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Performance Evaluation Voice over WLAN Capacity in Three
Standards IEEE 802.11
Sarah Ali Abdullah1,
Affiliations
1Department Media Technology
and Communications
Engineering,
Engineering College,
Information Technology and
Communications University,
Baghdad, Iraq.
Correspondence
sarahaabdullah@uoits.edu.iq
Received
12-October-2023
Revised
20-November-2023
Accepted
28-November-2023
Doi:
10.31185/ejuow.Vol11.Iss3.488
:ةصخلا IP
LANVoWLAN
OPNET 14.5 ModellerVoIPWLAN
IEEE 802.11 WLANabg
VoWLAN IEEE 802.11g
WLAN.
1. INTRODUCTION
Since the early 1970s, the concept of Voice over Internet Protocol (VoIP) was widely discussed, and the idea and
technology were developed over time. However, this concept failed to find widespread acceptance and usage by
either side of users and telecommunication providers. This is largely due to the lack of infrastructure that can support
Internet Protocol (IP). At the time, circuit-switched calling was a far more dependable alternative, amplified by the
fact that early VoIP calls had rather poor quality. The rapid growth of internet technology by the 1990s, as well as
the World Wide Web, coupled with significant investments in the infrastructures of IP networks by businesses and
other stakeholders all led to VoIP becoming a valid replacement for earlier technologies and a viable option for
sending voice data over public switched telephone networks (PSTN) [1]. Over time, VoIP quickly rose to become
the most desired type of service for wired and infrastructure-based wireless networks of any size [2]. In Wireless
Local Area Networks (WLANs) computers are connected through a wireless connection to central devices such as
a Wireless router. To prioritize simple and best-effort communication, the IEEE 802.11 WLAN standard was
developed by the Institute of Electrical and Electronics Engineers (IEEE). The standard was first released in 1997
but has since gone through various iterations all keeping the same main goals [3].
Wasit Journal of Engineering Sciences
Journal homepage: https://ejuow.uowasit.edu.iq
Keywords: Wireless, VoIP, IEEE 802.11, Data rate, Codec types.
Abstract
In the modern landscape of telecommunication, wireless mobile connectivity
and migrating voice telephone services to IP technology are two of the most
prominent developments that are transforming the landscape. These two
concepts can be utilized together using networks which carry voice services
over wireless LAN (VoWLAN). However, due to the unique characteristics of
each, certain issues inevitably arise and must be handled to allow for successful
deployment. In this paper Dijlia university campus is simulated using OPNET
14.5 modeller carry out extensive simulation scenarios to examine the VoIP
capacity in a single cell WLAN in regards to three IEEE 802.11 WLAN
standards which are (a, b, and g) as well as applying different packet sizes, data
rates and codec types in VoWLAN scenarios. Depending on this evaluation,
selection IEEE 802.11g and decrease in the number of users consider the best
choice for transmission voices over WLAN in college.
Abdullah
Wasit Journal of Engineering Sciences 2023 11 (3) pg72
VoIP over WLAN (VoWLAN) refers to the use of wireless LANS to provide IP voice services, generally 802.11-
based (commonly known as voice over WIFI). A VoWLAN system’s process is to translate a Private Branch
Exchange (PBX) telephone call to IP packets, and then send these packets over an 802.11 WLAN [4]. VoWLAN
has been gaining traction as a type of infrastructure that can provide wireless voice services at a low cost. However,
the implementation of VoWLAN introduces several challenges due to the nature of wireless networks and
contention-based protocols [5].
In the modern wireless communication landscape, Voice over WLAN has grown to become an integral part of
business necessities. Allowing users to remain connected greatly improves a company or business in terms of
communication and collaboration, at the same time this allows them to maintain a high level of quality whilst the
user makes use of the WLAN [6]. In a global market that has been significantly changed post the COVID-19
pandemic, VoWLAN market growth was projected at approximately $35.2 Billion Dollars figure for the year 2022.
Furthermore, it is predicted to grow to $89.2 Billion Dollars by 2030, growing at a compound annual growth rate
of 12.3% over the of 2022 to 2030 covered by the analysis. Figure 1 shows the trend of independent VoWLAN
likely going up in upcoming years [7].
Fig.1. Market Forecasts for VoWLAN.
