communication, cooperation and coordination in an ad

ISBN: 978-972-8924-56-0 © 2008 IADIS
COMMUNICATION, COOPERATION AND
COORDINATION IN AN AD-HOC ENVIRONMENT
Diego Casado Mansilla, Andrés Navarro Guillén & Juan R. Velasco
Universidad de Alcalá. Departamento de Automática.
Crtra. N--II, Km 31,600, 28871. Alcalá de Henares, Madrid, Spain.
ABSTRACT
Wireless Networks and the usage of mobile devices are becoming popular in our daily routine, and step by step this
technology is growing in the emergency, disaster recovery and health care fields. This paper focuses on real telematic
service provisioning in scenarios where there is a lack of fixed communication infrastructure due to natural disasters
(fires, earthquakes, tsunamis ...). In these environments the use of mobile devices is mandatory, and in order to
communicate the mobile devices only Ad-hoc Networking can carry this out.
Mobile devices focuses their efforts of creating a network infrastructure and use it to route all the data information. Since
the main device's problems are well known in an Ad-hoc environment (power limitation, QoS, efficiency, Bandwidth
etc..) the usage of agents technology has been proposed to reduce them, and more specifically mobile agents which could
play a very important role controlling the communication flow and simplifying the exchange of services and cooperation
between nodes.
In this research we present a real scenario, where a fire has occurred and therefore the lack of fixed communication is
obvious. In this situation, a fire brigade must go to the disaster zone, deploy their groups to cover the fire area and always
be communicated and coordinated to remedy the damage that the fire might cause as soon as possible. It is possible that
assistants may go to the disaster area to analyze and solve the firefighters' needs. To achieve this, we propose the use of
Ad-hoc networks to keep an organized communication's structure, agents technology to manage and coordinate the
communication and services offered.
KEYWORDS
Ad-hoc Networks, Mobile Agents, Nomadism, Service Discovery, Emergency & Disaster Recovery.
1. INTRODUCTION
Now a days we are evolving into a less sedentary society. In this way the people's requirements tend toward
mobile technology because the communication and cooperation are one of the most important needs in our
private and professional lives.
From this simple concept were born the wireless networks. Initially, this kind of technology was
increasing overall in the scientific, military and industrial fields. Currently, it is obvious that it is becoming
widespread and famous in other environments like academic, emergencies, conventions, etc..
Wireless networks are divided into two completely different approaches: Centralized wireless networks
and completely decentralized networks named Ad-hoc, where every device which takes part in this network
acts as an autonomous node and could communicate directly with each node through the wireless medium.
The mobility concept is closely related to dynamic topology, thus, each mobile device if free to move
anywhere and may change its group location continuously, so, the communication maintenance at network
layer and coordination in an ubiquitous environment is almost impossible. In this scenario the agent
technology and the multi-agents system take the leading role to perform the communicative act between
devices.
Gathered together with mobility and dynamic topology, it is important to stand out the nomadism
concept. As was remarked above the nodes which take part in the scenario are moving around and each one
carries mobile agents. So, the nodes involved in Ad-hoc environments, should have to move and change its
physical location in order to reach other devices to communicate with them or exchange services outside the
boundary of their wireless radio-link.
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Agents are processes that perform their tasks in every device within the Ad-hoc network and exchange
the data information effectively at the application layer. These agents define and create communication
protocols, organize and offer every service within the network and in summary, get an efficient platform
organization.
The main features of the agents are: autonomy, proactivity, intelligence, adaptability, sociability and
mobility. Mobile agents are software applications that have the inherent feature to move through the devices
within the network and are able to execute their tasks in different nodes even if those nodes do not have the
code to define them.
The usage of multi-agents systems and mobile agents over Ad-hoc networks may contribute to reduce the
data load over the network, balance the bandwidth, obtain asynchronous communications, avoid the bottle
necks caused in Client/Services application, enables cooperation between agents and enables user oriented
systems.
This research works in a scenario where it is impossible to use fixed communications. Each mobile
device which takes part in this network should be able to communicate with others and might offer a service
or do use of a service offered by another node. Mobile multi-agents system offers a distributed service
platform facilitating the interoperability between users and successfully solve every communication problem
over an ubiquitous environment. This research is involved in the IMPROVISA [1] project which addresses
the issue of real service provisioning in scenarios lacking a fixed communications infrastructure, where the
cooperation of humans and electronic devices is paramount..
