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QoS Improvements of VoIP in WiFi Networks. Undergraduate Students: Chris Higgins, Linda Tran Ph.D. Student Advisor: Ala Khalifeh Faculty Advisors: Prof. Kevin Tsai, Prof. Henry Lee. Summary. Introduction: VoIP/VoWLAN, 802.11, 802.11e

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Qos improvements of voip in wifi networks

QoS Improvements of VoIP in WiFi Networks

Undergraduate Students: Chris Higgins, Linda Tran

Ph.D. Student Advisor: Ala Khalifeh

Faculty Advisors: Prof. Kevin Tsai, Prof. Henry Lee


  • Introduction: VoIP/VoWLAN, 802.11, 802.11e

  • 1st Quarter: Linux, MADWiFi, testing tools, design, building knowledge base

  • 2nd Quarter: Soekris, Configurations, Testbed setup

  • Results: Knowledge, future goals, direction


  • To study and improve the QoS (Quality of Service) performance of Voice over IP (VoIP) traffic in Wireless Local Area Networks (WLAN).

VoIP* in the WLAN* (VoWLAN)


  • -Wireless Access Point (AP)

  • -Network Devices

    • Computers

    • Scanners

    • Printers

    • Blackberries

    • Etc.

*VoIP: Voice Over IP

*WLAN: Wireless Local Area Network


  • Integration of VoIP with WLAN (VoWLAN)

    • Benefits

      • Cost-effectiveness

      • Mobility

      • Use already available “common infrastructure” (Lin et al. 1)

    • Problems

      • Limited Distribution Coordination Function (DCF) and Point Coordination Function (PCF) in 802.11 WLAN systems impacting VoIP traffic

      • High packet loss and delays (jitter and end-to-end)

      • Tradeoff between security protocols and delays

802.11 Protocol Architecture

  • -Unbiased distribution of resources between Access Class (AC) Parameters:

    • Voice

    • Video

    • Background

    • Best Effort

  • PCF: Point Coordination Function (Initial provision for priority traffic, unimplemented in legacy 802.11 hardware)

  • DCF: Distributed Coordination Function (Global scheme for traffic resource sharing in legacy routers)

802 11

  • DCF and PCF operates on a “listen-before-talk scheme” (Mangold 1) known as CSMA/CA

  • Wait a fixed amount of time before sending, according to the DCF/PCF interframe space (DIFS/PIFS)

  • Ready to Send (RTS) and Clear to Send (CTS) phase, where the access point and endpoint basically have a small exchange that reserves the medium for use

802 11e 802 11 enhancements
802.11e (802.11 Enhancements)

  • Uses Hybrid Coordination Function (HCF), a combination of DCF and PCF.

  • Contention-based channel access known as Enhanced Distributed Channel Access (EDCA) is located in the CP

  • Controlled channel access known as HCF Controlled Channel Access (HCCA) encompasses both the CP and CFP

  • Direct Link Protocol (DLP) which allows two computers in a Basic Service Set (BSS) to directly communicate and avoid network loading

802.11e: QoS Support Standard

(Current IEEE Draft)


  • Voice (VO)

  • Video (VI)

  • Best Effort (BE)

  • Background (BK)

*DIFS: DCF Interframe Space

*AIFS|AC: Arbitration Interframe Space

Parameters being measured
Parameters Being Measured

  • Packet loss: arriving packets or already-queued packets dropped (Kuros, 19)

  • Jitter: variability of packet delays within the same packet stream (570)

  • End to end delay: delay from source to destination (43)

1 st quarter linux madwifi testing tools design building knowledge base

1st Quarter: Linux, MADWiFi, Testing Tools, Design, Building Knowledge Base

Operating system
Operating System

  • Linux

    • Fedora Red Hat – Core 5 (2.6.18-1.2200.fc5)

      • x84_64: 64 bit architecture

      • i386: 32 bit architecture

Linux kernel device driver for Atheros-based Wireless LAN devices

Operational modes: station, ap, ad-hoc, monitor, and wireless distribution station

Allows modification of EDCA parameters (follows the WMM-WiFi Multimedia standard)

Preliminary testbed setup
Preliminary Testbed Setup devices

  • Two laptop dual-boot PCs

  • Equipped with Windows XP and Fedora Core 5 (2.6.18-1.2200)

  • Currently Ethernet cable enabled network to test program functionality

Wireless connections
Wireless Connections devices

  • Hardware:

    • Linksys Router

      • WRT54GS

    • Linksys PCI card

      • WMP54G (For Desktop AP).