The expansion and widespread deployment of VoWLAN has proven to be an exceptionally challenging task for
many network experts and engineers. The most critical parts of a VoWLAN system are considered to be Voice
codec and IEEE 802.11. Due to this, accurate analytical models capable of capturing the characteristics of network
traffic are a vital part of maximizing the efficiency of data transfer in future network design. This paper order as
follows; introduce and background about the development of VoIP and VoWLAN first given in section 1. Then we
will discuss in section 3 the features of IEEE 802.11 WLAN architecture. In order to understand some inhibitors
and challenges in transfer voice over WLAN will be discussed in section 4. System model design and simulation
results are described and analysed in section 5. Finally, section 6, has concluded the whole work.
2. LITERATURE REVIEW
Several studies have investigated the voice services over WLAN performance and the utilization of different service
classes coupled with different network types. Researchers in [4], discussed the general issues arising from the use
of voice over WLAN, the research compared the functionality and features of 802.11 phones available in the market.
From testing VoWLAN new challenges were introduced such as greater latency when tests in which both nodes are
wireless and observed that there was a slight disruption in the sound when a handoff occurred for the node connected
to the wireless network during a call. Researchers when comparing the insecure and secure calls noticed that the
sound quality was the same as in both cases. Nattavut Smavatkul et al [8] on the other hand, examined the general
transmission of voice as well as isochronous traffic over an 802.11a WLAN, then compared the practical and
simulation-based methods of capacity estimation as well as studying the impact of traffic in the network on voice
capacity. A metrics-based analogue voice signal measurement was presented by Robert Blatnik et al [10] alongside
performance testing for Voice over WLAN 802.11a enabled equipment in academia, reasonably controlled RF
environment, automating of testing scenarios and improved synchronization of captured voice samples with several
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Wasit Journal of Engineering Sciences 2023 11 (3) pg73
thousand statistically analysed measurement, with experimental VQ test-beds results assured adequate qualification.
Sangho Shin et al, [11] also utilized a wireless IEEE 802.11b testbed to compute the VoIP traffic capacity and
contrast it with the capacity theoretically obtained via simulation. Capacity estimates for both the experimental and
simulated network were 15 calls for 64 kb/s CBR VoIP traffic and 38 calls for VBR VoIP traffic with a packetization
interval of 20ms and an activity ratio of 0.39 respectively. A quality of service management architecture that is
session-based was proposed by Badis Tebbani et al [12] to accommodate for the low capacity of VoIP calls in an
IEEE 802.11 wireless local area network as well as resolve the issues that occur when new calls are added to a
network that has reached its capacity. Several researchers have studied the throughput and traffic generation
parameters of an 802.11 wireless local area network [13] [14]. On the other hand, a performance model was
proposed by Nidhi Hegde et al [15] for voice over WLAN with distributed control. By using classical decoupling
arguments, the model allows for an analytical approach to evaluating the capacity of the network based on tuning
the protocol parameters. Ali M. Alsahlany [16], analysed the performance VoIP based integrated wireless
LAN/WAN and evaluated it based on different voice encoding schemes. The codes, G.711, G.729A, and G.723.1
were used for the comparison since they are the most suitable for improving QoS for VoIP. The results of the
evaluation suggested that G.729A produces the best results for VoIP. In research by Shreekant Gurrapu et al [17],
the performance of various VoIP codes was compared and studied in non-mobility scenarios by adjusting some
parameters and plotting the throughput, End-to-end Delay, MOS, Packet delivery Ratio, and Jitter graphs using
Network Simulator version. Ziyad Khalaf Farej et al. [18], evaluated the Quality of Service (QoS) application and
its effect on the performance of random topology WLAN using IEEE 802.11n, according to the results, a maximum
improvement of 86.4%, was shown for throughput, as well as 33.9% for delay, 52.2% for data drop and 68.9% for
retransmission attempts.
