Comparisons of QoS in VoIP over WIMAX by Varying the Voice codes and Buffer size

International Journal of Computer Applications Technology and Research
Volume 5–Issue 7, 455-459, 2016, ISSN:2319–8656
www.ijcat.com 455
Comparisons of QoS in VoIP over WIMAX by Varying the
Voice codes and Buffer size
Nueafun Pimwong
Department of Computer
Science and Engineering
Thapar University, Patiala,
India
R.K. Sharma
Department of Computer
Science and Engineering
Thapar University, Patiala,
India
Visit Boonchom
Division of Computer and
Information Technology,
Faculty of Science,
Thaksin University, Thailand
Abstract: Voice over Internet Protocol (VoIP) is developed for voice communications system based on voice packets transmitted over
IP network with real-time communications of voice across networks using the Internet protocols. Quality of Service (QoS) mechanism
is applied to guarantee successful voice packets transmitted over IP network with reduced delay or drop according to assigned priority
of voice packets. In this paper, the goal of simulation models is present to investigate the performance of VoIP codecs and buffer size
for improving quality of service (QoS) with the simulation results by using OPNET modeler version 14.5. The performance of the
proposed algorithm is analyzed and compared the quality of service for VoIP. The final simulated result shows that the VoIP service
performance best under G.729 voice encoder scheme and buffer size 256 Kb over WiMAX network.
Keywords: VoIP, Codecs, QoS, WiMAX, Buffer size
1. INTRODUCTION
Worldwide Interoperability for Microware Access (WiMAX)
is a standard based on IEEE 802.16 broadband wireless access
metropolitan area technology. It is an air-interface standard
for microwave and millimeter-wave band. This server can act
as a wireless extension cable and DSL technology, enabling
wireless broadband access. The signal cover of WiMAX
technology ups to 50km, WiMAX data rates between 1.5 to
75 Mbps. Also, it supported multimedia applications such as
voice over IP (VoIP)
VoIP is developed for voice communications system based on
voice packets transmitted over IP network, in possibility to
reduce a communication costs. It provides real-time
communications of voice across networks using the Internet
protocols with Quality of Service. QoS transmitted over IP
network which can reduced delay or drop according to
assigned mechanism is applied to guarantee successful voice
packets priority of voice packets.
In the present study, OPNET simulator is use to implement
the proposed VoIP Network. We examine all the various
buffer size that can drop the quality of service over wireless
network (WiMAX). Accordingly to this study, it is relied on
using codecs and buffer size to explore its impact on packet
delay, jitter and throughput, are calculated and analyzed. The
comparisons were carried out between different codecs
(G.711, G.723, G.729 and GSM) and different buffer size
(32kb, 64kb, 128kb and 256 kb) with are the most appropriate
to improve QoS for VoIP.
This article is organized in five sections. Section 1 introduces
the work. Section 2 gives the Materials and Methods for
improving quality of service (QoS). Section 3 shows the
results and analysis based on the modeling and simulation
study. Section 4 describes the experimentation carried out in
this work. Section 5 concludes the paper.
2. Materials and Methods
2.1 Quality of Service (QoS)
One can broadly divide QoS in two types: QoS for network
and QoS for user. QoS for network guarantees that the packet
for the voice communication shall not be delayed or dropped.
A QoS for user corresponds to the degree of user satisfaction
in service. These parameters are explained below:
Delay Takes place when the packets of data that contain the
voice in digital form take more than estimated time in order to
reach the destination. Delay can be caused by a number of
factors, in factors, including, type of network, queuing
discipline and type of voice packet traffic [1].
Jitter take place while transporting the voice and packet over
switched network, the data may have a time variation in order
to reach the destination. When some of data packets take more
time in order to reach the destination the effect of this
variation shall result into a jitter, for the listener at the
destination [1].
Throughput Shall take place when the total received packets is
given to each traffic class and measured as the mean of the
number of packets produced per unit time. Throughput is
inversely proportional; robust network has a lower degree of
packet drop [1].
2.2 Codecs for VoIP
Codecs are the algorithm that is used to convert voice data
format from analog to digital in VoIP process. In VoIP
process, when a user talks using telephone or microphone, the
voice format is first converted into digital format, compressed
and then encoded into a predated format using codecs. Codecs
is vary in the sound quality. There are many types of codecs
developed and standardized by ITU-T such as G.711, G723
and G.729 for this purpose [2]. Consequently, packets are
transmitted through IP network to the destination. At the
destination, the digital form is converted back into the voice
form.

