A simulation testbed for a MIH enabled system

Abstract

Interoperability between heterogeneous wireless access networks will help the operators to improve the quality of service offered to the users and the networks resource utilization. Media Independent Handover (MIH) standard is designed by IEEE to optimize the handover between heterogeneous networks. This paper presents a solution for mobility management in heterogeneous networks which is based on the MIH framework. It is presented the architecture and the simulation testbed used for system validation. QualNet simulator was chose to implement the proposed solution.

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A Simulation Testbed for a MIH enabled system

Şerban Georgică Obreja, Octavian Fratu, Alexandru Vulpe
The Faculty of Electronics, Telecommunications and Information Technology
University POLITEHNICA of Bucharest
Bucharest, Romania
serban@radio.pub.ro, ofratu@elcom.pub.ro, alex.vulpe@yahoo.com


Abstract— Interoperability between heterogeneous wireless
access networks will help the operators to improve the quality of
service offered to the users and the networks resource utilization.
Media Independent Handover (MIH) standard is designed by
IEEE to optimize the handover between heterogeneous networks.
This paper presents a solution for mobility management in
heterogeneous networks which is based on the MIH framework.
It is presented the architecture and the simulation testbed used
for system validation. QualNet simulator was chose to implement
the proposed solution.
Keywords: IEEE 802.21, MIH, vertical handover, simulation
I.
INTRODUCTION
The convergence of communication networks and services
consist a great challenge for network engineers. While at the
core level the convergence will lead to an all IP network, at the
access level several technologies coexist offering great
opportunities for services availability and quality. To take
advantage of these opportunities a common mobility
management framework is required. It should be able to
provide service continuity, to optimally manage the network
resources in order to improve the system performance and
capacity, and implicitly the service quality offered to the users.
Much functionality required to provide session continuity
depend on complex interactions that are specific to each
particular technology. IEEE 802.21 standard provides a
framework that allows higher levels to interact with lower
layers to provide session continuity without dealing with the
specifics of each technology. It provides the missing,
technology-independent abstraction
technology-specific primitives. This abstraction can be
exploited by the IP stack (or any other upper layer) to better
interact with the underlying technologies, ultimately leading to
improved handover performance [1]. With networks supporting
vertical handover (VHO), terminals can move between these
networks without losing connectivity or interrupting active
services. Not only this allows users to move freely but also
does not bother them with the network selection or other
related activities.
layer, thus hiding
In this paper a mobility management system for
heterogeneous access network is presented. It defines a
framework which provides a set of mechanisms for seamless
handover based on the IEEE 802.21 standard. This system was
proposed and is being implemented in the RIWCOS NATO
project.
Due to the relevance of interoperability between
heterogeneous mobile networks there are several related work
on this topic. European Union also funded some projects based
on Media Independent Handover. The Ambient Networks
project defined a novel trigger-based architecture for handover
optimization [7]. The HURRICANE project targets to specify,
design, implement and test innovative vertical handover
mechanisms, providing seamless inter-technology mobility [8].
In [9], [10] and [11] mobility management solutions based on
MIH framework are presented. In [9] presents novel handover
procedures to address seamless mobility in heterogeneous
environments. The proposed scheme is an enhanced version of
the IEEE 802.21 MIH platform, called enhanced Media
Independent Handover Framework (eMIHF). In [10], Media
independent preauthentication (MPA) provision is suggested.
MPA provides a significant reduction in handover delays for
both network-layer and application-layer mobility management
protocols.
The paper is structured as follows. The following section
summarizes the main features and functionalities described by
the IEEE 802.21 standard. In the third Section the RIWCoS
architecture for a mobility management system based on MIH
