This document summarizes research on vertical handoff performance in wireless local area networks (WLANs). It examines the data traffic received by different access points as mobile stations move between them. Graphs show how throughput and delay are impacted during handoffs. It also evaluates the performance of file transfer between wireless clients and servers connected by a WLAN backbone network comprising two routers. The document analyzes the effects of station mobility on metrics like traffic, delay, and throughput. In conclusion, it demonstrates vertical handoff triggering between a WiMAX and WLAN network as mobile nodes roam between the base stations.

1. International Journal of Research in Advent Technology, Vol.2, No.7, July 2014
E-ISSN: 2321-9637
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Vertical Handoff Performance in WLAN Wireless
Networks
Renu1, Anil Dudy2
Electronics and communication1, 2,Shri Baba Mastnath Engg. college1, 2
Email:renudalal89@gmail.com1, anildudy10@gmail.com2
Abstract- The WiFi handoff setup compares the data traffic received by different APs in the network. Since
the initial stations of AP_0 are mobile ones, AP_0 receives data traffic only at the beginning and then at end of
simulation when its stations start their tour and come back. Additionally, it receives data traffic when the
stations started from south visit its section and get connected to it. In contrast to AP_0, AP_2 has stable stations,
so the data traffic received by it does not drop to 0 like AP_0's traffic. As expected, its received data traffic
doubles when the moving stations from west and south cross its section. AP_3 is visited by all moving stations
at the same time. Hence, its received data traffic is tripled when this happens during simulation. Hence the
throughput and delay for the wlan MS is obtained. The vertical handover setup consists of a gateway,
application server providing voice service to the wimax BS and to the wlan router.
Index Terms- AP, DCF, PCF, LAN, WLAN
1. INTRODUCTION
Communication is always necessary in building
relations to mankind, when two persons meet they
need some medium to interchange their views but due
to distance barriers some tools are required to
communicate each other. At the end of 19th century,
renowned scientist Graham Bell laid the first stone in
the field of communication using different tools
regardless of distance. He invented first wired base
telephony equipment. It was the solution for the voice
communication for the people how far apart they are.
After this radio based communication systems Era
started. It was an extension of wired based networks.
In the beginning it was developed for some special
purposes like military and police usage. With the
passage of time these systems emerged to allow
common peoples to communicate with each other,
rather than using wired based network. After this the
age of faster communication and capabilities of voice
get started and evolved into new telecommunication
system. The capability to achieve wireless access
anywhere, anytime, and anyplace has become
common expectation as it provides significant
flexibility and freedom in mobility. But to achieve
global mobility in heterogeneous networks for any
mobile device requires seamless connectivity using
vertical handoff. Since none of the existing wireless
frameworks provide practical solutions for vertical
handoff. End-to-End Vertical Handoff (E2EVH)
proposed in this paper offers a new concept to
perform vertical handoff between heterogeneous
wireless networks. To deliver network services
without interruption, E2EVH present a novel design
to monitor the network availability, it then picks the
best accessible network for application layer [1].
2. WIRELESS LAN SYSTEM
The Wireless Local Area Network (WLAN) is an
unlicensed band of 802.11 ISM frequency band.
802.11 is one of the recent communication
technologies of IEEE standard. It specifies
medium access control (MAC) and physical layer
that is why it is called Wireless LAN. It has three
widely used types which operates on different
frequency bands. These three types are 802.11a,
802.11b and 802.11g. 802.11a operates on 5 GHz
frequency band and it gives the maximum data rate
speed of 54 Mbps, which is higher than 802.11b
because 802.11b operates on 2.4 GHz frequency
band and give the maximum data rate speed of
11Mbps. 802.11b operates. 802.11g is recently
developed standards of Wireless LAN. It also
operates on 2.4 GHz frequency band and give the
maximum data rate speed of 54 Mbps. In 802.11
Wireless LAN standards, the two types of MAC
protocols Distributed Coordination Function (DCF)
and Point Coordination Function (PCF) are used.
Nowadays the most applications available in the
markets are uses DCF because it is simple,
robust and easy to implement.
DCF is the basic MAC layer function in Wireless
LANs, Which used Carrier Sense Multiple Access
technique (CSMA) also with an addition of
Collision Avoidance of (CA). It resolves the CA
problems of the packets transmitted at the same
time.
Architecture of Wireless LAN
Wireless Local Area Network instigate as an
overlay to the Wired Local Area Network.
Lightweight and Autonomous are two discrete
architectures used in WLAN environment.

