Transcript from Edmedia 2004: APEX

Building Distributed Educational
Applications using P2P
Tomasz Müldner* and Gregory Leighton
Jodrey School of Computer Science, Acadia University,
Wolfville, NS, Canada
* presenting
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Contents
• Distributed computing
• Peer-to-Peer (P2P)
•JXTA P2P framework
• APEX
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Distributed Applications
A distributed system:
data and functionality
are distributed
across multiple
machines
connected by a
network
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Examples of Distributed
Educational Applications
• groupware or computer-supported
cooperative work (CSCW)
• electronic classrooms
• shared workspaces
• others
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Distributed Applications:
Limitations
Problems:
• firewalls
• dynamic IP addresses
• network address
translation (NAT)
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Goals and Requirements for
Distributed Educational Systems
Platform Independence:
users of heterogeneous systems must be able to
access the application:
– Corba
– Web Services and the underlying XML technology
– Java technology
Security:
an authentication and a permission system with
access control rules:
– authentication e.g. using digital signatures
– encryption e.g. using private or public key systems
– auditing
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Goals and Requirements (2)
Customizability:
an application can be customized
Extensibility:
new tools can be added without affecting
the operation of existing tools.
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Goals and Requirements (3)
Connectivity:
– work on course documents while
disconnected;
– synchronized upon the next reconnection
Identification:
– Availability of the identities of users who are
currently available (independent of her current
location)
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Goals and Requirements (4)
Categorization:
two kinds of user’s roles:
- a single user
- a group
Collaboration:
– threaded discussions, messaging,
– collaborative viewing and editing of shared
documents
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Goals and Requirements (5)
Discovery:
users can discover and join course groups:
– course group contains a set of services specified by
the instructor
– services are dynamically discovered when a user
joins a course group
Scalability:
the addition of new entities or services to the
network does not significantly hinder application
performance
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Goals and Requirements (6)
Reliability:
the availability of the application must not
depend on the availability of any single
application instance;
Accessibility:
application entities must be able to
communicate with one another
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P2P
• Each peer typically acts in both
the client and server roles
• A peer may initiate requests on
services hosted by other peers
• A peer can service incoming
requests on locally-hosted
services
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Introduction to JXTA
• A set of protocols to establish an overlay
network on top of existing network protocols
such as TCP/IP and HTTP.
• The overlay network transparently connects
systems in a reliable and persistent manner
• The atomic entity in the JXTA network is the
peer:
a software program that uses the JXTA
protocols to interact with other peers.
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APEX
An extendable architecture:
various components can be added to
provide the required functionality; e.g.:
– an instant messaging component
– other components may be added as required,
(e.g. components that support cooperation
and collaboration)
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Authentication
• APEX performs authentication of each
peer as it joins the network via a lookup on
the institution’s registration records
• Each course section is modelled as a
separate JXTA peer group
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User Roles
•
•
•
•
Student peers
Teaching assistants
Instructors
Administrators
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Architecture and Functionality
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Example of an Instant
Messaging Component IM
Each member of the course peer group runs an instance of IM:
– maintaining a collection of ongoing conversation sessions
involving the local user,
– associating incoming chat messages with the appropriate
conversation session
– forwarding outgoing chat messages to the appropriate
conversation partner
– displaying an ongoing history of each ongoing
conversation session to the end user.
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Conclusions
• We have designed and partially
implemented APEX, an educational
application, based on JXTA.
• All implementation requirements have
been satisfied.
• APEX forms a base
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Future Extensions
Future extensions to APEX :
– electronic submission and grading of course
assignments
– The addition of a component for audio/video
conferencing
– A dynamic course syllabus could be provided
to specify assignment due dates and
scheduling of midterms and final exams.
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