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1 Mobile Agents for Enabling Mobile User Aware Applications Akhil Sahai, Christine Morin INRIA-IRISA Campus de beaulieu 3542, Rennes CEDEX, France Abstract Mobile agents based computing has been propounded as the possible approach to next generation computing. The approach has been shown to be eective in dierent domains, especially in the area of mobile and partially connected computing. We describe the design and implementation details of MAGENTA (Mobile AGENT environment for distributed Applications) and the mechanisms it provides for enabling applications supporting mobile users. MAGENTA is a generic mobile agent environment and provides the agents the capabilities of autonomy, reactivity, proactivity and communication. In order to demonstrate the functionalities provided by MAGENTA to mobile users we have applied it in the domain of network management in order to implement a Mobile Network Manager (MNM). We also present the performance evaluation results of MAGENTA. Keywords: 1 Introduction mobile agents, mobile computing, Java. Mobile users pose a new problem to the applications catering to static users. The mobile user aware applications must thus utilize special mechanisms in order to be useful to mobile users. Mobile users are characterized by the costly and fallible link they utilize and the resource constrained computer they operate on. In order to support mobile users the mobile agent paradigm can be used as it is ideally suited to the partially connected mode of computing. Mobile agents are autonomous programs that can move through a network from host to host under their own control, interacting with resources and other agents. The motivation behind MAGENTA was to adapt it to real-world situations. As the networks are becoming more and more complex and mobile user coexist with the static users, it is necessary to support a variety ofusers in realworld applications. MAGENTA environment was developed to provide support services for intermittently connected computing. MAGENTA is a generic mobile agent environment which satises weaker notion of agency i.e the agents exhibit autonomy, reactivity, proactivity and social ability. The agents perform goal-directed behaviour, interact with the system as well as the other agents, move and perceive the changes in the environment toachieve a predened goal. MAGENTA also provides easy extensibility, fault-tolerance, dynamic adaptability tochanges in the environment, exibility in the location of code, remote execution and simultaneous execution which go a long way inproviding support to mobile users. MAGENTA environment has been developed in Java and has been utilized for implementation of a Mobile Network Manager (MNM) which isanetwork manager executing on a portable computer. The rest of the paper is structured as follows. The subsequent section provides details about the characteristics of mobile computing. This, is followed by a brief overview of mobile agents and their utilization in the domain of mobile computing. We present the support features of the MA- GENTA environment which make it capable of providing for mobile users in the subsequent section. Section 5 details the application of MAGENTA in a mobile user aware application. Section 6 provides the performance results before concluding. 2 Characteristics of a mobile computing environment Mobile computing as the name suggests, is a domain encompassing the mobility aspects of computing. The mobility could be one of the following types: Only the users are mobile while the computers are stationary. Although the user and the computer are both mobile within the network, they are both stationary while working. The users while working on their computers are mobile. In this case the problems of locating mobile entities as well as message routing and connection management are to be dealt with. Mobile computing is characterized by the resource constrained portable computer and the communication. The mobile computer need to be small and light-weight. Thus such devices are decient in memory and processing power. As a result they are capable of supporting only those programs which donot take uplotof resources. The mobile computers being battery powered are also prone to frequent disconnections which might beentailed because of battery discharge. The power sources of typical palmtops range from

2 8 AA batteries (each AA battery has 9 mah at 1.2V) to rechargeable NiCd batteries (2.4Ah at 1.8 V) which gives a low battery life of typically between 3 to 8 hours. The IBM ThinkPad 76EL we used for experimentation has a capacity of (3. Ah at 1.8V cc) which limits its battery life to approximately 3 hours. The mobile computer can either connect to the wired network permanently or on a temporary basis. The permanent connection can be achieved by radio links whereas temporary connections are made through telephone lines and modems. The temporary connections are usually made using telephone lines and the PPP or SLIP protocol. In such a case no movement is possible during the communication and the bandwidth oered by the telephone networks is poor. Permanent connection requires the additional overhead of mobility management and routing. In [9] [1] various approaches towards the mobility management insuch cases have been proposed. The permanent connections are made using wireless techniques. The wireless networks that are available for usage are cellular networks, wireless LANs, wide area wireless networks and paging networks. These wireless networks do not have a large bandwidth available to them as compared to their wired counterparts. Some of the wireless LANs that are available are NCR's wavelan, Motorola's ALTAIR, Proxims Range LAN and Telesystem's ARLAN. They operate in the MHz (ISM) band and the specications ranges from 25bps to 2 Mbps with a range of 5 to 1 meters, indoors and a range of few kilometers outdoors [13]. 