An emulation of VoD services using virtual network environments

Electronic Communications of the EASST
Volume 17 (2009)

Workshops der
Wissenschaftlichen Konferenz

Kommunikation in Verteilten Systemen 2009
(WowKiVS 2009)

An emulation of VoD services using virtual network environments

Walter Fuertes and Jorge E. López de Vergara

14 pages

Guest Editors: M. Wagner, D. Hogrefe, K. Geihs, K. David
Managing Editors: Tiziana Margaria, Julia Padberg, Gabriele Taentzer
ECEASST Home Page: http://www.easst.org/eceasst/ ISSN 1863-2122

http://www.easst.org/eceasst/

ECEASST

An emulation of VoD services using virtual network environments
Walter Fuertes1 and Jorge E. López de Vergara2

1 walter.fuertes@uam.es, http://www.uam.es/
2 jorge.lopez vergara@uam.es

Departamento de Ingenierı́a Informática, Escuela Politécnica Superior
Universidad Autónoma de Madrid, Madrid, Spain

Abstract: Virtualization platforms are a viable alternative for the implementation of
IP network experimentation environments. These platforms facilitate the conducting
of tests as if a real environment were used and therefore can reduce the risk of failure
as well as investment and experimentation costs. This paper proposes to develop a
method to improve the results obtained in virtual network environments, trying to
resemble those obtained in a real environment. To carry this out, we have emulated
a video-on-demand service over ADSL using Xen as a virtualization tool, just as
it would have been through a real ADSL connection. Connectivity, IP addressing,
switching, routing and video streaming were tested to check the functionality of
virtual network environments. Then, the bandwidth, the delay, and the inter-arrival
time of video streaming packets were measured both in real and virtual environ-
ments. Finally, these parameters were tuned in the virtual network environments
obtaining a similar behavior in clients and servers of both cases.

Keywords: Emulation, performance measurement, traffic monitoring, video strea-
ming, virtualization.

1 Introduction

Virtualization platforms are a potential technology to reproduce a real network topology using a
virtual environment. They enable interconnected equipment to be emulated, which only requires
the resources of a single physical computer. Virtualization can be used to maintain, execute and
test multiple software environments [MHH+07], and to provide facilities for network dimension-
ing. In addition, virtualization platforms allow the evaluation of network service provisioning
prior to production; therefore they can reduce the risk of network failures, as well as investment
and experimental costs.

Currently there are at least two ways to achieve the networks dimensioning and comparative
performance measurements. One alternative is to set up a mock-up network infrastructure in
parallel, but this would require new equipment and hardware devices making it an expensive
solution. The other alternative is to use simulation tools, such as NS2 [NS2], among others,
which are used to evaluate the performance of networks. Nevertheless, these simulators are
trying to replicate the performance of a real system (end-to-end delay, packet loss, etc.), using
software, but are not able to closely reproduce the features and behavior of the hardware in a real
system (emulation of new devices, configurations, architectures) [Rim07].

Facing these two alternatives, this work proposes to use virtualization platforms to assess the
network service provision. According to the results obtained in [Mun08], virtualization tech-

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mailto:walter.fuertes@uam.es
http://www.uam.es/
mailto:jorge.lopez_vergara@uam.es

An emulation of VoD services using virtual network environments

nologies are approximately close to the ones derived from a real and simulated environment.
However, virtualization technology generates a performance overhead caused by the virtualiza-
tion layer [BDF+03]. This would mean that virtualization has not yet matured to ensure results
close enough to the network service provision in real environments. Hence, which factors would
be required to improve the results of such emulation? And, which operational conditions sug-
gested for virtualization can be most effective?

In this context, as a contribution, this paper proposes to implement a method to improve the
results obtained in virtual network environments, trying to resemble those obtained in real en-
vironments. In particular, our main goal is to obtain a result as close as possible to a real case.
These improvements will provide strategies to interact with real time applications and to ensure
their service delivery in similar conditions before putting them into production. In addition, these
enhancements could improve user perception.