standard is presented. Then, we discuss a testbed for
implementing an architecture based on 802.21, and finally we
draw conclusions and emphasize future work needed to
implement this standard.
II.
OVERVIEW OF IEEE 802.21
A. 802.21 Objectives
The purpose of this standard is to improve the user
experience by providing MIH functionality that facilitates both
mobile-initiated and network-initiated
standard[1] consists of the following three main elements:
handovers. The
•
A framework that enables service continuity while a
mobile node (MN) transitions between heterogeneous
networks. It relies on the presence of a mobility
management protocol stack within the network
elements that support the handover.
•
The MIH function (MIHF), which is an entity
consisting of a set of handover-enabling functions
within the protocol stacks of the network elements
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•
Service access points (SAPs), which define both
media-independent and media-specific interfaces. They
offer both access for MIH Users to the MIH function
and help for the MIHF to collect link information and
control link behavior during handovers.
Additionally, the standard defines a set of secondary goals.
These are:
•
Service continuity. One of its main goals is to
eliminate or avoid as much as possible the need to
restart an application after a handover has taken place.
•
Quality of service (QoS)-aware handovers. 802.21
provides the necessary functions in order to make
handover decisions based on QoS criteria
•
Network discovery. This feature allows MIH Users to
be provided with information on candidate neighbor
networks for a handover.
•
Network selection assistance. The 802.21 framework
provides the necessary functions to assist making the
handover decision based on several factors (e.g., QoS,
throughput, billing etc.). Note that it does not make
handover decisions, which are left to higher layers.
•
Power management. The standard allows the MN to
discover different types of wireless networks, avoiding
powering-up of multiple radios and/or excessive
scanning at the radios. Thus power consumption can be
minimized.
B. MIH function services
IEEE 802.21 defines three services that facilitate handovers
across heterogeneous networks. These are managed and
configured by a fourth service which is called the management
service. Through the service management primitives, the MIHF
is capable of discovering other MIHF entities [2].
•
Media Independent Event Service (MIES): detects
events and delivers triggers from both local and remote
interfaces.
•
Media independent Command Service (MICS):
provides a set of commands for the MIHUs to control
handover relevant link states.
•
Media Independent Information Service (MIIS):
provides the information model for query and
response, thus enabling more effective handover
decisions across heterogeneous networks.
III.
RIWCOS ARCHITECTURE
RIWCoS is a project that aims to integrate different
wireless communications technologies into a common hybrid
“easy to use” communication infrastructure.
The main technological objective is to develop, implement
and demonstrate an open, secure, fast-reconfigurable content
delivery platform based on MIH framework, for high quality
multimedia services (transport and distribution), through any
type of wireless access networks to mobile and residential end-
users. The project specific goal is to exploit the synergy
between Broadcast Networks (DVB-T, DVB-H), Cellular
Mobile Telecommunication Networks (HSDPA, UMTS), and
IP-based Wireless Networks (WLAN, WMAN).
RIWCoS project addresses terminal mobility, i.e., the
action which allows a mobile node to move between IP subnets
while continuing to be reachable for incoming requests and
maintaining sessions across subnet changes. Other types of
mobility include: session mobility, which allows a user to
maintain a session even while changing terminals, personal
mobility, which allows to address a single user located at
different terminals by the same logical address and service
mobility, which allows users to maintain access to their
services even while moving or changing devices and network
service providers.
It also monitors the parameters for the active link to detect
when to trigger the handover. The handover could also be
triggered by the MAC events. The IM has a MAC specific
component, called Interoperability module, for each technology
specific MAC. It is used to add MIH functionalities for each
type of MAC layer. At the PoA the IM has the following
functionalities: provision of information to mobile terminal