  • Software:

    • MADWiFi (Atheros Chipset software/drivers)

Available tools
Available Tools devices

  • Interface Monitoring

    • Ethereal*

  • TCP/UDP Traffic Generators

    • Thrulay*

    • Iperf*

    • Netperf

  • VoIP Traffic Generators

    • RTP Tools

    • VoIP Generator

*Refers to programs chosen to be used

Iperf devices

  • It measures UDP and TCP bandwidth performance

  • Reports bandwidth, delay jitter, datagram loss.

  • Can be run in bi-directional mode

Iperf testing commands
Iperf Testing Commands devices

  • Server Side:

    • Iperf –s -u –i 60 (s = server, u = UDP)

  • Client Side:

    • Iperf –u -c 192.168.1.X –t 1000 -i 60 –b <1..2000> (c = client, u = UDP, t = test time, b = bandwidth)

Thrulay devices

  • Sends bulk TCP or UDP streams over network

  • Measures RTT, throughput, and jitter

Thrulay testing commands
Thrulay Testing Commands devices

  • Server Side:

    • Thrulayd

      • must locate and be in the “thruldayd” folder.

      • find –iname thrulayd (in root ‘/’ folder)

      • ‘cd’ into that directory

      • Execute ‘./thrulayd’

      • No confirmation screen will pop up, it will be implied the server is running.

  • Client Side:

    • Thrulay –t60 –l40 <host I.P.> (t = test time, l = packetsize)

Parsing program for thrulay output
Parsing Program devices (For ThruLay Output)

use strict;

use Spreadsheet::WriteExcel;

my ($inFile, $outFile) = @ARGV;

if ((!defined $inFile)||(!defined $outFile))


print "ERROR... USAGE -> grep.pl <infile> <outfile>\n";



open (INI, "<$inFile")|| die "ERROR... Unable to open '$inFile' for reading.\n";

$outFile =~ s/\..*//;

$outFile .= ".xls";

my $Book = Spreadsheet::WriteExcel->new("$outFile");

my @times = scalar gmtime();

my($day, $month, $year) = (gmtime())[3,4,5];

my $Sheet = $Book->add_worksheet(($month+1) . '-' . ($day+1) . '-' . ($year+1900));

my $line = 1;

my @heading = ("ID", "Begin, s", "End, s", "Mb/s", "RTT delay, ms", "Jitter");


while (<INI>)


my $in = $_;

$in =~ s/\s+//;

if ($in =~ /^[\[|\#].*/)




my @words = split (/\s\s+/, $in);




$Book->close() or die "Error closing file: $!";

Goals to accomplish for 2 nd qtr
Goals to Accomplish for 2 devices nd Qtr.

  • Synchronization between computers (Using NTP and correction script)

  • Create a more aggressive 802.11 based software application to transport VoWLAN packets, effectively meeting a certain QoS standard

  • Create a standardized testbed for testing.

  • (UROP Proposal) Create a stable 802.11e based testbed for VoWLAN trafficking

  • Solidify Tools and Metrics

1 synchronization between computers
1. Synchronization between computers devices

  • Use NTP (Network Time Protocol) for initial time adjustments (multiple millisecond accuracy)

  • Create Synchronization Software for precise time measurements (microsecond precision)

2 802 11 based software upgrade for voip
2. 802.11 Based Software Upgrade for VoIP devices

  • Create a more aggressive transportation protocol for VoWLAN applications

  • Duplication algorithms could provide necessary WLAN availability where current TCP/UDP transportation dominates

3 testbed planned
3. Testbed: Planned devices

  • Desktop PC acting as an 802.11e based “access point”

  • Multiple PC-embedded boards with Linux platforms based on the Soekris net4826 acting as client stations