3. IEEE 802.11 WLAN ARCHITECTURE
In the field of network architecture, two categories have been defined for 802.11 WLAN standards: Infrastructure
and Ad hoc networks. The infrastructure networks aim to provide a communication medium between devices known
as the Basic Service Set (BSS), which are wireless clients, wired network resources, and an access point connecting
them. Via a distribution system, multiple BSSs can be connected to a backbone, wired or wireless, to support an
Extended Service Set (ESS). In comparison, the Ad hoc or point-to-point network achieves reciprocal
communication between wireless clients and is typically a spontaneous creation that does not allow access to wired
networks. This configuration, shown in Figure 2, is referred to as an Independent Basic Service Set (IBSS) [19]
[20]. IEEE employed various standards for the development of the 802.11 family which are (a, b, and g). IEEE
802.11a operates in the 5-GHz band i.e., at frequencies between 5,150 and 5,825 MHz, and at a speed of up to 54
Mbps. Although it is notably fast, its transmission range is limited to about 60% that of IEEE 802.11b by the higher
frequencies it utilizes. IEEE 802.11g operates in the 2.4-GHz band, similar to IEEE 802.11b and at 802.11a speeds.
[21] A full breakdown of the three standards is shown in Table 1.
Fig. 2. IEEE 802.11 network architecture.
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Wasit Journal of Engineering Sciences 2023 11 (3) pg74
Table 1. The standards used by IEEE for the advancement of the 802.11 family [10].
4. VOWLAN CHALLENGES
VoIP is expected to become a necessity for multi-hop wireless networks of future cities. However, the deployment
of VoIP service in wireless networks that cover large areas and consist of several hops comes with several
challenges. With VoIP calls occurring in a network consisting of multiple hops, interference can cause packet loss
and increased delay, which would greatly affect the VIP calls’ quality from beginning to end. Increased amounts of
traffic will increase the amount of medium conflict, which in turn leads to significantly higher packet loss compared
to there being only a single hop in the network [22].
In order to achieve high-quality conversational voice transmission, the desired end-to-end one-way delay is lower
than 150 milliseconds. Otherwise, the delay becomes noticeable to the average user. Several factors can contribute
to the one-way delay in VoIP connections. As such, a WLAN setup is only allowed to utilize a small portion of the
150-millisecond allocated for delay. In a representative Enterprise network, the delay in communications between
a wireless phone and an access point should not exceed 50 ms, the phone on the other hand must be able to roam in
under 50 ms from one access point to the other [23]. Due to several limitations, it is difficult to achieve widespread
implementation of VoWLAN in the enterprise. A traditional WLAN infrastructure approach will produce a few
inhibitors [24]:
• Extreme latency.
• Sensitivity to jitters.
• Limited coverage.
• Deployment of insecure services.
• Transmission degradation and missing packets.
• Lower call capacity.
• Voice and data convergence quality of service.
• Power consumption considerations.
5. VOWLAN SIMULATED SCENARIOS
In this research, the OPNET simulator was utilized for network modelling. OPNET which is developed by OPNET
Technologies is a certified communication system simulator [15]. In this paper, the maximum VoIP capacity in a
single-cell WLAN is evaluated for different standards, specifically a, b, and g. The goal is to examine the effect of
changing packet payload size (in terms of the number of frames) as well as the effect of changing the data rate for
each standard under acceptable QoS constraints in VoIP systems utilizing the G.711 voice codec.
5.1 Simulation Parameter
The VoIP application and profile parameters have the same value in the same subnet in wireless LAN network
attributes are shown in Table 2 and Table 3.
Table 2. Application Definition Window.
Parameter
Value
Silence length (sec)
Default
Talk spurt length (sec)
Default
Symbolic Destination Name
Voice Destination
Encoder Scheme
G.711
Voice Frames per Packet
1
Type of Service
Best Effort
Signaling
SIP
IEEE 802.11
Standard
Frequency Band
(GHz)
OTA estimates
(Mbps)
MAC SAP
estimate (Mbps)
a
5
54
25
b
2.4
11
5
g
2.4
54
25
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Wasit Journal of Engineering Sciences 2023 11 (3) pg75
Table 3. Profile Definition Window.
Parameter
Value
Profile Name
Profile
Start time Offset (sec)
Constant (0.0)
Duration (sec)
Exponential (120)
Number of repetitions
Unlimited
Repetition pattern
Serial
Duration (sec)
End of Simulation
Repeatability
Once at the start time
The wireless network will be connected to the Internet, which will be represented by (the IP32 cloud from the
Internet toolbox in the object palette) through a point-to-point link. Furthermore, an SIP (Session Initiation Protocol)
Server used to manage VoIP sessions will be connected to an IP cloud through a (PPP) link. The configuration of
this server and each mobile node that used the SIP protocol service is shown in Figure 3.