MIH Protocol
IM Engine
Net
Res
Link
Res
Mobility
Manager
MIH_SAP
MIH_LINK_SAP
MIH_NET_SAP
Figure 2: Interoperability module

MIH_LINK_SAP
MIHF
Resource
Manager
Interoperability
Manager
MIH User
MIH_SAP
Interoperability
Module
802.11 802.16
MIH_NET_SAP
MIH Mobile Node
MIH_LINK_SAP
Resource
Manager
Interoperability
Manager
MIH_SAP
Interoperability
Module
802.11 802.16
MIH PoA

Figure 1: RIWCOS Architecture
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about the neighbor networks, provision of link state
information, MIH messages handler.
The RM module deals with network selection and resource
allocation [2] [4]. Based on the monitoring performed by the
Interoperability Managers, the RM selects the destination PoA
for the mobile node. The selection process takes into account
the user profile, the network load, in a way which assures an
optimal resource allocation while providing the desired service
quality to the mobile user.
The modes in which the RM can operate are: Emergency
Mode, BatteryLowMode and Normal Mode. In the Normal
Mode, the Decision block does simple switching of the user
demands to what is available as a resource in the repository,
selecting the resources that best fit with the user’s demand in
terms of QoS. In the BatteryLowMode the Decision block
selects the technology that best fits the battery saving, thus
reducing QoS (the selected technology may not be best fitted
for the QoS of the application). In the Emergency mode
(started when LinkDown trigger from IM is received), the RM
module uses specially designed algorithm implemented in user
and network RM modules for sorting applications and serves
them as sorted.
IV. THE RIWCOS TESTBED
Because MIH enabled equipments are not available on the
market yet it was decided to use a simulation environment for
the RIWCoS system validation. The simulation environment
used is Qualnet. The RM module was developed as a separate
application so, in order to integrate the system, a link between
RM and the simulated testbed was realized via socket interface
(figure 3). This will lead to an undesired increase in the
handover delay. Since the RM is mainly focused on the user
side, the external RM application is logically linked with the
Qualnet simulated MIH enabled mobile node.
The communication between the IM and RM modules is
done via the MIH SAP interface. Because the modules will run
on different virtual machines and they will be connected via
socket interface, a mapping of the MIH SAP functions in
socket messages was done. Only the relevant parameters are
carried via socket, the other ones are added at the message
reception. In this way the message dimension is reduced
fastening the communication speed via the socket interface.
QualNet uses a layered architecture similar to that of the
TCP/IP network protocol stack, within which data moves
between adjacent layers. The QualNet protocol stack consists
of the following layers (from top to bottom): Application,
Transport, Network, Data Link (MAC) and Physical Layers
[5]. The Interoperability Manager components were integrated
in the layer 2 and layer 3 in the QualNet stack: The
interoperability module, which is technology dependent, was
integrated at the MAC level of the different technologies. The
Interoperability manager was integrated at leyer 3 because it
contains the MIH protocol which uses IP to communicate
between different PoA.
The message sequence chart depicted in figure 4 illustrates
the MIH signaling involved in triggering the handover between

two heterogeneous networks. A mobile node attached to an
802.11 access point detects that the link quality is degrading
and sends a Link_Going_Down.indication primitive to its
Interoperability Manager (IM). The IM forwards this indication
to the Resource Manager (RM) located within a node inside the
network. In order to find out the link parameters of the
potential candidate points of attachment, the RM initiates a
procedure for collecting the link parameters for the potential
candidate networks, in this case a WiMAX network.
To find the potential candidates the RM uses the MIH
Information Server. After it gets the link parameters for the
candidate networks it applies the selection algorithm and
selects the optimal network. After the network was selected the
handover is initiated.
First the procedure of establishing a layer 2 connection with
WiMAX base station is initiated. If the connection is
successfully established then the user data is forwarded from
the WiFi AP to the WiMAX base station. After the transfer is
completed the WiFI link is released by the mobile node.
V.
CONCLUSIONS AND FUTURE WORK
In this paper a simulated testbed for a mobility management
system for heterogeneous networks, proposed in the RIWCoS
project, was presented. The testbed is based on the QualNet
simulator. The system implementation is not completed yet,
only the mobility framework was done, which includes the
Interoperability Manager, the MIH protocol and some basic
functionality for the Link Interoperability Modules.
For the near future we intend to finish the system
implementation in the QualNet environment. It will permit us
to evaluate the system’s performances such as the handover
delay, the packets lost, etc. Also a Qualnet implementation for
the RM module is considered in order to evaluate the
improvement in the handover delay while comparing with the
actual implementation with socket interface between RM and
the simulated testbed.
Another improvement that is intended for the next phase is
to add support for IP mobility. This will be done by integrating
support for the MIP protocol.