3 Mobile agents for mobile computing In a wired network, the machines interact over the network through a logical connection. They exchange messages in order to carry out this interaction. The client-server paradigm although being highly prevalent in a wired network and in spite of attempts to utilise this technology in the domain of mobile computing has been found to have unsatisfactory performance. The client-server paradigm assumes a tight coupling between the machines and assumes the presence and reliability of the machines as well as the bandwidth in case of a prolonged interaction between them. However in the domain of mobile computing, the link is highly fallible, has serious bandwidth constraints and has high latency and is prone to sudden failures such as when a signal from a cellular modem is blocked by an obstacle. The mobile devices are inherently short of energy due to the limited acceptable weight of their batteries. The mobile agent approach decouples the interacting partners. The mobile agent approach provides a means of asynchronous and remote execution and thus does not necessitate the presence of the partners. This approach also removes the constraints of message passing and constant bandwidth requirement. Mobile agents have been used for mobile computing in AgentTCL [14]. Adocking mechanism has been used to provide for the disconnected mode of operation of the portable computer. However, this scheme diers from the scheme we propose in the paper. Concordia [15] agents provides support for mobile computing as well as oine processing in a manner transparent to the user. Telescript one of the premier mobile agent systems from General Magic which supported mobile devices like PDAs is being replaced by Odyssey [4]. The design and implementation details of Odyssey are not clear. There are several other projects which are developing agent environments and few of them are Tacoma [16], Ara [18], Mole [17]. However, the few projects mentioned above have not considered mobile platforms as yet. Some distributed le systems provide support for disconnected operation, as in Coda[1] and Ficus [2]. In the Rover system [3] queued RPC and relocatable dynamic objects are used. These relocatable dynamic objects are incapable of moving halfway through their execution and thus cannot be classied as mobile agents. 4 MAGENTA for mobile users The architecture of MAGENTA comprises of lieus and agents as shown in Figure 1. A lieu is a place or location where an agent can originate, reside, execute and interact with the system as well as with other agents. An agent is a program which moves between the lieus and utilises the lieu to perform it's functions. The agents have globally unique name, have apurpose which denes its type and behave autonomously. Theymove between the lieus carrying with them their data and program state. They have afolder to carry their results and can meet with other agents and exchange notes. A meet operation is enabled by the lieu to enable local communication between the agents. They also carry a history which stores all the tasks performed by the agent and knowledge which stores the information it gathers about the failed sites as it traverses its itinerary. s have unique names. A lieu provides the execution environment for the incoming agents. The incoming agents are rst authenticated to determine their suitability for execution. After the agent passes the security requirements of the lieu, the agent is allowed to access the services available at the lieu through the service access point. The lieu facilitates the agents to communicate with other agents and to move to other sites. They also allow the agents to reside. This becomes important in the case when lieus running on mobile devices disappear either in a planned or in an unplanned manner. The agents destined for such lieus reside at the last lieus of their itinerary waiting for such lieusto reappear. It is also important in the case of meet operation where an agent might have towait at a lieu to meet another agent. Each lieu has a repository of all the agents created and dispatched by it and of the agents executing on it and so it keeps the trace of the agents. A lieu also maintains information about all the executing agents. They maintain the backup copies of agents absent locally as long as they do not get the instruction from another lieu to delete the copy. The architecture of MAGENTA in addition to general features provides support mechanisms for mobile users. Some of the important mechanisms are as follows: 4.1 Remote Execution A lieu can be requested by a remote site to launch anagent on its behalf and can collect the results of the computation performed by the agent remotely. The requesting site could be a lieu or a non MAGENTA site. On request, the agents are launched by the lieu after authenticating the remote site. MAGENTA thus provides extremely resource constrained devices like Personal Digital Assistants(PDAs) the facility to utilise the mobile agent functionalities and obtain the results of the computation without executing a lieu. Portable computers executing a non-java capable OS can also request a MAGENTA lieu to launch agents on its behalf.

