Active Networking based Service Infrastructure for

Cellular WLANs

Reiner N. Schmid

, Cornel Klein

, and Thomas Becker

Siemens AG, Munich, Germany

Fraunhofer Institute FOKUS, Berlin, Germany

Abstract. An approach of managing a service infrastructure for wireless local

area networks (WLANs) is presented. This approach uses Active Network tech-

nology as developed in the IST project FAIN in order to deploy and run services

at appropriate locations in the network. By introducing a service which monitors

trafﬁc and adaptively controls the access of mobile users it is possible to dynam-

ically bind particular users to speciﬁc access points, thus transforming conven-

tional WLAN to cellular WLAN. This service is made up from components in

the data and control plane of the network. Additional components in the manage-

ment plane are used for the deployment and runtime management of the service

components. The usefulness of this approach is corroborated with the outline of

key scenarios.

1 Introduction

WLAN [2] networks have become very popular for a wide range of users and services

and are rapidly deployed as public hot spots in areas such as airports, conference rooms,

restaurants, shopping malls and public fairs. WLAN has emerged as the technology of

choice used for wireless data transfer in public areas. From a technological point of view

it is comparable to Ethernet as it establishes a shared medium for data exchange without

provisions for exclusive access. This concept is quite opposite to mobile communication

technologies such as GSM or UMTS, which have mechanisms for exclusive channels

and cellular structures, being the basis for the provisioning of Quality of Service (QoS)

guarantees and other mechanisms for resource control.

WLAN, as standardised by IEEE, offers only a limited support for advanced cellu-

lar mechanisms and roaming. Though there is emerging support for inter access point

communication in the recently established standard IEEE 802.11.f – deﬁning commu-

nication between the access points about re-association of terminals – this is limited

to facilitate the deployment of large scale networks consisting of many WLAN access

points.

WLAN, based on IEEE 802.11b, allows for transmission rates up to 11 Mbps, which

is sufﬁcient for audio transmission and to a limited extent also for video streaming given

that the streaming bandwidth is adapted to the available transmission bandwidth (see

e.g. [3]). Though the newer and faster WLAN standards (e.g. IEEE 802.11g) allowing

N. Schmid R., Klein C. and Becker T. (2004).

Active Networking based Service Infrastructure for Cellular WLANs.

In Proceedings of the 3rd International Workshop on Wireless Information Systems, pages 134-141

DOI: 10.5220/0002674801340141

 SciTePress

for higher data rates are now available, support for dedicated Quality of Service is lim-

ited and not sufﬁcient to support service environments with different services using the

same WLAN network at the same time.

In this paper we focus on WLAN application scenarios in semi-public areas (air-

ports, hotels etc.), which require a ﬂexible service provisioning infrastructure concept

in order to fulﬁl the requirements of users and services alike. With respect to these

scenarios as discussed in section 2, more ﬂexible and sophisticated mechanisms for

support of service infrastructure by WLAN are required. Though this isn’t part of the

MAC layer speciﬁcation of WLAN by IEEE, it is shown in this paper that this ser-

vice infrastructure can be implemented by using Active Networking [1], a promising

method of solving the demands of next generation networking infrastructures. The ba-

sic concept of Active Networks is to allow third parties (service providers, end-users,

etc.) to inject application speciﬁc service code into the network. Active Network nodes

expose open interfaces and execution environments for running services, thereby mak-

ing the network ‘programmable’. Wireless local area networks (WLANs) prove to be a

particular interesting application domain for Active Networking [4].

Active Networking concepts, in particular the Active Node architecture of FAIN as

presented in section 3, are used to implement a ﬂexible, application adaptable resource

management of WLAN networks. This includes the establishment of virtual service

environments and dynamic access control for WLAN resources thus providing cellular

mechanisms for WLAN management.

The main idea of our approach is to transfer concepts of cellular mobile networks

to WLAN establishing a cellular WLAN, thus complementing out-of-the-box WLAN

with state-of-the-art concepts of mobile networks. This is shown in Section 4 which

presents the details of a service for dynamic control of access to a WLAN. Conclusions

are discussed in Section 5.

2 Mobile Active Networking Scenarios

We mainly consider WLANs in so-called semi-public areas. By a semi-public area we

denote a geographically separated area with a network infrastructure which is populated

by a huge variety of stakeholders, but which is owned and controlled by a particular

institution, e.g. a company. In contrast to completely private areas with very restricted

access, it is frequented by a large number of users with different objectives and interests.

Some examples for such semi-public areas and the users of their WLAN infrastructure

are:

– airports with users like passengers, airlines, shops, airport personnel;

– trade shows with users like visitors, exhibitors, organiser’s personnel;

– shopping centres providing WLAN support for visitors, shops clerks, service per-

sonnel, etc.;

– hotels with guests, conference organiser, hotel personnel;

– corporate campuses with employees, external visitors, different organisational units.