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G.711 is defined in ITU-T standard for speech codec. It
delivers precise speech transmission and takes very low
processor requirements. It employs pulse code modulation
(PCM) or Analog-to-Digital Converter (ADC). The PCM
sampling rate for the voice is 8000 frequencies per second;
with a tolerance rate voice bandwidth of 4000 Hz. PCM
processed samples are represented in 8 bit format, and with a
high bit rate of 64 Kbps [3]. In addition, there are two
versions of G.711, namely, A-law and U-law. A-law is
designated for computer processing and its sample rate encode
is 13 bit samples, this E1 standard is used in most of the rest
of the world (other than North America and Japan). U-law is
the T1 standard used in North America and Japan. Its rate
encode is 14 bit samples [3]. Codec G.711 provides a higher
signal range and it is the codec used by the PSTN network and
is believed to be good for VoIP.
G.723 is based on the ITU-T standard that was designed for
voice and multimedia communication over stand phone
system. It gives high compression with high quality audio. It
uses lots of processor power; these particulars are specified by
the H.323 and H.324 series standards. It provides two
compressed stream bit rate 5.6 Kbps and 6.3 Kbps. The higher
bit rate is indicate greater quality. The code operates on
speech frames of 30 ms corresponding to 240 samples at a
sampling rate of 8000 voice frequencies per second [4]. It has
been optimized to represent high quality speech with low
bandwidth requirements using a limited amount of complexity
and suitable for applications such as VoIP.
G.729 is another ITU-T standard and it has the ability to
compress the payload for low bit rate by using an algorithm
know as Conjugate Structure – Algebraic Code Excited Liner
Predication (CS-ACELP). It gives excellent bandwidth
utilization and is error tolerant. This coder offers good quality
speech at a reasonably low bit rate of 8 Kbps and works on a
frame of 80 speech samples [5]. It allows moderate
transmission delay and is very useful in applications such as
teleconferencing or visual telephony where quality, delay and
bandwidth are important. Nowadays Skype is taking benefits
from this standard.
GSM stands for Global System for Mobile communication
this based on the codec operating with a bit rate of 13 kbps.
The GSM codec provides good-quality speech. The speech
input is a 16 bit word sampled at 8 KHz is analyzed by LP.
2.3 WiMAX Network
Worldwide Interoperability for Microware Access
(WiMAX), is a standard based on IEEE 802.16 broadband
wireless access metropolitan area technology. It is an air-
interface standard for microwave and millimeter-wave band.
This server can act as a wireless extension cable and DSL
technology, enabling wireless broadband access. The signal
cover of WiMAX technology ups to 50 km, WiMAX data
rates between 1.5 to 75 Mbps. Also, it supported multimedia
applications such as voice over IP (VoIP) [6]. WiMAX
support its application through four distance traffic classes:
Best Effort (BE) is designed for application such as web
browsing [7] that do not require QoS.
Non Real-Time polling service (nrtPS) support non
real-time application such as File Transport Protocol (FTP)
[7] that requires variable size of data.
Unsolicited Grant service (UGS) supports Constant Bit
rate (CBR) application such as VoIP without silence
suppression [8] where Base Station (BS) assigns a fixed
bandwidth to users.
Real-time Polling service (rtPS) supports real-time
applications with variable size data such as MPEG [8] where
BS allocates bandwidth based on Subscriber Station (SS)
request.
2.4 Buffer size
Buffer is memory location within router where packets are
placed in queues before they get processed upon their turn [9].
The intermediate devices like router and switch in a network
have buffer where the packets wait in a queue before and
after processing. Depending on the packet arrival rate and the
packet departure rate, which may be higher or lesser then
packet departure rate, the packet size may have an impact in
the percentage of discarded packets. As multiplexing
increases the packet size, big packets are expected to be
discarded in the bigger percentage than small ones.
3. MODELLING AND SIMULATION
3.1 OPNET Modeler
OPNET (Optimized Network Engineering Tool) is a tool to
simulate the behavior and performance of VoIP network,
Quality of Service (QoS) analysis of and performance of VoIP
network, Quality of Service (QoS) analysis of simulator of
network communication and network device and protocols.
OPNET provides performance analysis of computer network
and applications [10] through this we can design;
3.1.1 Simulation Model
Figure. 1 The Simulation Network Model
The following figure 1 present the network model. This
simulation model was run in different scenarios to determine
the best audio encoding schemes and buffer size of utilizing
VoIP over integrating wireless (WiMAX). All the scenarios
follow the similar structure and the similar topology. Each
scenario is implementing with the codec G.711, G723, G729
and GSM furthermore buffer size such as 32kb, 64kb, 128kb
plus 256 kb. Various comparisons are conduced to fine the
value of various parameters.
3.1.2 Simulation Parameter Setup
VoIP in Fixed WiMAX network Base Station (BS) were
simulated with fifteen (15) mobile devices, where mobile
devices subscriber’s stations are place around each BS. All
BSs were connected to the IP back bone (internet) using

