2004 IEEE International Conference on Systems, Man and Cybernetics
Wireless Distributed Systems with JADE* Edward Chen
Dorian Sabaz
William A. Gruver
School of Engineering Science Simon Fraser University Bumaby, BC, Canada
[email protected]
Intelligent Robotics Corporation North Vancouver, BC, Canada
School of Engineering Science Simon Fraser University Bumaby, BC, Canada
[email protected]
[email protected]
Abstrad - Agent platforms such as JALIE, JXTA. FIPAOS, JACK, and V-NET have been developed to operate with wired network infastructures. With the increase usage ofwireless technolagies, there is a greater need for wireless peer to peer connectbib andfunctionality. This paper presents a novel approach to extend JADE so that it can operate over wireless, peer-to-peer networks. By modeling JALIE over a wired network, we introduce functinnalities that can simulate wireless environments. By these means, we establish the core functionalities for J#E tofLnction on a wireless network, thereby avoiding the need to build a wireless infastructure.
With the rapid increase in both the size and complexity modem computer networks and the need to roam freely during the exchange of information, centralized approaches fail. A decentralized, peer-to-peer wireless architecture is needed to overcome these issues. Software environments have been developed to facilitate the implementation of a peer-to-peer, distributed systems over wired networks. Examples of these include JADE (Java Agent Development framework) [I], JXTA [2], FIPA-OS [3][4], JACK [5]and V-NET [6]. However, since these software environments are designed for wired infrasmctures, they cannot be directly employed for wireless networks.
Keywords: Distributed systems, agents, JADE, peer-topeer connectivi@, virtual wireless environment, agent plotforms
1
A Wireless Distributed System ( W D S ) is a decentralized system that is capable of routing information among its peers. Due to the wireless nature of the system, a node is only aware of other nodes within its signal range. For this node to communicate with peers beyond its signal range, it will require the assistance of nodes between itself and the destination to route infomation, as illustrated in Figure 2.
Introduction
Traditional centralized network topologies are usually implemented with database, file and application servers [l]. The clients’ connectivity, however, is limited by the physical topology of the wired infrastructure.
Figure I. Centralized client-server topology Figure 2. Wireless distributed system topology This topology is adequate only when the number of clients is unlikely to increase significantly. When such an increase does occur, the central server will be ovenvhelmed with requests which degrade the overall network performance.
In order for an 802.11 local area network to communicate in the Infrastructure Mode, access points are required to route information to destinations as shown in Figure 3. Using this approach, the sender cannot communicate directly with the recipient.
* 0-7803-8566-7/04/$20.00 0 2004 IEEE.
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2 JADE Architecture
Access Poim
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JADE'S communication system follows the standards developed by FIPA, an international organization producing standards to achieve interoperability of heterogeneous s o h a r e agents [3]. There are three roles that must be present in a FIPA compliant agent platform and their interactions, as shown in Figure 5.
Figure 3. Wireless LAN environment Because all nodes are equal in a WDS, however, a centralized access point is not needed for nodes to communicate. Each node directly communicates with neighboring nodes and each node is independent. The IEEE 802.11 wireless standard does allow a form of peerto-peer connectivity, called Ad-Hoc Mode. However, the Ad-Hoc Mode only provides point-to-point communication, as illustrated in Figure 4, rather than multi-point-to-multi-pointcommunication. Figure 5. FIPA agent model [l] 2.1 Agent Management System ( A M s )
The AMS is an agent that is responsible for managing the operation of an Agent Platform (AP), such as the creation of agents, the deletion of agents and overseeing the migration of agents to and from the AF' [3]. 2.2 Directory Facilitator
Figure 4. Multipoint-to-multipoint communication
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The DF is an agent that provides "yellow page" services to other agents. It stores descriptions of the agents and the services they offer. [3]
Ideally, we would like to combine the IEEE 802.1 1 wireless protocol with the functionality of a peer-to-peer collaborative system environment. Although this type of system is not yet available as a commercial product, we investigate what would be required to do this with JADE. In this paper, the emphasis will be placed on JADE and its role in the implementation of a wireless distributed system.
