AUTOMATIC CONFIGURATION OF SERVICE DIRECTORIES

IN MULTIAGENT SYSTEMS

Martin Krebs, Karl-Heinz Krempels, Janno von St¨ulpnagel and Christoph Terwelp

Informatik 4, Intelligent Distributed Systems Group, RWTH Aachen University, Aachen, Germany

Keywords:

Distributed Service Directory, Automatic Conﬁguration, mDNS, DNS-SD, Multiagent System.

Abstract:

Service directories provide basic functionalities for service discovery and service announcement in Multiagent

Systems (MAS). A manual conﬁguration of distributed MAS and their service directories is a time consuming

and complex task and thus an automatic mechanism is highly desirable. Furthermore, the requirement for a

fast response and processing time for agent queries still remains. Existing approaches do not fulﬁll these re-

quirements in a satisfactory way. Thus, a new approach based on multicast DNS and DNS Service Discovery

(DNS-SD) was developed and implemented for the multiagent framework JADE (Java Agent DEvelopment

Framework). The architecture enables the automatic conﬁguration of agent platforms in dynamic local net-

works as well as the later federation of the service directories which is necessary for a distributed service

discovery operation.

1 INTRODUCTION

Service directories (SD) contain service descriptions

of services provided by agents and agent plattforms.

Agent interactions are based on service requests or

queries among agents. To determine the participants

for an interaction an agent has to query a directory

for suiteable agents. Thus, service directories provide

essential support for agent interactions. SD are pro-

vided on Agent Platforms (AP) as a basic service for

agents. Every agent that provides a service for other

agents has to register this service with the service di-

rectory. Therefore, the agent submits to the service

direcory a formal service description that contains the

service name, the ID of the service providing agent,

ontologies supported by the service, and interaction

protocols supported by the agent to access the service.

The paper is outlined as follows: Section 2 gives

an overview of existing solutions for service direc-

tories in distributed MAS and their drawbacks. In

section 3 a new approach for a distributed service di-

rectory is introduced. The implementation of the ap-

proach is discussed in section 4 and its evaluation in

section 5. Conclusions and future developements are

discussed in section 6.

2 STATE OF THE ART

Service directories provide basic functionalities for

service discovery and therewith for the interaction

among agents. For this reason service directories

are subject of standards related to agent technology.

The Directory Facilitator (DF) speciﬁaction (FIPA-

SC00001G, 2002) describes the interface of the ser-

vice directory, the format for agent and service de-

scriptions, and the ontologies and interaction proto-

cols supported by the DF. Existing implementations

of the DF speciﬁcation use polling oder lease-time

mechanisms to keep the registered service description

up to date:

Polling: consists of periodic update requests initiated

by the service directory for registered service de-

scriptions, independent of the rate of change of the

information. The time interval for update requests

is constant for polling.

Lease-time: expects information updates from each

registered service by itself. For each service a

time interval is deﬁned in which the next update

has to take place. Otherwise the service is re-

moved from the directory.

558

Krebs M., Krempels K., von Stülpnagel J. and Terwelp C. (2009).

AUTOMATIC CONFIGURATION OF SERVICE DIRECTORIES IN MULTIAGENT SYSTEMS.

In Proceedings of the International Conference on Agents and Artiﬁcial Intelligence, pages 558-563

DOI: 10.5220/0001791105580563

 SciTePress

The ﬁrst world wide service directory infrastructure

for MAS was implemented in the Agentcities project

(Willmott, 2004), founded by the EU. In the Agentci-

ties service directory the registered agent and service

descriptions were kept up to date with the help of the

polling mechanism. During the essential operation

time the number of registered services touched 200

agent platforms and about 1000 agents. The minimal

information update cycle caused by this polling load

was close to 5 minutes. This interval was however to

long for dynamic agent based applications with short-

lived agents (Kirn et al., 2003) (Kirn et al., 2006)

(Woelk et al., 2006).

A new approach for distributed service directo-

ries was developed in the X-OpenNet project (Will-

mott et al., 2004a), the successor of the Agentcities

project. This approach was based on a two-level ar-

chitecture. The upper level consisted of a full-meshed

federation of 16 nodes, which were monitored by all

other nodes of the same level with the help of a com-

bined polling-lease-time-mechanism. The lower level

of the architecture consisted of the local DF of each

connected agent platform. This DF either answered

a search request itself or forwarded it to one of two

preselected nodes of the upper layer. The complex

conﬁguration task in the upper layer for the deploy-

ment of X-OpenNet infrastructure services caused a

low user acceptance and popularity of the whole in-

frastructure.

