Review of Minimizing a Vertical Handover in a Heterogeneous Wireless Network

Abstract

Nowadays many different types of networks communicate among themselves to form heterogeneous -networks. Vertical handovers between them are required to supply ongoing internet access to mobile nodes who switch from one coverage area to another with different characteristics. Mobility management techniques between heterogeneous network are necessary to reduce latency time and professionally treat the insufficient radio access resources to indemnity specific quality of service. This paper reviews literatures that are related to minimizing a -vertical -handover in heterogeneous wireless networks. This paper reviews literatures that are related to minimizing a vertical handover in heterogeneous wireless networks. This review investigated various handover management technologies for providing pure mobility between different access techniques such as GPRS, UMTS, and WI-FI. More of these solutions used mobile IP (MIP), transmission control protocol (TCP), stream control transmission protocol (SCTP) and session initiation protocol (SIP) to support integration between WLAN and UMTS. From the review we conclude that SCTP is much more robust against packet loss and delay -compared to TCP, SIP, and MIP. This fact makes SCTP a potential scheme for heterogeneous wireless networks.

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IETE TECHNICAL REVIEW | VOL 27 | ISSUE 2 | MAR-APR 2010
IETE TECHNICAL REVIEW
March - April 2010 | Volume 27 | Issue 2
Published bimonthly by the Institution of Electronics and Telecommunication Engineers
Note: The Instuon of Electronics and Telecommunicaon Engineers assumes no responsibility for the statements and
opinions expressed by individual author.
Contents
Does the Journal Peer Review Select the “Best” from the Work Submitted?
The State of Empirical Research
Lutz Bornmann ..................................................................................................................................................................93
Review of Minimizing a Vertical Handover in a Heterogeneous Wireless Network
Bashar J. Hamza, Chee Kyun Ng, N. K. Noordin, M. F. A. Rasid and A. Ismail ................................................................97
A Smoothed Naïve Bayes-Based Classier for Activity Recognition
A. M. Jehad Sarkar, Young-Koo Lee and Sungyoung Lee ..............................................................................................107
Microstrip Monopulse Feed for Parabolic Dish Tracking Antenna Used in a Radio
Theodolite System
Tapas K. Bhuiya, Rajesh Harsh, and K. R. Tuckley .........................................................................................................120
Mobile Sensor Deployment Optimization for
k
-Coverage in Wireless Sensor
Networks with a Limited Mobility Model
Xingzhen Bai, Shu Li and Juan Xu ..................................................................................................................................124
Speaker Recognition from Excitation Source Perspective
Debadatta Pati and S. R. Mahadeva Prasanna ...............................................................................................................138
Gesture Recognition Based on Motion Inertial Sensors for Ubiquitous Interactive
Game Contents
YoungKee Jung and ByungRae Cha ...............................................................................................................................158
Automatic Multi-document Summarization Based on Clustering and Nonnegative
Matrix Factorization
Sun Park, ByungRea Cha and Dong Un An ....................................................................................................................167
On the Discovery of a Polarity-Dependent Memory Switch and/or
Memristor (Memory Resistor)
Suresh Chandra ...............................................................................................................................................................179
Reply to – “On the Discovery of a Polarity-Dependent Memory Switch and/or
Memristor (Memory Resistor)”
R. Stanley Williams ..........................................................................................................................................................181

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IETE TECHNICAL REVIEW | VOL 27 | ISSUE 2 | MAR-APR 2010
Review of Minimizing a Vertical Handover in a
Heterogeneous Wireless Network
Bashar J. Hamza, Chee Kyun Ng, N. K. Noordin, M. F. A. Rasid and A. Ismail
Department of Computer and Communication Systems Engineering, Faculty of Engineering, Universiti Putra Malaysia,
UPM Serdang, 43400, Selangor Darul Ehsan, Malaysia
Abstract
Nowadays many different types of networks communicate among themselves to form heterogeneous
networks. Vertical handovers between them are required to supply ongoing internet access to mobile nodes
who switch from one coverage area to another with different characteristics. Mobility management tech-
niques between heterogeneous network are necessary to reduce latency time and professionally treat the
insufficient radio access resources to indemnity specific quality of service. This paper reviews literatures
that are related to minimizing a vertical handover in heterogeneous wireless networks. This paper reviews
literatures that are related to minimizing a vertical handover in heterogeneous wireless networks. This review
investigated various handover management technologies for providing pure mobility between different ac-
cess techniques such as GPRS, UMTS, and WI-FI. More of these solutions used mobile IP (MIP), transmis-
sion control protocol (TCP), stream control transmission protocol (SCTP) and session initiation protocol
(SIP) to support integration between WLAN and UMTS. From the review we conclude that SCTP is much
more robust against packet loss and delay compared to TCP, SIP, and MIP. This fact makes SCTP a potential
scheme for heterogeneous wireless networks.