2.3 Agent Communication Channel (ACC)
The ACC is an agent that uses the information provided by the A M s to route messages between agents either within or agents that reside on other platforms. The ACC provides Message Transport Service for FIPA ACL messages [3].
An effective tool for extending JADE for a wireless, peer-to-peer environment is to utilize its current functionality for wired environments and convert it into a virtual wireless environment. A Virtual Wireless Environment (VWE) will be constructed to model any WDS by establishing intelligent links between nodes in a wired network. With such a system, we will be able to create scenarios in a wireless environment, such as signal failure, dynamic link establishment, and data quality over multiple hops.
As shown in Figure 6, the AMs and DF are automatically created when the JADE platform is launched. The ACC allows message communication within and toifrom different platforms. The agent platforms can be split among several hosts and only one Java application is executed per host (with one Java V i 1 Machine). The Main Container hosts the AMs and DF, and other containers, which are possibly on other hosts, are connected to the Main Container to provide a complete run-time environment [7]. 990
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B
A
C
Figure 8. Local area network whereas Node-C can communicate with Node-B and Node-E, as summarized in Table 1. To model this system with a wired network, restrictions are placed on the nodes so that the Sender Node (SN) can only communicate with its list of available Recipient Nodes (RN).Suppose that Node-A wishes to send messages to Node-€?, then the message can no longer be routed directly as in a wired network. First, the message will be sent to Node-B, and then to Node-E. This particular scenario models a node in a WDS communicating with a node that is out of range. The SN depends on neighboring nodes to route messages to its RN.
For communication between agents residing in the same platform, JADE uses its Intemal Message Transport Protocols (IMTP) for message delivery. If both the sender and the receiver agents reside in the same container, JADE uses event passing for delivery of the message. When tbe sender and the receiver reside in different containers, JADE uses Remote Method Invocation (RMI) for message delivery [7].
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Figure 7. JADE messaging architecture [I] Figure 9. Example of a Wireless Distributed System
3 Virtual Wireless Environment The links that are established need not be constantly available. Intelligent links can model different scenarios that may occur in a WDS, such as roaming and dynamic link cougestiodfailure. For example, in the wireless scenario shown in Figure IO, we suppose that Node-A is a roaming node. At f= to, Node-A has only Node-B as its RN.
At the present time, there is no established environment available to properly test a wireless distributed system. Wireless LANs are not fully distributed because access points are required to route information. In a wired network, nodes are physically connected and information is passed directly from sender to recipient without going through intermediate nodes. However, in a wireless environment, each node is not fully aware of the extent of the entire network and with wbom they can communicate directly. As an example, consider a wired network consisting of 5 nodes, shown in Figure S. Suppose that we wish to model the following wireless network consisting of 5 nodes, as shown in Figure 9 where the enclosed circles represent signal range. In this example, Node-A can only communicate with Node-B
Table 1. Node connectivity
r
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Sender Node
I
Available Recipients
I
4 JADE in a Virtual Wireless Environment JADE is a software development framework for developing distributed systems and peer-to-peer applications. The major advantage of using JADE is that it simplifies the communication transport and message encoding through the middleware [I]. However, because JADE is designed for a wired network, inodifications are needed before it can be fully implemented with a wireless distributed system. Figure 10. Roaming node with intelligent links at f=to
JADE has the facility to communicate with other JADE peers that are w i t h i reach of the wired network. However, in a wireless environment multiple hops may be required. To simulate multiple hops in a virtual wireless environment, the following two agents are added a Broadcusf Agenf that handles broadcasted messages toifram other nodes, and a Send-Receive Agent that senddreceives messages and determines the most efficient route for messages. In the V i 1 Wireless Environment, a SN can only send messages to its list of restricted RN, as determined by a user-defined scenario. This limitation is used to model the wireless nature of the WDS.