In the following years many approaches from

the peer to peer (P2P) area have been considered

to remove the drawbacks from the upper level of

the X-OpenNet architecture. Particularly the cre-

ation of federations with the help of the JXTA

Framework(Brookshier et al., 2002) (FIPA-PC00096,

2004) (Chen et al., 2006) and the Jabber Framework

(C´amara et al., 2006) (Fischer et al., 2006).

The JXTA Framework provides a robust infras-

tructure for P2P networks. It consists mainly of ser-

vice directories, signaling mechanisms, and program-

ming interfaces for the development of client applica-

tions. In (Chen et al., 2006) (FIPA-PC00096, 2004)

the integration of the JXTA-Framework with JADE is

discussed. The paper states that the deployment ef-

fort of an distributed agent platform can be reduced

by the conﬁguration of the service directory, but is

still bound by the conﬁguration time of the agent plat-

form. Furthermore, the signalling load produced by

the JXTA framework seems to be very high. Thus,

this approach seems to remove only a part of the

drawbacks.

The Jabber Framework consists of a collection of

network protocols for instant messaging, ﬁle transfer

and signalling to transport messages and ﬁles, and to

show the presence of communication parties. The in-

tegration of the Jabber Framework with JADE is sim-

pler to implement than the integration of the JXTA-

Framework. Furthermore, the setup of a Jabber-client

is much easier than the setup of a JXTA-client. How-

ever, the drawbacks of this integration include also the

signalling load and the requirement that all the com-

munication parties have to be well known and have

to be provided in advance. The Jabber Framework

supports the discovery of communication parties only

with the help of a centralized directory.

All approaches presented here are a tradeoff be-

tween the required conﬁguration effort for the com-

munication interface of an agent platform, the limita-

tions of the actuality of registration records in the ser-

vice directories, and the distribution level of a MAS.

The conﬁguration of service directories in dis-

tributed MAS is a complicated and time-consuming

job that becomes more complex in dynamic network

environments, like ad-hoc networks. However, this

setup is often provided for the demonstration track in

conferences and in developer workshops in academic

or touristic environments.

Thus, to become able to show distributed pro-

totypes of agent-based applications at a conference,

e.g. (Kirn et al., 2003) (Kirn et al., 2006) (Woelk

et al., 2006), or to setup a development environment

for agent-based applications, e.g. (Dale et al., 2003)

(Willmott, 2004) (Willmott et al., 2004b) (Scholz

et al., 2005), there is a need to conﬁgure distributed

MAS and to federate their service directories in a fast

way.

3 APPROACH

The presented architecture for automatic conﬁgura-

tion of service directories in MAS is based on a ﬂat

structure, i.e. there is no hierarchy. All agent plat-

forms which provide a directory service establish a

fully-meshed federation. This meshed graph is the ba-

sis for an efﬁcient distributed service discovery oper-

ation. The corresponding agent platforms are conﬁg-

ured automatically with a conﬁguration and signaling

system which ensures that all nodes use the same IP

address range and namespace.

In the following, we ﬁrst present the setup of the

directory federation in an ad-hoc network. In the next

step the processing of the search queries in the feder-

ation is explained in detail which is followed by a de-

scription of the used signaling and conﬁguration sys-

tem.

Every node which offers a directory service an-

nounces its availability in the network, see Fig. 1. A

AUTOMATIC CONFIGURATION OF SERVICE DIRECTORIES IN MULTIAGENT SYSTEMS

559

(a) Federation of two DFs

(b) Extension of the federation by one

(d) Federation with six DFs

Figure 1: Federation of Service Directories.

federation is established if there are at least two nodes

which intend to form a federation. The Figs. 1(a) up to

1(d) show the incremental expansion with the nodes

C, D, E, and F. Finally, the federation forms a fully-

meshed graph. The main advantage of a ﬂat directory

structure is the high actuality of the resource records,

because the registration, update and delete operation

is done at the corresponding local agent platform. Ac-

cordingly, most of the queries can be replied directly

by this platform which is based on the assumption that

an agent interacts most of the time with other agents

of its direct neighborhood or otherwise prefers a mi-

gration (Diepolder and Krempels, 2006) (Krempels

et al., 2006).

The discovery of a service in the established fed-

eration is depicted in Fig. 2. The most common case

is shown in Fig. 2(a) where a search for a service can

be satisﬁed by the local AP. The request (1) of agent

a at directory A is realized by an internal lookup at

directory (2). Finally, the matching services are sent

back to the requesting agent (3). If the service request

does not match at the local directory (see Fig. 2(b)),

the request is forwarded (3) to the directory E and

replied by it (4). The reply is ﬁnally forwarded to the

requesting agent. The most complex case occurs (see

Fig. 2(c)), if the request of agent a cannot be replied

by the local directory (2) or the update of an outdated

resource record fails (3,4). In this case it is required,

that the request is forwarded to all directories in the

federation (5) and only the successful replies are sent

back to the local directory A (6).