Keywords
Integrating wireless local area networks/universal mobile telecommunications system networks, Mobility
management, Vertical handover, 3G network.
1. Introduction
A heterogeneous wireless network (HWN) is a network
that has different operating systems and protocols to con-
nect computers with other devices. The HWN consists of
an ensemble of different wireless access networks that
can be employed by subscriber to access the internet. A
HWN collected of cable portions, radio access, and satel-
lite is shown in Figure 1. HWN parts may be managed by
various service providers that may use various propaga-
tion means such as cable, radio access, and satellite and
may execute different protocols [1,2].
The complementary characteristics of cellular networks
third generation (3G) such as the wireless local area net-
works (WLANs) and Universal Mobile Telecommunica-
tions System (UMTS) make it possible to combine these
two techniques. WLANs achieve low mobility and low
communication cost over a geographically small area with
higher data rates to mobile nodes, while UMTS cellular
networks offer wide coverage area with relatively low
bandwidth, and high communication cost to MN with
high mobility [3,4]. Naturally, integrating HWN will offer
service at anywhere / anytime mobile connectivity and
communication cost very low to those MNs who want
high-speed wireless access [5,6]. In this way, the future
mobile wireless network will be a HWN, which consists
of various wireless techniques including WLAN, GSM,
Figure 1: Architecture of a heterogeneous wireless network.

98 IETE TECHNICAL REVIEW | VOL 27 | ISSUE 2 | MAR-APR 2010
Hamza BJ, et al.: Vertical Handover in HWN
and cellular network UMTS as shown in Figure 2.
To obtain smooth mobility across the UMTS/WLAN
networks, MNs mechanically vary an available IP address
based on propagation data rate, user preference, bit
error rate, received signal strength, and another factors
while avoiding degradation of communication perfor-
mance. Note that the kind of handover across UMTS/
WLAN networks is referred to as a vertical handover
(VHO) [6,7]. VHOs are to supply ongoing internet access
to MNs that switch from one network to other with dif-
ferent characteristics as shown in Figure 3.
Vertical handovers are implemented across various
networks, which differ in many aspects like commu-
nication cost, data rate, bandwidth, coverage area, and
operation frequency [8,9]. Many researchers propose
enhancement to selection mechanisms during a VHO to
enable global roaming between different access networks.
Yilmaz et al. [10] studied ve different network selection
algorithms based on different input parameters. The algo-
rithms are evaluated and compared in terms of achieved
transmission bit rate and results indicate that in some
scenarios, the simple access selection principle WLAN,
if full coverage, gives good enough results such as low
bit error, little packet loss, and high throughput. Ormond
et al. [11] proposed a consumer surplus-based algorithm
for access network selection selecting the best available
network for transferring non-real-time data, with user-
specied time constraints. The basic assumption is that
users’ willingness to pay depends on the required transfer
completion time. The proposed access network selection
scheme is evaluated through simulations in NS-2 against
an always cheapest network selection strategy.
Ylitalo et al. [12] employed an interface selection
mechanism for multihomed mobile nodes. Mobile node-
dened rules dene which wireless interface to use for a
specic ow. Decisions are depended on availability and
characteristics of the various wireless interfaces at any
time taking data link layer, network layer, and application
layer information into account. Also, network originated
information is considered. Buddhikot et al. [13] presented
a wireless interface selection technique that uses two fac-
tors to perform wireless interface selection. These include
priority and the strength of current received signal of
wireless interfaces selection. The priority and received
signal strength of wireless interfaces selection can hardly
be applied to meet the QoS or power requirements of the
mobile user or active applications.
The rest of this paper is organized as follows: Section 2 is
a general overview about WLAN and 3G networks while
Section 3 introduces the conventional VHO process in
UMTS/WLAN. Section 4 covers some proposed works
to enhance the mobility management. Also, integrated
UMTS/WLAN systems are presented in Section 5.
