Bernd Eßmann, Thorsten Hampel, Thomas Bopp
Heinz Nixdorf Institute
University of Paderborn
urstenallee 11, 31102 Paderborn
Mobile Computing, Spontaneous Collaboration, Distributed Knowledge Spaces, CSCW.
Today Computer Supported Cooperative Work (CSCW) is used in broad areas of human cooperation. With the
propagation of radio-based communication and ad hoc networking it may enter new areas of human cooper-
ation. One important aspect is the new quality in CSCW of being independent from special network-enabled
places. Another aspect is the more intuitive support of face-to-face cooperation utilizing personal mobile de-
vices. To open this field of collaboration our approach featuring Distributed Cooperative Knowledge Spaces
specifically addresses conceptual issues pertaining to the transition from classical, server-centered to mobile,
distributed collaboration environments. With this concept we introduce persistent and personal knowledge
spaces as well as so-called temporary knowledge areas and groups. Our prototypical application for sponta-
neous collaboration implements this approach. We are able to draw here on many years of experience in the
development and testing of our concept of Cooperative Virtual Knowledge Spaces.
In recent years, the CSCW world has created sev-
eral cooperation environments to support inter-human
work using network technology provided by the In-
ternet. We, for our part, have developed the sTeam
system, based on the concept of Cooperative Vir-
tual Knowledge Spaces. Knowledge Spaces allow
users to structure their knowledge spatially in virtual
rooms (also called areas”). sTeam is designed as
a client/server system with a central server provid-
ing the cooperation environment, which is accessible
from any device connected to the Internet. The idea is
that users should be able to cooperate independently
of specific locations such as conference rooms.
The need for collaboration environments that are
independent of specific locations is the reason for
our conviction that network-supported cooperation
will change in the near future. Ad hoc networks
are encouraging the emergence of this feature. Such
networks allow devices to be connected sponta-
neously without planning an infrastructure. This
makes network-based cooperation environments in-
dependent of network-connected locations.
One problem we face when using these new net-
work topologies is that data is often distributed across
several devices. For our cooperation environment,this
means that the Knowledge Spaces of the cooperation
partners are also distributed across their devices. The
original sTeam system ensured consistency of the un-
derlying data by managing it through one server. It
was not planned to store the data on multiple servers.
This means that areas of the Distributed Knowledge
Spaces can be connected across several devices.
An additional problem is that the availability of de-
vices in an ad hoc network is not guaranteed because
its structure is highly dynamic. This means that parts
of the Knowledge Spaces could also disappear when
hosted on a vanishing device.
One of our goals, then, is to expand our architecture
to cover these network requirements, allowing us to
create Knowledge Spaces across several devices with-
out much need for administration by the users. An-
other is to support both the classical, proven concepts
of CSCW and new concepts for spontaneous network-
ing. By doing so, we seek to transfer our well-proven
concept of Cooperative Virtual Knowledge Spaces to
such a network environment.
After consideration of related work, Section 3 of
this paper describes future network structures based
on MIP and Multihop Ad Hoc Networks (MANETs).
Such a new network structure will change the pos-
Eßmann B., Hampel T. and Bopp T. (2004).
In Proceedings of the Sixth International Conference on Enterprise Information Systems, pages 337-343
DOI: 10.5220/0002622503370343
sible concepts for the desired cooperation environ-
ment. For this reason, we discuss the new concept
of Distributed Knowledge Spaces in Section 4. This
new concept extends Cooperative Virtual Knowl-
edge Spaces to include distributed environments like
MANETs without neglecting existing structured net-
works like the Internet. In addition, this concept is ca-
pable of combining both network topologies and en-
riching the concepts for classical infrastructures.
These two factors, the network structure and the
concepts, influence the design of the application for
the cooperation environment. We introduce and dis-
cuss this design in Section 5. We present the technolo-
gies used, JXTA, mDNS and sTeam, as well as initial
prototypes for evaluating the technology and our con-
In the final section, we discuss our experience so
far and look at the tasks ahead.
