A CONTRIBUTION TO LABORATORY PERFORMANCE

MEASUREMENTS OF IEEE 802.11 B,G WEP

POINT-TO-POINT LINKS

J. A. R. Pacheco de Carvalho

1,2

, H. Veiga

1,3

, N. Marques

1,3

, C. F. Ribeiro Pacheco

U. de Detecção Remota,

Dept. de Física,

Centro de Informática

Universidade da Beira Interior, 6201 Covilhã, Portugal

A. D. Reis

1,2,4

Dept. de Electrónica e Telecomunicações, Instituto de Telecomunicações

Universidade de Aveiro, 3810 Aveiro, Portugal

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

Performance.

Abstract: Wireless communications using microwaves are increasingly important, e.g. Wi-Fi. Performance is a

fundamental issue, resulting in more reliable and efficient communications. Laboratory measurements are

made about several performance aspects of Wi-Fi (IEEE 802.11b, g) WEP point-to-point links using

available access points from Enterasys Networks (RBTR2). Through OSI levels 4 and 7, detailed results are

presented and discussed from TCP, UDP and FTP experiments, namely: TCP throughput, jitter, percentage

datagram loss and FTP transfer rate. Conclusions are drawn about link performance.

1 INTRODUCTION

Wireless communications are becoming increasingly

important for their versatility, mobility, speed and

favourable prices. It is the case of microwave and

laser based technologies, e.g. Wi-Fi and FSO,

respectively. 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 equipments with a wired based LAN through a

switch/router. Therefore a WLAN, based on the AP,

is formed. Wi-Fi has had an increasing presence in

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 specialized

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

(IEEE Std 802.11-2007). Due to increasing used of

2.4 GHz band, 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 specified. 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, where 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 fundamentally

important issue, giving more reliable and efficient

communications. New telematic applications are

specially sensitive to performances, when compared

to traditional applications. Application

characterization and requirements have been

discussed for several cases such as voice, Hi Fi

audio, video on demand, moving images, HDTV

images, virtual reality, interactive data, static

165

A. R. Pacheco de Carvalho J., Veiga H., Marques N., Ribeiro Pacheco C. and D. Reis A. (2010).

A CONTRIBUTION TO LABORATORY PERFORMANCE MEASUREMENTS OF IEEE 802.11 B,G WEP POINT-TO-POINT LINKS.

In Proceedings of the International Conference on Wireless Information Networks and Systems, pages 165-168

DOI: 10.5220/0003031501650168

 SciTePress

images, intensive data, supercomputation, electronic

mail, and file transfer (Monteiro & Boavida, 2002).

E.g. requirements have been given for video on

demand/moving images (1-10 ms jitter and 1-10

Mbps throughputs) and for Hi Fi stereo audio (jitter

less than 1 ms and 0.1-1 Mbps throughputs).

Wi-Fi microwave radio signals can be easily

captured by everyone. WEP was initially intended to

provide confidentiality comparable to that of a

traditional wired network. In spite of its weaknesses,

WEP is still widely used in Wi-Fi communications

for security reasons. A shared key for data

encryption is involved. In WEP, the communicating

devices use the same key to encrypt and decrypt

radio signals.

Several performance measurements have been

made for open Wi-Fi (Pacheco de Carvalho et al.,

2008a, 2009a, 2009b), as well as WiMAX and very

high speed FSO (Pacheco de Carvalho et al., 2008b,

2008c). In the present work further Wi-Fi (IEEE

802.11 b,g) results arise, using WEP, through OSI

levels 4 and 7. There is interest in comparing two

technologies working in the 2.4 GHz bands, using

WEP in the same AP equipments. Performance is

evaluated in laboratory measurements of WEP

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

In the measurements we used (Fig. 1) Enterasys

Networks RBTR2 level 2/3/4 access points

(Enterasys, 2005), equipped with IEEE 802.11 a/b/g

radio cards similar to the Agere-Systems model

0118 type, and firmware version 6.08.03, 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 i.e. micro cell, point-to-point,

LAN to LAN mode, using the antenna which was

built in the card. Interference free communication

channels were used in the communications. WEP

encryption was activated, using 128 bit encryption

and a shared key for data encryption composed of 13

ASCII characters. No power levels above the

minimum were required, as the access points were

very close.

A laboratory setup arrangement was planned and

implemented, as shown in Fig. 2. 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.

The PCs were portable computers running

Windows XP. They were configured to maximize

the resources allocated to the present work. Also,

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. Each PC had a second network adapter, to

permit remote control from the oficial IP University

network, via switch.

3 RESULTS AND DISCUSSION

The RBT-4102 access points were configured, for

each standard IEEE 802.11 b, g, with typical fixed

transfer rates (1, 2, 5.5 and 11 Mbps for 802.11b; 6,

9, 12, 18, 24, 36, 48, 54 Mbps for 802.11g). For

every fixed transfer rate, data were obtained for

comparison of the laboratory performance of the

links, measured namely at OSI levels 1, 4 and 7

using the setup of Fig. 2. 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 Figs. 3-6. At OSI level 1, SNR was

monitored.

In Fig. 3, polynomial fits were made to the TCP

throughput data, where R

is the coefficient of

determination. It is seen that the best TCP

throughputs are for 802.11g. The average values are

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2.42 and 12,61 Mbps for 802.11b and 802.11g,

respectively. In Figs. 4 and 5, the data points

representing jitter and percentage datagram loss

were joined by smoothed lines. In Fig. 4, the jitter

data are on average slightly higher (1.8+-0.1 ms ) for

802.11g than for 802.11b (1.6+-0.1 ms). Fig. 5

shows that, generally, the percentage datagram loss

data (1.2+-0.1 % 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 802.11b, 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 Fig. 6.

Polynomial fits to data were made for the

implementation of each standard. It was found that

the best FTP performance was for 802.11g. These

results show the same trends found for TCP

throughput. FTP transfer rates were also measured

without WEP activation.

Generally, the results measured for WEP links at

OSI levels 4 and 7 agree reasonably well, within the

experimental errors, with corresponding data

obtained for open links.

Figure 1: Switch (A) (http://www.enterasys.com) and

access point (B) (http://www.alliedtelesis.com).



Figure 2: Laboratory setup scheme.

Figure 3: TCP throughput versus technology and nominal

transfer rate.

Figure 4: UDP – jitter results versus technology and

nominal transfer rate.

Figure 5: UDP – percentage datagram loss results versus

technology and nominal transfer rate.

Figure 6: FTP transfer rates versus technology and

nominal transfer rate.

A CONTRIBUTION TO LABORATORY PERFORMANCE MEASUREMENTS OF IEEE 802.11 B,G WEP

POINT-TO-POINT LINKS

167

4 CONCLUSIONS

In the present work a laboratory setup arrangement

was planned and implemented, that permitted

systematic performance measurements of available

access point equipments (RBTR2 from Enterasys)

for Wi-Fi (IEEE 802.11b, g) in WEP 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 was found for 802.11g. The jitter data

are on average slightly higher for 802.11g than for

802.11b. Generally, the percentage datagram loss

data agree reasonably well for both standards.

At OSI level 7, the best FTP performance was

for 802.11g. This result shows the same trends found

for TCP throughput.

Generally, the results measured for WEP links

agree reasonably well, within the experimental

errors, with corresponding data obtained for open

links.

Additional performance measurements either are

under way or are planned using several equipments

to permit several comparisons, not only in laboratory

but also in outdoor environments involving, mainly,

medium range links.

ACKNOWLEDGEMENTS

Supports from University of 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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