Finally, the conclusion is presented in Section 6.
2. Overview of Wireless Local Area Network
and 3G Networks
In the previous years, WLAN has gained strong popu-
larity in a many of academic areas, including care of
health, industrializing, and vertical markets. Nowadays
WLANs are becoming widely recognized as a common
rationale connectivity alternative for business customer’s
broad range. Many wireless network standards have
appeared up to now [14]. IEEE 802.11 WLAN has been
widely deployed in ofces, homes, campus, airports,
and hotels given its low communication cost, high data
rate (11_Mbits/s), and ease of proliferation. However,
a serious disadvantage of 802.11 is the small coverage
area (up to 300 m) and low mobility [15,16]. The most
known standards belong to the IEEE 802.11 family, which
Table 1: IEEE 802.11 families
802.11 Date Fr. band
and mod
Throughput
(typical)
(Mbit/s)
Net bit
rate
(Mbit/s)
Range
(indoor)
m
802.11b Oct. 99 2.4GHz/DSSS ,511 ,38
802.11a Oct. 99 5 GHz/OFDM 27 54 ,35
802.11g Jun 03 GHz DSSS or OFDM ,22 54 ,up to 100
Figure 2: Different wireless technologies.
Figure 3: Vertical handover between universal mobile tele
communications system/wireless local area networks.

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Hamza BJ, et al.: Vertical Handover in HWN
includes the popular 802.11b, the 802.11a, and the 802.11
g as shown in Table 1.
Any device that can transmit or receive data at 144 Kbps
or better is called 3G. International Telecommunication
Union (ITU) denes 3G as devices that can transfer data
at up to 384 Kbps. As a comparison, Global System for
Mobile Communications (GSM) bandwidth is up to
14.4 Kbps and General Packet Radio Service (GPRS)
bandwidth is around 53.6 Kbps used in 2G and 2.5G,
respectively [14]. UMTS is a 3G wireless protocol that is
part of the ITU. UMTS is expected to deliver low-cost,
high-capacity mobile communications, offering data
rates of about 1 Mbps. The wireless radio access network
for UMTS contains the User Equipment (UE), and the
UMTS Terrestrial Radio Access Network (UTRAN),
which includes the Node-B and Radio Network Con-
troller (RNC) [14-18]. The packet domain core network
includes two MNs: The serving GPRS support node
(SGSN) and the gateway GPRS support node (GGSN)
as shown in Figure 4.
GGSN is the gateway to external data networks. It
provides control signalling toward external IP networks
for authentication and IP-address allocation, and mobility
within the mobile network. GGSN supports functions for
forwarding and handling user information (IP packets)
to and from Internet [19]. SGSN supports data session
management and acts as an anchor point for the MN, i.e.,
mechanisms for establishment, maintenance, and release
of end-user Packet Data Protocol (PDP) contexts. It also
provides mobility management and supports vertical
handovers between mobile networks. SGSN also keeps
track of the location of individual user equipments [20,21].
3. Universal Mobile Telecommunications
System/Wireless Local Area Network
Vertical Handover
Vertical handover is a technique that allows a MN to
roam between different networks and access technolo-
gies, in a manner that is transparent to the applications
and users, without disrupting connectivity. The differ-
ent characteristics of the networks involved make the
implementation of a vertical handover more challenging
as compared to a horizontal handover [14].
The vertical handover process may be divided into three
phases [22]: Network discovery, handover decision, and
handover implementation. Network discovery is the
process where a MN discovers an accessible neighboring
wireless network. A MN must activate the multiple inter-
faces at time to receive service advertisements, which are
broadcasted by diverse wireless technologies. To achieve
secure pre-authentication with a neighboring wireless net-
work, a MN needs to obtain an IP address of the authentica-
tion server from the neighboring wireless network when
the mobile is still outside the neighboring wireless net-
work and then to establish a security association with the
authentication agent in the neighboring wireless network.
The simplest way to search an accessible neighboring
wireless network is keeping all interfaces on at all times.
However, saving an interface at all the times may dis-
cover the accessible neighboring network quickly but its
battery may run out very soon even without receiving/
sending any packets as shown in Table 2 [23]. The second
phase, handover decision, is the ability to decide which
network should be used to trigger the handover. A deci-
sion for the VHO may depend on many factors (such as
network bandwidth, load, coverage, cost, security, and
QoS) relating to the network to which the MN is already
connected and to the one that it is going to VHO [24].