To carry out this work, we have emulated a real network service, namely video-on-demand
(VoD) over ADSL by means of the Xen virtualization tool [BDF+03]. Firstly, we designed and
implemented the required test-bed to make the comparisons between virtual and real environ-
ments. Secondly, we adjusted the network environment parameters to emulate the operational
aspects of the real environment. With these results, we have found new guidelines to adjust the
emulation parameters in virtual network environments.

The remainder of this paper has the following organization: Section 2 provides some back-
ground concerning virtualization networks, the Xen virtualization tool, video streaming and
VideoLAN solution. Then, in section 3 the experimental setup is described which is used to
emulate the VoD over ADSL service in the virtualization platforms. Section 4 shows a set of
tests which were performed to improve our evaluation results. Section 5 discusses related work.
Finally, the conclusions and future work are given in Section 6.

2 Background

2.1 The virtual network environment

Within the scope of this research, virtualization is in essence a technique to share hardware
resources. It can be used to partition physical equipment to support multiple virtual machines,
interconnect them, and to share hardware resources, such as CPU, memory and input/output
devices. It provides an extra abstraction layer between the hardware and the operating system
(OS). This technique enables, via hardware, to have several guest OSs of diverse types executing
simultaneously [Jon06].

In this paper a virtual network environment can be defined as a set of virtual equipment (both
end systems, routers and switches) connected collectively in a given topology deployed on one
or multiple hosts, which emulates an equivalent system in which the environment is perceived
as if it were real. The virtual network environment encapsulates a set of applications within a
virtual network, enabling service configurations for a specific network in a realistic way.

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2.2 Xen

Xen [BDF+03], is an open source virtualization tool, based on the para-virtualization technique.
Xen provides more efficient processing and minor overhead which results in better performance
than other virtualization platforms. Within the context of this paper, Xen provides the infrastruc-
ture to deploy and manage a virtual network environment which can be configured to emulate
the provision of the VoD service. Finally, based on the above and considering that a lower con-
sumption of CPU and memory of the host results in a better response of virtual machines, we
have chosen Xen to be the tool used in our research. It provided the best results in our previous
assessments published in [FV07] and confirmed in [BDF+03] and [WCCG08].

2.3 Video streaming

Video streaming is a method to transfer digital data in real-time. This process converts video and
audio into a compressed digital format, and then distributes the data through the computer net-
works. The diverse ranges of video communication and streaming applications that do exist have
different operating conditions and properties. Video communication applications may be used
for point to point, for multicast, or broadcast communications, and video may be pre-stored,
so-called VoD, or may be encoded in real-time, e.g., video conferencing [ATW02]. However,
systems that provide these services currently require large amounts of centralized resources and
significant bandwidth to accommodate their subscribers. Considering the aforementioned rea-
sons, and because it is a widely used service, we have chosen VoD here with the aim of trying to
measure their network parameters and emulate this service using virtual network environments.

2.4 VideoLAN Solution

VideoLAN [Vid] is a software solution for video streaming designed to stream moving picture
experts group (MPEG) videos or audio video interleave (AVI) files on high bandwidth networks.
The VideoLAN VLC (initially VideoLAN client) can be used as a video server or as a client (as
a video player) to receive, decode and display MPEG streams under multiple OSs.

In the context of this paper, we have selected the VideoLAN solution because it is free video
transmission software for both for VoD and live video. In addition, the video format can be
changed. VideoLAN is also a portable multimedia player that works both for Microsoft Windows
and Linux and it can use diverse media storage and transmission.

In this article the VideoLAN solution basically has two main functions: i) as server to transmit
video files of different format to the client; and, ii) as a client, it to control the communication
between the client and the server, and implement the video play classic functions.

