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

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Summary

• 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

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Motivation

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

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VoIP in the WLAN (VoWLAN)
Applications

• -Wireless Access Point (AP)
• -Network Devices
• Computers
• Scanners
• Printers
• Blackberries
• Etc.

VoIP Voice Over IP WLAN Wireless Local Area
Network
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Background

• 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

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802.11 Protocol Architecture

• -Unbiased distribution of resources between
  Access Class (AC) Parameters
• Voice
• Video
• Background
• Best Effort

1. PCF Point Coordination Function (Initial
   provision for priority traffic, unimplemented in
   legacy 802.11 hardware)
2. DCF Distributed Coordination Function (Global
   scheme for traffic resource sharing in legacy
   routers)

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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

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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

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802.11e QoS Support Standard
(Current IEEE Draft)
AC

1. Voice (VO)
2. Video (VI)
3. Best Effort (BE)
4. Background (BK)

DIFS DCF Interframe Space AIFSAC Arbitration
Interframe Space
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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)

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

• Linux
• Fedora Red Hat Core 5 (2.6.18-1.2200.fc5)
• x84_64 64 bit architecture
• i386 32 bit architecture

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• 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)

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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

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Wireless Connections

• Hardware
• Linksys Router
• WRT54GS
• Linksys PCI card
• WMP54G (For Desktop AP).
• Software
• MADWiFi (Atheros Chipset software/drivers)

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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
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Iperf

• It measures UDP and TCP bandwidth performance
• Reports bandwidth, delay jitter, datagram loss.
• Can be run in bi-directional mode

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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
  lt1..2000gt (c client, u UDP, t test time, b
  bandwidth)

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Thrulay

• Sends bulk TCP or UDP streams over network
• Measures RTT, throughput, and jitter

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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 lthost I.P.gt (t test time, l
  packetsize)

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ThruLay Preliminary Test
ID Begin, s End, s Throughput (Mb/s) RTT delay, ms Jitter
( 0) 0 1 93.313 19.173 4.001
( 0) 1 2 93.318 17.833 5.629
( 0) 2 3 94.366 17.197 5.624
( 0) 3 4 93.841 16.195 5.614
( 0) 4 5 94.362 21.049 5.596
( 0) 5 6 93.318 21.116 5.59
( 0) 6 7 94.368 16.561 5.52
( 0) 7 8.001 93.318 16.103 5.603
( 0) 8.001 9 94.395 16.125 5.524
( 0) 9 10.001 94.331 16.069 5.517
( 0) 10.001 11.001 93.849 16.085 3.999
( 0) 11.001 12.001 93.317 20.001 4
( 0) 12.001 13.001 94.366 16.358 4
( 0) 13.001 14.001 93.842 20.001 4
( 0) 14.001 15.001 94.366 16.982 4
( 0) 15.001 16.001 93.317 16.015 4
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Parsing Program (For ThruLay Output)

• use strict
• use SpreadsheetWriteExcel
• my (inFile, outFile) _at_ARGV
• if ((!defined inFile)(!defined outFile))
• print "ERROR... USAGE -gt grep.pl ltinfilegt
  ltoutfilegt\n"
• exit
• open (INI, "ltinFile") die "ERROR... Unable to
  open 'inFile' for reading.\n"
• outFile s/\..//
• outFile . ".xls"
• my Book SpreadsheetWriteExcel-gtnew("outFile"
  )
• my _at_times scalar gmtime()
• my(day, month, year) (gmtime())3,4,5
• my Sheet Book-gtadd_worksheet((month1) . '-'
  . (day1) . '-' . (year1900))

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Goals to Accomplish for 2nd Qtr.

1. Synchronization between computers (Using NTP and
   correction script)
2. Create a more aggressive 802.11 based software
   application to transport VoWLAN packets,
   effectively meeting a certain QoS standard
3. Create a standardized testbed for testing.
4. (UROP Proposal) Create a stable 802.11e based
   testbed for VoWLAN trafficking
5. Solidify Tools and Metrics

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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)

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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

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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 2.6.8.1 Kernel

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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

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Proposal Itemized Budget
Item Price Qty Total
Soekris net4826-50 Board and Case Tax Shipping 224 7 1568
Power Supply, 12V, 1.5A, US/Canada 110V, Small Switch Mode, for all boards. Tax Shipping 14 7 98
ATHEROS WI-FI MINI-PCI WIRELESS 802.11G Tax Shipping 44 7 308
Null Modem Cable Shipping 5 1 5
USB to RS232 DB9 9-Pin Cable Adapter Shipping 10 1 10
Power Strip 5 2 10
TOTAL 1999
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2nd Quarter Soekris, Configurations, Testbed
Setup, Experimentation
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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

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Network Setup for testing 802.11e
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Synchronization
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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.

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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

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Soekris 4826
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Soekris 4826

• Power LED, Activity LED, Error LED

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Soekris 4826

• 1 10/100 Mbit Ethernet ports, RJ-45
• 1 Serial port, DB9.

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802.11a/g/b Wireless Mini PCI Card

• SENAO EMP- 8602

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Mini PCI on Soekris Board
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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.

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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
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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

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EDCA Parameters for 802.11e
Parameter AC1 Background AC2 Best Effort AC3 Video AC4 Voice
AIFS 7 3 2 2
CWmin 15 15 7 3
Cwmax 1023 1023 15 7
TXOPLimit (ms) 0 0 3008 1504
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Network Setup Current
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Documentation
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Installation/Configurations

• Soekris Installation
• Debian PXEboot
• Full installation of Fedora Linux
• MADWiFi Installation
• Server setups
• DHCP
• TFTP
• NFS
• PXEboot
• Synchronization tool

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Experimental Results and Analysis
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Network Loading (bytes/sec)
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Network Loading (bytes/sec)
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Network Loading (bytes/sec)
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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.

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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.

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Future Work

• Continued wireless testbed at UCI
• Expand testbed to video testing
• Increase real time protocols in wireless testing
• Test various network design schemes

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Socioeconomic Issues

• Socioeconomic (economic repercussions resulting
  from social shifts)
• As consumers turn toward VoIP-enabled technology
  (conglomerate Internet, telephone, TV, gaming),
  it is industrys 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

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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.

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Economical Issues

• Possible growth of major conglomerates
• Convergence of technologies under one medium
• Necessitates new companies with a focus on VoIP

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Upcoming Activities

• UROP
• Finalize Soekris boxes
• Further 802.11e testing
• Make installation/
• configuration documentation globally available

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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)

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Project Website

• http//www.donjohnii.com/wireless
• Programs
• Configuration guides
• How-To

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References

• Arte Marketing, Inc. Linksys WIP300,
  www.voip-info.org/wiki/view/LinksysWIP300.
  (February 21, 2007).
• ATT. ATT, http//www.corp.att.com/presskit/voi
  p/. (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).

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Acknowledgements

• Ph.D. Student Advisor Ala Khalifeh
• Prof. Kevin Tsai
• Prof. Henry P. Lee