International Journal of Engineering Trends and Technology (IJETT) - Volume4 Issue6- June 2013
Proposal of NS2 Simulation Based Study of IP Multimedia Applications on
IEEE 802.11 Based Network Comprising Virtual Server Arrays
Dr.V.Karthikeyani1
Mr.T.Thiruvenkadam2
1
Asst.Professor, Department of Computer Science, Thiruvalluvar Govt., Arts College, Rasipuram.
Asst.Professor, Department of Computer Science, K.S.Rangasamy College of Arts and Science, Tiruchengode.
2
Abstract
The market for IEEE 802.11 wireless local area networks
(WLANs) continues to grow at a rapid pace. Business
organizations, educational institutions and universities are
value the simplicity and scalability of WLANs as well as the
relative ease of integrating wireless access with existing
network resources. WLANs support user demand for
seamless connectivity, flexibility and mobility. But Current
WLAN systems suffer difficulties due to the increasing
expectations of end users and unstable bandwidth Delayboundary demands from new higher data rate services, such
as
high-definition
television
(HDTV),
video
teleconferencing, multimedia streaming, voice over IP
(VoIP), file transfer, and online gaming. Besides this recently
Virtual machine (VM) consolidation has become a common
practice in clouds, Grids, and datacenters. While this practice
leads to higher CPU utilization, we observe its negative
impact on the TCP throughput of the consolidated VMs. As
more VMs share the same core/CPU, the CPU scheduling
latency for each VM increases significantly.
When
multimedia applications streaming from this kind of
consolidated virtual servers to the WLANs client leads to
increase the slower progress. This article provides an
overview of wireless networks, the 802.11 WLAN standards
and virtualization technologies, followed by a presentation of
work planned to identify and analysis the problem and make
recommendations for designing optimal WLAN network for
streaming multimedia applications for virtual networks to
ensure good quality and performance for end users.
Keywords:
IEEE802.11 Wireless LAN, Medium Access Control (MAC),
Quality-of-Service (QoS), DCF, PCF, Virtualization, Server
consolidation
I. INTRODUCTION
As usage and deployment of wireless local area networks
(WLANs) increases, it is reasonable to anticipate that the
demands to be able to run time-bounded applications on them
will be comparable as on wired networks. The IEEE 802.11
Wireless Local Area Networks (WLAN) is being deployed
widely and rapidly for many different environments,
including office, enterprise, home, public access networking.
The main characteristics of the 802.11 standards are
simplicity and robustness against failures due to the
distributed approach of its medium access control (MAC)
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protocol. Today, IEEE 802.11 can be considered wireless
version of Ethernet by virtue of supporting best report service
(not guaranteeing any service level to users/applications). For
different type of applications, there are different requirements
for the Quality of Service (QoS). For example, real-time
applications such as voice and video are delay sensitive.
However the delay is not critical for non real-time
applications such as File Transfer and some delay can be
tolerated. The IEEE 802.11 working group is currently
defining new supplement to the existing legacy 802.11
medium access control (MAC) sub-layer in order to support
Quality of Service (QoS). Many researchers have been done
on the performance analysis of the MAC protocols of IEEE
standards, most of them concentrating on the improvement of
QoS parameters of wireless networks. But none of them have
been concentrating on performance of virtual network since
Virtual machine (VM) consolidation has been increasingly
adopted in cloud (e.g., Amazon EC2, Eucalyptus and
Nimbus), Grid, and datacenter environments. It is necessary
to study the performance of IP Multimedia applications on
IEEE 802.11-based network comprising virtual server arrays.
The remainder of this paper is organized as follows. Section
II provides Introduction to wireless networks. Section III
describes Overview of virtualization. Section IV presents the
research background and context and Section V discusses the
future work and finally, section V concludes the paper.