Using mobile devices in cooperation scenarios is an
attractive prospect. Our research focuses on develop-
ing a collaborative working environment using spon-
taneously connected devices with the option of ac-
cessing services in structured networks like the Inter-
net. Many projects explore the use of spontaneous
The ELAN project
aims to develop an infrastruc-
ture for e-learning in mobile ad hoc networks (Lauer
and Matthes, 2002). Unlike our approach featuring
distributed knowledge spaces for collaborative knowl-
edge construction in mobile settings, this project fo-
cuses on pure e-learning issues in these networks.
The project ConcertStudeo being conducted by the
Fraunhofer Integrated Publication and Information
Systems Institute’s (IPSI) Concert work group com-
bines an electronic blackboard with handheld devices
for enhancing face-to-face learning using interactive
learning tools (Wessner et al., 2003). This approach
is based on special tools (e.g. voting tools) for specific
learning settings. The cooperation concept focuses on
e-learning only; it does not use ad hoc networks for
the learning environment.
Another IPSI project, called MIRIAM, aims to set
up a reference installation for Mobile IP over IPv4
(MIPv4). Concrete installations based on MIPv4
are evaluated in an application scenario for scien-
tists (Berier 2001). The results of this project can
help us to select a suitable network for our research
The ELAN project is part of the German Research
Foundation’s (DFG) Priority Programme 1140 ”Basic Soft-
ware for Self-Organizing Infrastructures for Networked
Mobile Systems”.
needs. Although the project analyzed mobile net-
working, it did not address ad hoc networks or focus
on e-learning scenarios.
The MIT has a research project called Oxygen
addressing various aspects of pervasive computing.
Oxygen seeks to enable pervasive, human-centered
computing by combining specific user and system
technologies. The term ”ambient intelligence” is used
in this context (Dertouzos, 1999; Hanssens et al.,
2002). The goal is to build an intelligent ambi-
ent environment enriched with a collaboration and
knowledge-access subsystem. This project does not
exploit the potential of Cooperative Virtual Knowl-
edge Spaces for knowledge structuring and manage-
ment as we do.
The above projects focus on one or two aspects of
the research needed to build, as our approach seeks to,
an environment based on ad hoc established and struc-
tured networks allowing users to tailor their own Co-
operative Virtual Knowledge Spaces with a minimum
of administrative effort. What we need is a compre-
hensive concept of Cooperative Virtual Knowledge
Spaces as in classical sTeam, ported to mobile dis-
tributed environments. This concept must take into
account hardware issues, network technology and ap-
plication frameworks, enabling scaling from powerful
hardware down to ultra-portable devices like PDAs.
An important factor in the design of the collaborative
work environment is the nature of the underlying net-
work structure. Put another way, the design of the
collaborative system influences the choice of network
structure. In our case, the idea is to use available net-
work technology, adapting it to match future network
structures and meet the needs of mobile learning en-
vironments. In our view, the network infrastructure
of the future must offer both maximum independence
from established infrastructures and the option of ac-
cessing classical networks like the Internet.
As cooperation occurs spontaneously, it should not
depend on existing network infrastructures. The net-
work infrastructure must be built from scratch, with
no need to configure the network devices manually.
Ad hoc networks meet these requirements. They set
up the network devices and establish routing schemes
appropriate to the network structure. Ad hoc networks
are able to maintain changing network infrastructures
on the fly when devices move within the network or
Although ad hoc networks would appear to be the
ideal solution for spontaneous collaboration, mobile
users still benefit from connecting to classical net-
work infrastructures like the Internet. Many use-
ful services are only available in classical networks,
and remote cooperation over long distances can be
achieved through Internet connection. This is why
we wish to retain the option of accessing the classi-
cal sTeam server, when reachable.
By combining these technologies, three criteria are
1. spontaneous networking without existing network
2. the use of existing network structures, if reachable
3. availability of the technology in near future, based
on already existing network structures and tech-
In a setting incorporating ad hoc and structured net-
works, reachable devices must be contactable through
both network topologies. A unique worldwide contact
address is needed because a device can move freely
within structured and ad hoc networks. Movement
within structured networks is called macro or inter-
domain mobility, movement within ad hoc networks
micro or intra-domain mobility.