In environments with dynamically assigned ad-

dresses und network names for agent platforms it is

necessary, that agent platforms are conﬁgured auto-

matically. Therefore, the protocols mDNS (Multi-

cast Domain Name System) and DNS-SD (Domain

Name System based Service Discovery) were cho-

sen (Cheshire and Krochmal, 2005) (Steinberg and

Cheshire, 2005). This approach satisﬁes the follow-

ing requirements:

• automatic assignment of IP-addresses without a

central DHCP server;

• automatic DNS name resolution and name assign-

ment without DNS or DHCP server;

ICAART 2009 - International Conference on Agents and Artificial Intelligence

560

(a) Answer of the search request from th-

elocal DF

(b) Answer of the search request from a

(selected) DF of the federation

the federated DFs

Figure 2: Processing of a search request by federated service directories.

• service discovery and registration in a local net-

work.

The here presented approach for the automatic conﬁg-

uration of directories in MAS allows for efﬁcient ad-

ministration of service information. Furthermore, the

fully-meshed structure allows an efﬁcient distributed

search for services. The conﬁguration and federation

of the architecture is done automatically with mDNS

and DNS-SD.

4 ARCHITECTURE

The approach was implemented for the Agent-

Framework JADE (Bellifemine et al., 2007). The

JmDNS Library has been used as mDNS and DNS-

SD protocol implementation. The work done here

was focussed on the integration of JmDNS into JADE

and the implementation of a conﬁguration service for

the service directories. JADE provides most basic ser-

vices as so-called Kernel-Services. JmDNS was inte-

grated as such a Kernel-Service. Every agent only

accesses the local service directory as it is done in

the non-distributed case. The directory services ac-

cess JmDNS through the Kernel-Service. As shown

in Fig. 4 when a directory service starts or stops it

broadcasts its state change through the serviceAdded

and serviceRemoved methods to the other agent plat-

forms in the local network. Such anouncements from

other agent platforms are processed by the DFSer-

viceListener and a federation is build.

5 EVALUATION

The implementation of this approach was evaluated

in a setup with four computers interconnected in a

WiFi ad-hoc network. The WiFi network interfaces

AUTOMATIC CONFIGURATION OF SERVICE DIRECTORIES IN MULTIAGENT SYSTEMS

561

Agent Platform

Age

JADE Plattform Services

jmDNS

Network

Agent

Figure 3: Integration of JmDNS in JADE.

of these computers were conﬁgured by the mDNS /

DNS-SD implementations of their corresponding op-

erating system: e.g avahi

on Linux, Bonjour on Ma-

cOS X

and Windows XP

. After the completion of

the network interface conﬁguration process an agent

platform was launched on each computer to serve as

measurement platform. For all measurements made

the federation of the service directories was estab-

lished immediatly after the launch of the platform.

On three of this platforms an agent was launched

that registered 2000 services in the service directory.

On the fourth platform a search agent was started that

requested the local service directory to search a ser-

vice with exactly one match on a service description

on each of the other platforms.

Table 1: Search time in four platforms.

measurement search time (ms)

1 94

2 62

3 63

4 78

5 63

6 62

7 63

8 62

9 78

10 94

average 71,9

For the ﬁrst series of measurements shown in Tab. 1

the platforms were restarted for each measurement.

The resulting mean value of 71,9 ms for the dis-

http://avahi.org

Bonjour and MacOS X are registered trade marks of

Apple Inc.

Windows XP is a registered trade mark of Microsoft

Inc.

ServiceListener

DFServiceListener

addServiceListener

<<implements>>

new

serviceAdded /

serviceRemoved

Figure 4: Kernel-Service for JmDNS.

tributed search processing is sufﬁciently fast to be

used in dynamic agent based scenarios, e. g. the

ones discussed in (Kirn et al., 2003) (Kirn et al., 2006)

(Woelk et al., 2006).

6 CONCLUSIONS AND

OUTLOOK

The combination of the agent framework JADE and

the JmDNS implementation of the mDNS / DNS-SD

protocols is an efﬁcient approach for easy, fast and

mostly automated conﬁguration of distributed MAS

in local networks. Even for large numbers of regis-

tered services a fast distributed search is possible.

The discussed improvements of the JADE frame-

work for automated conﬁguration and federation of

service directories were presented to the JADE com-

munity and will be included in the next release of the

JADE framework.

ACKNOWLEDGEMENTS

This work is motivated by experiences made in the

German priority research programme 1083 Intelligent

Agents in Real-World Business Applications (2000-

2008).