3 A Service Access Point C B Service Access Point Figure 1: An overview of MAGENTA 4.2 Appearance and disappearance of lieus Service Access point The mobile computers are characterized by their intermittently connected mode of operation. They usually disconnect a short while after connection which is most of the times preplanned and sometimes unplanned (because of break in connection). They are also likely to connect randomly. MA- GENTA provides for such likelihoods. In MAGENTA the lieus can appear dynamically and disappear dynamically. This disappearance can be planned or unplanned. In case of planned disappearance a mechanism of exit is provided to the lieus. The lieu informs all the other lieus about its imminent disappearance and then quits gracefully. When the lieu reappears subsequently all the lieus in the environment are informed about the appearance of the new lieu. Adis- tributed update of information is thus carried out. In case of abrupt disappearance of the lieu, fault-tolerance mechanisms are provided for detecting such disappearances. To communicate with other lieus, every lieu maintains information about all other lieus in the system. To update this information and to detect abrupt disappearances of lieus, the following mechanism is used. Each agent, moving from a lieu to another avoids the unavailable lieus found during its travel, dynamically changing its itinerary and keeping track of the failed lieus in its variable knowledge. When the agent arrives at the last destination of its itinerary, itprovides the lieu information about the unavailable lieus, if there are such failed lieus, then the destination lieu informs all other lieus about the disappeared lieus. On receiving this information, all other lieus update their local information. So the failure of a lieu running on a mobile computer which disconnects abruptly can be discovered by an agent not launched by it but having it in its itinerary. A lieu executing on a portable computer might disappear abruptly after launching an agent. The agent after nishing its itinerary moves to the last destination lieu on the wired network. It tries to move to the mobile lieu but it fails in its attempt. It informs the lieu of residence about its failure which in turn informs all other present lieus about the abrupt disappearance of the mobile lieu. Thus a failed lieu is also discovered by the agents launched by it when they try to come back to it at the end of itinerary. The agent in this case waits on the last static lieu for the mobile lieu to connect back. 4.3 Flexible choice of location of the code to be executed The code of an agent moving from a sending lieu to a receiving lieu can exist on the receiving lieu or on the sending lieu. In the latter case the agent brings its code of execution to the receiving lieu. So, the choice can be made depending on the resources available on the machine executing the sending lieu and the receiving lieu. If the code is predened and is to be constantly used over a period of time, the code could be placed at the receiving lieu. If however the program is going to change over time and the sending lieu machine has enough resources to provide for saving of les locally the code could be stored at the sending machines and the agent thus carry their code when they leave the sending lieu. MA- GENTA thus provides a exible policy in placement of code. Depending on the resources of the host machine the choice could be made. 4.4 Minimization of code overhead In order to execute an agent the template of the agent and the code which needs to be executed by theagent are required. New agents can be created and utilized irrespective of the location of the agent template code. In order to do that, the feature of Java (programming language used to implement MAGENTA) have been used. Especially, a class loader for the class that implements the agent object has been designed. At the rst occurrence of this class, the class loader loads the agent template class from the network. Afterwards, the loaded class is put in a local hash table from which it is retrieved in the future. In this way, it isn't necessary to have in each host copies of the same class implementation, thus a mobile computer sending an agent to a remote site in a wired network need not store the agent template which are stored at a predened site in the wired network. As soon as the agent migrates from the mobile computer to another lieu the related agent classes are loaded by the class loader of the new lieu from the mobile computer and in the absence of agent template on the mobile computer they are loaded from the predened lieu. Thus the resources consumed of the mobile computers is reduced. 4.5 Tolerating site failures The agents and the lieus can fall prey to numerous accidents. The agents and the lieus might disappear because of abrupt disconnection of the portable computer or the crashing of the system executing the lieu. Fault tolerance schemes have been provided to minimize the overheads associated in detection and recovery from such site failures. In MAGENTA we provide for disappearance and recreation of agents from a single fault at a time. We maintain backup copies of the agents in order to take care of abrupt disappearance of an agent. In order to reduce the number of backup copies and to reduce the communication which results in case of disappearance of an agent we employ a scheme to maintain judicious number of copies. A lieu before sending an agent to the next lieu saves a copy of it and takes the temporary responsibility of detecting the failure of the next lieu. The next lieu after sending the agent to another lieu informs the lieu with the backup to remove the backup. The lieu with the backup periodically performs checks on the next lieu until it receives a message from the next lieu to destroy the backup. In case such a message is not received by the lieu with the backup within timeout and