The Internet Engineering Task Force (IETF) work
group’s Mobile IP (MIP) is a network technology pro-
viding macro mobility and reachability, irrespective
of the network point to which the device is connected
(Perkins, 1997; Perkins, 1998). MIP was originally
designed for IPv4 (MIPv4) and can be used for IPv6
(MIPv6) (Johnson et al., 2003).
While MIP supports macro mobility, it is not
suitable for micro mobility and lacks independence
from established networks. Mobile ad hoc networks
(MANETs) are therefore used for building networks
without the need to connect to established networks
(Perkins, 2001). If an MIP agent is in the range of the
MANET, devices able to connect to the agent can pro-
vide access to the structured network as a service to
the other devices in the MANET (Tseng et al., 2003).
In this case, a bridge between the two networks is es-
tablished. As soon as this bridge exists, all clients of
the ad hoc network are able to connect to their home
agent and are reachable from outside . Conversely, the
loss of the bridge does not affect the ad hoc network;
communication between the ad hoc-attached devices
is still possible (Campell et al., 2002).
In recent years, several routing protocols for
MANETs have emerged. They allow establishment
of the previously discussed spontaneous networks. So
far, however, none of them has been established as
a standard for ad hoc networking
. The only proto-
col for establishing ad hoc networks available in most
The Ad hoc On-Demand Distance Vector (AODV)
Routing is specified in an RFC (Perkins et al., 2003), but
is not available as standard protocol stack in current operat-
ing systems.
operating systems is the link-local protocol (Cheshire
et al., 2003)
. The main drawback of the link-local
protocol is that it is not a multi-hop protocol. This
means that it is not able to build larger ad hoc net-
works. Our approach is to use it for spontaneous net-
working in small groups, which meet at one location
and are within range of all other radio network de-
For bigger scenarios, it should be possible to es-
tablish multi-hop networks like the one mentioned in
(Perkins, 2001), where every device can be a router
for other devices, which would allow ad hoc networks
to be established over large areas. This would allow
connection to the Internet with mobile IP. Our short-
term goal is to create some test installations of this
network to evaluate them in everyday use.
In the described networks, client/server applica-
tions would make no sense because loss of the server
from the network would render all affected clients
useless. Unlike client/server structures, peer-to-peer
technology meets the needs of such a network topol-
ogy perfectly.
Knowing the characteristics of the network in-
frastructure for the learning environment, we must
integrate our current cooperative knowledge spaces
into this combination of structured networks and
MANETs. Our goal is to integrate the current con-
cepts of cooperative knowledge spaces into this inno-
vative network topology.
The concept of Cooperative Virtual Knowledge
Spaces has been successfully applied for a number
of years. Our work aims to provide learners with
Distributed Knowledge Spaces based on innovative
network infrastructures for mobile devices. We be-
gin by evaluating the potential of handheld devices to
provide user interfaces for virtual knowledge spaces,
go on to address the task of building an environment
for mobile collaborative learning, and finally discuss
our concepts for distributed cooperative knowledge
spaces and spontaneous learning sessions.
Our goal is to facilitate state-of-the-art mobility-
supporting network technology, as described in Sec-
tion 3, and evaluate it in terms of our aims. Based on
these networks, we seek to build an application that
allows users to cooperate with a minimum of admin-
istrative effort.
The link-local protocol is part of MacOS X, Linux and
newer Windows versions
Handheld devices are small enough to support
portability, often have enough power to compute the
software for these environments, and the wireless net-
work interfaces now frequently included allow con-
nectivity with other devices. To evaluate the spe-
cial characteristics of PDAs, we developed clients for
our sTeam client/server environment. While the first
prototypes were HTML-based (Eßmann and Hampel,
2003), the newer generation is Java-based, to benefit
from sTeam’s event mechanisms.
While the developed user interfaces meet the needs
of PDAs? small displays and pen-based input, they
are still classical clients in a client/server infrastruc-
ture. Parallel to this, we built the middleware for
finding other peers and communicating with them in
MANETs and structured networks. We describe this
middleware in Section 5 and it is the main focus of
this paper. Our application is thus designed as a peer-
to-peer architecture capable of running on mixed net-
work topologies .
