Interworking of 3G cellular networks and wireless LANs.
ABSTRACT The Third Generation (3G) cellular networks provide ubiquitous connectivity but low data rates, whereas Wireless Local Area Networks (WLANs) can offer much higher data rates but only cover smaller geographic areas. Their complementary characteristics make the integration of the two networks a promising trend for next-generation wireless networks. With combined strengths, the integrated networks will provide both wide-area coverage and high-rate data services in hotspots. There are many aspects involved in their interworking, such as mobility, security and Quality of Service (QoS) provisioning. In this paper, we present a survey of most recent interworking mechanisms proposed in the literature, and outline some important open issues to achieve seamless integration.
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ABSTRACT: In this paper, basic mechanisms of interoperability between long-term evolution LTE as 4G cellular system and mobile WIMAX networks as 4G wireless are introduced. Two cost-based mechanisms are investigated to represent two interoperability functions: initial network selection INS and inter-network handover INH. Simplified approaches that ease the evaluation of related cost functions CFs are proposed. The necessary assumptions for the implementation of a joint LTE-WIMAX system level simulator platform, through a real coexistence scenario, are proposed. Numerical results show a considerable enhancement in terms of selected performance metrics such as blocking and dropping probabilities. Weight values readjustments are also tested to highlight the critical key factors affecting interoperability mechanisms.International Journal of Information and Communication Technology 02/2013; 5(1):1-21.
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ABSTRACT: In this paper, enhanced mechanisms of interworking (interoperability) between High Speed Downlink Packet Access (HSDPA) as 3.5G cellular network and HIPERLAN2 (H2) as wireless LAN are proposed and their performances are evaluated by system level simulation. Two cost-based techniques: Initial User Assignment (IUA) and Inter-System Handover (ISH) are selected, covering all possible assignment and handover key factors, to represent the interworking criteria. Results show a considerable enhancement in terms of selected performance metrics such as blocking and dropping probabilities. Weight values readjustments are also tested to highlight the critical key factors affecting interworking mechanisms.International Journal of Wireless and Mobile Computing 07/2012; 5(3):249-258.
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ABSTRACT: In recent years, Cellular wireless technologies like GPRS, UMTS, CDMA and Wireless Local Area Network (WLAN) technologies like IEEE 802.11 have seen a quantum leap in their growth. Cellular technologies can provide data services over a wide area, but with lower data rates. WLAN technologies offer higher data rates, but over smaller areas, popularly known as ‘Hot Spots’. The demand for an ubiquitous data service can be fulfilled, if it is possible for the end-user to seamlessly roam between these heterogeneous technologies. In this paper, a novel framework is proposed consisting of intra-ISP network called ‘Intermediate Switching Network’(ISN) fused between UMTS and WLAN networks as well as data (Internet) services for providing seamless mobility without affecting user’s activities. The ISN uses MPLS and Multiprotocol-BGP to switch the data traffic between UMTS to IEEE 802.11 networks, as per the movements of the user. The ISN is integrated with the UMTS network at the GGSN-3G and at the Access Point for IEEE 802.11 network respectively. The simulation result shows the improved performance of the ISN based framework over existing schemes.Wireless Networks 05/2013; 19(4):411-429. · 0.74 Impact Factor
Int. J. Wireless and Mobile Computing, Vol. 2, No. 4, 2007
Interworking of 3G cellular networks and
Wei Song and Weihua Zhuang*
Centre for Wireless Communications,
Department of Electrical and Computer Engineering,
University of Waterloo,
Waterloo, ON, Canada N2L 3G1
Wireless Technology Department,
5099 Creekbank Road,
Canada L4W 5N2
Abstract: The Third Generation (3G) cellular networks provide ubiquitous connectivity but low
data rates, whereasWireless LocalArea Networks (WLANs) can offer much higher data rates but
only cover smaller geographic areas. Their complementary characteristics make the integration
of the two networks a promising trend for next-generation wireless networks. With combined
in hotspots. There are many aspects involved in their interworking, such as mobility, security
and Quality of Service (QoS) provisioning. In this paper, we present a survey of most recent
interworking mechanisms proposed in the literature, and outline some important open issues to
achieve seamless integration.