The paper schema is presented as follow: Section 2 describes the Ad-hoc networks main features,
advantages and disadvantages. Section 3 introduces mobile multi-agent systems over Ad-hoc networks and
how this technology is used to perform communication, collaboration, service management and discovery
and finally Section 4 summarizes the document.
2. AD-HOC NETWORKS
A wireless Ad-hoc network is a collection of autonomous nodes or terminals that communicate with each
other by forming a multi-hop radio network and maintaining connectivity in a decentralized manner [2].
Since the nodes communicate over wireless links, they have to contend with the effects of radio
communication, such as noise, fading, and interference [3]. Each node in a wireless Ad-hoc network
functions as both a host and a router, and the control of the network is distributed among the nodes. The
network topology is in general dynamic, because the connectivity among the nodes may vary with time due
to node departures, new node arrivals, and the possibility of having mobile nodes.
Currently, the research in this field is focused mainly in routing. Obviously, it is not really effective nor
scalable because it assumes the different devices will only communicate in the same radio link, thus, limiting
their mobility. From this concept the Mobile Ad-hoc NETworks (MANET) was born [4]. These kind of
networks, have the same features as regular Ad-hoc networks, but they increases the complexity because of
the data routing through the nodes within the platform.
Devices involved in a MANET, have to set up algorithms and applications in order to manage the data
packet which will be send through them, so the communication between nodes in this fashion is performed at
the application layer.
Determining viable routing paths and delivering messages in a decentralized environment where network
topology fluctuates is not a well-defined problem. In our research, we have not yet developed a routing
protocol in the different devices within the network, but we use the concept of Ad-hoc network to deploy our
communication system. Thus, each device is able to interoperate solely with the nodes inside their own radio
link.
3. AGENTS AND MULTI-AGENT SYSTEMS OVER AD-HOC
NETWORKS
Multi-agent systems inherit every agent feature discussed above and add some other advantages in terms of
efficiency (split functionality between agents to perform complex tasks, avoid the data centralization splitting
enormous amounts of data in different devices, contribute with QoS, etc.). Furthermore, the usage of mobile
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agents in those associations allows asynchronous communication and flexible query processing avoiding the
client/server paradigm. Thus, a mobile agent is autonomous deciding whether a task delegated to it must be
performed at once or could be delayed otherwise. Obviously all these features fit perfectly in Ad-hoc
environments since they reduce network traffic, balance the data load, save battery-life and simplify the
communication, cooperation and coordination between agents.
Multi-agent systems require a special environment to be developed and to deploy every feature mentioned
above. This environment is named multi-agent platform, which moreover might offer security, unique
identity, communication channel, discovery and location of agents and services. Some examples of these
platforms are: IBM(Aglets) [5], ObjectSpace(Voyager)[6], IKV(Grasshopper) and JADE[7].
In our research we have adopted JADE(Java Agent DEvelopment Framework) as the middleware to
develop the multi-agent system presented here. JADE is a software Framework fully implemented in Java [8]
language and is free software. It simplifies the implementation of the multi-agent systems through a
middleware that complies with the FIPA [9] specifications and through a set of graphical tools that supports
the debugging and deployment phases.
3.1 Service Discovery & Fault Tolerance
This section presents how the agents are able to discover the services offered in the working platform, and
interact with all of them.
In the proposed scenario where a fire has occurred, there will be some devices (each allocating one or
more agents) spread out in the disaster location which represent a group of firefighters who must collaborate
to extinguish the fire. These agents have to be developed properly to manage every service offered within the
platform. Because we use JADE as middleware to deploy our multi-agent system and it complies with FIPA
specifications, there must be a register where allocate every service available in the platform, called
Directory Facilitator (DF) and in the same line a new register called Agent Management System (AMS) to
control each agent present on the platform.
This research adopts the idea where initially the DF is kept by an agent allocated in a main device. Every
agent within the platform knows exactly which node stores the DF and AMS and where it is located. It is
possible an external agent could enter the platform and not know which device is the main one. Because the
foreign agents want to join the multi-agent platform, and the registration against the AMS is mandatory to
perform it, this research proposes, that every agent that originally takes part of the platform creates a ring of
fault tolerance. Thus, the new agent could register itself with any agent whether or not the principal one on
the platform, and know through this one what services are offered.
When deploying emergency applications, fault tolerance is often one of the main requirements that must
be met. The usage of the AMS and DF registers is clearly a potential single point of failure that must be
effectively managed to ensure the platform remains fully operational even in the event of a main container
failure [10]. This is achieved by combining the following two features:
•
Main container replication. This feature allows the main container and the AMS agent within it to
be replicated, to keep all replicas fully synchronized and to ensure that if fails, another can take
over.