II.INTRODUCTION TO WIRELESS NETWORKS
The wireless networks are making integrated networks a
reality by bringing fundamental changes to data networking,
telecommunication. A wireless network enables people to
communicate and access applications and information
without wires anywhere and anytime. This provides freedom
of movement and the ability to extend applications to
different areas. Wireless networking has witnessed an
explosion of interest from consumers in recent years due to
its applications in mobile and personal communications. This
network is getting popular nowadays due to easy to setup
feature. One can connect computers without the need for
wires. All the communication in the world including satellite
communication, mobile communication, internet, telephones
and WANs is due to the networking. Wireless networks have
changed the era of life. Users are happy to get the data on
time and without any problem. The use of the authentication
and biometrics and other security mechanisms can improve
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International Journal of Engineering Trends and Technology (IJETT) - Volume4 Issue6- June 2013
the security to some extent. Still Hackers’ can exploit the
sensitive data. The main purpose of the wireless networks is
to establish a secure, fast and reliable communicate channel
among the people.
A. Overview of IEEE 802.11 WLAN
Wireless local area network, an emerging and innovative
activity in the field of computer networks, supported by
flexibility and mobility, in turn attracts the interests of
various academia and industry people A wireless network
makes its users capable to connect their mobile systems to
the enterprise network instantly with an almost effortless
approach. One of the main benefits of wireless is its scope to
the distant areas where cabling would be costlier and
difficult. Mobility remains the most attractive feature of
wireless networks which allows its users to move within the
network which in turn also attracts wireless internet service
providers’ interest in the exploitation of wireless networks.
The most influential factors of wireless networks is the
provision of higher data rates, lower packet losses and a fair
level of Quality of Services. Different types of traffic flows
whether it is data flows or multimedia flows like real time
voice, streaming voice, video demands access to high data
rates and guaranteed QoS in terms of higher throughput, less
delay, less no. of collisions and lower packet losses, whereas
achieving these factors is very difficult as wired networks is
highly time variant and noisy. These requirements led the
engineers of IEEE association to keep on working upon the
improvement of WLAN standards so that wireless users can
satisfy their usage demands from wireless networks. IEEE
802.11 is the most commonly used standard of WLAN [1]. In
time, there has been a tremendous growth in the deployment
of WLAN standards; network traffic has also been classified
as multitude of classes where each class requires a different
level of service from the network. Moreover, invention of
time bounded applications like VOIP or video streaming
requires hard real time constraints. So, it becomes implied
that, the WLAN standards should meet these requirements of
service differentiation and prioritization. Unfortunately,
IEEE802.11 WLAN standard does not satisfy the constraints
of QoS parameters. Therefore, IEEE has evolved with an
enhanced version IEEE 802.11e which implements QoS
mechanisms to a fair level [3]. Many investigations have
been made in the performance of 802.11e standard. IEEE
802.11 working group has enhanced the MAC sub layer of
the standard to support the QoS constraints.
B. Overview of IEEE 802.11 PHY
The IEEE 802.11 PHY layer specification concentrates
mainly on wireless transmission. The original specification
was first approved in 1997 [1] and includes a primitive MAC
architecture and three basic over-the-air communication
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techniques with maximal raw data rates of 1 and 2 Mb/s.
Because of their fairly low data bandwidths, further
amendments have been proposed throughout the years: IEEE
802.11a [2], 802.11b [3], and 802.11g [4]. Both 802.11aand
802.11b were finalized in 1999 and support raw data rates up
to 11 Mb/s and 54 Mb/s, respectively. In June 2003, a third
PHY specification (802.11g) was introduced, with similar
maximum raw data rate as 802.11a but operating in separate
frequency bands. For this period, there were many
amendments and countless research works for improved PHY
specifications that mostly aim to provide reliable connections
and higher data rates. This is mainly because there is a
continuous rapid increase in user demand for faster
connections. In spite of establishing novel techniques that
theoretically can be used for higher data transmission rates,
the throughput outcomes at the MAC data are surprisingly
low and in most cases, half of what the underlying PHY rates
can offer.