The last one is the handover implementation; it needs
the actual exchange of information with a new wireless
trafc in order to send by a different path and allow the
MN to switch through HWN, while saving its data packet
ows. The desired goal of exchanging data packets of a
MN with the new network is to reduce the latency delay
in the trafc ows of MN [25, 26].
Many approaches have been used to solve the vertical
handover problem; these approaches have been presented
by many authors. Stemm et al. [27] proposed a personal
digital assistant (PDA) to determine the power consump-
tion of wireless network interface when the interface is
on. Their work show that the power consumed when the
wireless network interface is idle and on is higher than
the cost of receiving data packets, and that the interfaces
consume an important fraction of the entire power on a
PDA. They show that the critical parameter is not the data
packets number of received\sent but the quantity of time
for that the interface of wireless network is in operation but
idle state. Bargh et al. [28] proposed different interfaces of
network in a multihomed mobile node to reduce energy
Table 2: Power consumption by 3G and wireless local area
network [23]
Technology Transmit mode
(W)
Receive mode
(mW)
Idle mode
(mW)
3G: CDMA 1 3 wireless modem 2.8 495 82
IEEE 802.11b 1.3 900 740
Figure 4: Universal mobile telecommunications system
architecture.

100 IETE TECHNICAL REVIEW | VOL 27 | ISSUE 2 | MAR-APR 2010
consumption. Their studies showed that the GPRS inter-
face of network consumes less or comparable quantities
of energy close to the one of Wi-Fi during idle IP con-
nectivity. In order to be accessible at the IP level, a MN
requires having idle IP connectivity. Thus, the interface
of GPRS has energy efcient more relatively for success
the MN at the IP level.
Chen et al. [29] proposed a “smart decision model” for
vertical handovers. A score function is dened as the
weighted sum of normalized parameters. The model is
implemented on top of a previously proposed handover
architecture building a complete seamless mobility
management solution where the model itself contains a
handover executor, a smart decision component, a device
monitor for each interface, and a system-wide monitor.
4. Mobility Management
When a MN transfers a user’s session from network to
other network, the IP address changes. In order to permit
the CN that the MN is connecting with to nd it correctly
and enable the session of data to continue, mobility man-
agement is used. The management of mobility problem
has been solved in various layers, like the application,
and transmission control protocol (TCP) layer. The most
common method is to use TCP, session initiation protocol
(SIP), mobile IP (MIP), and stream control transmission
protocol (SCTP) [17,30].
4.1 Transmission Control Protocol
TCP is a transport layer protocol layered between IP and
the application layer. It is a connection-oriented layer
protocol, which is responsible for the end-to-end reliable
transfer of the data from the mobile node application to
correspondent node application over an unreliable net-
work. The transport protocol recovers packets lost during
handovers and controls transmission speed to achieve
efcient communication [18]. Kazuya et al. [31] presented
TCP at the transport layer to support host mobility across
diverse wireless access networks, and to operate in
various layers of the network architecture. Experimental
results of TCP show that it can handle multiple con-
nections simultaneously, achieve seamless throughput
performance in the vertical handover, supports efcient
communication during WLAN/UMTS handovers, and
is able to transmit packets on multiple separate data link
interfaces, i.e., transmission and controlling buses (TCB)
can be maintained as shown in Figure 5.
Dong et al. [32] presented concurrent TCP (cTCP) which
is an extension of the current TCP protocol which was
used to optimize end-to-end connection, throughput,
packet loss rate, and to enhance end-to-end connection
fault tolerance in a heterogeneous network. The proposed
protocol supports concurrent data transfer (CDT) through
multiple interfaces binding on one connection. Xiuchao
et al. [33] presented a new management scheme using
intelligent TCP for the heterogeneous Internet. Intelligent
TCP, that can dynamically change congestion control
algorithms for each connection according to its current
network path characteristics, is proposed to improve
TCP performance in the heterogeneous Internet. The
framework of Intelligent TCP supports dynamically per
connection and/or network congestion control congura-
tion. Intelligent TCP is very suitable for transport layer
congestion control and more robust against interferences
than multiple TCP due to better network path estimation.