Keywords: 3G/WLAN interworking; tight/loose coupling; mobility management; quality of
services; QoS provisioning.
Reference to this paper should be made as follows: Song, W., Zhuang, W. and Saleh, A. (2007)
Vol. 2, No. 4, pp.237–247.
Biographical notes: Wei Song received a BSc in Electrical Engineering from Hebei
University, China, in 1998, an MSc in Computer Science from Beijing University of Posts and
Telecommunications, China, in 2001 and a PhD in Electrical Engineering from the University
of Waterloo, Canada, in 2007. Currently, she is a PostDoctoral Fellow in the Department of
Electrical and Computer Engineering, at the University ofWaterloo, Canada. Her current research
interests include resource allocation and Quality-of-Service (QoS) provisioning for the integrated
cellular networks and Wireless Local Area Networks (WLANs). She received the Best Student
PaperAward from IEEE WCNC’07.
Weihua Zhuang received a PhD in Electrical Engineering from the University of New Brunswick,
Canada. Since October 1993, she has been with the Department of Electrical and Computer
Engineering, University of Waterloo, Canada, where she is co-author of the textbook Wireless
Communications and Networking (Prentice Hall, 2003). Her current research interests include
multimedia wireless communications, wireless networks and radio positioning. She received the
Premier’s Research Excellence Award in 2001 from the Ontario Government for demonstrated
excellence of scientific and academic contributions, the Outstanding PerformanceAward in 2005
and 2006 from the University of Waterloo, and the Best Paper Awards from IEEE WCNC’07,
IEEE ICC’07 and Qshine’07. She is the Editor-in-Chief of IEEE Transactions on Vehicular
Technology and an Editor of IEEE Transactions onWireless Communications, EURASIP Journal
on Wireless Communications and Networking and International Journal of Sensor Networks.
Aladdin Saleh received a PhD in Electrical Engineering from the University of London, England,
in 1984. Since then, he has held several positions both in the academia and the industry. In 1998,
Copyright © 2007 Inderscience Enterprises Ltd.
W. Song, W. Zhuang and A. Saleh
wireless Internet application projects. He has also developed Bell Canada technology strategy
for the IEEE 802.11/WiFi, IEEE 802.16/WiMAX, and the integration of 3G cellular networks
and WLAN. He is also an Adjunct Professor of Computer and Electrical Engineering at the
University of Waterloo, Canada. He is a Fellow of IEE and a Senior Member of IEEE. His
current research interests are in the areas of next-generation wireless networks and wireless
In the last decade, there has been successful deployment
and fast evolution of various wireless networks. Different
environments. It iswell-recognised
generation wireless networks will integrate heterogeneous
technologies to achieve enhanced performance.
attractive and complementary characteristics presented by
cellular networks and Wireless Local Area Networks
(WLANs) make them promising candidates.
Originally aiming at providing high-quality circuit-
switched voice service to mobile users within wide areas,
cellular networks have been well deployed around the
world and have evolved to the Third Generation (3G). Two
the Universal Mobile Telecommunication System (UMTS)
and cdma2000, which are specified by the 3G partnership
projects, that is, 3GPP and 3GPP2, respectively. Both
systems are based on Code-Division Multiple Access
such as Multimedia Message Service (MMS) and Wireless
Application Protocol (WAP) service. In cdma2000, for
example, the nominal 1.25MHz bandwidth can achieve a
demands for bandwidth-intensive data applications.
On the other hand, usually operating at unlicensed
frequency bands, WLANs provide data services with lower
cost. Moreover, the large bandwidth available for WLANs
makes it possible to achieve higher data rates. For example,
a WLAN can have a bandwidth more than 20MHz. IEEE
802.11b operates at the licence-exempt Industrial, Scientific
and Medical (ISM) frequency band from 2.4 to 2.483 GHz.