C. IEEE 802.11 MAC
The MAC architecture is based on the logical coordination
functions, which determine who accesses to the wireless
medium at each time. In the legacy IEEE 802.11 standard,
there are two types of access schemes: the mandatory
distributed coordination function (DCF), which is based on
the carrier sense multiple access with collision avoidance
(CSMA/CA) mechanism; and the optional point coordination
function (PCF), which is based on a poll-and response
mechanism. These MAC schemes are inadequate to resolve
differentiation and prioritization between frames and
multimedia applications such as VoIP and audio/video
conferencing with strict performance constraints. Due to
these applications have become widely popular, a new
extension was vital. In late 2005, IEEE 802.11 TG approved
the IEEE 802.11e amendment [5] to provide an acceptable
level of quality of service (QoS) for multimedia applications.
The 802.11e proposes the hybrid coordination function
(HCF), which uses a contention-based channel access
method, known as enhanced DCF channel access (EDCA).
EDCA has the ability to operate simultaneously with a
polling-based HCF controlled channel access (HCCA). In
addition to the differentiation and prioritization that IEEE
802.11e offers, the transmission opportunity (TXOP) was
introduced in order to improve MAC efficiency. A TXOP is
an interval of time in which multiple data frames can be
transferred from one station to another (also known as
bursting). During a TXOP period the station can transmit
multiple data frames without entering the backoff procedure,
reducing the overhead due to contention and backoff period.
Along with frame bursting, another type of acknowledgment
(ACK), known as block ACK, was established. Receivers can
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acknowledge multiple received data frames efficiently by
using just a single extended ACK frame.
III. OVERVIEW OF VIRTUALIZATION
Today, in the era of space & power crunch, Virtualization
technologies are getting lot of research interest because of
their capability to share the hardware resources among
multiple operating systems and still maintain isolation
between virtual machines.[6] Advancements in virtualization
technology allows enterprises and service providers to
optimize the utilization of their server and storage resources
by eliminating the traditional, inefficient “one server, one
application” model. Virtualization enables a single physical
server (or storage array) to host multiple “virtual machines”
(VMs) called server consolidation. It allows flexible sharing
of physical system resources across multiple VMs running
multiple applications or services.
A. Types of Virtualization
Core of any virtualization technology is Hypervisor or
Virtual Machine Manager (VMM). Hypervisor is a piece of
software which allows each virtual machine to access &
schedule the task on resources like CPU, disk, memory,
network etc. At the same time hypervisor maintains the
isolation between different virtual machines. Virtualization
can be classified by the method in which hardware resources
are emulated to the guest operating system. They are as
follows
• Full Virtualization - Hypervisor controls the hardware
resources & emulates it to guest operating system. In full
virtualization guest do not require any modification. KVM is
an example of full virtualization technology.
• Paravirtualizaion - In paravirtualization hypervisor controls
the hardware resources & provides API to guest operating
system to access the hardware. In paravirtualization, guest
OS requires modification to access the hardware resources.
Xen is an example of paravirtualization technology.
B. The Benefits of Virtualization
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There are a number of key business benefits that are
motivating enterprise IT organizations to adopt virtualization
technologies. Some of the most significant reasons include:
 Business continuity and disaster recovery
 Flexibility and agility
 Reduced downtime
 Server consolidation
Business Continuity and Disaster Recovery
Virtualization allows easier software migration, including
system backup and recovery, which makes it extremely
valuable as a Disaster Recovery (DR) or Business Continuity
Planning (BCP) solution. Virtualization can duplicate critical
servers, so IT does not need to maintain expensive physical
duplicates of every piece of hardware for DR purposes.
Business Agility
Virtualization can greatly increase business agility and
flexibility. By decoupling business processing from physical
hardware, virtualization improves agility by enabling IT to
respond to rapid changes in demand.
Reduced Downtime
Reduced downtime is another key driver for virtualization.