4.2 Mobile IP
MIP offers seamless mobility for IP connections by
offering a constant home IP address for layer 4 sessions.
The MN requires connectivity to the home agent to per-
form the handover. In brief, MIP operates as follows.
two IP addresses can be assigned to MN are a care of
address (CoA) and a permanent home address, which is
linked with the wireless network which the MN is visit-
ing. Information about MNs visiting its wireless network
stores in a foreign agent. Foreign agents also advertise
CoAs, which are employed by MIP [34].
A node wanting to talk with the MN employs the xed
home IP address of the MN as the destination address
for transmit data. Due to the home IP address physically
belong to the wireless network connected with the home
agent, mechanisms of IP routing sent these data to the
home agent. In place of sending these data to a destina-
tion that is logically in the same wireless network as the
home agent, the home agent reroutes these data toward
the foreign agent. The home agent seeks for the CoA in a
special table known as a binding table, and then tunnels
the data to the MN’s CoA by appending a new IP header
to the primary IP packet, which protects the primary IP
Figure 5: Throughput performance in the vertical handover
when the wireless signal strength changes ve times at 1-s
intervals.
Hamza BJ, et al.: Vertical Handover in HWN

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IETE TECHNICAL REVIEW | VOL 27 | ISSUE 2 | MAR-APR 2010
header. The packets are encapsulated at the end of the
tunnel to remove the IP header added by the home agent,
and are delivered to the mobile node [19,34]. The basic
operation of MIP is shown in Figure 6.
Jong et al. [35] presented a new handover scheme for
seamless mobility in heterogeneous networks using
MIP to solve long latency time and triangle routing
problems. The proposed scheme supports L3 mobility
using the L2 information of terminal and data tunneling
between edge routers. The simulation results show that
the proposed scheme has reduced handover latency
time and transmission delay of data packet as shown
in Figure 7.
In the area of MIP performance, Hernandez et al. [36]
showed that MIP have several limitations in terms of
packet loss, handover latency, and throughput of a
train moving at different velocities and the effect of
different base station interleaving distances on QOS.
Saleh et al. [37] proposed the MIP in the context of an
integrating architecture between 802.11 WLAN and
CDMA cellular networks.
4.3 Session Initiation Protocol
SIP is protocol of application layer that can terminate mul-
timedia sessions, establish, and modify [19]. SIP explains
some logical entities, proxy servers, redirect servers, user
agents, and registrars. SIP inherently assists service and
terminal mobility and can be extended to support personal
mobility [38]. Terminal mobility enables a MN to switch
between IP subnets, while stay to be connectable for incom-
ing requests and saving data sessions over subnet changes.
The terminal mobility support of SIP is used to manage the
mobility management of hosts in HWN. Figure 8 shows
that the data session between a CN and a MN during VHO.
Wu et al. [39] proposed the delay associated analysis
with VHO using SIP in the internetworking environ-
ments of WLAN/UMTS. Their analysis’s show that
the WLAN to UMTS VHO incurs not satisfactory delay
for assisting multimedia services of real time, and is
chiey due to broadcast of SIP signalling messages over
erroneous and data rate limited wireless network traf-
cs. Fathi et al. [40] proposed a practical evaluation for
setup delay of SIP data session. Their studies showed
that SIP-over-TCP makes the data session setup delay
more than SIP-over-UDP. Authors found that mobility
of SIP is suitable for supporting seamless internet access
to MNs that switch from one access network to another.
Seok et al. [41] presented an extension of SIP to support
soft handover named mobile SIP (mSIP). The mSIP
handover with bicasting can reduce handover loss and
latency during soft handover, because MN will com-
municate with CN using bicasting over two IP addresses
in the handover area. Figure 9 shows the comparison
between mSIP and the existing SIP handover.
4.4 Stream Control Transmission Protocol
SCTP is an order of data packets delivery between two
endpoints. It has high reliable transport layer protocol
that provides stability (similar to TCP) and also pre-
serves boundaries of data message (similar to UDP).
However, unlike TCP and UDP, SCTP offers advantages
Figure 8: Session intiation protocal-based mobility management.
Figure 6: Standard mobile IP.
Figuer 7: The latency time of the handover procedure.
Hamza BJ, et al.: Vertical Handover in HWN

102 IETE TECHNICAL REVIEW | VOL 27 | ISSUE 2 | MAR-APR 2010
such as capabilities of multihoming and multistream-
ing, which both enhance reliability and availability.