Contributions to the implementation of the pre-

sented approach and to its evaluation were made

by Milan Fort, Sven Lilienthal, Andreas Kelle-

Emden, and Moaffak Assassa. Special thanks to Uta

Christoph for her critical suggestions, lovely reviews,

and unlimited patience.

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562

REFERENCES

Bellifemine, F. L., Caire, G., and Greenwood, D. (2007).

Developing Multi-Agent Systems with JADE. Wiley.

Brookshier, D., Govoni, D., Krishnan, N., and Soto, J. C.

(2002). JXTA: Java P2P Programming. Sams, Indi-

anapolis, IN, USA.

C´amara, J. P., Gregori, M. E., Bada, G. A., Garc´ıa-Fornes,

A., Juli´an, V., and Botti, V. J. (2006). Adding new

communication services to the ﬁpa message transport

system. In (Fischer et al., 2006), pages 1–11.

Chen, E., Sabaz, D., and Gruver, W. (2006). Jade and jxta

extensions for the implementation of distributed sys-

tems. Systems, Man and Cybernetics, 2006. SMC ’06.

IEEE International Conference on, 1:740–745.

Cheshire, S. and Krochmal, M. (2005). DNS-Based Ser-

vice Discovery. Technical report, Internet Engineering

Task Force.

Dale, J., Burg, B., and Willmott, S. (2003). The agentc-

ities initiative: Connecting agents across the world.

Innovative Concepts for Agent-Based Systems, pages

453–457.

Diepolder, S. and Krempels, K. H. (2006). Mobile agenten.

mobile agents. PIK - Praxis der Informationsverar-

beitung und Kommunikation, 29(4).

FIPA-PC00096 (2004). FIPA JXTA Discovery Middleware

Speciﬁcation.

FIPA-SC00001G (2002). FIPA Abstract Architecture Spec-

iﬁcation.

Fischer, K., Timm, I. J., Andr´e, E., and Zhong, N., editors

(2006). Multiagent System Technologies, 4th German

Conference, MATES 2006, Erfurt, Germany, Septem-

ber 19-20, 2006, Proceedings, volume 4196 of Lec-

ture Notes in Computer Science. Springer.

Kirn, S., Heine, C., Herrler, R., and Krempels, K.-H.

(2003). Agent.Hospital - Agentenbasiertes offenes

Framework f¨ur klinische Anwendungen. In Uhr,

W., Esswein, W., and E.Schoop, editors, Medien -

M¨arkte- Mobilit¨at, pages 837–857. Wirtschaftsinfor-

matik 2003, Physica Verlag, Heidelberg.

Kirn, S., Herzog, O., Lockemann, P., and Spaniol, O.

(2006). Multiagent Engineering: Theory and Applica-

tions in Enterprises. International Handbooks on In-

formation Systems. Springer-Verlag New York, Inc.,

Secaucus, NJ, USA.

Krempels, K.-H., Spaniol, O., Scholz, T., Timm, I., and

Herzog, O. (2006). Interaction design. Multiagent

Engineering, pages 383–403.

Scholz, T., Krempels, K.-H., Nimis, J., Schiemann, B.,

Woelk, P.-O., Braubach, L., and Pokahr, A. (2005).

www.agententerprise.net – a mmas-based web-portal

for planning and Control of Complex Manufacturing

Supply Chains managed by ASCML – the Agent So-

ciety Conﬁgurator Manager and Launcher. In AA-

MAS 2005 Demonstration Proceedings, volume open-

Net Networked Agents Demonstration for AAMAS

2005.

Steinberg, D. H. and Cheshire, S. (2005). Zero Conﬁgura-

tion Networking. O’Reilly. Not yet released.

Willmott, S. (2004). Deploying intelligent systems on a

global scale. Intelligent Systems, IEEE, 19(5):71–73.

Willmott, S., Bonnefoy, D., Constantinescu, I., Thomp-

son, S., Charlton, P., Dale, J., and Zhang, T. (2004a).

Agent based dynamic service synthesis in large-scale

open environments: experiences from the agentcities

testbed. Autonomous Agents and Multiagent Systems,

2004. AAMAS 2004. Proceedings of the Third Inter-

national Joint Conference on, pages 1318–1319.

Willmott, S., Rana, O., Krempels, K.-H., McBurney, P.,

and Weichart, G. (2004b). Networked Agents: To-

wards Large-scale Deployment of Agents in Open

Networked Environments (NET AGENTS). AgenLink

News, (16):22–23.

Woelk, P.-O., Rudzio, H., Zimmermann, R., and Nimis, J.

(2006). Agent.enterprise in a nutshell. Multiagent En-

gineering, pages 73–90.

AUTOMATIC CONFIGURATION OF SERVICE DIRECTORIES IN MULTIAGENT SYSTEMS

563