Virtual images are easier to restore after a failure – either an
operational failure (such as a virus infection) or a hardware
failure. The portability of virtual images allows new and different hardware to be used for recovery, further reducing the
downtime
Server Consolidation
Server consolidation and improved server utilization is
another driver for virtualization adoption. Virtualization
allows enterprises to combine the workload from multiple
underutilized physical machines into a single physical
system. This dramatically reduces the overall hardware
spending, as it requires far fewer physical systems for the
same application workload. It also has a dramatic effect on
the overhead costs, including power, cooling, storage, and
physical administration.
Virtual machine (VM) consolidation has become a common
practice in clouds, Grids, and datacenters. While this practice
leads to higher CPU utilization, we observe its negative
impact on the TCP throughput of the consolidated VMs: As
more VMs share the same core/CPU, the CPU scheduling
latency for each VM increases significantly. Such increase
leads to slower progress of TCP transmissions to the VMs.
An application's performance in a virtual machine
environment can deliver markedly from its performance in a
non virtualized environment because of interactions with the
underlying virtual machine monitor and other virtual
machines. At the same time, a large category of
communication intensive distributed applications and
software components exist, such as web services, high
performance grid applications, transaction processing, and
graphics rendering, that often wish to communicate across
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Current WLAN systems which endure difficulties due to the
increasing expectations of end users and volatile bandwidth
Delay-boundary demands from new higher data rate services,
such video teleconferencing, multimedia streaming, file
transfer, and online gaming.
IV. RESEARCH BACKGROUND AND CONTEXT
Performance of voice and video traffic on WLANs has been
one of the favourite topics of the academic researchers. A
number of research studies have been conducted to evaluate
various architectures and schemes of quality of service in
WLANs. Berthou, Gayraud, Aphand and Prudhommeaux and
Diaz [8] have revealed that the CSMA/CA mode of DCF
communications in 802.11b networks with Dynamic Rate
Shifting (DRS) settings do not yield acceptable performance
in 802.11 networks. The Enhanced DCF introduced in
802.11e was expected to enhance multimedia performance
but Zhu, Li, Chlamtac, and Prabhakaran [8] argued that
EDCF should be configured in priority mode and bandwidth
reservation should be carried out. Lee, Hall, Yum, Kim, and
Kim [9] employed a simulation based study to estimate the
amount of bandwidth required to be reserved per 802.11
stations for streaming multimedia traffic. They discovered
that it is a very challenging task in cross-traffic mode (with
voice and video streaming simultaneously to assure real time
performance). The estimates vary stochastically with size of
packets and size of video resolution and window size. In a
similar study by Zhai, Chen and Fang [10], it is revealed that
QoS provisioning in WLAN networks and the bandwidth
required per station for multimedia streaming traffic are
vague and can only be estimated for aggregate traffic rate at
access point. Also, the estimates may differ for fixed and
mobile users because the fading on the channels may have to
be taken into account for mobile users. Based on this
estimation, as demonstrated by Bejerano and Bhatia [11], the
number of access points required can be estimated for given
number of users within a coverage area. There is hardly any
flexibility available especially if high bit rate real time
multimedia is employed. Khayam, Karande, Radha and
Louinov [12] estimated that high density multimedia traffic
on WLANs may contain lots of useless and corrupt packets
that cannot be estimated by the network administrator and the
performance does not increase consistently by increasing the
bandwidth because background packets related to the
streaming session may get stuck in the buffers that should be
flushed out quickly otherwise the video session gets starved
of bandwidth slowly and is ultimately terminated. This
phenomenon is also observed by Cranley and Davis [13].
They also observed that the high burst nature of streaming
traffic of high bit rate results in high queuing delays at the
access points. These authors concluded those packet size and
packet rates are the key determinants of performance in
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WLANs. Lower these attributes higher will be the effective
utilisation of bandwidth per access point and higher will be
the number of WLAN stations supported. In this context,
Natkeniec and Pach [14] demonstrated that the best way to
estimate the performance of multimedia streams in WLAN
networks is to carry out simulations at full load on various
architectures and conclude the optimal configurations.