SCTP with dynamic association reconguration (DAR)
allows IP addresses to be added and removed from an
SCTP association, meaning that data packets can then
be transmitted to the new destination. This enables a
MN to move to a new network and implement a VHO
at the transport layer [42]. Before peer SCTP users can
forward data packet from one to the other, to handshake
data packets between two endpoints the communication
must be established. This communication is named an
association in SCTP context. To offer high protection
against attacks security through a four way handshake
data packet a cookie (a unique context identifying this
proposed connection) technique is used through the
initialization of an association in SCTP. Figure 10 shows
a sample SCTP message ow [19]. To overcome on the
problem of delayed packet movement with the four way
handshake data packet, SCTP allows data packet to be
included in the COOKIE-ECHO and COOKIE-ACK data
packets respectively.
Li Ma et al. [43] presented a new method to facilitate
the seamless vertical handover between wide-area
cellular data networks such as UMTS and WLANs using
the SCTP. The multihoming capability and dynamic
address conguration extension of SCTP was applied
in an UMTS/WLAN overlay architecture to decrease
the handover delay and improve throughput perfor-
mance. Experimental results show that the proposed
scheme can overcome the problem of long interruption
time during handover, especially in the dual-homing
SCTP conguration as shown in Figure 11.
Keun et al. [44] presented a SCTP efcient ow control
(SCTP EFC) technique through VHO by enabling a
MN to freely move between IP addresses acquired in
HWN. SCTP EFC reduces a change of link data rates
and enhances the throughput improvement signi-
cantly through a VHO. The result shows that SCTP EFC
adjusts to wireless network architecture after the VHO.
SCTP EFC shows the rate of transmit enhancement for
many seconds after a VHO. It utilizes an available wire-
less network resource in an efcient manner. It is also
appropriate for QoService due to it maintains trafc
Figure 9: Handover latency of the session initiation protocol
and mobile session intiation protocol handover. Figure 10: Stream control transmission protocol message ow.
Figure 11: Delay performance of the proposed vertical handover
scheme (from UMTS to WLAN).
Figure 12: Integrated universal mobile telecommunications
system/wireless local area networks.
Hamza BJ, et al.: Vertical Handover in HWN

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data rates constant through the VHO.
5. Integrated Universal Mobile
Telecommunications System/Wireless
Local area network Systems
There are one more suitable methods to design an
integrated UMTS/WLAN network, explained as loose
coupling and tight coupling methods as shown in
Figure 12. The difference between loose and tight cou-
pling is whether the subscriber’s link is forwarded during
the core of cellular UMTS network or not [45,46].
In the design, of tight coupling integrating the WLAN
joined the core of cellular UMTS network in the similar
style as other radio access of cellular UMTS networks.
The gateway of WLAN executes all the UMTS protocols
(such as authentication, billing, and smooth mobility
management.) needed in the radio access of cellular
UMTS network. SGSN and GGSN require to be updated
to be capable to treat the higher data rates supported
by the WLAN. The benet of this scheme is that the
techniques for QoS, security, and mobility in the core of
cellular UMTS network can be forwarded immediately
across the WLAN [47]. However, tightly coupled meth-
ods have been highly specic to require wide access
interface standardization of WLANs beyond the existing
standards and the cellular UMTS technology. In contrast
to the loose coupling method, the gateway of WLAN
does not have any direct link to the core of cellular UMTS
network. Instead, it connects directly to the internet
access. WLAN link would not move through the core of
cellular UMTS network. In this method, UMTS/WLAN
network can use different techniques and protocols to
treat billing, mobility management, and authentication.
Even so, they can use the same customer database for
functions like billing, security, and management of sub-
scriber as peer IP domains [47].
Varma et al. [48] proposed solutions in integrated GPRS
and WLAN using MIP or SIP for mobility management.
Their studies addressed issues only on location manage-
ment instead of seamless intertechnology handover in
the loose coupling approach. Although Lampropoulos
et al. [49] concentrated upon the architecture of loose
coupling, their studies presented a complicated new net-
work part named the IOTA integrating access gateway
in the WLAN, and novel service access software on the
user equipments to interwork WLAN with UMTS. MIP
agent functionality is executed in the IOTA system to
support technique of MIP.