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point-to-point protocol (PPP) without any server BS. Basic
parameters associated with VoIP in WiMAX Configuration
attributes, application’s configuration, application profiles,
task’s definition, BSs and SSs for the model were configured
as show in figure 1.
Table 1. Subscriber Station Parameters
Parameter Value
Antenna Gain (dBi) -1 dBi
Type of SAP IP
Match Value Interactive Voice (6)
Server ice das s Name Gold
Max Transmission Power Adaptive
PHY Pro file 0.5 W
PHY Profile Type
Wireless OFDMA 20
MHZ
Multipatch Channel Mode OFDM
Patholoss Model
Vechicular
Emifonrnaits
Terrain Type Terrain Type A
Table 2. Base Station Parameters
Parameter Value
Antenna Gain (dBi) 15 dBi
Match Value Interactive Voice (6)
Server ice das s Name Gold
PHY Profile Type
Wireless OFDMA 20
MHZ
Perm Has e 3
4. Simulation results and Discussion
This paper investigates the performance of WiMAX network
using different quality of service (QoS) with are explained
below.
4.1.1 Quality of Service (QoS)
Quality of Service (QoS) represents the whole performance
of a WiMAX network, witness by the users of the network.
To evaluation the quality of service, various related aspects
of network service are often considered, for example error
rates, bandwidth, throughput, load, transmission delay,
availability, jitter etc.
4.1.2 Performance Parameters
The performance parameters are used to analyze simulation
with based on the simulation results; a comparison between
the effects of different codec G.711, G723, G729 and GSM
as well buffer size such as 32kb, 64kb, 128kb the last 256 kb
on QoS of VoIP. As stated earlier, three QoS measurements,
such as voice packet end to end delay (sec), voice packet jitter
(sec) and throughput (packet/sec).
Figure. 2 Delay (sec) under various audio codes
Average end to end delay metric is show in figure 5: G711
present the best performance with respect to the other codes.
Figure. 3 Jitter (sec) under various audio codes
Figure 3 describe the average voice jitter comparison using
different codecs. From graph, the jitter of G.711, G.723,
G.729 and GSM increased and become very close to zero.

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Figure. 4 Throughput (sec) under various audio codes
In figure 4, network scenarios indicated that G.729 scenario is
the best in traffic send and receive in comparison with other
scenarios.
Figure. 5 Delay (sec) under various buffer size
In figure 5, it is presented in average end to end delay metric
with various buffer size: 64 Kbits present the best
performance with respect to the other buffer size. While high
buffer size (128 kbits and 256 kbits) increased delay value.
Figure. 6 Jitter (sec) under various buffer size
The performance analysis is illustrated in figure 6. The
investigations present that buffer size 256 Kbits increased and
become much closed to zero.
Figure. 7 (sec) under various buffer size
The simulated voice throughput in figure 7, it is observed that
both 128 Kbits and 256 Kbits have same throughput at 400
(packet/sec) and this value is more than buffer size other
(32 Kbits and 64Kbits).
5. CONCLUSIONS
In this paper various performance of QoS such as Jitter, Delay
and Throughput, are analysed on VoIP codes and different
buffer size with the help of the observation obtained from
different codes and buffer size, it was found that as the no. Of
buffer size increases, the value of QoS parameters (Delay and
Throughput) also increases; an optimized value of QoS
parameter is obtained.

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6. ACKNOWLEDGMENTS
The authors are thankful to Department of Computer Science
and Engineering Thapar University. Special Thanks Professor
R.K. Sharma for suggestion and sweet sorghum for carrying
out this project.
7. REFERENCES
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of Quality of Service (QoS). In Proceeding of the IEEE.
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[4] Ade, M., Lee, Y.C. and Kasumawait, W,. L. 2010.
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