Given these challenges presented by the scholars, we want to
solve the question on how a large scale WLAN network can
be implemented in a virtualised environment to offer IP
multimedia streaming services. we want to present a study
with modelling of a multilayer WLAN network for a
virtualisation based network comprising of large arrays of
WLAN stations per access point and the WLAN stations in
turn connected through WLAN access switches. We will
employ the NS2 simulator and model the network. We will
add an array of multimedia streaming servers sharing load
through massive parallel processing (a key feature of
virtualised server arrays) that shall be accessed by the WLAN
stations through “application demand” configurations on
NS2. We will vary the bit rate and video resolution of the
video streams and will use multiple codecs in the audio
streams and will conclude upon an optimal traffic
configuration for the network. To ensure QoS configuration,
we will configure Priority Queuing. To ensure high load, we
will model large number of WLAN stations on the network
(say, 100). Our focus will be on throughput, queuing delay,
jitters and packet losses to analyse the quality of multimedia
services experienced by the end users of the 802.11 network
providing access to the virtualised server array configured to
deliver workload sharing for collectively serving the IP
multimedia users.
V.DISCUSSION AND FUTURE WORK
We will implement the above configurations in a Fast
Ethernet switched network and will compare performance.
Primarily, we will try to find the rise in threshold of bit rate
and video resolution on wired networks against wireless
networks. After getting the results of the simulations, we will
make recommendations for designing optimal WLAN
network for streaming multimedia applications for virtual
networks.
A. Aim and Objectives
Our aim is to study the behaviour of WLANs running
multimedia streams by modelling and simulating a high load
WLAN on NS2 and recommend optimal configurations to
ensure good quality and performance for end users. The
objectives of the study are proposed to be:
(a) Create a multi-layer WLAN model on NS2 with high
load multimedia streams delivered by a large array of
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International Journal of Engineering Trends and Technology (IJETT) - Volume4 Issue6- June 2013
(b)
(c)
(d)
(e)
virtual servers (say, 20) accessed by large number of
users simultaneously (say, 100).
Provide high bandwidth on the network to ensure that
bandwidth is not a limitation and then run simulations
for different packet size, packet rates and video
resolution size for video streams and different codecs for
audio streams.
Observe the throughput, queuing delay, jitters and packet
losses in all the configurations and choose the optimal
one.
Compare these attributes with a fast Ethernet switched
network and observe to what extent the thresholds can be
raised.
Based on the results, make recommendations to
implement an optimal WLAN for corporate networks
that can ensure good performance for the end users.
VI.CONCLUSION
The benefits of server virtualization are widely accepted and
the majority of organizations have deployed virtualization
technologies. The main advantage of server virtualization is
efficiency and using one machine to simulate multiple
servers saves time, energy and money. Less heat is generated
and less electricity is used. Virtualization allows data centers
to consolidate their server inventories and clear up old or
unnecessary equipment. Companies in data-intensive
industries with thousands of servers can decrease their
physical space requirements significantly. Despite the
advantages of server virtualization, significant downsides
exist. Virtualization splits the physical machine’s processing
power and gives a portion to each simulated server. This
makes the clients with high-demand needs to slow down its
performance. At the same time the use of IEEE 802.11
WLANs growing at a rapid pace. The falling cost of WLAN
products has also led to their increased use in consumer
homes. Although currently WLANs are predominantly used
for data transfer, the higher bandwidth provided by new
WLAN technologies such as IEEE 802.11g and IEEE
802.11e will ultimately lead to their increasing use for
multimedia transmissions. However, the delivery of
multimedia applications from a virtualized central server to a
large number of WLAN clients is a challenging and resource
intensive task and delivering multimedia content over this
kind of network faces many challenges. Many researchers
and manufacturing agencies interested in the transmission of
multimedia streams over networks. However none of them
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have been concentrated on multimedia streams delivered by a
virtual server, since the server consolidation is widely
accepted and the majority of organizations have deployed
virtualization technologies the attention must be given to the
improvement of QoS parameters of wireless networks to
ensure good quality and performance for end users.
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