3 Emulation experiments

This section describes the method developed to improve the results obtained in virtual network
environments. This method has been divided into five steps, as shown in the next flowchart
(see Figure 1). Its design, implementation details, settings and assessment are the basis of our
research and will be explained in the following paragraphs:

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An emulation of VoD services using virtual network environments

Describe de real

environment

Topology design and

virtual environment

implementation

Begin

If equal

End

Network parameters

adjustment

Network traffic

measurement

Adaptation of other

operational

conditions

Step 1

Step 2

Step 3

Step 4

Step 5

If equal

Start a real network

service provision

Start an emulated

network

Bandwidth, jitter,

throughput, delay, …

If the real environment traffic-measures

are equal to the virtual environment

traffic-measures with adjustments
YES

YES

Memory, HD and CPU

consumption, timer,

workload, and so on

Put the service in

production

If the real environment traffic-measures

are equal to the virtual environment

traffic-measures with adjustments

including Step 5

Figure 1: Flowchart to implement the method to improve the results obtained in virtual network
environments.

3.1 Step 1: Description of real environment

As outlined in the flowchart, the first step was to describe the real environment and describe
the experiment (see Figure 2). In this research we selected the VoD in an ADSL connection.
ADSL was chosen because it was specifically designed to exploit the one-way nature of most
multimedia communication. i.e., the large amounts of information flow toward the user and only
a small amount of interactive control information is returned. Next we tested the emulation of
the service conditions for streaming VoD versus a classic 1.2 Mbps ADSL connection. Finally
we accomplished the experiments described in Subsection 3.3.

Before proceed to Step 2, it is important to mention that in this research we did not consider
the emulation of different transmission characteristics of ADSL connections concerning the last
mile ( e.g., cable length, signal attenuation, or concurrent users). We focused on the bandwidth
and delay, and we supposed that other properties would be masked by them. Given the obtained
results (see section 4), this assumption can be considered acceptable.

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U N I V E R S I T YU N I V E R S I T Y

ADSL

modem
spliter

spliter

Switch C.O.

DSLAM
Internet

PSTN
Central Office

xDSL

modem

Client

Frame Relay
ATM

VideoLAN

Server

1.2 Mbps

telephone

P
O

T
S

256 Kbps

downlink

uplink

Figure 2: Testing environment of an ADSL connection.

3.2 Step 2: Design and implementation of the virtual network environment

As a second step in the method, to experiment the VoD service, we designed and implemented
the virtual network environment shown in Figure 3. In this new environment, we installed and
configured the VideoLAN server in a virtual machine located on one server in our laboratory at
the University. On the other side we installed a VLC media player as a client on the same host, to
display the video, especially given the need to handle a graphical environment and considering
that Xen has limitations in such requirements. Then we fine tuned the link between Router 2 and
Router 1 to make it similar to the case of an ADSL connection.

Virtual

VideoLAN

Server

Router 1

Router 2

Router 3

Virtual

Environment

Uplink limited
to 1.2 Mbps

delay of 67,8ms

eth1

10.0.10.1

eth2

10.0.4.1

host

10.0.10.2

eth1

10.0.4.2
eth2

10.0.5.2

eth1

10.0.5.1

eth0

10.0.3.1

10.0.3.3

Figure 3: Virtual network environment used to emulate a VoD over an ADSL connection.

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An emulation of VoD services using virtual network environments

As shown in Figure 3, the elements of the virtual environment can be mapped to some elements
of the real ADSL environment in Figure 2. ( i.e., the VideoLAN Server in each environment as
well as the clients). Similarly, Router 1 maps to the home ADSL router, Router 2 maps to the
ISP router, and Router 3 maps to the server router. Other routers could be also considered in the
path between Router 2 and 3 if necessary.