Tsao et al. [50] presented gateway, MIP, and emulator
methods for UMTS/WLAN integrating relative to vari-
ous deployment scenarios. Most of these implementa-
tions and proposals notice that the method of tight
coupling may provide higher performance in terms
of VHO latency time. However, the method of tight
coupling has bad exibility. The architecture of loose
coupling permits trafc engineering and independent
deployment of WLAN and UMTS, and therefore intro-
duces many benets in the architectural over the tight
coupling method.
Altwelib et al. [51] proposed an integrated scheme
coupling the WLAN and UMTS using the gateway hot-
spot support node (GHSN). Their studies showed that a
GHSN should be added to integrate a WLAN access point
(AP) to GGSN as shown in Figure 13. The main functions
of GHSN are summarized as follows: To radio interface
with UMTS and WLAN, to deliver packets from/to AP
and from/to GGSN, and to manage radio resources
in WLAN and map them onto the radio resources on
UMTS and vice versa. Experimental results show that
the throughput of an MN connected to a WLAN network
interface is much higher than that obtained through
a UMTS network interface, and the vertical handover
latency between UMTS and WLAN is 182 ms.
Leung et al. [52] proposed a new method to facilitate a
seamless VHO between UMTS and WLAN networks
using M SCTP with single-homing FS and dual-homing
FS. The multihoming capability and DAR extension of
SCTP are applied in the UMTS/WLAN overlay architec-
ture. M SCTP introduces the idea of multihoming [53],
where a single endpoint can support multiple connec-
tions with different interfaces and IP addresses simul-
taneously.
To support multihoming capability, two endpoints of
SCTP replace lists of IP addresses through the beginning
of an association. In order to get the smooth mobility and
ongoing VHO, the changing of SCTP endpoint's address
will be listed during the run of association by using the
DAR SCTP extension. By using address conguration
(ASCONF) data chunks, SCTP DAR allows two end-
points to add, delete, and change original IP address
automatically in an active connection. SCTP with its DAR
extension is named mobile SCTP (mSCTP). Experimental
results showed that throughput and delay performance
have been enhanced in an important manner using the
conguration of dual homing. In the conguration of
Figure 13: Universal mobile telecommunications system/
wireless local area network system architecture.
Hamza BJ, et al.: Vertical Handover in HWN

104 IETE TECHNICAL REVIEW | VOL 27 | ISSUE 2 | MAR-APR 2010
dual homing, duplicated buffered packet transmission
on old/new links may aid sender/receiver to adjust to
a sudden modify in trafc characteristics quickly and
easily through a VHO.
Af et al. [55] proposed a new scheme by using modica-
tions of the congestion control algorithms in the SCTP to
take into account information sent by MN to the network
GGSN via QoS measurement chunk for the EGPRS/
WLAN handover. QoS measurement chunk used to
bear radiotransmission conditions to the transport layer
in order to adjust congestion control factor to the radio-
transmission conditions. Experimental results showed
that SCTP with QoS measurement chunk presents more
usefully than the conventional SCTP and achieves much
higher rate of transfer and allows data handover to be
performed more usefully than with normal transport
layer protocols inside part of radio access of heteroge-
neous technique.
6. Conclusions
The deployment of WLANs has provided network
service providers with an option of integration with
3G wireless wide-area networks, such as UMTS.
Such integration allows mobile users to move among
these heterogeneous networks in a seamless manner.
However, the integration of 3G networks and WLANs
presents some considerable challenges which include
the demand for seamless handover, continuity of
data trafc, and multimedia sessions across the two
networks. To achieve a seamless handover, several
mobility protocols have been proposed. The paper
review showed some of the mobility protocols: MIP,
SIP, SCTP, and mSCTP which work at the different lay-
ers. Both MIP and SIP approaches offer some level of
vertical handover support between UMTS and WLANs.
Results have shown that it is difcult to keep the stabil-
ity of data sessions during handover due to the long
handover latency and large overhead of tunneling IP
packets, while SCTP and mSCTP are useful for sup-
porting vertical handover between any heterogeneous
wireless networks in general and not limited to UMTS
and WLAN integration. The SCTP VHO scheme does
not require the addition of components such as home
and foreign agent or SIP server to the existing network.