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Each of the architectures has wide impact on
wired LAN architecture. The selection of
WLAN architecture is based on the consideration
of building, future proof, integrated wired and
Wireless LAN to accomplish high return on
investment. Both architectures are popular but
Lightweight architecture has plus advantages over
the WLAN market.
2.1 Lightweight Model
Lightweight is the part of WLAN architecture.
With most of wireless intelligence which residing
at central controlling device, lightweight Wireless
Access Point architecture have narrow
functionality.
Fig 1: Lightweight Architecture Model
Lightweight model is simple. The devices that
provide the communication to the end user as
Access Layer are identified by lightweight.
Distribution layer provide the inter
communication and the top layer (Core Layer) of
Lightweight model is responsible fast and
consistent data between networks.
Wireless Access Point (WAP) resides at the
interface of access layer and provides the
communication interface to end user. In
lightweight architecture model, the
management of operation is easy because it give
the permission to WAP from single device,
because the lightweight WAP have the knowledge
of visibility and attentiveness of the neighbours
WAPs. They can observe and if any one of their
neighbours becomes the victim of fault it notifies
the wireless controller.
Lightweight WAP may be Self-healing because
to pay compensation for unsuccessful counterpart,
controller commands the neighbouring WAP to
regulate their power level, where as in
autonomous there is no concept of the visibility of
its WAP neighbouring and in this case to perform
self healing it cannot adjust the power level.
If single WAP is busy or overloaded then in
this situation wireless controller can relieve the
wireless client to neighbouring WAP. In critical
applications such as VoIP, self-healing and load
balancing are important issues.
2.2 Autonomous Model
In Autonomous Model WAP is not mandatory as
shown in Fig. 2.
Fig 2: Autonomous Architecture Model
Autonomous Wireless Access Point sustains
the switching and strong security as well as
networking function that are indispensable to
route the wireless traffic. As in autonomous
system there is no concept of the visibility of
WAP so it cannot make the load balancing.
Autonomous model cannot differentiate whether
nearest WAP is part of WLAN infrastructure or
illegal rouge WAP. The difference between the
autonomous and lightweight is negligible. The
difference is only this that lightweight have one
extra component (WLAN controller).
VERTICAL HANDOVER
Between the heterogeneous wireless networks the
handover process can be set apart in to handover
execution and handover decision process. In
handover decision process both the mobile node
and network decides that when the handover
process will be occur. After taken handover
decision, the handover execution process
continues. The handover decision process
involves supplementary network information such

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as replica address detection time in Mobile IPv6,
when handover decision and detection process
overlaps. The handover delay can be alienated in
to three main mechanisms.
Discovery Time (td)
In this process via link layer beacon, the mobile
terminal perceive that it is in the under the range
of new wireless network from where it get the
Router Advertisement (RA) of new access router.
Through the RA and triggered-based router
solicitation from access router in the visited
network, the MT detects the coverage on new
network.
Address Configuration Period (tc)
In this period the MT receive the Router
Advertisement (RA) and updates its routing
table and assign the new Care of Address (CoA)
to all its interfaces. This new CoA based on
new access router accessible form RA.
Network Registration Period (tr)
In this period the binding updates are transmit to
Home Agent (HA) as well as correspondent node
and collect the acknowledgement from
correspondent node. As binding
acknowledgement from correspondent node is
elective, so we consider the situation when
mobile node accept packet from correspondent.
Thus an IP level handover consist of td, tc and
tr. This recommended that by optimizing IP-level
vertical handover delay would really involve
minimizing the discovery time and network
registration period, where as address
configuration period based on mobile device
computing potential.
3. Simulation results
Horizontal handoff in WiFi network
This scenario shows the mobile station performance
during horizontal handoff (roaming) between eight
APs while the MS is moving in clock wise
direction. This scenario shows WiFi wireless
technology. This scenario also comprise one video
conferencing server, one client connected to the
server via L3 switch and wlan stations surrounding
the access points. STA_0, STA_1, STA_2,
STA_18, STA_19, STA_20 are roaming at a speed
of 30 m/s around the access points and rest all
stations are stationary. All the links used here are
100 BASE T links. The MS is roaming from AP0 to
AP7 at the speed of 1 m/sec. The throughput of the
MS that is stable between 10k – 20k bit/sec. But the
throughput drops down during the handoff. The
maxim delay points are 0.040 sec., which is
considered to be tolerable for most applications.
Fig. 3 : Set–up of WiFi Handoff
Table 1 : Wireless LAN Parameters (for mobile
node)
BSS Identifier 0
Access Point
Functionality
Disabled
Physical Characteristics Direct Sequence
Data Rate (bps) 11 Mbps
Transmit Power (W) 0.002
Packet Reception-
-95
Power Threshold (dbm)
CTS-to-self Option Enabled
Short Retry Limit 7
Long Retry Limit 4
AP Beacon Interval
(secs)
0.02
Max Receive Lifetime
(secs)
0.5
Buffer Size (bits) 256000
Roaming Capability Enabled
Large Packet
Processing
Drop
Initially due to set up time, the delay is more. Then
the mobile node and the stations start roaming
around the access points and hence the delay is
almost constant. Then after 9 minutes there is small
increase in the delay which is again due to the non

