Adapting Asynchronous Messaging Middleware to Ad Hoc Networking

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Adapting Asynchronous Messaging Middlewareto Ad
Hoc Networking

• Mirco Musolesi
• Cecilia Mascolo
• Stephen Hailes
• Dept. of Computer Science
• University College London
• MPAC04

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Outline

• Motivation
• Background
• EMMA
• Current research directions
• A few ideas for a research roadmap

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Motivation

• Our research goals
• Enabling communication in ad hoc networks
  environments also in presence of disconnections
  is a hard problem
• Providing support for the development of
  distributed applications in these environments
• Not only a pure theoretical problem, but also
  practical
• communication among disconnected communities in
  poor areas of the world
• indoor communication
• interplanetary communication

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Motivation

• In presence of disconnections, synchronous
  communication mechanisms are not sufficient
• Asynchronous communication seems a suitable
  paradigm for mobile ad hoc network settings
  characterised by frequent disconnections and
  network partition

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Challenges

• Not only the classic issues of distributed
  environments but also
• Frequent disconnections
• Limited resources
• Topology changes
• Temporary network partitions
• Heterogeneous mobile devices
• Different possible deployment scenarios (and
  consequently different requirements)

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Middleware solutions for ad hoc environments

• The use of middleware solutions is an effective
  choice since by adopting them it is possible
• to hide the complexity of the underlying networks
  
• to deal with the increasing heterogeneity of the
  devices (laptops, mobile phones, PDAs, sensors,
  etc.)
• to design a set of primitives for the adaptation
  and the configuration of the system

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Message oriented middleware for ad hoc
environments

• Starting from these considerations, message
  oriented middleware based on asynchronous
  communication mechanism seems a good solution to
  provide a support for communication also in
  presence of intermittently connected clouds of
  hosts
• Based on the same abstractions of systems for
  fixed networks, but many additional design issues

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Existing middleware systems

• Many examples of middleware for mobile computing
  for communication also in the case of
  intermittent disconnections
• Tuple based (i.e., LIME)
• Sharing of complex data structures (i.e.,
  XMIDDLE)
• Message oriented middleware for mobile computing
• Academic projects Pronto, Mobile JMS, STEAM,
  etc.
• Industrial products WebSphere MQ EveryPlace,
  Broadbeam ExpressQ, SoftWired IBus Mobile, etc.
• However, they do not support pure ad hoc network
  environment with intermittent connectivity!

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EMMA

• Message oriented middleware for mobile ad hoc
  networks environments
• Adaptation of JMS
• Implementation of both point to point
  publish/subscribe models
• Message delivery based on a pure epidemic routing
  protocol in case of disconnections
• Based on a different levels of priority for a
  smart use of buffers

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Epidemic-style routing
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Point to point model

• Queues positioned on a certain number of hosts
• Queues advertised using the epidemic mechanism
• If a host is in reach, the message is delivered
  immediately
• If a host is not currently in reach, the epidemic
  style routing is used

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Publish-subscribe model

• Delivery mechanisms based on an epidemic style
  routing protocol in case of disconnections as in
  the point to point model
• Single message with multiple recipients, instead
  of multiple messages with multiple recipients.
• In order to delete the other possible replicas
  around the networks, we exploit acknowledgment
  messages
• Adaptation of the semantics of durable and non
  durable subscriptions

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Adaptation of the JMS Message Model

• Implementation of a subset of the JMS Message
  Model specification with a different semantics
• Definition of persistent and non persistent
  messages
• Support for messages with different priorities
• Expiration time used to free space in the buffers

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Evaluation of EMMA

• We have implemented a prototype of our platform
  using the J2ME Personal Profile
• The size of the executable is about 250KB
  including the JMS 1.1 jar file
• We have tested our prototype on HP IPaq PDAs
  running Linux and on a number of laptops with the
  same network interface interconnected with
  WaveLan.
• We also evaluated the middleware platform using
  the OMNET discrete event simulator in order to
  have some simulation results considering scenario
  composed of a realistic number of hosts.

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Simulation parameters

• Number of hosts 16/24/32
• Simulation area 1 Km x 1 Km
• Propagation model free space
• Antenna type omni-directional
• Transmission range (radius) 200 m
• Mobility model clustered random way point
• Number of clouds 4
• Cloud area 200 m x 200 m
• Node speed 1-3 m/s (randomly generated)
• Cloud speed 1-2 m/s (randomly generated)
• Number of messages sent 100
• Number of recipients (pub/sub) 80 of the number
  of hosts
• Max number of hops 15
• Message buffer size 10 to 100
• Routing table size 20 entries
• Max distance 15
• Max allowed delay time 4 minutes

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EMMA performance
Point to point model (scenario with 32 hosts)
delivery ratio of persistent and non persistent
messages vs buffer size.
Point to point model (scenario with 32 hosts)
delivery ratio of persistent and not persistent
messages vs population density.
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EMMA performance
Publish-Subscribe model (scenario with 32 hosts
delivery ratio distribution of persistent
messages with different priorities
Publish-subscribe model (scenario with 32 hosts)
delivery ratio distribution of persistent
messages vs buffer size.
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Limitations of EMMA

• Epidemic algorithms are efficient in terms of
  delivery ratio and delay time but they are really
  expensive from a resource consumption point of
  view
• Discovery process not optimised
• Queues are not replicated
• No adaptation
• Limited set of primitives

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Towards a new middleware platform

• EMMA is our initial effort we are currently
  working towards the definition of a new
  middleware
• Substitution of the epidemic protocol with a more
  optimised and adaptive Context-Aware Routing
  protocol (CAR)
• Definition of a new set of primitives
• Support for geocasting

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Context-aware middleware for ad hoc networking

• Exploitation of context information for the
  optimisation of the delivery process in terms of
  resource consumption (memory, battery, etc.)
• Design of prediction mechanisms based on the
  evaluation of the history of context information
  (mobility, co-location, battery level, etc.)
• Replication mechanisms in accordance with the
  level of required reliability

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Cross-layering

• Current trend in mobile ad hoc networking
• We think that it is possible to extend this
  methodology to the design of middleware and
  applications
• Optimisation and adaptation of the system can be
  realised by the integration of the network level
  software components in the middleware platform.

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A few ideas for a roadmap for ad hoc networks
middleware research

• Many open issues or problems not explored
  sufficiently in depth
• Design of adaptive and autonomic systems
• Self-optimising systems
• Self-healing systems
• ...
• Positioning and replication of data and entities
• Auto-configuration
• Exploitation of the properties of the underlying
  network
• Cross-layering based design
• Security

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Conclusions

• Cross-layering is a promising methodology for the
  design of middleware solutions for mobile ad hoc
  computing
• EMMA is a first example of a platform for
  asynchronous messaging in ad hoc networks
  designed using a cross-layering approach
• Necessity of new mechanisms for optimisation and
  context adaptation in such a dynamic environment

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Questions
Mirco Musolesi Dept. of Computer Science,
UCL m.musolesi_at_cs.ucl.ac.uk http//www.cs.ucl.ac.u
k/staff/m.musolesi