Qos improvements of voip in wifi networks
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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).

Qos improvements of voip in wifi networks

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

Qos improvements of voip in wifi networks

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

Qos improvements of voip in wifi networks

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

Qos improvements of voip in wifi networks

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

  • 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

  • Hardware:

    • Linksys Router

      • WRT54GS

    • Linksys PCI card

      • WMP54G (For Desktop AP).

  • Software:

    • MADWiFi (Atheros Chipset software/drivers)

Available tools

Available Tools

  • Interface Monitoring

    • Ethereal*

  • TCP/UDP Traffic Generators

    • Thrulay*

    • Iperf*

    • Netperf

  • VoIP Traffic Generators

    • RTP Tools

    • VoIP Generator

*Refers to programs chosen to be used



  • 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

  • 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)



  • Sends bulk TCP or UDP streams over network

  • Measures RTT, throughput, and jitter

Thrulay testing commands

Thrulay Testing Commands

  • 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)

Thrulay preliminary test

ThruLay: Preliminary Test

Parsing program for thrulay output

Parsing Program (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 2nd 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

  • 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

  • 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

  • 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

  • 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

Proposal itemized budget

Proposal: Itemized Budget

2 nd quarter soekris configurations testbed setup experimentation

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

Design approach

Design Approach

  • 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

Network setup for testing 802 11e

Network Setup for testing 802.11e



Synchronization software

Synchronization Software

  • 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

  • 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

Soekris 48262

Soekris 4826

  • Power LED, Activity LED, Error LED

Soekris 48263

Soekris 4826

  • 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 Mini PCI Card

  • SENAO EMP- 8602

Mini pci on soekris board

Mini PCI on Soekris Board

Installing fedora linux on soekris

Installing Fedora Linux on Soekris

  • 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)

  • 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?

  • 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

Edca parameters for 802 11e

EDCA Parameters for 802.11e

Network setup current

Network Setup: Current



Installation configurations


  • Soekris Installation

    • Debian PXEboot

  • Full installation of Fedora Linux

  • MADWiFi Installation

  • Server setups

    • DHCP

    • TFTP

    • NFS

    • PXEboot

  • Synchronization tool

Experimental results and analysis

Experimental Results and Analysis

Qos improvements of voip in wifi networks

Network Loading


Qos improvements of voip in wifi networks

Network Loading


Qos improvements of voip in wifi networks

Network Loading


Analysis 802 11

Analysis: 802.11

  • 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

  • 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

  • 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

  • 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

  • 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

  • Possible growth of major conglomerates

  • Convergence of technologies under one medium

  • Necessitates new companies with a focus on VoIP

Upcoming activities

Upcoming Activities

  • UROP

    • Finalize Soekris boxes

    • Further 802.11e testing

  • Make installation/

    configuration documentation globally available

Knowledge gained

Knowledge Gained

  • 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

  • http://www.donjohnii.com/wireless

    • Programs

    • Configuration guides

    • How-To



  • 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).



  • Ph.D. Student Advisor: Ala Khalifeh

  • Prof. Kevin Tsai

  • Prof. Henry P. Lee

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