•
DF persistence. This feature allows the catalogue of the DF agent to be recorded in a relational
Data Base (DB). In the case of main container failure a new DF agent is automatically started in the
new master main container and can recover its catalogue from the DB.
Applying these features to our emergency system, the centralization problem is avoided. Initially, the
main device creates the platform and adopts the leader role. Then, every agent which takes part in the
platform, must perform a replica of this main agent. In this way, a ring of fault tolerance is created and each
device is aware of any changes that may happen in the platform.
4. TESTING SCENARIO
Continuing towards the research presented in this paper and focusing on the scenario where the fire brigade is
deployed along the disaster area, an overview of the created system is presented: The proposed scenario is
composed of five different groups which create an Ad-hoc network; The main component originally creates
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the agent platform and will manage and control the firefighter groups. This principal device allocates an
agent that periodically checks the water storage and the location of each firefighter group spread out along
the area. The four remaining components, must fight against the fire in different zones. Initially these
firefighter groups have a completely filled water storage, but as the time goes by, this water storage
decreases. In each firefighter group, there is an agent continuously executing. Its main target is to keep in
touch with the main agent and to reply to the needs of the main agent. To keep the groups coordinated and
have knowledge of the fire's status, an agent is in charge of recording images of the disaster and sending
those images to the control device as a new service. This agent will always be attached to any group within
the platform.
To test the nomadic behavior in Ad-hoc environments, our scenario puts forward the idea of a real
situation in the disaster area. Since the water storage is continuously decreasing in the groups depending on
their water needs, a group could be in trouble if the water capacity becomes empty. The main agent, which
looks after the firefighter groups, will send a warning message to the group to inform them about the
dangerous involved if they continue in the zone. The main agent is aware of the location of every group, so,
the message sent will also contain the new location where the group have to move to be safe and once there,
they will help the new group in the extinguishing operations. In this manner agents are physically moving
within its mobile device around the Ad-hoc network. Furthermore, agent mobility is present into all proposal:
the agent responsible for recording images will be moving through different devices and performing its task
depending on the necessities of the management agent to control different disaster areas.
5. CONCLUSION
In this paper we have proposed a model to develop multi-agent systems over Ad-hoc networks. We have
focused our research in this technology as a solution to emergency and disaster recovery scenarios where
there is a complete lack of fixed communication. Ad-hoc is synonymous for sporadic, dynamic,
unpredictable and overall, decentralized topology, so the paper has shown a solution to adapt mobile multiagent systems to this outline. Managing and maintaining communication between agents, as well as sharing
and discovering services over the created platform, have been the main topics discussed in the paper.
ACKNOWLEDGEMENT
This research is part of the IMPROVISA project. Three Spanish universities are working down this project:
Universidad de Alcalá, Universidad Politécnica de Madrid and Universidad Carlos III de Madrid.
The project has been supported by the Education and Science Ministry. MEC-TSI2005-07384-CO3-03
REFERENCES
Juan R. Velasco, Miguel A. López-Carmona, M. Sedano, 2006, Role of Multi-agent system on minimalist infrastructure
for service provisioning in ad-hoc networks for emergencies. Proceedings of First International Workshop on Agent
Technology for Disaster Management, AAMAS'06. Hakodate, Japan, pp. 151-152.
NIST. Advanced Network Technologies Division, 2001, Wireless Ad-hoc Network. Proceedings of
http://w3.antd.nist.gov/wahn_home.shtml
S. Corson, J. Macker, 1999, Mobile Ad hoc Networking (MANET): Routing Protocol Performance Issues and Evaluation
Considerations. In RFC 2501.
IETF. Internet Engineering Task Force, 2000, MANET.Working Group, Mobile Ad-hoc Networks, Proceedings of
http://www.ietf.org/charters/manet-charter.html
Glass, G. et al,1999. Mobility: Processes, Computers, and Agents. Addison-Wesley.
Lange, D. B. and Oshima, M. et al, 1998. Programming and Developing Java Mobile Agents with Aglets. AddisonWesley
Bellifemine, F., Caire, G. and Greenwood, D. et al., 2007. Developing multi-agent sytems with JADE. Addison-Wesley
Sun Micro Systems. JAVA, Sun Developer Network. Proceedings of http://java.sun.com/
FIPA, 1999. Foundation for Intelligent Physical Agents Homepage. Proceedings of http://www.fipa.org
C.Giovanni & F.B., 2006.JADE Administrator's guide. Proceedings of http://jade.tilab.com/
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