It extends the physical layer based on Direct Sequence
Spread Spectrum (DSSS) specified in the original 802.11
standard and supports a higher data rate up to 11Mbps.
The subsequent revisions such as 802.11a and 802.11g adopt
Orthogonal Frequency-Division Multiplexing (OFDM) and
offer a maximum rate of 54Mbps at the unlicensed 5 and
extension to the wired ethernet, a WLAN can only cover
a small geographic area. For instance, an 802.11b Access
Point (AP) can communicate with a Mobile Station (MS)
within up to 60m at 11Mbps and up to 100m at 2Mbps
with omnidirectional antennas. Consequently, with lower
cost and much higher data rates, WLANs can effectively
supplement the 3G networks in hotspot areas, where
bandwidth-demanding applications are concentrated. As a
result, by effectively combining 3G cellular networks and
mobile users can be provided with both ubiquitous
connectivity and high-rate data services in hotspots.
In the following sections, we first discuss the important
challenging issues involved in this integration problem.
Then we briefly review some typical interworking solutions
proposed in the literature. In the concluding remarks, some
open research issues are outlined.
2 Challenges for 3G/WLAN interworking
The heterogeneous technologies employed in 3G cellular
networks and WLANs bring many challenges to the
interworking. Based on different radio access techniques,
in terms of mobility management, security support and
Quality of Service (QoS) provisioning. In order to achieve
seamless integration, these issues should be carefully
addressed while developing the interworking schemes.
After three-generation evolution, relatively mature and
complete technologies have been established in cellular
networks to address issues such as mobility, security,
QoS, etc. With widely deployed infrastructure from radio
access networks to core networks, ubiquitous connectivity is
provided to mobile uses over wide areas. Different mobility
levels are supported from fast vehicles moving on highways
to stationary users in an indoor environment.
In contrast, the WLAN specifications only focus on the
physical layer and Medium Access Control (MAC) layer.
As for the upper layers, it assumes to adopt the same
protocols as those in wired networks, for example, the
links to avoid performance degradation. A de facto WLAN
system is given in Ahmavaara et al. (2003), in which the
layer-2 distribution system connects multiple APs, while
access routers in turn connect the layer-2 distribution
system to an IP backbone network. In some proposed
interworking schemes (to be discussed), the access routers
offer rich functionalities more than the basic function of
IP routing, for example, transferring authentication and
Through border gateways in the IP backbone network,
WLAN terminals are provided IP connectivity to external
IP networks such as the public Internet or a corporation
intranet. Instead of providing continuous coverage over wide
areas, WLANs are usually disjointly deployed in public or
private hotspots such as cafés, airports and offices. Users
in these areas normally have a very low mobility level, as
most of these areas are located in indoor environments.Also,
cellular coverage is available in these areas. As a result, a
non-uniform overlay topology structure has to be considered
for 3G/WLAN integration.
Interworking of 3G cellular networks and wireless LANs
2.1Seamless roaming across 3G cellular
networks and WLANs
Taking into account the distinct mobility management
a rather challenging task to support seamless roaming across
the two networks. Either the cellular networks or WLANs
should have inherent mechanisms for location and handoff
management to support the layer-2 or link layer mobility.
In 3G networks (e.g., UMTS or cdma2000), with the aid
of core networks, tunnelling protocols are used to support
roaming within the Public Land Mobile Network (PLMN)
or across 3G PLMNs of different operators with roaming
agreements. For example, in UMTS, the General Packet
Radio Service (GPRS) Mobility Management (GMM) is
used. However, link layer mobility is not enough to provide
network-layer transparency to upper-layer applications.
To avoid disruption of upper-layer sessions due to IP address
changes when user mobility results in changes of network
attachment points, the network-layer IP mobility is needed.