The novel feature of using CSCW environments for
mixed network structures is not only the advantage
of independence from specific locations but also the
loss of guaranteed services within these spontaneous
networks. This loss of guarantees poses a number of
challenges in terms of adapting concepts from clas-
sical CSCW environments. In peer-to-peer topolo-
gies, all resources for needed services must be able
to be hosted on all clients. An important problem
are persistent knowledge areas of classical sTeam,
in which learners cooperate by communicating and
managing documents. We need a concept to distribute
the knowledge space over the mobile devices in such a
way that the required knowledge areas are accessible
to all users.
Spontaneous networks are by nature highly dy-
namic. The existence of a node in this network is
not guaranteed. The node containing the desired
knowledge area must not be a member of the net-
work or may suddenly disappear from it. Whole
parts of a network may also be separated from each
other. In (Feeney et al., 2001), this problem is called
network partitioning.
Since users can move around, the availability of a
certain knowledge area is not predictable. Given the
uncertain availability of knowledge areas on foreign
hosts, users may want to take interesting areas with
them. To do so, users need their own instances of
interesting knowledge areas to work with in case
they are disconnected from their co-workers. This
results in redundant storage of the objects involved.
If one user changes the content of an object within
a certain area, all other instances become outdated.
Problems may arise if two instances are combined
again when two peers reconnect with each other.
This is what (Feeney et al., 2001) calls network merg-
ing. If the instances of an area change, this poses the
Proxy Object
Persistent Area
Local Copy for Backup
Active Connection
Backup Connection (Read Only)
Synchronizing Connection (One Way)
Hosting Peer Remote Peer
Hosting Peer Remote Peer
Connected Peers
Disconnected Peers
Figure 1: Remote and hosting peer when connected and
when disconnected
challenge of synchronizing them between the affected
In order to explore practical solutions to these prob-
lems, we began by adopting the pragmatic approach
of creating persistent and personal knowledge areas.
Our next step was to design temporary knowledge ar-
eas and temporary user groups.
4.1 Persistent and Personal
Knowledge Areas
In classical client/server environments, all users work
on the same instance of a knowledge area. This in-
stance remains persistent on the server until an au-
thorized user destroys it. These persistent knowledge
areas can be guaranteed because all users work on the
same objects. In ad hoc networks, there is no such
guarantee, not even for personal work areas. In Dis-
tributed Knowledge Spaces, we distinguish between
personal and persistent knowledge areas.
Personal knowledge areas are hosted only on the
learners’ personal device and are only accessible
to them. Unlike personal knowledge areas, persis-
tent knowledge areas are areas for cooperative work
hosted on precisely one node in the network (hosting
peer). All connected nodes (remote peers) may per-
form changes within this area through a proxy object
pointing to the original area. As shown in Figure 1,
nodes are also allowed to create a synchronized lo-
cal read-only instance in case they are disconnected.
When offline from the hosting peer, the remote peer
may read-access the local copy.
The problem of local copies becoming outdated
poses a challenge that it is hard to meet with tech-
nical solutions. Classical synchronization for mobile
clients as in PalmSync or CPISync is designed to syn-
chronize changing datasets between only two or three
Device n
Device 1
Temporary Knowledge Spaces Persistent Knowledge Spaces
Figure 2: Temporary knowledge areas may reference per-
sistent knowledge areas but not vice versa
hosts in one or the other direction (Trachtenberg et al.,
2002). Dynamic synchronization of a complete net-
work’s nodes is an even tougher task. Our concept
enables this problem to be evaded.
4.2 Temporary Knowledge Areas
and Groups
Another difference from classical learning environ-
ments is the fact that in mobile scenarios collabora-
tive work is often not planned with the goal of creat-
ing persistent knowledge spaces for future work but
to use knowledge spaces for spontaneous knowledge
construction. Consequently, the developed knowl-
edge space can be destroyed as soon as the session
is finished. It may be the case that one or more partic-
ipants in the session wish to keep some of the results
or even the whole area. Since this cannot be decided
when the session starts, it must be possible to trans-
fer the results of the session, or even parts of it, to
a persistent knowledge space. The same applies to
the spontaneously established groups because the de-
cision to hold a subsequent session may have been
reached after the group was established.
