by which a client finds a service/device of
interest from a Lookup services is called Lookup
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The process of using a service by the client is called
Service
Provider
register
Service
Registry
(Lookup Service)
lookup
Service
User
Service Invocation
Saad Liaquat Kiani
Kyung Hee University
15
Real Time & Multimedia Lab
Jini Architecture
Network
Services
Java Spaces
•••
Other Services
Lookup
Jini
Discovery/Join
RMI
Java
Java
Java
Solaris
Mac
Windows
x86
Saad Liaquat Kiani
Kyung Hee University
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Real Time & Multimedia Lab
Jini Benefits
• Self Healing Networks through Leasing
– Leasing provides a method of managing resources in an environment where
network failures can occur
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A service is only provided for a certain amount of time unless the provider re-registers it (renews the lease)
• Similarly, resource is not granted to a consumer for indefinite period, but
“leased” for a finite time
– Keeps dead services from accumulating in the lookup servers over time
• Distributed Events
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Extends Java event model to allow it to work in a distributed network
– Register interest, receive notification
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Event Mailboxes (Asynchronous event mechanism)
– receive event notifications on behalf of their clients and deliver them later upon
request
– supports disconnected operations, unexpected failures of modules and
maintaining history of events of interest
Saad Liaquat Kiani
Kyung Hee University
17
Real Time & Multimedia Lab
OSGI
•
The OSGi™ specifications define a standardized , component oriented , computing environment
for networked services .
– Adding an OSGi Service Platform to a networked device (embedded as well as servers), adds the
capability to manage the life cycle of the software components in the device from anywhere in the
network.
• Software components can be installed, updated, or removed on the fly without having to disrupt the
operation of the device.
• Software components are libraries or applications that can dynamically discover and use other components.
• Software components can be bought off the shelf or are developed in house.
– The OSGi Alliance has developed many standard component interfaces that are available from
common functions like
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HTTP servers
Configuration
Logging
Security
user administration
XML
– Plug compatible implementations of these components can be obtained from different vendors with
different optimizations.
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Software component architectures address an increasing problem in software development:
– The large number of configurations that need to be developed and maintained.
– The standardized OSGi component architecture simplifies this configuration process significantly.
Saad Liaquat Kiani
Kyung Hee University
18
Real Time & Multimedia Lab
OSGI Framework
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The OSGI Framework provides a standardized environment to applications (called
bundles).
The Framework is divided in a number of layers.
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L0: Execution Environment
L1: Modules
L2: Life Cycle Management
L3: Service Registry
The L0 Execution environment is the specification of the Java environment.
– Java 2 Profiles, like J2SE, CDC,, MIDP etc. are all valid execution environments.
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The L1: Modules layer defines the class loading policies.
– The OSGi Framework is a powerful and rigidly specified class loading model.
– It is based on top of Java but adds modularization.
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The L2: Life Cycle layer adds bundles that can be dynamically installed, started,
stopped, updated and uninstalled.
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The L3 layer adds a Service Registry.
The service registry provides a comprehensive model to share objects between bundles.
A number of events are defined to handle the coming and going of services
Many services are server like objects, like an HTTP server, other services represent an object
in the real world, for example a Bluetooth phone that is nearby
Saad Liaquat Kiani
Kyung Hee University
19
Real Time & Multimedia Lab
OSGi
• The OSGi specifications are so widely applicable
because it is a small layer that allows multiple, Java™
based, components to efficiently cooperate in a single
Java Virtual Machine (JVM).
• The presence of OSGi based middleware in many
different industries is creating a large software market
for OSGi software components.
• The rigid definition of the OSGi Service Platform
enables components that can run on a variety of
devices, from very small to very big.
Saad Liaquat Kiani
Kyung Hee University
20
Real Time & Multimedia Lab
Protocol Services
• The OSGi Alliance has defined a number of services that map
an external protocol to an OSGi service.
– Http Service – The Http Service is, among other things, a servlet runner.
• Bundles can provide servlets, which becomes available over the Http
protocol.
• The dynamic update facility of the OSGi Service Platform makes the Http
Service a very attractive web server that can be updated with new servlets,
remotely if necessary, without requiring a restart.
– UPnP Service – Universal Plug and Play (UPnP) is an emerging standard
for consumer electronics.
• The OSGi UPnP Service maps devices on a UPnP network to the Service
Registry.
• Alternatively, it can map OSGi services to the UPnP network. This is a
recommended Release 3 specification.
– Jini Service – Jini is a network protocol used to discover Jini services on a
network and download those services in the host as Java code and execute
them.
• This is recommended Release 3 specification.
Saad Liaquat Kiani
Kyung Hee University
21
Real Time & Multimedia Lab
References
• UPnP
– http://www.upnp.org
• Jini
– http://www.artima.com/jini
– http://www.jini.org
– http://www.sun.com/software/jini/
• OSGI
– http://www.osgi.org
Saad Liaquat Kiani
Kyung Hee University
22