The following procedure has been used to implement the proposed design in a virtual network
environment: First of all we created the first virtual machine and installed the guest OS, Linux
Debian. Then, we cloned the first virtual machine to the remaining virtual machines, in order
to reduce the installation time. At this point, it should be noted that the routers depicted in
Figure 3 are virtual machines to which the functionality of routing devices was assigned. After
this, we added virtual interfaces, configured IP addresses, routing and started services. Then,
we synchronized the clock of each virtual machine with a network time protocol (NTP) server
within the real host. This allowed the virtual machines to synchronize their system time. This
is very necessary because virtual machines (and routers in this case) work by time-sharing the
host physical hardware, and a virtual machine cannot exactly duplicate the timing behavior of a
physical machine. Lastly, we created and executed the respective programs that automatically
constructed and started the environment. As a final point, we installed the software for traffic
monitoring both in the virtual network environment and the host. It is also worth mentioning that
all tests were done using open source software.

3.3 Step 3: Network Traffic Measurement

Once both environments were implemented, we took appropriate network traffic measurements
according to step 3 of our method. We transmitted video files both in the real (Figure 2) and
virtual (Figure 3) environments in the downstream direction from the VideoLAN server to the
client. We conducted several tests to confirm that the traffic data capture was error-free.

To capture traffic for the two experiments described below, we used Tcpdump [JLM] and
disabled the promiscuous mode in the corresponding interfaces. Tcpdump is a command-line
tool whose main utility is to analyze the traffic going through the network. The logs obtained
were visualized with Wireshark [Wir], which is a network protocol analyzer. Then, filters were
applied to create flat files which were processed with a script to obtain the cumulative distribution
function (CDF) of the video packet inter-arrival time. These probability distributions have been
used to contrast the results, following the methodology presented in [GAH+07] to compare the
performance of multimedia services on IP networks.

3.3.1 Real ADSL experiment

The first experiment consisted in the capture of video on real-time transport protocol (RTP)
traffic in the real ADSL environment during the transfer of video (see Figure 2). This capture
was made simultaneously both in the client at home and in the server located in the laboratory at
the University, to obtain the CDF of the video packet inter-arrival time.

To obtain an appropriate value of the delay between the VideoLAN server and the ADSL
client we applied the ping command with fixed-size packets of 1370 bytes. Ping measures the
round-trip time (RTT) using the Internet control message protocol (ICMP) echo messages. With

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this, based on the 4300 messages sent over 45 minutes we obtained a mean (u) of 135.6 ms, with
a correlation r(0) of 40% and a standard deviation of 17ms for the RTT. It should be noted that
the packet loss was negligible in the traffic measurement.

We used RTT instead of one way delay (OWD) that would be a better option for ADSL, given
that OWD must be calculated between two synchronized nodes, which was not possible in the
real environment where the experiment was carried out.

3.3.2 Virtualized environment experiment

The second experiment consisted in the capture of RTP video traffic in the virtual network envi-
ronment (see Figure 3). All tests were carried out on a single host (Pentium D, 2.80 GHz, 1 GB
RAM) with Linux Debian 4.0 and one Ext3 partition with 120 GB. In all virtual machines the
same file systems and the same kernels (2.6.18-xen-686-GNU/Linux Debian) were installed.

3.4 Step 4: Adjustment of virtual network environment parameters

According to step 4 of our method, we adjusted the values of the parameters obtained in the
previous experiment before transferring the video, to calculate the CDF of the video packet
inter-arrival time in this environment and contrast the results. From these values the delay was
configured to 67.8 ms (given the asymmetry of ADSL, we supposed as an approximation a
symmetrical end-to-end delay and taking half of the RTT obtained for the real case). In addition,
we limited the bandwidth on the link from Router 2 to Router 1 to 1.2 Mbps. It was also possible
to emulate the ADSL uplink with a smaller bandwidth, but for the experiment this was not
necessary because the video service is unidirectional ( i.e., from the VideoLAN server to clients).