For this reason, our concept allows temporary
groups to be established with an appropriate knowl-
edge area. This mechanism is specially designed for
spontaneous face-to-face learning sessions, where all
participants meet at a certain location and wish to col-
laborate. The users only need their connected devices.
An important restriction on temporary knowledge
areas is the linking of objects. While in classical
sTeam systems any object may be referenced by a
link, links to temporary knowledge areas are prohib-
ited (see Figure 2. To reference a temporary knowl-
edge area, it must first be transformed into a persistent
knowledge area.
Like the area, the temporary group exists as long as
at least one user is participating in the session. When
the last participant leaves, the group is automatically
destroyed. If the hosting device withdraws from the
network, the session still exists but the other partic-
ipants have only a read-only copy, as in the case of
persistent knowledge areas. These conventions ensure
that only one active instance of the area exists.
This concept is evaluated by implementing proto-
types for the cooperation environment, as described
in the following section. Evaluation results relating to
the concept of Cooperative Virtual Knowledge Spaces
can be found in (Hampel and Keil-Slawik, 2003).
The last two sections discussed the network environ-
ment for our application and described collaboration
techniques matching such network environments.
The devices the application has to run on may be
as heterogeneous as the network. They include any
network-connected device, ranging from cell phones
and handheld devices to full-featured PCs and servers.
This heterogeneous situation yields some important
criteria for our application:
Open Architecture The application must be portable
to almost any platform/device. Standardized proto-
cols and interfaces must therefore be used. Also, it
must scale to the capabilities of the hosting devices.
Automatic Configuration The application must be
able to configure to meet the requirements of the
actual environments with a minimum of adminis-
trative effort. Also, it must reconfigure dynami-
cally for changing environments.
Spontaneous Networking The application must able
to establish spontaneous sTeam networks within
heterogeneous IP-based network environments.
This includes the option of sharing resources within
the network and connecting to classical sTeam
The goal of our development process is to build an
open, self-configuring and well-scaling architecture.
Our architecture is based on our work on the classical
client/server sTeam system, which has been shown to
work well in common IP-based network infrastruc-
tures. Since every resource in sTeam is represented
by an steam-object, which can be both a user in the
system and a knowledge area or document, we speak
only of objects, regardless of the kind of object we are
talking about.
A node in a sTeam a peer-to-peer network may have
limited and possibly low resources. For this reason,
nodes must manage resources very carefully. Typi-
cal critical resources on mobile nodes are memory,
computing power (CPU), battery life and bandwidth
(Meyer, 1995).
One component in our architecture manages the re-
sources of a node. We call this component Resource
Handler. The Resource Handler warns about low
resources and is configured with policies on how to
Resource Handler
sTeam Peer-to-Peer
IP-based Services
sTeam Server
Network Application Hardware
Figure 3: The Resource Handler controls the network com-
ponents the peer may offer to the network according to the
available hardware resources
take care of resource conflicts. An example policy is
used for peers with low battery power. The Resource
Handler invokes the migration of shared objects from
the low-energy peer to another peer with better bat-
tery resources. This allows the drained peer to save
battery power by reducing its network activity while
other remote peers can still work on the shared ob-
jects. Even if the node disappears from the network
because of its low battery power, it does not affect
the remotely working peers. Similar policies exist for
low memory, CPU performance, bandwidth and any
other resource monitored by the Resource Handler.
The Resource Handler balances available resources
between nodes by communicating with its counter-
parts in other sTeam peers via the network.
Another way to save a node?s resources is to ac-
tivate/deactivate several services to the network, as
shown in Figure 3. Thus, a node on a low-featured
device like a mobile phone would merely access other
remote resources but offer no services to other nodes.
Better equipped devices can even offer conventional
services to access a knowledge area (e.g. ftp access).
We will discuss this option later on.
To build our application, we opted for the JXTA
peer-to-peer framework, which implements a over-
lay peer-to-peer network that allows communication
between any network-connected device, from cell
phones and handheld devices to personal computers
and servers. Figure ?? shows a small JXTA network.