Fig. 3. SIP configuration
5.2 Simulated Projects
VoIP stations are configured to converse in pairs. In essence, this means each station is talking with exactly one
other station permanently. The caller (red) station is assigned by a VoIP profile station which is assigned by a VoIP
service as shown in Figure 4. The simulated projects are:
1. Simulation VoIP in Wireless Campus Network with Increased Number of Users:
This simulation provides a high-level overview of a generalized network topology. In this setting, a campus network
is configured to represent a simplistic proposed model for Dijlah University in the Al-Sydea campus in Baghdad-
Iraq. The simulated network is built to connect one main building with the aim of achieving cost-effective data and
voice communication. The network is comprised of 10 subnets for each department in the college (Computer
sciences, Building and construction engineering, Business administration, Computer techniques, Law, Finance and
Banking, Optics techniques, medical, analysis, and media). Each subnet contains one WLAN cell of IEEE 802.11g
standard. These subnets are connected to a main switch using a 1000 base duplex link of 1Gbps Ethernet connection,
then to a firewall device using 10Gbps Ethernet connections, and lastly to the IP cloud through a router as shown in
Figure 5. There is also an SIP server used to manage VoIP sessions. These sessions are created as peer-to-peer calls
between two nodes in different subnets. The networks are tested for two cases: First, when 6 mobile nodes
(minimum number of customers in each room department in college) are connected at each cell, and second, when
the number of nodes is increased to 12 (maximum number of customers in each room in each department in college).
This is done on the G.711 codec for one-voice frames per packet and assumes there is another application in the
network.
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Fig. 4. Dijlah campus network for 10 department (proposed design).
Fig. 5. Dijlah campus network with an increase in the number of users.
2. Simulation VoIP in Wireless Campus Network Compare between WLAN Standards (a, b, g)
This simulation uses different standards in WLAN cells and provides a comparison among them. The first is a
WLAN (IEEE 802.11a) standard that is capable of supporting data rates up to 54Mbps. All mobile nodes in this
cell have their physical characteristics assigned as OFDM (802.11a) as shown in Table 4.
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Table. 4. WLAN parameters using 802.11a standard.
Parameter
Value
BSS Identifier
1
Physical characteristic
OFDM (802.11a)
Data Rate
54 Mbps
Access Point Functionality
Enable
Roaming Capability
Disable
Transmit Power
0.005 W
Power Threshold
-95 db
Short Retry Limit
7
Long Retry Limit
4
The second scenario is using WLAN IEEE 802.11b which can support data rate up to 11Mbps, a scenario is
conducted to evaluate the effect of call capacity for this data rate. All mobile nodes in this cell have the
physical characteristics assigned as a direct sequence according to 802.11b physical layer characteristics as
shown in Table 5. Table 5. WLAN parameters using 802.11b standard.
Parameter
Value
BSS Identifier
1
Physical characteristic
Direct Sequence
Data Rate
11 Mbps
Access Point Functionality
Enable
Roaming Capability
Disable
Transmit Power
0.005 W
Power Threshold
-95 db
Short Retry Limit
7
Long Retry Limit
4
The third scenario uses the IEEE 802.11g standard which extends the 802.11b standard data rate up to
54Mbps. In this scenario, the project is implemented with the same settings as the WLAN project. All mobile
nodes in this cell have the physical characteristics assigned as extended rate PHY (802.11g) as shown in
Table 6. Table 6. WLAN parameters using 802.11g standard.
Parameter
Value
BSS Identifier
1
Physical characteristic
Extended Rate PHY (802.11g)
Data Rate
54 Mbps
Access Point Functionality
Enable
Roaming Capability
Disable
Transmit Power
0.005 W
Power Threshold
-95 db
Short Retry Limit
7
Long Retry Limit
4
5.3 Simulation Results
The results of the simulated projects were plotted using OPNET. OPNET can demonstrate two types of statistics as
results: Global and Object Statistics. Global statistics represent results collectively gathered from all nodes in a
network; meanwhile, object statistics are collected from the discrete nodes in the network.