  • Atheros Chipsets/Wireless Cards

  • MADWiFi Enabled Wireless Drivers

  • Linux Kernel

4 proposal budget justification
4. Proposal: Budget Justification devices

  • The need to simulate real VoWLAN networks

  • Individual endpoints (Soekris boards) are necessary for the test bed of this project

  • Real life simulation of packet collision and router allocation is necessary to test fabricated protocols and allocation guidelines

2 nd quarter soekris configurations testbed setup experimentation

2 devices nd Quarter: Soekris, Configurations, Testbed Setup, Experimentation

Design approach
Design Approach devices

  • Phase 1: Initial Network Setup

    • Expected availability of MADWiFi

    • Planned EDCA parameters (802.11e setup)

  • Phase 2: Final Network Setup

    • Unavailability in means of testing and manipulating 802.11e parameters

    • Based on EDCA parameters available

Synchronization software
Synchronization Software devices

  • Endpoint.pl accompies accessPoint.pl to complete the end to end network

    • It creates a file based on the IP address of the host (endpoint) computer and one for the AP

  • AccessPoint.pl, in turn, will send pings to various user-specified endpoints and receive pings from those endpoints.

  • Evaluate.pl must be used to compute the delays/synchronization differences from both the access point and end point log files.

Soekris 4826
Soekris 4826 devices

  • Compact, low power, low cost computer

  • Specifications

    • 266 Mhz AMD Geode SC1100

    • 256 Mbyte SDRAM, soldered on board

    • 4 Mbit BIOS/BOOT Flash

    • Board size 4.0" x 5.2"

  • Software

    • comBIOS for operation over serial port

    • PXE boot rom for diskless booting

Soekris 48261
Soekris 4826 devices

Soekris 48262
Soekris 4826 devices

  • Power LED, Activity LED, Error LED

Soekris 48263
Soekris 4826 devices

  • 1 10/100 Mbit Ethernet ports, RJ-45

  • 1 Serial port, DB9.

802 11a g b wireless mini pci card
802.11a/g/b Wireless devices Mini PCI Card

  • SENAO EMP- 8602

Installing fedora linux on soekris
Installing Fedora Linux on Soekris devices

  • Mininimal linux installation on a spare system.

  • Configure system to run with only a serial console

  • Make it as small as possible, removing unneeded files.

  • Copy that system over to an NFS server

  • Configure a PXEboot configuration for the Soekris system, using the new tree as NFS root.

  • Boot the soekris over PXE

  • Partition the CF disk, and make a filesystem on it, then copy the FS from the NFS server to the CF disk.

  • Boot over PXE, but now using the CF disk as root.

  • Install the GRUB bootloader, and reboot from CF disk.

Edca parameters 802 11e
EDCA Parameters (802.11e) devices

  • CWmin: a random backoff time will be chosen between 0 and CWmin and added onto the interframe space

  • CWmax: maximum CW

  • AIFS (similar to DIFS/PIFS in 802.11): duration that medium must be idle before backoff countdown

  • TXOPlimit: time that a station can spend transmitting on the medium once it has won transmission opportunity

*Ng and Mal, 19

How can the parameters be adjusted to fully utilize 802 11e
How can the parameters be adjusted to fully utilize 802.11e? devices

  • Large TXOP can allow multiple packets at each station can be transmitted at every transmission opportunity (Malone et. al., 19)

    • ↑ TXOP (μs), ↑ throughput

  • ↑ AIFS, ↑ throughput

  • ↓ CWmin (smaller delay between transmission),

    ↑ throughput


Documentation devices

Installation configurations
Installation/Configurations devices

  • Soekris Installation

    • Debian PXEboot

  • Full installation of Fedora Linux

  • MADWiFi Installation

  • Server setups

    • DHCP

    • TFTP

    • NFS

    • PXEboot

  • Synchronization tool

Experimental results and analysis

Experimental devices Results and Analysis

Network Loading devices


Network Loading devices


Network Loading devices


Analysis 802 11
Analysis: 802.11 devices

  • Bandwidth: As the loading on the network increases, the available bandwidth for VoIP transportation decreases.