4 if it detects that the next lieu has crashed it recreates the agent from the backup copy. This can be better explained with an example. Before an agent moves from a lieu, lets call it a lieu A to the next lieu, say lieu B it makes a copy of itself on lieu A. B processes this agent and makes a copy of it before moving it to the next lieu, say lieu C. As soon as the agent is successfully moved to the lieu C, lieu B requests lieu A to delete the copy of the agent. In case lieu B discovers that it is not possible to move the agent to lieu C because of some problem, it tries to reach lieu D. In case this operation is successfully carried out it asks lieu A to delete the copy. B after successfully moving the agent to the next lieu waits for a message from the next lieu, say lieu C. In case, the lieu C fails to send message to lieu B, lieu B understands that lieu C has not been able to move the agent to the next site in the itinerary because of some problems. It thus rst does its own check to nd out the problem. In case lieu C has crashed the backup copy of the agent on lieu B is used to create the agent and is passed to the next alive lieu. This scheme thus takes care of single fault and regeneration of agent by keeping the messages to a bare minimum. A B Agent copies itself and moves from A to B A B C Agent successfully moves to C from B. A B C B request A to delete its copy. A B D B does not receive message from C which crashes. B checks and sends agent to D instead. Figure 2: The implementation of fault-tolerance scheme in MAGENTA 4.6 Directory services for agents In MAGENTA a directory service has been provided so as to trace the agents. Every lieu can request all the other lieu about the latest information about the agents present on them and launched by them. This comes in handy to the mobile lieu which after launching an array of agents can connect back and determine the status of all the agents sent by it. 4.7 Simultaneous and fast execution The agents' execution on a lieu is multi threaded in nature so that all the agents can run simultaneously on the same lieu. This enables a portable computer to launch a large number of agents without bothering about their itinerary and performance before disconnecting. Thus the mobile user need not wait for other agents to nish operation before launching new agents. 5 MAGENTA in a mobile user aware application The MAGENTA environment being generic in nature it can be utilised for a variety of applications supporting mobile users. we utilized the MAGENTA environment in the domain of network management. In this context we enabled a Mobile Network Manager (MNM) to manage a network from a portable computer. The administrator of the network in this case is thus the mobile user. In order to appreciate the functioning of the MNM, the basics of network management in brief are presented. 5.1 Network Management Network management comprises essentially of monitoring and control of network elements. Network monitoring involves observing and analyzing the status of the network, and thus does not involve interference in the network functioning. Network control involves active interference and conguration of the state of the network. ANetwork Management System (NMS) essentially comprises of a manager managing the network elements and using a management protocol. The management protocol which has found extensive usage is the SNMP (Simple Network Management Protocol) [2]. The manager communicates with the SNMP agents executing on the managed nodes through a set of management primitives. The SNMP agents are static programs which execute on the managed nodes and provide the manager the information it requests from time to time. A NMS provides the functionalities of conguration of the network, monitoring of the network, studying the performance of the network, handling of security of the network and studying of the alarms being generated in the network Mobile Network Manager A MNM is a network manager executing on a portable computer and managing a network comprising of static network components executing SNMP agents. The MNM queries the SNMP agents about the network management variables and obtains their values. In order to demonstrate the functionalities of the MAGENTA environment wehave enabled the MNM through mobile agents. The MNM and the SNMP agents are integrated with MAGENTA lieussothattheyare capable of sending, receiving and storing the agents as shown in Figure.3. The agents are utilized to study the performance of network components, install software, audit the network components (by collecting the information on disk usage, users utilizing the machine, application conguration etc) and for network discovery. The MNM operates in either tethered mode or in wireless mode. The MNM typically sends a large number of agents to implement a variety of desired actions. After sending the agents it might disconnect, the agent after completing its itinerary waits at the last lieu of its itinerary. If the MNM had quit gracefully informing all other lieus about its disappearance, the agent waits for the MNM lieu to connect back. In case the MNM had disappeared abruptly, the agent tries to reach the MNM lieu being unaware of its absence. As it fails to reach the MNM lieu the agent again waits for the MNM lieu to connect back. The lieu hosting the agentat this moment informs all other lieus about the disappearance of MNM lieu. When the MNM connects back all the lieus are informed about the appearance of the MNM lieu. The agent waiting for the MNM at the last lieu returns back to it with the results.