However, at t = f f , the sender (Node-A) will be at a different location, as shown in Figure 11, and a different RN set (Node-D and Node-E).
Figure 11. Roaming nodewith intelligent links at t = f f This situation models a roaming node where its linkages are changing so that the list of RNs on individual nodes within a wired network will also be dynamic. Figure 12. Wireless agent communication channel in an agent framework
We could also model other scenarios such as
dynamic link congestiodfailnre by setting the links between nodes to be deleted or created as a function of time. Such a scenario can also be used to model the uncertainty of wireless transmission.
These two agents allow us to extend the functionality of the ACC to model a wireless environment. This latter feature has been implemented by a model we call the Wireless Agent Communication Channel (WACC), as illustrated in Figure 12.
Timing and administrative overhead issues can also be determined with a Virtual Wireless Environment. We can calculate the time required by messages to travel from one end of the network to another and the effects of multiple messages. We can measure the effectiveness of routing algorithms and also peer-to-peer environments.
Unlike a wired network in which all nodes are aware of the existence of all other nodes, a wireless system is only aware of nodes within its signal range. When a new node becomes available, that information must be made available to the network by broadcasting its presence to neighboring nodes, which they broadcast to their neighbors. The process is repeated until all nodes become aware of the presence of a new node. We incorporate this multi-hop functionality in JADE by adding a Global Directory Facilitator (GDF) that is 992
responsible for maintaining a current list of all agents and their services within each node's multi-hop signal range. This is an extension of the Directory Facilitator (DF) created by JADE that enables a node to be aware of other agents within its immediate surroundings, see Figure 13.
I F -
are needed, however, to accommodate their use with wireless systems. By allowing the user to control the connectivity and functionality of JADE peers, any wireless environment can be modeled using a wired network. In addition, since these subsystems are incorporated in JADE, the core functionality to manage a wireless environments is available. This Virtual Wireless Environment (VWE) can then be configured with wireless parameters such as dynamic link failures and latency. By extending the JADE framework so that it has the capability to create virtual environments, wired networks can be employed to allow algorithm and system developers the capability to simulate scenarios that occur in wireless environments. The extension enables JADE to have the functionality to function as a simulation environment for wireless system development and also to operate over wireless networks.
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Figure 13. Global directory facilitator in an agent framework
References
In addition, administrative overhead at the network level requires extension of the AMS. The Global Agent Management System (GAMS), which extends the functionalities of the AMs, is in direct communication with the GDF. The modified agent framework for a WDS is illustrated in Figure 14. By extending JADE with three subsystems (WACC, GDF, and GAMS), we have packaged the multi-hop functionality required for wireless communications from the normal JADE operational services.
[I] JADE, Java Agent Development framework, http://jade.cselt.it [2] JXTA, http://www.jxta.orgl
[3] FIPA -Foundation for Intelligent Physical Agents, http://www.fipa.org [4] FIF'A-OS, hap://www.nortelnetworks.com/ products/announcements/fip~
[5] Agent Oriented Software Group, http://www.agentsoftware.com [6] C. Ng, D. Sabaz and W. A. Gmver, "Distributed Algorithm Simulator for Wireless Peer-to-Peer Networks," Proc. of fhe IEEE Infemational Conference on Sysfem, Man, and Cybernetics. Hague, Netherlands,
2004. [7] E. Cortese, F. Quarta, and G. Vitaglione, "Scalability and Performance of the JADE Message Transport System," Proc. of the AAMAS Workshop on AgentCifies, Bologna, Italy, July 2002.
Figure 14. Modified agent framework for a WDS
5 Conclusions A Wireless Distributed System is a scalable network that decentralizes the system into multiple, independent nodes capable of routing information to recipients. Agent platforms such as JADE, JXTA, FIPA-OS, and V-NET may be used to develop distributed systems. Modifications
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