  • RTT: The round trip time has an inverse effect to the bandwidth. As the loading increases so does the RTT.

  • Jitter: Just like RTT, random jitter increases as more background traffic is added.

Analysis 802 11e
Analysis: 802.11e devices

  • Unlike 802.11, 802.11e should alleviate the adverse effects on the following variables for VoIP traffic.

  • Bandwidth: As the loading on the network increases, the available bandwidth for VoIP transportation should remain constant or only slightly suffer.

  • RTT: Even though the round trip time has an inverse effect to the bandwidth, in 802.11e RTT should minimally vary with the same test.

  • Jitter: Just like RTT, random jitter should only slightly increase with the progression of tests.

Future work
Future Work devices

  • Continued wireless testbed at UCI

  • Expand testbed to video testing

  • Increase real time protocols in wireless testing

  • Test various network design schemes

Socioeconomic issues
Socioeconomic Issues devices

  • Socioeconomic (economic repercussions resulting from social shifts)

    • As consumers turn toward VoIP-enabled technology (conglomerate Internet, telephone, TV, gaming), it is industry’s responsibility to aggressively keep up with those changes in order to maintain a stable domestic economy and employment rate.

      • Partnership between companies

      • Domestic technological research

Social aspect
Social Aspect devices

  • VoIP will allow ease of use, availability, increase performance, efficiency, and lower costs.

  • This will encourage acceptance of these new technologies.

  • Disadvantages: This will, however, necessitate new hardware in every aspect this affects.

Economical issues
Economical Issues devices

  • Possible growth of major conglomerates

  • Convergence of technologies under one medium

  • Necessitates new companies with a focus on VoIP

Upcoming activities
Upcoming Activities devices

  • UROP

    • Finalize Soekris boxes

    • Further 802.11e testing

  • Make installation/

    configuration documentation globally available

Knowledge gained
Knowledge Gained devices

  • Linux and its architecture

    • Fedora

    • MadWiFi

    • Debian

  • Wireless systems: 802.11, 802.11e

  • Servers: NFS, DHCP, TFTP, HTTP

  • PXEboot

  • Computer architecture

  • Network transportation (UDP, TCP, ICMP)

Project website
Project Website devices

  • http://www.donjohnii.com/wireless

    • Programs

    • Configuration guides

    • How-To

References devices

  • Arte Marketing, Inc. “Linksys WIP300”, www.voip-info.org/wiki/view/Linksys+WIP300. (February 21, 2007).

  • AT&T. “AT&T”, http://www.corp.att.com/presskit/voip/. (February 21, 2007).

  • California State Washington in St. Louis. “Wireless LANs”, http://www.cse.seas.wustl.edu/. (February 21, 2007).

  • Invocom. “Medium Access Control Protocols”, http://www.invocom.et.put.poznan.pl/~invocom/C/P1-4/p1-4_en/p1-4_8_1.htm. (February 21, 2007).

  • Leith, Douglas J., Malone, David, Ng, Anthony C.H. Ng. “Experimental Evaluation of TCP Performance and Fairness in an 802.11e test-bed.” SIGCOMM ’05 Workshops August. 2005: 17-22

  • Kurose, James F. and Ross, Keith W. Computer Networking: A Top-Down Approach Featuring the Internet. Pearson Education. Boston, MA. 2005

  • Mangold, Stefan. “Analysis of IEEE 802.11e for QoS Support in Wireless LANs.” IEEE Wireless Communications December. 2003: 40-50.

  • Ohrtman, Frank. Voice Over 802.11. Boston: Artech House, 2004.

  • Pan, Jianping, Pang, Ai-Chung, Yi-Bing Lin, and Shen, Xuemin. “Voice Over Wireless Local Area Network.” IEEE Wireless Communications February. 2006: 4-5.

  • Smile Design. “Smile Group”, http://www.smilejogja.com/. (February 21, 2007).

  • “VoIP Telephone”, http://www.logoandco.com/p/voip-telephone--iHox3AZVYOho.htm. (February 21, 2007).

Acknowledgements devices

  • Ph.D. Student Advisor: Ala Khalifeh

  • Prof. Kevin Tsai

  • Prof. Henry P. Lee