To emulate the network parameters (bandwidth, end-to-end delay) at the eth1 interfaces of
Router 2 and Router 1 of the virtual network environment we used the following Linux traffic
control utilities: i) traffic control (tc) [Bro06], that encompasses the sets of mechanisms and
operations by which packets are queued for transmission/reception on a network interface; ii)
network emulator (NetEm) [Hem05], which is an enhancement of the traffic control facilities of
Linux that allows adding delay, packet loss and other parameters [Kel06]. At this point we used
this tool to emulate the end-to-end delay similar to what was obtained in an ADSL environment;
and, iii) hierarchical token bucket (HTB), which is a useful queue discipline to limit the band-
width rate. As shown in Figure 2, the ADSL connection last-hop has a maximum bandwidth rate
of 1.2 Mbps, which must be limited in the virtual network environment. Once these adjustments
were made, video traffic was captured in the virtual network environment, in order to make the
comparisons described in section 4.

3.5 Step 5: Adaptation of other operational conditions

As a final step of the proposed method, the following conditions of the system operation where
the emulation experiment was executed should be analyzed. This will identify mechanisms that
can help to improve the method.

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An emulation of VoD services using virtual network environments

3.5.1 Dedicated server

Previous experiments were conducted in a dedicated server just for VoD service. When we added
another service such as file transfer in the virtual network environment, performance degradation
was increased. In summary, the degradation in response time can be explained because CPU
resources are shared in the system. Among other solutions, this problem can be solved by adding
the appropriate amount of resources [Fer06]. But the finest solution should be to balance the
workloads in virtual machines.

3.5.2 Timer resolution

The OS uses these timers to provide a multitude of services. In the case of the virtual network
environment, since there are several virtual machines running on a single platform, there is a
variety of approaches to map the virtual clock into the physical platform clock, and any of these
can cause clock skew. In addition, any changes in the clock behavior could lead to errors in com-
puting the delivered performance. Due to clocking issues, utilization measurements from within
virtual network environments are unreliable [Fer06]. In any case, to improve the measurements,
the virtual network environment must be able to get access to high resolution timers. Higher
resolution timers are needed to enable the system to process data at more accurate intervals. One
manner to implement it is by adding patches to introduce a new subsystem, e.g., high-resolution
kernel timers (Linux hrtimers).

On the other hand, since the virtual machines must share the resources of the same CPU (pro-
vided by real host) and especially due to the complexities caused by emulating virtual hardware,
such features are very time sensitive, leading to inaccuracy in system time of virtual machines.
This fact has been well documented in [MRM06, Inc08]. Moreover, the installation of specific
software for virtualization platforms, called Additions, is a better solution to enhance this syn-
chronism [MRM06].

3.5.3 Other performance metrics

Besides of the traditional metrics that are already tested, the measuring of other performance met-
rics should also be considered such as number of users, number of virtual machines, workloads
response time, CPU and memory utilization node, and so on. Moreover, as a final suggestion,
the number of virtual CPUs must be equal to the number of physical core CPUs in the real envi-
ronment, and; the amount of physical memory assigned to virtual machine must be equal to the
physical memory in the real environment [CGS06]. This will create a fairer comparison.

4 Experimental results and discussion

4.1 Comparison between the ADSL server and virtual server

Figure 4 shows the results obtained by the CDF of video packet inter-arrival time for the real
ADSL server and the virtual server. It is clear that the probability distributions are similar,
although there is some disparity because of the overhead produced by the virtualization layer.

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0 0.005 0.01 0.015 0.02 0.025 0.03
0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1
CUMULATIVE DISTRIBUTION FUNCTION, SERVERS

P
ro

b
a
b
ili

Packet inter−arrival time (ms)

ADSL−Server
Virtual−Server

Figure 4: Cumulative probabilistic distribution of video packet inter-arrival time between the
ADSL server and virtual server.

4.2 Comparison between real ADSL client and virtual environment client

Figure 5 shows the results obtained by the CDF of video packet inter-arrival time for the ADSL
client, virtual client without adjustments, and virtual client with adjustments. This figure illus-
trates that the virtual client without adjustment is completely different from the experimental
results of virtual network client with adjustments. Then again, the traces of the probability dis-
tribution of the two environments are also visually similar, but minor differences were found in
the curves. This reveals the achievement of our method. Nevertheless, as noted in Figure 4, the
CDFs are not exactly equal on the server side and hardly would be accurate on the client side.
These results are related to adjustments made in step 4 (subsection 3.4) of our method.