802.16e
BS
Resource
Manager
802.11
AP
WiFi MIH
Qualnet
simulated
network
Gateway
WIMAX MIH

Socket
communication
MIIS
MIH MN
Real network
Figure 3: RIWCoS simulated testbed
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ACKNOWLEDGMENT
This work is sponsored by NATO's Public Diplomacy
Division in the framework of “Science for Peace” through the
SfP-982469 "Reconfigurable Interoperability of Wireless
Communications Systems (RIWCoS)" project and by
Romanian Authority of Scientific Research in the framework
of PNCDI 2 “Partnership” through the 12-126/2008 “Hybrid
wireless access system with unique addressing (SAWHAU)”
project.
VI. REFERENCES
[1] IEEE802.21-2008, Standard for Local and Metropolitan Area Networks
- Part 21: Media Independent Handover Services. s.l. IEEE Computer
Society, January 2009.
[2] O. Ognenoski, V. Rakovic, M. Bogatinovski, V. Atanasovski and L.
Gavrilovska, “User perception of QoS and economics for a WiMAX
network in a backup scenario”, 1st International Conference on Wireless
Communications, Vehicular Technology, Information Theory and
Aerospace & Electronic Systems Technology (Wireless VITAE 2009),
Aalborg, Denmark, May 2009.
[3] A. de la Oliva, A. Banchs, I. Soto. “An overview of IEEE 802.21: Media
Independent Handover Services”. IEEE Communications Magazine.
August 2008, pg. 96-103.

[4] E.C. Popovici, V. Atanasovski, RIWCoS SfP-982469 Architecture v1.3.
November 2008.
[5] L. Gavrilovska, V. Atanasovski,”Reconfigurable Interoperability
towards Seamless Communications”, 10th International Symposium on
Wireless Personal Multimedia Communications (WPMC 2007), Jaipur,
India, December 03-06, 2007.
[6] O. Fratu, A.C. Boucouvalas, L. Gavrilovska, R. Prasad. Reconfigurable
Interoperability of Wireless Communications Systems (RIWCoS) Final
Proposal, RIWCoS SfP-982469. 14 December 2006.
[7] K. Pentikousis et al., The Ambient Networks Heterogeneous Access
Selection Architecture, in Proc, First Ambient Networks Workshop on
Mobility, Multiaccess, and
Sydney,Australia, Oct. 2007, pp. 49-54.
[8] Á. Gomes, N. Carapeto, P. Neves et al., HURRICANE: D2.1: Handover
reference scenarios, requirements specification and performance metrics.
[9] P. Neves, F. Fontes, S. Sargento, M. Melo, and K. Pentikousis,
“Enhanced Media Independent Handover Framework”, Proc. IEEE 69th
Vehicular Technology Conference (VTC2009-Spring), Barcelona,
Spain, April 2009.
[10] L. Eastwood et al., “Mobility Using IEEE 802.21 in a Heterogeneous
IEEE 802.16/802.11-Based, IMT-Advanced (4G) Network”, IEEE
Wireless Communications Magazine, pp. 26-34, April 2008.
[11] G. Lampropoulos et al., “Media Independent Handover for Seamless
Service Provision in Heterogeneous Networks”, IEEE Communications
Magazine, pp. 64-71, Jan. 2008.
Network Management (M2NM),




































MS
Link_Action.req()
MIHF
WIMAX
RM
WIFI
AP WiFI
MIHF
WIMAX
RM
BS WiMAX
MIHF
WIMAX
RM
Link_Detected.ind
Link_Going_Down.ind
MIH_Link_Detected.ind
MIH_Link_Going_Down.ind
Local Link Events
MIH_MN_HO_Commit.request (target PoA)
RNG_REG & SBC_REQ &REG_REQ
RNG_RSP & SBC_RSP & REG_RSP
Link_Action.rsp
MIH_MN_HO_Commit.response
Establish a new L2 connection - WIAMX
Link_Action.req(LINK_DISCONNECT)
MIH_Link_Action.req(LINK_DISCONNECT)
Deregistration& Disassociation req
Deregistration& Disassociation resp
Link_Action.rsp
MIH_Link_Action.rsp
Release old connection - WiFi








Get Parameters procedure for the candidate networks – initiated by RM
MIH_Link_Action.req(DATA_FWD_REQ)
Link_Action.req(DATA_FWD_REQ)
Link_Action.rsp()
MIH_Link_Action.rsp
Forward data from WiFI to WiMAX




























Figure 4: The MSC for a vertical handover between WiFI and WiMAX
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