COMPARATIVE PERFORMANCE STUDIES OF WI-FI IEEE

802.11 A,G LABORATORY POINT-TO-POINT LINKS

J. A. R. Pacheco de Carvalho

1,2

, P. A. Gomes

1,2

, H. Veiga

1,2

, C. F. Ribeiro Pacheco

, N. Marques

Centro de Informática,

U. de Det. Remota-Dept. de Física, Universidade da Beira Interior, 6201 Covilhã, Portugal

A. D. Reis

2,3

Dept. de Electrónica e Telecomunicações / Instituto de Telecomunicações, Universidade de Aveiro, 3810 Aveiro, Portugal

Keywords: WLAN, Wi-Fi, IEEE 802.11a, IEEE 802.11g, Point-to-Point Links, Wireless Network Laboratory

Performance Measurements.

Abstract: The importance of wireless communications has been growing. Performance is a very relevant issue,

leading to more reliable and efficient communications. Laboratory measurements are made about several

performance aspects of Wi-Fi (IEEE 802.11 a, g) point-to-point links. A contribution is given to

performance evaluation of this technology, using available access points from Enterasys Networks. Detailed

results are presented and discussed, namely at OSI levels 4 and 7, from TCP, UDP and FTP experiments:

TCP throughput, jitter, percentage datagram loss and FTP transfer rate. Conclusions are drawn about the

comparative performance of the links.

1 INTRODUCTION

Wireless communications are increasingly important

for their versatility, mobility and favourable prices.

It is the case of microwave based technologies, e.g.

Wi-Fi.

The importance and utilization of Wi-Fi have

been growing for complementing traditional wired

networks. Wi-Fi has been used both in ad hoc mode

and infrastructure mode. In this case an access point,

AP, is used to permit communications of Wi-Fi

devices with a wired based LAN through a

switch/router. In this way a WLAN, based on the

AP, is formed. Wi-Fi has reached the personal home,

forming a WPAN, allowing personal devices to

communicate. Point-to-point and point-to-multipoint

configurations are used both indoors and outdoors,

requiring specific directional and omnidirectional

antennas. Wi-Fi uses microwaves in the 2.4 and 5

GHz frequency bands and IEEE 802.11a, 802.11b

and 802.11g standards, contained in IEEE Std

802.11-2007. As the 2.4 GHz band becomes

increasingly used and interferences increase, the 5

GHz band has received considerable interest,

although absorption increases and ranges are shorter.

Nominal transfer rates up to 11 (802.11b) and 54

Mbps (802.11 a, g) are permitted. CSMA/CA is the

medium access control. Wireless communications,

wave propagation (Mark & Zhuang, 2003),

(Rappaport, 2002) and WLAN practical

implementations (Bruce & Gilster, 2002) have been

studied. Detailed information is available about the

802.11 architecture, including performance analysis

of the effective transfer rate. An optimum factor of

0.42 was presented for 11 Mbps point-to-point links

(Schwartz, 2005). Wi-Fi (802.11b) performance

measurements are available for crowded indoor

environments (Sarkar & Sowerby, 2006).

Performance has been a very important issue,

resulting in more reliable and efficient

communications. Telematic applications have

specific performance requirements, depending on

application. New telematic applications present

special sensitivities to performances, when

compared to traditional applications. Application

characterization and requirements have been

discussed for cases such as voice, Hi Fi audio, video

on demand, moving images, HDTV images, virtual

reality, interactive data, static images, intensive data,

supercomputation, electronic mail, and file transfer

(Monteiro & Boavida, 2000). E.g. requirements have

115

A. R. Pacheco de Carvalho J., A. Gomes P., Veiga H., F. Ribeiro Pacheco C., Marques N. and D. Reis A. (2009).

COMPARATIVE PERFORMANCE STUDIES OF WI-FI IEEE 802.11 A,G LABORATORY POINT-TO-POINT LINKS.

In Proceedings of the International Conference on Wireless Information Networks and Systems, pages 115-118

DOI: 10.5220/0002238601150118

 SciTePress

been quoted as: for video on demand/moving

images, 1-10 ms jitter and 1-10 Mbps throughput;

for Hi Fi stereo audio, jitter less than 1 ms and 0.1-1

Mbps throughputs.

Several performance measurements have been

made for 2.4 GHz Wi-Fi (Pacheco de Carvalho et

al., 2008a), as well as WiMAX and high speed FSO

(Pacheco de Carvalho et al., 2008b), (Pacheco de

Carvalho et al., 2008c). In the present work further

Wi-Fi (IEEE 802.11 a,g) results arise, through OSI

levels 4 and 7. Performance is evaluated in

laboratory measurements of point-to-point links

using available equipments.

The rest of the paper is structured as follows:

Chapter 2 presents the experimental details i.e. the

measurement setup and procedure. Results and

discussion are presented in Chapter 3. Conclusions

are drawn in Chapter 4.