In all these cases there are a couple of groups with different requirements when us-

ing the WLAN infrastructure. For instance, at a trade show the visitors may prefer best-

effort or QoS-based Internet access, depending on their willingness to pay. Exhibitors

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may want to use WLAN for providing location-based services to visitors, e.g. to attract

people to visit their exhibition places. Additionally, exhibitors could use WLAN for

their internal communication as do the employees of the trade show organiser. In that

case it is likely that WLAN based telephony will only be used if it is ensured that it

doesn’t interfere with other WLAN usage, e.g. ongoing data transfer.

To summarise, the requirements of the different users towards WLAN operation are

quite speciﬁc and diverse. Ad-hoc approaches, where different WLANs are installed

and operated by (or for) the different stakeholders aren’t suited to accommodate their

joint requirements for the following reasons:

– Setting up separate WLANs is likely to be more expensive than using a shared

infrastructure, in particular, if they are used only for a short period of time.

– Overall Quality of Services requirements can only be implemented if access to the

underlying shared resources as WLAN channels and bandwidth is controlled by a

common entity.

– Moreover, a powerful shared infrastructure is beneﬁcial for high-volume peak times,

as, for instance, an application with high bandwidth requirements can be shifted to

a speciﬁc WLAN channel or access point.

Since the involved stakeholders and their requirements in the presented examples

are changing quite frequently, static approaches to the conﬁguration of such a common,

shared infrastructure aren’t well suited. In particular, it is rather unlikely that all required

services are conﬁgured by the infrastructure’s operator in advance. What we need is an

infrastructure which among others implements the following requirements:

– Delegation: part of the management of the infrastructure can be delegated to its

stakeholders, allowing them to manage their part of the network on their own. The

provided management functionality should be as ﬂexible as possible w.r.t. to the

kind of applications they have in mind.

– Virtualisation: the different stakeholders shouldn’t interfere with each other, but

should get their own (virtual) private network, both w.r.t. to management function-

ality and user trafﬁc.

– Resource Management: it should be possible to ﬂexibly allocate, release and mon-

itor the underlying shared resources on a per stakeholder/per users basis.

The Active Networks based service infrastructure presented in this paper realises these

requirements complementing existing approaches for deploying and operating large

WLANs. For this reason we don’t deal with issues like network planning (e.g. access

point placement), but we rather take for granted viable approaches for dealing with

these problems.

3 FAIN Active Node

The management layer of the FAIN Active Node [4] is of particular importance in the

FAIN architecture. The purpose of this layer is to manage active services in the scope of

a network node on the data, control, and management planes. It serves as an abstraction

layer between services and the node’s operating system by abstracting from operating

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system speciﬁc interfaces and making them available as so called basic node services

to higher-level services. In this way the management layer provides a uniform way to

deal with functionality provided by the node as well as dynamically added extensions

in the form of active services.

Since services may be implemented using different technology and thus require

different execution environments (EEs) the FAIN node architecture doesn’t deﬁne a

single type of EE but rather allows for a variety of them. For example, complex services

in the control or management plane may be well executed in a user-space EE providing

considerable ﬂexibility and robustness while services in the data plane may require a

kernel-space EE for performance reasons.

We want to mention two types of EEs developed in the FAIN project, namely the

JAVA-based EE [4] and the PromethOS EE [5]. With the JAVA EE complex services can

be rapidly prototyped making use of the broad functionality provided by the JAVA API.

It is also used for the implementation of the FAIN active node’s management layer. The

PromethOS EE is an extension of the Linux Netﬁlter framework and running in kernel-

space. In particular it allows to dynamically add services in the data path in the form of

modules. Thus it is predestined for services working on data packets and requiring high-

performance which wouldn’t be possible when data had to be copied from kernel-space

to user-space and vice versa.

For specifying, implementing, and managing services a component-based approach

was chosen. This approach offers a couple of advantages:

– Aspects such as lifecycle management, conﬁguration, access control, monitoring,

etc. can be separated from the service logic and are supported by the components’

runtime environment. Thus the developer of a service can concentrate on the service

logic and frequently needed aspects don’t have to be implemented over and over

again.

– Complex services can be built by combining available components.

– By providing means to dynamically interconnect components a high degree of ﬂex-

ibility can be reached. After the initial setup services may be reconﬁgured during

runtime by adding new components, removing components, or changing connec-

tions between components.

Other systems with different or no component abstractions can be wrapped with proxy

components residing in the management layer thus making available the mentioned

advantages. Similarly, the abstraction of modules provided by the high-performance

PromethOS EE was mapped to components on the management layer.

The FAIN Active Node architecture deﬁnes some basic node services which are

available to later installed services. The basic services comprise management of com-

ponent environments, control of access to services and resources, packet dispatching

among components, and trafﬁc control.

There are two different kinds of component environments: the already mentioned

execution environments (EEs) implemented with a speciﬁc technology and virtual en-

vironments (VEs) which abstract from a particular EE implementation and are used to

group resources belonging to the owners of VEs. A special privileged VE is owned by

the node’s operator and has full access to the node’s resources. This is where the basic

node services are installed when the node is booted.

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The next section will describe a speciﬁc service used for controlling the access to a

WLAN. The service is made up from components in the data and control planes and is

running in two different types of execution environments.