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availability of stations. (bits/sec). The simulation
time is 10 min. The throughput drops during
handoff.
Fig 4 : Throughput and delay for MS in the WiFi
set-up
Wlan Backbone
OPNET WLAN models support wireless-LAN
backbones that consist of routers with WLAN
interfaces belonging to the same BSS. These
backbones can serve to WLAN EBSSs as well, where
they are connected to the wireless backbone via their
access points like they would be connected to a wired
backbone. This scenario is built to provide an
example on configuring such networks.
Fig 5 : Wlan network with wireless sever, router,
wireless clients
The network contains wireless FTP clients and a
wireless FTP servers. The clients and server belong
to different wireless- LANs, BSS 0 and BSS 1,
respectively. These two LANs connected to each
other with two routers. These routers, which have
two WLAN interfaces, serve as the access points for
BSS 0 and BSS 1 and also compose the WLAN-backbone,
which is the BSS 2. To achieve this,
among the two WLAN interfaces of Wireless
Router 0, the first interface, IF0, was configured as
an access point and its BSS ID was set to 0. The
access point fuctionality of the other interface, IF1,
was disabled and its BSS ID was set to 2. The
second router was also configured similarly. Hence,
IF0s on the routers became the access points, and
IF1s were connected to the backbone. The
backbone-LAN, BSS 2, does not have an access
point and doesn't need to have one, though it is
possible to configure one of the backbone interfaces
as an access point. Additionally the physical layer
technology used by IF1s on the routers are set to
"OFDM (802.11a)" to enable 802.11a data rates and
their data rates are set to 54 Mbps. In other words,
BSS 2 deploys the 802.11a PHY, while BSS 0 and
BSS 1 use 802.11/11b PHYs. FTP client 5 is
moving at a speed of 1 m/s in the defined trajectory
path. While all other clients are stationary.
Two routers form a wireless backbone network.
FTP server, wireless router 1 is in one BSS,
wireless router 0 and wireless router 1 are in other
BSS, the FTP clients and wireless router 0 are in
another BSS.
Table 2 : Wireless LAN Parameters (for
Wireless FTP clients)
BSS Identifier 0
Access Point
Functionality
Disabled
Physical Characteristics Direct Sequence
Data Rate (bps) 2 Mbps
Transmit Power (W) 0.005
Packet Reception-
-95
Power Threshold (dbm)
CTS-to-self Option Enabled
Short Retry Limit 7
Long Retry Limit 4
AP Beacon Interval
(secs)
0.02
Max Receive Lifetime
(secs)
0.5
Buffer Size (bits) 256000
Roaming Capability Enabled
Large Packet
Processing
Drop

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The performance of all the wireless FTP clients is
observed and graphs obtained for delay, throughput
and traffic received, traffic sent for the FTP clients.
Since the FTP data is sent and received in the form
of packets, hence the graphs show various sharp
peaks.
Simulation time is taken as 4 Minutes.
Fig 6: Traffic received and traffic sent (packets/sec) for FTP
client 5
Fig 7 : delay and throughput for FTP client 5
Fig. 8 : Delay and throughput for FTP client 2
Fig. 9 : Traffic received and traffic sent (packets/sec) for FTP
client 2
The differences in the delay, throughput of FTP
client 5 and FTP client 2 can be easily seen from the
above graphs. As we know that FTP client 5 is
roaming in BSS 0 following some defined
trajectory, while FTP client 2 is stationary as all
others are. And hence the traffic received (bits/sec),

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traffic sent (bits/sec), delay (sec), throughput
(bits/sec) is different for them.
Figure 10: Delay and throughput for the Wireless
FTP Server
From the above graph it is clear that the set up time is
more than 1 minute, after which the FTP data packets
transmission starts.
Results saved with the scenario indicate the FTP
traffic successfully flowing over the WLAN backbone
between the wireless clients and server.
4. CONCLUSION
The vertical handover setup consists of a gateway,
application server providing voice service to the
wimax BS and to the wlan router. Initially both the
mobile nodes are placed near the wimax BS from
where they start roaming towards the wlan router. As
they reach near the router, the wimax throughput is
reduced and the WLAN throughput starts increasing
which depicts vertical handoff triggering properties.
The graphs for throughput and delay are obtained as
expected.
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