2 EXPERIMENTAL DETAILS

The measurements used Enterays Networks RBT-

4102 level 2/3/4 access points, having IEEE 802.11

a/b/g transceivers based on the Atheros 5213A

chipset, internal dual band diversity antennas,

firmware version 1.1.51 (Enterasys Networks, 2006)

and 100-Base-TX/10-Base-T Allied Telesis AT-

8000S/16 level 2 switches (Allied Telesis, 2008).

The configuration of the access points was for

minimum transmitted power and equivalent to point-

to-point, LAN to LAN mode, using the internal

antennas. Interference free communication channels

were used in the communications. WEP encryption

was not activated. No power levels above the

minimum were required as the access points were

very close (30 cm).

The laboratory setup is shown in Figure 1. TCP

and UDP experiments at OSI level 4, were as

mentioned in (Pacheco de Carvalho et al., 2008c),

permitting network performance results to be

recorded. Both TCP and UDP are transport

protocols. TCP is connection-oriented. UDP is

connectionless, as it sends data without ever

establishing a connection. For a TCP connection,

TCP throughput was obtained. For a UDP

communication with a given bandwidth parameter,

UDP throughput, jitter and percentage loss of

datagrams were obtained. TCP packets and UDP

datagrams of 1470 bytes size were used. A window

size of 8 kbytes and a buffer size of the same value

were used for TCP and UDP, respectively. One PC,

with IP 192.168.0.2 was the Iperf server and the

other, with IP 192.168.0.6, was the Iperf client.

Jitter, which represents the smooth mean of

differences between consecutive transit times, was

continuously computed by the server, as specified by

RTP in RFC 1889. This scheme was also used for

FTP measurements, where FTP server and client

applications were installed in the PCs with IPs

192.168.0.2 and 192.168.0.6, respectively.

Batch command files were written to enable the

TCP, UDP and FTP tests. The results were obtained

in batch mode and written as data files to the client

PC disk.

3 RESULTS AND DISCUSSION

The access points were configured, for each standard

IEEE 802.11 a, g, with typical fixed transfer rates.

For every fixed transfer rate, data were obtained for

comparison of the laboratory performance of the

links, measured namely at OSI levels 4 and 7 using

the setup of Figure 1. For each standard and every

nominal fixed transfer rate, an average TCP

throughput was determined. This value was used as

the bandwidth parameter for every corresponding

UDP test, giving average jitter and average

percentage datagram loss. The main results are

shown in Figures 3-6. In Figure 2, polynomial fits

were made to the TCP throughput data. It is seen

that the best TCP throughputs are for 802.11a. The

average values are 13.9 and 10.0 Mbps for 802.11a

and 802.11g, respectively. In Figures 4 and 5, the

data points representing jitter and percentage

datagram loss were joined by smoothed lines. In

Figure 3, the jitter data show some fluctuations

which are generally within the error bar sizes , being

on average lower for IEEE 802.11a (1.3 ms) than for

802.11g (2.3 ms). Figure 4 shows that, generally, the

percentage datagram loss data (1.3 % on average)

agree reasonably well for both standards.

At OSI level 7 we measured FTP transfer rates

versus nominal transfer rates configured in the

access points for the IEEE 802.11a, g standards.

Every measurement was the average for a single

FTP transfer, using a binary file size of 100 Mbytes.

The results thus obtained are represented in Figure 5.

Polynomial fits to data were made for the

implementation of each standard. It was found that

the best FTP performance was for 802.11a. FTP

results agree with the trends found for TCP

throughput.

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Figure 1: Laboratory setup scheme.

Figure 2: TCP throughput versus technology and nominal

transfer rate.

Figure 3: UDP – jitter results versus technology and

nominal transfer rate.

Figure 4: UDP – percentage datagram loss results versus

technology and nominal transfer rate.

Figure 5: FTP transfer rates versus technology and

nominal transfer rate.

4 CONCLUSIONS

In the present work a simple laboratory setup was

planned that permitted systematic performance

measurements of available access point equipments

(RBT-4102 from Enterasys) for Wi-Fi (IEEE

802.11a, g) in point-to-point links. Through OSI

level 4, TCP throughput, jitter and percentage

datagram loss were measured and compared for each

standard. The best TCP throughput and average jitter

were found for 802.11a. For the percentage

datagram loss, a reasonably good agreement was

found for both standards. At OSI level 7, the best

FTP performance was for 802.11a. FTP results agree

with the trends found for TCP throughput.

Additional performance measurements either started

COMPARATIVE PERFORMANCE STUDIES OF WI-FI IEEE 802.11 A,G LABORATORY POINT-TO-POINT LINKS

117

or are planned using several equipments, not only in

laboratory but also in outdoor environments

involving, mainly, medium range links.

ACKNOWLEDGEMENTS

Supports from Universidade da Beira Interior and

FCT (Fundação para a Ciência e a

Tecnologia)/POCI2010 (Programa Operacional

Ciência e Inovação) are acknowledged. We

acknowledge Enterasys Networks for their

availability.

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