By using JXTA applications are able to communicate
on a peer-to-peer basis without knowing the underly-
ing network structure (Gong, 2001).
An important requirement for our application is the
ability to connect automatically to its counterparts to
form a spontaneous application network. JXTA shows
this behavior even in a hybrid architecture of struc-
tured and ad hoc networks.
While JXTA offers services to other JXTA nodes,
other IP-based applications are unable to access the
resources on the sTeam peer. To be as cooperative as
possible with other parts of the network, our applica-
tion is able to offer services to classical clients, e.g.
web browsers or ftp clients. These additional services
can be provided depending on the capabilities of the
node. Furthermore, the sTeam peer is able to use stan-
dard IP-based services for its purposes. This leads to
the problem of finding services in ad hoc networks
where no fixed namespaces exist and where access to
DNS servers cannot be guaranteed.
For publishing and finding such services, we use
Multicast DNS (mDNS). mDNS broadcasts informa-
tion about provided services to the network. This in-
formation can be read by any mDNS-capable applica-
tion to determine which IP address and port to connect
to for which service. mDNS is part of the Zeroconf
specification carried out by IETF’s Zeroconf Working
Group and is described in (Cheshire and Krochmal,
The second optional network protocol is the COAL
protocol. This is the proprietary standard sTeam pro-
tocol for connecting to classical sTeam servers and
clients. Thus, the peer can communicate with sTeam
servers and provide objects to classical sTeam clients.
The use of optional services allow peers to scale
their provided services to suit their resource capabil-
ities. In addition to the above-mentioned resources,
the Resource Handler also controls the provided net-
work services according to available bandwidth, com-
puting power, memory, etc. This leads to high scala-
bility. The application can scale both on the JXTA
part by scaling from Minimal Peer up to Rendezvous
or Relay Peer (Gong, 2001) and on the sTeam part
by scaling from a pure remote peer, only working on
knowledge areas hosted on other nodes, up to a net-
work server, offering access to its knowledge areas via
http, ftp, COAL, etc. This concept enables the applica-
tion to adapt to devices like cell phones, full-featured
laptops or even workstations.
As part of our development process, we built a pro-
totype of an sTeam peer node using the JXTA tech-
nology. The prototype is quite a simple peer, which
is able to send messages containing XML structures,
steam-objects or Java objects from one peer to an-
other. This is done without any administrative effort
on the part of the users. The peers find each other
autonomously without any configuration. This proto-
type shows that it is feasible to build an sTeam peer-
to-peer network with the basic required communica-
tion mechanisms using the JXTA framework.
Parallel to this, we built a Java-based framework
for implementing mDNS-capable Java applications. It
is based on the Multicast DNS implementation jRen-
dezvous of Strangeberry Inc.. Our framework pro-
vides a Java interface class, which must be imple-
mented by an application to provide an mDNS service.
As with the JXTA prototype, instances of the chat ap-
plication are able to find each other and establish con-
nections without any configuration by the users. With
our mDNS interface and the JXTA prototype, we now
have the basic components for our sTeam peer-to-peer
application. We hope to be able to present the results
of our ongoing work at the conference.
The described prototype for collaboration in mobile
ad hoc networks constitutes a further step toward
network-supported, location-independent collabora-
tion. Our concept enables the users of mobile col-
laboration environments to cooperate via their mo-
bile devices without the need for any existing network
infrastructure, and at the same time allows them to
use classical services when available. By doing so,
we avoid the trade-off involved in using spontaneous
peer-to-peer networks or established client/server so-
Both concepts are consolidated in our approach.
Our prototype demonstrated that it is possible to
transfer our well-proven concept of Cooperative Vir-
tual Knowledge Spaces from common network infras-
tructures to the innovative hybrid network structures
described in Section 3. To do so, we are adapting
Cooperative Virtual Knowledge Spaces to dynamic
network structures. Our goal is to develop a con-
cept for Distributed Knowledge Spaces. Distributed
Knowledge Spaces allow Knowledge Spaces to be dis-
tributed over multiple dynamic connected nodes in
spontaneous and classical networks.
Computer-supported cooperation can thus accom-
pany users through the sort of situations encountered
in their daily lives. This is our primary research goal.
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