In cdma2000, Mobile IP (MIP) (Perkins, 2002) provides
IP mobility within the same Packet Data Serving Node
(PDSN) and between different PDSNs. However, in current
a UMTS network with the same Gateway GPRS Support
Node (GGSN). It is being considered to introduce IP for
inter-UMTS or inter-technology IP mobility through a three-
state evolution in 3GPP (2000).An overview of the mobility
management in UMTS and cdma2000 can be found in Pang
et al. (2004).
The mobility management in WLANs is much simpler
since they are only oriented to local areas. In IEEE
802.11WLANs, the distribution system (e.g., an 802.3-type
Extended Service Set (ESS). Each BSS is under the control
of an AP in the infrastructure mode. In this case, mobility
The Inter-Access Point Protocol (IAPP) specified in 802.11f
further facilitates the user roaming betweenAPs of different
vendors. When IP connectivity is provided in the WLAN
system, IP micromobility protocols can be introduced to
further support IP layer mobility.
and WLANs in mobility management, to achieve seamless
roaming across the two networks, either a unified mobility
management mechanism is followed, or both networks
maintain proper interoperation.
2.2 Enhanced security level
Network security covers diverse issues such as user
authentication, data confidentiality and integrity and key
management. The security mechanisms in 3G networks such
as UMTS are built upon those used in the second-generation
communications (GSM). In particular, user authentication
in UMTS adopts the Authentication and Key Agreement
(AKA) procedure, which relies on the Universal Subscriber
Identity Module (USIM) running in a smart-card at the
user terminal. In addition to authenticating the subscriber’s
identity, cipher and integrity session keys are also generated
from the long-term preshared secret key stored in the
USIM module and Home Location Register/Authentication
Centre (HLR/AuC). A good introduction to the access
security in 3G networks is given in Koien (2004); Rose and
In the original 802.11 standard, rather weak security is
provided due to lack of key management and flaws of the
it fails the claimed objectives with respect to user identity
privacy and data confidentiality. The 802.11i standard aims
control standard IEEE 802.1X is introduced to enhance
authentication and key management using the Extensible
Authentication Protocol (EAP) (Aboba et al., 2004).Also, as
an interim solution, Temporal Key Integrity Protocol (TKIP)
is specified to fix the vulnerabilities of WEP, while the
long-term solution is based on Advanced Encryption
Standard (AES) in place of the stream cipher RC4 used in
WEP. More details on 802.11 security are given in Edney
For 3G/WLAN interworking, if comparable security cannot
be provided by both networks, adversaries can break into
the system through the weakest component in the security
level. Also, appropriate independence between them should
effect when one of them is broken.
2.3Consistent end-to-end QoS guarantee
The shared nature of radio link necessitates proper MAC
to coordinate multiple connections to access the shared
multiple access. Moreover, by introducing packet-switched
mode a higher resource utilisation can be achieved for bursty
data traffic by statistical multiplexing. For the multiple
access uplink (from MS to base station), a two-phase
request-grant access procedure is used in 3G networks.
First MSs send transmission requests to the Base Station
(BS) through a contention channel. The BS acknowledges
those successful requests and reserves resources for data
transmission to follow. Then the MSs are notified the
resource assignments. This type of centralised control and
reservation-based resource allocation, together with proper
admission control to limit the traffic load, enables fine QoS
provisioning in 3G cellular networks.
On the other hand, the original WLAN specifications
only support best-effort data service with contention-based
random access protocol, for example, the Distributed
Coordination Function (DCF) of 802.11 WLAN based
on Carrier Sense Multiple Access/Collision Avoidance
(CSMA/CA). In this mode, the AP competes for access
with MSs instead of scheduling the resource assignments
as a BS in 3G networks. The other centralised control
mode, Point Coordination Function (PCF), is based on
polling by the AP. It is rarely implemented in reality due to
unresolved problems such as uncontrolled transmission time
of polled MSs. The distributed and contention-based control
leads to weak QoS support capability. To achieve better
W. Song, W. Zhuang and A. Saleh
QoS, 802.11e develops new approaches by means of MAC
enhancements. The above two access modes are improved
with service differentiation. Also, admission control and
multimedia applications with stringent QoS requirements.