5 A MNM operating in tethered mode makes a PPP/SLIP connection to the wired network. In such a case after the connection is established the portable computer is assigned a internet address local to the LAN to which it connects. This connection can be teared down after launching the agents and might be reestablished once the administrator deems it t to reconnect. In wireless computing the total domain is divided into cells. Each ofthecellshave a Mobile Support Station (MSS) of their own. The responsibility of serving the Mobile Host (MH) as it moves from one cell to another cell changes from one MSS to another [9][1]. The operation of MNM in case of a wireless network is shown in Figure.3. The MNM sends an agent from a particular cell and moves to another cell. The agent moves on its itinerary and tries to come back to the MNM after accomplishing its task. The agent isdirected to the new cell of the MNM by the MSS. The agent thus returns with the results of tasks performed by it. Wired network Mobile agent MSS MSS Manager Initial cell of the portable Manager Mobile IP Mobile agent Final cell of the portable Figure 3: Mobile Network Manager in the wireless mode 6 Performance Evaluation 6.1 MAGENTA in general The performance evaluation was carried out by executing lieus on two machines, wallace and boule (Sun Sparc machines executing SunOS 5.5). These two machines are connected by a 1 Mbps ethernet with no intervening router. The average time to launch an agent i.e to send an agent after initializing it from one lieu executing at wallace was found to be.371 seconds while the time for starting remote execution i.e requesting a remote lieu running at boule to startanagent on behalf of wallace was found to be.52 secs as it involved sending a message. In the former case the agent is sent by the lieu on wallace while in the latter case a simple request is sent toboule to prepare for a launch ofthe agent on its behalf. However, the time to request the results of the computation from boule by wallace was found to be.48 secs as it involved sending a request, searching ofthe results at boule and sending of the results back towallace. A comparison with dierent locations of code was also tried out. In the rst case the agent was sent from wallace to boule with only its state while the code to be executed was placed at boule. The code retrieves a le from the local le system and stores it in the agents folder. The time for the agent to return back after performing its task was found to be.931 secs. In the second case the agent was sent withits code and state from wallace to boule and the time measured was.993 seconds. So it is apparent that with larger size of the code to be transported and executed the response time would be higher in the latter case. 6.2 MAGENTA in a mobile user aware application We intended to study the suitability of mobile agents in the context of its utilization in mobile user aware applications as compared to the existing client-server mechanisms. Especially in the case of mobile users the network bandwidth usage and the response times are important factors as they have a fallible and costly link which should not be overused and they also need to know the response times so that they can reconnect back afterapproximately known time. The MNM was executed on a IBM ThinkPad 76 EL, a Pentium PC, 133 MHz, having 16Mo memory, executing windows 95 connected onto a 1Mbps Ethernet. In order to compare the usefulness and applicability of mobile agents in implementing the basic network management functionalities we have compared it with the client server mechanism. We thus implemented two MNMs, one utilizing mobile agents exclusively and the other utilizing the client server mechanism. The Figure 4 displays the comparison of bandwidth utilization when the client-server and mobile agent technologies are used to obtain given number of samples of a single SNMP variable from a SNMP agent. As is evident from the chart the client-server technique is suitable for SNMP monitoring when it is to be done for a limited amount of time. When large number of samples are desired, in terms of bandwidth utilization it is better to use the mobile agent technique. In our case the threshold we obtained was of 3 samples and with a sampling rate of.5 secs, we can derive that if a NMS intends to observe a SNMP variable for more than 2 min 3 secs it needs to use the mobile agent technology. The curve for mobile agent based MNM starts at 2 Kbytes as the agent size is 1K and the minimum cost of utilizing an agent for a round trip is 2K. In Figure 5 a similar comparison is shown but samples of5snmpvariables are obtained. The threshold in this case reduces to 6 samples. In Figure 6 the comparison of bandwidth utilization, when a single agent issent in a itinerary to retrieve 4 samples of a single SNMP variable from multiple machines and client-server technique is shown. The client-server mechanism is used from the manager machine to the SNMP agent machines separately and the requests are made in parallel. We observe that for this particular case an itinerary of no more than 18 machines is desirable. In Figure7 the response times between the client-server and the mobile-agent technology are compared. From the manager machine the time (in millisecs) it took for both the agents and the client-server technique to retrieve the given number