4.3 Kullback-Leibler divergence

To compare the obtained results in our experiment we have calculated the Kullback-Leibler di-
vergence [KL51], which measures the difference from a true probability distribution function
(PDF) r to an arbitrary PDF v, as defined in equation (1):

DKL(R ‖V ) =

∞∫

−∞

r(x)log
r(x)
v(x)

dx. (1)

Where r(x) and v(x) denote the PDF of R (real ADSL client) and V (virtual client) packet
interarrival random variables.

The evaluation of equation (1) for the PDFs of the real ADSL client and the virtual client
with ajustments gives a result of divergence = 0.0473. In addition, if the PDF of the real ADSL
client is compared to the PDF of the virtual client without adjustments gives a result of diver-
gence=1.9972. As expected, these results show that the disparity is higher when the parameters
are not adjusted in the virtual client.

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0 0.005 0.01 0.015 0.02 0.025 0.03
0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1
CUMULATIVE DISTRIBUTION FUNCTION, CLIENTS

P
ro

b
a
b
ili

Packet inter−arrival time (ms)

Virtual−Client without adjustments
ADSL−Client
Virtual−Client

Figure 5: Cumulative probabilistic distribution of video packet inter-arrival time between the
ADSL client, virtual client with adjustments, and virtual client without adjustments.

4.4 Discussion

As the experimental results have shown, our method has obtained relative similar results to emu-
late the conditions of a real environment using a virtual network environment. On the other hand
this paper has demonstrated the viability of conducting these experiments. Moreover, given that
a similar real infrastructure is not always available to compare the performance measurements,
this research has shown that virtualized environments can be used to emulate a specific network
service, whose results have been close to the real environment. Therefore, the results of the ex-
periment have provided qualitative data related to how the services work, the perceptual quality
of video service in terms of delay and limited bandwidth, the configurations required to transmit
video in unicast or multicast, etc. Logically, these experiments can be done using real equipment.
However, our proposal is intended to demonstrate that the virtualization platforms can be useful
for the same task with lower hardware costs.

During the experiment we tried to control several factors. However, certain factors remain
beyond our control (or they can not be controlled as yet). Some of them have been analyzed in
this paper. Other factors such as the virtualization complexity and the virtual network hardware
performance are out of the scope of this research. These factors generated some disparity in our
results. In particular, because of: i) the overhead produced by the virtualization layer; ii) the
conditions of network emulation (load, timers resolutions, and settings). The latter was caused
because the parameters that NetEm could control were not sufficient to describe a complex net-
work like ADSL and Internet, especially due to its dynamics and complexity [Hem05]; and
finally, iii) the software and hardware components, in particular, do not provide high-precision
timing guarantees [BGG+08].

Regarding scalability, it is possible to add more hops in the topology of the virtual envi-
ronment, depending on the host real capabilities, where the virtual environment was deployed.
Moreover, if the environment requires more resources, it is possible to distribute it among several

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hosts, as proposed in [GFFM08].
With regard to virtualization as an approach to network emulation, the virtual network envi-

ronment has fulfilled the aim to mimic the behavior of a VoD service, with the particularity that
the functionality is not just theoretical or simulated, but rather a real time execution. Conse-
quently, the advantage of this work, (despite the overhead imposed by the virtualization layer),
is that these results give some certainty to experiment with other similar services without having
to deploy them in a real environment.

Finally, the results obtained through the application of this method, lead us to research new
guidelines to adjust the emulation parameters. In addition, it guides us to improve the conditions
to provide the ideal environment for new experiments in virtualized environments.

5 Related work

There are very few papers that discuss the results of service emulation using virtualization en-
vironments. A first comparable research has been described by Fernando [Fer06]. In this paper
the author explores the benefits of virtualization and discusses the difficulties in measuring such
results in the real world. This work measures resource utilization from both the virtual machine
monitor (VMM) kernel and the virtual machines. Our goal, however, is focused on finding guide-
lines to achieve better results in performance measurements in the virtual network environment.