Various QoS mechanisms for 802.11 are explored in Zhu
et al. (2004). Nevertheless, WLANs still cannot be expected
to support the same level of QoS as 3G networks.
Considering the differences of 3G networks and WLANs
in QoS provisioning and the aforementioned overlaying
structure, different services can be admitted to either
the cellular network or the WLAN according to their
traffic characteristics and QoS requirements. For example,
whereas the delay-tolerant data traffic can be admitted to the
WLAN to enjoy the high throughput. It is also an important
issue to maintain consistent or smoothly adapted QoS during
vertical handoff (i.e., handoff between the cellular network
and the WLAN).
Currently, WLANs may be owned by a 3G operator, a
(e.g., airports or property management corporations) or
a business enterprise for internal use (Salkintzis, 2004).
The interworking mechanisms are directly related to the
ownership of WLANs. More exposure is possible to
integrate the WLANs owned by the cellular operator itself.
The objective penetration level between the 3G networks
and WLANs and the provisioned services lead to different
requirements for the interworking mechanisms. The services
supported in future integrated 3G/WLAN networks are
envisioned in Axiotis et al. (2004). However, the integration
of the two technologies will be a gradual development
process. From the perspective of a 3G operator,
step-wise approach is proposed in 3GPP (2003b), which
defines six interworking scenarios with each scenario
specifying an incremental set of service and operational
features. The first scenario only requires common billing
and customer care. In the second scenario, a 3G subscriber
roaming to the WLAN is authenticated and charged by its
3G home network. Only IP access service via the WLAN
is provided to the roaming user. In the third scenario, the
3G packet-switched services are also open to users attached
to the WLAN, such as MMS, WAP service, IP multimedia
and location-based services. The fourth and fifth scenarios
improve the third scenario with higher requirement for
service continuity. The sixth scenario allows the access to
the 3G circuit-switched services (such as conventional voice
andWLANs. So far, a lot of research in the literature focuses
on the four scenarios in the middle.
3 3G/WLAN interworking architectures
The standardisation for 3G/WLAN interworking is well in
progress by 3GPP and 3GPP2. The high-level interworking
requirements, architecture and procedures (e.g., network
specified in 3GPP (2004a). In ETSI (2001) the integration
architecture is classified into two categories according to the
interdependence between the two access networks, that is,
tight coupling and loose coupling. Different interworking
mechanisms are developed to support mobility, security,
QoS, charging and billing in the tightly coupled and loosely
coupled heterogeneous networks.
3.1Tightly coupled and loosely
In the tight-coupling architecture, the WLAN is connected
to the 3G core network as one 3G radio access network.
Figure 1 illustrates a simplified architecture for interworking
UMTS/GPRS networks with 802.11 WLANs. The lines
with tags ‘a’ and ‘b’ are examples for tight coupling
with different integration points. Typical tight-coupling
architectures include the first architecture proposed in
Salkintzis et al. (2004) and Buddhikot et al. (2003b).
We can see that, in this type of integration architecture,
the cellular radio is simply replaced with WLAN radio
providing equivalent functions. As a consequence, the 3G
protocols and existing network infrastructures can be reused.
For example, the user roaming across the two domains is
thus enhancing the interdomain mobility management
for highly mobile users in hostile outdoor environments may
not operate properly for WLANs (Pichna et al., 2000). The
main disadvantages of the tight coupling approach include:
1an interface in 3G core networks exposed to WLAN is
required, which is a challenge as the two domains are
likely developed and deployed independently by
2 a large volume of WLAN traffic will go through the 3G
core network, possibly making the latter a network
3and the WLAN needs to have a protocol stack
compatible with that of the 3G networks.
On the contrary, for the loose-coupling approach (shown
with the line ‘c’ in Figure 1), the WLAN is connected
to the cellular core network indirectly through an external
IP network such as the Internet. The second architecture
proposed in Salkintzis et al. (2004) and Buddhikot et al.
(2003b), respectively, and the operator WLAN system
in Ala-Laurila et al.(2001) belong to this category.