6 of samples were noted and plotted as shown. The response time in retrieving the samples were initially found better in client-server technique. But for larger number of samples the response time was better in sending an agent toretrieve the values than using client-server technique to continuously query and obtain the values of the SNMP variable from the SNMP agent. BW usage (in Kbytes) Comparison of Client Server and mobile agent technology Client Server Mobile Agent No of Samples Figure 4:Comparison of bandwidth utilization BW utilisation CS Agent Comparison BW utilisation No machines Figure 6:Comparison of bandwidth utilization 7 Conclusion BW usage (in Kbytes) Comparison of BW usage of client server and mobile agent techniques Client Server Mobile Agent No of Samples of 5 SNMP variables obtained Figure 5:Comparison of bandwidth utilization Time Taken (in MilliSecs) x 14 Comparison of Client Server and mobile agent techniques Client Server Mobile Agent No of Samples Figure 7:Comparison of response times MAGENTA is a generic mobile agent environment whichprovides mechanisms to enable functioning of mobile user aware applications. This mobile agent environment alsosatises the weaker notion of agency. Being generic in nature, it can be utilised for a number of applications. In order to demonstrate the support mechanisms for mobile users we have utilized MAGENTA environment inthe realm of network management to construct a Mobile Network Manager (MNM). We have also presented the performance evaluation of some of the interesting features of MAGENTA and have studied its performance in the context of its application in MNM as well. With respect to the existent client-server mechanism, we have found it to perform better in terms of bandwidth usage and response time for retrieval of large number of management variables. 8 Acknowledgments We would like to thank Dr. Michel Banatre for his support to the project. We would also like to thank Tiziana Signorelli and Janusz Wisniewski for their contributions to the implementation of the environment. Acknowledgments are also due to Serge Lassabe for his suggestions and feedbacks. References [1] B. Lily, M.R. Ebling and M. Satyanarayanan. Exploiting weak connectivity for mobile le access. in Proceedings of the Fifteenth ACM Symposium on Operating Systems Principles, Pg , December 1995 [2] P. Reiher, J. Heidemann et al. Resolving le conicts in the Ficus le system. in Proceedings of the 1994 Summer USENIX Conference, Pg , 1994 [3] A.D. Joseph, A. F. delespinasse, et al. Rover: A toolkit for mobile information access. in Proceedings of the Fifteenth ACM Symposium on Operating Systems Principles, Pg , December 1995 [4] Odyssey at General Magic Inc. Information available at [5] R. Beale and A. Wood. Agent Based Interaction in People and Computers IX : Proceedings of HCI'94,Glasgow,UK, August 1994, pp [6] G. Colin, Harrison et al. Mobile Agents: Are they a good idea? IBM T.J. Watson Research Center Technical report [7] N. Jennings, M. Wooldridge. Software Agents. IEE Review, January 1996, pp1 7-2 [8] D. Chess et al. Itinerant Agents for Mobile Computing IBM T.J. Watson Research Center Technical Report RC [9] A. Bakre and B.R. Badrinath. I-TCP:Indirect TCP for Mobile Hosts.Technical Report DCS-TR-314, Department of Computer Science, Rutgers University, 1994 [1] Markku, Kojo et al. Enhanced Communication Services for Mobile TCP/IP Networking. Technical Report C , Deptt. of Computer Science, University of Helsinki [11] T. Magedanz, K. Rothermel, S. Krause. Intelligent Agents: An Emerging Technology for Next Generation Telecommunications? INFOCOM' 96, USA, March 24-28, [12] P. Maes. Agents that reduce work and information overload. Communications of the ACM, 37(7):31-4, [13] Tomasz Imielinski, B.R. Badrinath. Mobile Wireless Computing: Challenges in Data ManagementCommunications of the ACM, October 1994, pp19-27 [14] R. Gray. Agent Tcl: Alpha Release 1.1, Computer Science Deptt, Dartmouth college, USA, rgray/transportable.html. [15] Mitsubishi Electric ITA. Concordia: An Infrastructure for Collaborating Mobile AgentsPresented and published in the proceedings of First International Workshop on Mobile Agents 97. [16] D. Johansen, R. V. Renesse and F. B. Schneider. An Introduction to TACOMA Distributed System Technical report CS-95-23, Department of Computer Science, Institute of Mathematical and Physical Sciences, University of Tromso.

7 [17] J. Bauman et al. Mole - A Java based Mobile Agent System. ECOOP'96 Workshop on Mobile Object Systems. [18] H. Peine, T.Stolpmann. The Architecture of the Ara Platform for Mobile Agents. First international Workshop on Mobile Agents, MA97 [19] Goldzmith, G. and Yemini Y. Decentralizing Control and Intelligence in Network Management.In the Proc. of 4th International Symposium on Integrated Network Management, Santa Barbara, CA 1995 [2] W. Stallings. SNMP, SNMPv2 and CMIP: The practical guide to network management standards. Addison- Wesley publication, 1994.