1. Simulation VoIP in Wireless Campus Network with Increased Number of User Results:
The first global statistics performance metric used to quantify voice services over WLAN is the delay variation
(Jitter). This is done on a different number of WIFI SS nodes as shown in Figure 6. In this scenario, the same
distances for all WIFI SS nodes are kept 50 meters away from the AP. Within the same office, the number of WIFI
users is increased from 6 to 12 users. The packets arrive at a different time, resulting in a notable voice jitter, which
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makes it difficult to understand. Increasing the number of users accessing the same AP, increases the end-to-end
delay and the packet delay variation for voice service.
Fig. 6. The delay-variation (Jitter).
As well as the rate of traffic received (packet/sec) in both global and object statistics are shown in figures 7 and 8
represent the average number of packets per second forwarded to all voice application nodes in the same department
by the transport layer in the network. When increased number of users time of the packet arrived increased.
Fig.7. traffic received P/S.
Packet Delay Variation
Time
Traffic Received (packet/sec)
Time
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Fig.8. Traffic Received P/S in Each Subnet.
The WLAN throughput, measured by bit/sec represents the total number of bits forwarded from WLAN layers to
the higher layer per second in all the network’s WLAN nodes. The WLAN router (AP) buffer size is 1024000 bits.
As the number of users increases, the number of bits received at the WLAN router increases, and the buffer quickly
overflows which leads to an increase in data dropped. In addition, the average IP traffic drop and throughput increase
approximately in the same order as the number of users increases. Figure 9 and 10 shows the WLAN throughput
results for both global and object statistics in each department in the college with the increased number of the user.
Fig.9. WLAN Throughput (bit/sec).
Time
Time
Traffic Received (packet/sec)
Throughput (bit/sec)
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Fig. 10. WLAN Throughput (bit/sec) in each subnet.
The total end-to-end delay of all data packets successfully received by the WLAN MAC and forwarded to the higher
layer is represented by Wireless LAN delay as shown in Figure 11 called analogue-to-analogue or mouth-to-ear de-
lay with the increased number of users showing the bad quality of speech.
Fig. 11. The wireless LAN delay in (sec).
2. Simulation VoIP in Wireless Campus Network Compare between WLAN Standards (a, b, g) Results:
In these scenarios, results are collected in global statistics only for three projects to find the max VoIP capacity in
three IEEE 802.11 WLAN standards (b, a, g). According to these campus models. Figure 12 shows the traffic
received by the VoIP application for three IEEE 802.11 WLAN standards (b, a, g) and data rate changes in Mbps.
The traffic received by the network with IEEE 802.11b (11 Mbps) shows less deviation from the comparative traffic
received with IEEE 802.11a (54 Mpbs) and IEEE 802.11g (54 Mpbs). Based on the analysis it can be observed that
the noise added in IEEE 802.11g networks is lower compared to the other network setups. As such this standard is
considered more efficient.
Time
Time
Throughput (bit/sec)
Delay (sec)
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Fig.12. traffic received P/S IEEE802.11 (A, B, and G).
Figure 13 shows that in the category of End-to-End delay, the max value of this parameter when comparing
the three IEEE 802.11 WLAN standards (b, a, g) shows that IEEE (802.11 a, g) presents the best performance
with respect to other setups. These results are a consequence of a lower transfer rate and packet size in AP.
On the other hand, the transfer rate and packet size significantly increased the end-to-end delay.
Fig. 13. VoIP End-to-End delays For IEEE 802.11 (A, B and G)
6. CONCLUSIONS
In this paper, several findings can be concluded from the system test of the modified scheme applied in a wireless
campus network. The simulated results showed that the VoIP service deployed will affect the performance of
the application when the number of users increases and the overall WIFI link performance degrades.
Furthermore, the WLAN single-cell VoIP capacity has been examined for three WLAN standards (a, b, and g) by
means of using different data rates. It was shown for each data rate. Cells of IEEE 802.11a and IEEE 802.11g
standards provide the max VoIP capacity compared to IEEE 802.11b standard since it provides up to 54Mbps data
rate, while the max data rate for IEEE 802.11b standard is 11Mbps. The IEEE 802.11g standard is considered
preferable to the IEEE 802.11a standard since it operates in the 2.4 GHz (ISM band), which is compatible with the
b-standard that operates in the same band. As well as being supported by most vendors.
Time
Time
Time
Time
Traffic Received (packet/sec)
Delay (sec)
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