This type of architecture imposes minimal requirements
to modify current WLAN standards, and allows for the
flexibility and independence of implementing individually
different mechanisms within each network. However, the 3G
such as MIP for mobility management and AAA support.
Moreover, as the two domains are separated, the mobility
signalling may traverse a relatively long path, thus inducing
enhancement mechanisms for MIP to reduce the handoff
latency, such as regional registration and dynamic Home
Interworking of 3G cellular networks and wireless LANs
Interworking architecture for 3GPP UMTS and IEEE 802.11 WLANs: (a) WLAN integrated at SGSN; (b) WLAN
integrated at GGSN and (c) WLAN integrated to external IP networks
Agent (HA) assignment. Overall, the loose coupling is the
it allows the gradual deployment of hotspots with no or little
modification on the 3G networks (Buddhikot et al., 2003a,b;
Koien and Haslestad, 2003).
It is well recognised that the future networks will be
all-IP networks. Therefore, it is a natural choice to glue
3G networks and WLANs with the pervasive IP technology.
In fact, we can see from the later sections that many
mechanisms proposed for the interworking follow the de
facto standards in the Internet community.
3.2Authentication and authorisation support
It is expected that in a 3G/WLAN integrated network the
wireless terminal will be dual-mode, which means that the
terminal will be equipped with network interfaces to both 3G
networks and WLANs (Axiotis et al., 2004). However, only
one subscription is needed with a 3G operator or a WLAN
service provider, who has roaming agreements to support the
interworking (Buddhikot et al., 2003a). A lot of research in
the literature considers the scenario in which a 3G subscriber
is provided WLAN access via independent WLAN systems.
Take the interworking of UMTS and 802.11WLAN as
an example. As mentioned in Section 2, 802.11WLANs
adopt 802.1X for access control, based on the EAP and
AAA framework. EAP sets no restriction on specific
authentication methods, while the AAA protocols, such
as remote authentication dial-in user service (RADIUS)
or its enhanced version Diameter,
attributes in the authentication messages. The selection of
RADIUS as the AAA protocol is not mandatory in the
802.1X or 802.11i; but it is in Wi-Fi protected access
(WPA) for interoperability. Considering the flexibility and
interoperability requirement, AAA server is introduced in
UMTS (3GPP, 2004b). By means of EAP-AKA, the 3G
home AAA server authenticates the UMTS subscribers
roaming to a WLAN through the UMTS AKA procedure
(Ahmavaara et al., 2003; Buddhikot et al., 2003a; Koien
and Haslestad, 2003; Salkintzis, 2004), while EAP-SIM can
be used for legacy GSM/GPRS system (Ala-Laurila et al.,
2001; Salkintzisetal., 2002).Theauthenticationinformation
and subscription profile can be retrieved from the Home
Subscriber Server (HSS) or HLR. Similar arrangements are
implemented in the cdma2000/WLAN interworking.
There are three entities defined in 802.11X, that is,
supplicant, authenticator and authentication server. It is
natural that the wireless terminal and the 3G AAA server
will perform the functions of the supplicant and the
authentication server, respectively. The authenticator is
responsible for relaying EAP frames sent by the supplicant
via EAP-Over-LAN (EAPOL), and repacketing them into
appropriate AAA messages for onward transmission to the
authentication server, and vice versa. In the interworking
mechanism, the functions of the authenticator can be carried
by the AP (Salkintzis et al., 2004), the WLAN access
router, or a separate WLAN AAA proxy (Salkintzis, 2004).
A successful authentication procedure is summarised in
In the operator WLAN architecture proposed for legacy
GSM/GPRS networks in Ala-Laurila et al. (2001), the
access controller actually acts as the access router shown in
Figure 1. It provides IP routing for WLANs and also relays
authentication messages for the terminal and authentication
and the authentication server is based on RADIUS, and
the SIM-based authentication is executed with the aid of
HLR. However, the authentication signalling between the
mobile terminal and the access controller is the operator