4 Wireless Access

Based on the component model of the FAIN project a service for controlling access to

a WLAN, that takes into account the requirements posed by scenarios as discussed in

section 2, has been implemented and demonstrated during the FAIN project [6]. The

service effects load balancing between a number of wireless access points. In order

to provide support not only for this particular service, but for a variety of services – a

key feature in this application domain – a generic framework for access control has been

developed. This framework makes use of the advantages of the kernel-space PromethOS

EE for processing data packets and the user-space JAVA EE for control purposes. With

this framework one can build access controllers equivalent to commercially available

solutions. Moreover, by exploiting the ﬂexibility provided by the EEs it is possible to

deploy new services on-the-ﬂy and to customise their behaviour according to different

applications’ needs. The establishment of application dependent resource control and

virtual network environments for the provision of resource shares to different users are

the key features of our implementation.

The framework for access control to wireless networks deﬁnes three entities situated

at different locations:

– terminal daemons located at the end users’ terminals,

– a WLAN access controller (WAC) located on a potential active node in the access

network, and

– components in the data plane on one or more active nodes supporting the WAC.

A sample network setup showing the deployment of the different components is

presented in ﬁgure 1. The details of their functionality are explained in the subsequent

paragraphs.

Terminal Daemon: The terminal daemon is responsible for managing the WLAN

driver of the terminal. It determines the access points to be used for association and

controls the WLAN roaming behaviour. Further, it obtains information about the avail-

able access points and their signal quality from the WLAN driver. The terminal daemon

sends this information to the WAC and receives instructions which are then enforced us-

ing the terminal’s WLAN driver.

WLAN Access Controller: The WAC’s main task is to exercise control on all issues

related with the management of users and usage of the WLAN. Based on the informa-

tion received by the terminals and its own monitoring results, it decides on access and

load distribution in the network. Conﬁguring the FAIN active nodes is a further task

of the WAC. The WLAN Access Controller is implemented based on the JAVA EE of

FAIN.

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Terminal/

Terminal Daemon

Router

Access

Point

Access

Point

Remote

Server

WLAN Access

Controller

Terminal/

Terminal Daemon

PromethOS

Active

Node

Module_1

Module_2

Fig. 1. Deployment of WAC system components

PromethOS Modules: The components in the data plane EE – i.e. modules in the

PromethOS EE – are responsible for IP layer decisions concerning the trafﬁc in the

WLAN network. They are conﬁgured by the WAC. In this respect the functionality of

the network node may be freely conﬁgured by the deployment of PromethOS modules.

However, a certain minimal set of basic functionality is always required:

– routing/bridging between different subnets of WLAN access points and other net-

works,

– load monitoring of data ﬂows from and to access points per user or by other moni-

toring criteria,

– routing to simulate bridging functionality of the active node, and

– receiving messages destined for the WAC.

An example demonstrating the interaction of the different entities for a load balanc-

ing service is shown in Figure 2. It shows a handover between different WLAN access

points. The terminal daemons are constantly doing measurements about the available

access points and their signal strengths. This measurements are reported to the WAC.

Similarly, the trafﬁc through the active node is measured and results are reported to the

WAC. Based on this information the WAC decides which terminal should be assigned

to which access point. In the case that a terminal should switch to another access point

the WAC sends instructions to the corresponding terminal daemon.

Based on the FAIN component model a very rapid development of the different

components could be made. In particular the JAVA components can be very efﬁciently

programmed. The PromethOS EE components are more sophisticated to program, as

they are implemented as Linux kernel modules.

Depending on the various needs of applications running on mobile terminals differ-

ent services can be deployed on demand. Making use of the component-based approach

a new service for wireless access control is deployed by installation of modules for the

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Perform Handover

Handover-Command

WLAN Access Controller

Handover-

Command

Handover-Command

Measurements

Access Point

Fig. 2. Interaction of entities in a handover scenario

PromethOS EE and WAC components for the user-space EE. The installation of service

components to different EEs is coordinated by the VE to which the EEs are attached.

The VE concept with the separation of resources allows to install multiple services in

parallel sharing the same underlying infrastructure.

5 Conclusions

In this paper, we presented the FAIN architecture for managing active nodes and an

application based on it for wireless networks. The introduction of virtual environments

in FAIN allowed integrating several execution environments with potential different

implementation technologies. Further, physical resources could be partitioned among

several node users – the service providers – with the help of virtual environments. To

achieve a ﬂexible and ﬁne grained control over service deployment and management

a component-based approach was chosen for the node level management layer. The

application in a wireless access systems turned out to offer a considerably increased

ﬂexibility compared to commercial off-the-shelf solutions already available for access

control in WLAN networks. Another strength of the Active Networking concept is the

possibility to effect an application dependent behaviour of network elements. The po-

tential beneﬁts of these capabilities that are easily installed in the framework for wire-

less access presented here remain to be investigated and are a ﬁeld of further study.

Acknowledgement

This paper describes work undertaken in the context of the FAIN project (www.ist-

fain.org). We would like to thank our colleagues of the FAIN consortium for valuable

140

discussions, in particular Lukas Ruf from ETH Zurich for implementing and supporting

the PromethOS EE. The FAIN project was partially funded by the Commission of the

European Union as IST project 10561.

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