A second comparable research has been described by Casazza et al. [CGS06]. Here, re-
searchers explain a workload methodology to characterize the performance of server virtual-
ization technologies to consolidate multiple physical servers. It presents a benchmark example
using web server, e-mail server and database server. Our work, however, is focused on providing
an infrastructure for conducting network dimensioning experiments. In addition, we have based
ourselves on traditional performance metrics. Lastly, the comparison was made directly with
data obtained between the two environments (real and virtual).

A third comparable work has been explained by Song et al. [SWL+07]. In this paper the
authors study the interaction of VoD and other typical enterprise services in a computer consol-
idation environment context. They compare their results using benchmarks. Compared to this
effort, our goal is to provide qualitative data associated to how the network services work using
virtualization environments; how virtual network environments reproduce this behavior and how
to mimic the results as much as possible to the real case.

Concerning service network emulation through virtualization environments, in [MHR07] net-
work emulation test-beds provide a configurable virtual network environment for comparative
performance measurements of real implementations. In the same context in [GGC+06] authors
address the implementation through virtualization techniques of an IP multimedia subsystem
(IMS) test-bed intended for the functional validation of services. Also, the research in [RSS07]
presents the VMedia multimedia virtualization framework, for sharing media devices among
multiple virtual machines. Compared with our work, these ones have the implementation of
complex topologies as their main goal, so performance is a secondary goal. Unlike us, we were
interested in finding a method to improve the results obtained in virtual network environments.
Therefore, the performance was our primary goal.

Finally, another comparable work can be found in [BBKW03], where the performance of

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virtual routers is evaluated for network research. However, our work has some differences. Apart
from the use of Xen virtual machines, we have compared the results of the virtual environment
with those obtained in a real environment, achieving similar values when applying our method
to improve the results.

6 Conclusions

In this work, we have implemented a method to improve the results obtained in virtual network
environments, contrasted with those obtained in real environments. We have performed a set
of emulated experiments of a real VoD service of ADSL in a virtual network environment with
Xen, using a single host computer. The experimental results have shown certain similarity in
video packet inter-arrival time between both environments in the server side and client side.
However, the probability distributions are not precisely the same, because the virtual network
environment introduces a not quantified overhead and because the emulated ADSL delay is an
approximation. In any case, the experiment results have provided qualitative data in relation
to how the services work, the perceptual quality of video service, the required configurations,
and so on. To conclude, we have presented a procedure to emulate network services in virtual
network environments, emphasizing those factors that affect the experimental results.

As future work we will focus on how to quantify the overheads produced by the virtualization
layer that affects the performance. We plan to study how the obtained results depend on the
number of virtual machines and the number of connected devices that consume resources. Finally
we will also explore how to implement and improve the delay emulation to increase the reliability
of the measurements.

Acknowledgements: This work has been partially funded by Spanish Ministry of Industry,
Tourism and Trade through Red.es under the PASITO project and by the Spanish Ministry of
Science and Innovation under the DIOR project (TEC2006-03246).

The authors would like to thank the comments and good advice of José Luis Garcı́a D., José
Alberto Hernández and Bas Huiszoon, who helped to significantly improve this paper.

Bibliography

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Introduction
Background
The virtual network environment
Xen
Video streaming
VideoLAN Solution

Emulation experiments
Step 1: Description of real environment
Step 2: Design and implementation of the virtual network environment
Step 3: Network Traffic Measurement
Real ADSL experiment
Virtualized environment experiment

Step 4: Adjustment of virtual network environment parameters
Step 5: Adaptation of other operational conditions
Dedicated server
Timer resolution
Other performance metrics

Experimental results and discussion
Comparison between the ADSL server and virtual server
Comparison between real ADSL client and virtual environment client
Kullback-Leibler divergence
Discussion

Related work
Conclusions