Finally, the loose coupling provides several advantages
over tight coupling in which it permits low investment
costs and easy independent deployment and trafc
engineering between UMTS and WLANS network
architecture. In loose coupling scheme, networks do not
need to change their network architectures or protocol
stacks while tight coupling needs a common ownership
of the two networks that does not make it a very feasible
deployment strategy.
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AUTHORS
Bashar Jabbar Hamza received the B.Sc. degree in
Communication Engineering from Technical College,
Najaf, Iraq, in 2002. He received the M.Sc degree
in Communication Engineering from Technology
University, Baghdad, Iraq, in 2007. He is currently a
PhD student in Wireless Communication Engineering
at Universiti Putra Malaysia. His main research interests
are Vertical handover, UMTS network, WLAN network and Heterogeneous
network between UMTS/WLAN.
E-mail: mrym_bashar@yahoo.com
Chee Kyun Ng received his Bachelor of Engineering
and Master of Science degrees majoring in Computer &
Communication Systems from Universiti Putra Malaysia,
Serdang, Selangor, Malaysia, in the years of 1999 and
2002 respectively. Presently, he has completed his
PhD programme majoring in Communications and
Network Engineering at the same university. He is
currently undertaking his research on wireless multiple access schemes
and smart antenna system. His research interests include mobile and
satellite communications, digital signal processing, wireless networking
and network security. Along the period of his PhD programme, he received
a scholarship award from the government of Malaysia under the National
Science Fellowship (NSF) scheme.
E-mail: mpnck@eng.upm.edu.my
Nor Kamariah Noordin received her B.Sc. in Electrical
Engineering majoring in Telecommunications from
University of Alabama, USA, in 1987. She became a
tutor at the Department of Computer and Electronics
Engineering, Universiti Putra Malaysia, and pursued
her Masters Degree at Universiti Teknologi Malaysia
and PhD at UPM. She then became a lecturer in 1991
at the same department where she was later appointed as the Head from
year 2000 to 2002. She is currently the Deputy Director of Corporate
Planning Division at the Office of the Vice Chancellor. During her more
than 15 years at the department she has been actively involved in teaching,
research and administrative activities. She has supervised a number of
undergraduate students as well as postgraduate students in the area of
DOI: 10.4103/0256-4602.60163; Paper No TR 135_09; Copyright © 2009 by the IETE
Hamza BJ, et al.: Vertical Handover in HWN
wireless communications, which led to receiving some national and UPM
research awards. Her research work also led her to publish more than 100
papers in journals and in conferences.
E-mail: nknordin@eng.upm.edu.my
Mohd Fadlee A. Rasid is the deputy director for
National Centre of Excellence on Sensor Technology
(NEST) at Universiti Putra Malaysia. He received
a B. Sc. in ele ctr ica l eng ine eri ng from Pu rd ue
University, USA and a Ph.D. in electronic and
electrical engineering (mobile communications)
from Loughborough University, U.K. He directs
research activities within the Wireless Sensor Network (WSN) group and
his work on wireless medical sensors is gaining importance in health
care applications involving mobile telemedicine and has had worldwide
publicity, including BBC news. He involves with UK Education and
Research Initiative under the British Council on wireless medical sensors
project that will allow a more patient-driven health service in improving
the efficiency of health care delivery. He is also part of the European
Union (EU) STIC Asia Project on ICT-ADI: Toward a human-friendly assistive
environment for Aging, Disability & Independence. He currently leads a
few research projects on WSN, particularly for medical and agriculture
applications. He was nominated for IEE J A Lodge Award for Outstanding
Work in Field of Medical Engineering, London, 2005 and was the proud
recipient of State of Selangor Young Scientist Award in 2006.
E-mail: fadlee@eng.upm.edu.my
Alyani Ismail received her B.Eng. (Hons) Electronic
and Information Engineering from University of
Huddersfield, United Kingdom in 1999. She received
her MSc in Communication, Computer and Human-
Centred Systems Engineering in 2001 and her PhD in
Electronics Engineering majoring in micromachined
microwave devices in 2006 from University of Wales,
UK. Her research in micromachined filter design at Birmingham was
sponsored by the UK Engineering and Physical Science Research Council. She
became a lecturer at the Faculty of Engineering, Universiti Putra Malaysia
(UPM) in 2006. Her research interest specializes in the development of
microwave devices particularly passive filters and antennas.
E-mail: alyani@eng.upm.edu.my