Wireless VoIP

Wireless VoIPWireless VoIP

C3C3

R94922096 R94922096 謝明龍謝明龍R94922088 R94922088 關尚儒關尚儒

OutlineOutline

Problems to use VoIP on wireless networkProblems to use VoIP on wireless network

Voice over WLANVoice over WLAN MAC methodMAC method

802.11e802.11e

Dual queue schemeDual queue scheme

VoIP and 802.11x standardsVoIP and 802.11x standards

VoIP on Wireless NetworkVoIP on Wireless Network

Wireless network – lower speed , noiseWireless network – lower speed , noise Upgrade physical speed , reduce noises (PHY)Upgrade physical speed , reduce noises (PHY) Real-time packet Real-time packet prioritize prioritize (MAC)(MAC)

1AP-to-many Station 1AP-to-many Station Upgrade the capacity of single APUpgrade the capacity of single AP Admission control Admission control

RoamingRoaming

Mobile device powerMobile device power

Wireless securityWireless security

Voice over WLANVoice over WLAN

802.11 supplements glossary802.11 supplements glossary

802.11a – 5GHz OFDM PHY layer 802.11a – 5GHz OFDM PHY layer 802.11b – 2.4GHz CCK PHY layer 802.11b – 2.4GHz CCK PHY layer 802.11c – bridging tables 802.11c – bridging tables 802.11d – international roaming 802.11d – international roaming 802.11e – quality of service MAC802.11e – quality of service MAC802.11f – inter-access point protocols 802.11f – inter-access point protocols 802.11g – 2.4GHz OFDM PHY 802.11g – 2.4GHz OFDM PHY 802.11h – European regulatory extensions 802.11h – European regulatory extensions 802.11i – enhanced security802.11i – enhanced security802.11n – MIMO ODFM PHY802.11n – MIMO ODFM PHY

PHY PHY 802.11n 802.11n

2.4GHz+5GHz (a/b/g)2.4GHz+5GHz (a/b/g)

MIMO+OFDM MIMO+OFDM MIMO (Multiple-In, Multiple-Out)MIMO (Multiple-In, Multiple-Out)

IEEE 802.11 MAC IEEE 802.11 MAC

Dual Queue StrategyDual Queue Strategy


The 802.11e MAC implementation cannot The 802.11e MAC implementation cannot be done by just upgrading the firmware of be done by just upgrading the firmware of an existing MAC controller chip onlyan existing MAC controller chip only

It is difficult to Upgrade (replace) the existiIt is difficult to Upgrade (replace) the existing APsng APs


aboveabove 802.11 the MAC controller 802.11 the MAC controller Original NIC driver Original NIC driver FIFO queue FIFO queue New NIC driver New NIC driver RT + NRT queue RT + NRT queue

Strict priority queuing Strict priority queuing

Effect of MAC HW QueueEffect of MAC HW Queue


VOIP AND ADMISSION CONTROL

VoIP VoIP codec codec G.711 G.711

64 kbps stream8-bit pulse coded modulation (PCM)sampling rate : 8000 samples/second

A VoIP Packet per 20msA VoIP Packet per 20ms

160-byte DATA + 12-byte RTP header + 8-byte UDP header+ 20-byte IP header + 8-byte SNAP header

= 208 bytes per VoIP packet


VoIP Admission ControlVoIP Admission Control assumptionsassumptions

ACK Packet transmitted with 2MbpsACK Packet transmitted with 2MbpsLong PHY preambleLong PHY preamble

Packet transmission MACPacket transmission MACDIFS deferenceDIFS deferenceBackoffBackoffPacket transmissionPacket transmissionSIFS deferenceSIFS deferenceACK transmissionACK transmission


VoIP packet transmission time ≒VoIP packet transmission time ≒ 981μs981μs VoIP MAC packet transmission timeVoIP MAC packet transmission time

192-μs PLCP preamble/header + (24-byte MAC header + 4-192-μs PLCP preamble/header + (24-byte MAC header + 4-byte CRC-32 + 208-byte payload) / 11 Mbits/s = 363 μsbyte CRC-32 + 208-byte payload) / 11 Mbits/s = 363 μs

ACK transmission time at 2 Mbits/sACK transmission time at 2 Mbits/s192-μs PLCP preamble/header + 14-byte ACK packet / 2Mbits/s = 248 μs

Average backoff durationAverage backoff duration 31 (CWmin) * 20 μs (One Slot Time) / 2 = 310 μs


Every VoIP sessioinEvery VoIP sessioin inter-activeinter-active 2 senders2 senders one voice packet transmitted every 20ms one voice packet transmitted every 20ms

Every 20ms time intervalEvery 20ms time interval 20 (= 20 ms / 981 20 (= 20 ms / 981 μs) voice packetss) voice packets

Maximum number of VoIP sessions over a Maximum number of VoIP sessions over a 802.11 LAN is 10802.11 LAN is 10

COMPARATIVE PERFORMANCE COMPARATIVE PERFORMANCE EVALUATIONEVALUATION

Using the ns-2 simulatorUsing the ns-2 simulator 802.11b PHY 802.11b PHY TrafficTraffic

Voice Voice two-way constant bit rate (CBR) session according to G.711 codec

DataData unidirectional FTP/TCP flow with 1460-byte packet size and 12-packet (or 17520-byte) receive window size.

COMPARATIVE PERFORMANCE COMPARATIVE PERFORMANCE EVALUATION EVALUATION

EVALUATION RESULTEVALUATION RESULT

Pure VoIPPure VoIP

Effect of VoIP with different TCP session Effect of VoIP with different TCP session numbersnumbers

Performance with Dual queuePerformance with Dual queue

Unfairness of NRT PacketUnfairness of NRT Packet


ObservationObservation

Compare to our EvaluationCompare to our Evaluation packet drop ratepacket drop rate

50 packets for the RT queue size50 packets for the RT queue size

Downlink is disadvantagedDownlink is disadvantaged

Simulation results are based on 11 MbpsSimulation results are based on 11 Mbps


Pure VoIPPure VoIP






Effect of queue sizeEffect of queue size


Pure VoIPPure VoIP






worst case delay 11msworst case delay 11ms Queuing delay with the single queue MAC HW queue wireless channel access

NRT queuesNRT queues Size = 50 or 100 increase as the number of

TCP flows increases Size = 500 almost no change in delay


Pure VoIPPure VoIP






Unfairness Unfairness between upstream and downstream TCP flow

s with the queue sizes of 50 and 100

Queue size for the AP should be large enoQueue size for the AP should be large enough - This is good for usugh - This is good for us


Pure VoIPPure VoIP






Delay of downlink voice packetsDelay of downlink voice packets increases linearly proportional to the MAC HW queue

size

Another effectAnother effect with the MAC HW queue size of 8, the worst delay is

observed with a single VoIP session

Large MAC HW queue size is still aceptableLarge MAC HW queue size is still aceptable <25ms

Brief SummaryBrief Summary

Driver of the 802.11 MAC controllerDriver of the 802.11 MAC controller

Strict priority queuingStrict priority queuing

Bottleneck of TCP in WLAN Bottleneck of TCP in WLAN downlink downlink

VoIP and 802.11e QoS stanVoIP and 802.11e QoS standardsdards

What’s the difference between What’s the difference between Wireless/Wired VoIP?Wireless/Wired VoIP?

MobilityMobility RoamingRoaming

SecuritySecurity Hidden UAHidden UA

Quality of ServiceQuality of Service Guarantee of voice qualityGuarantee of voice quality

Hidden Node ProblemHidden Node Problem

Quality of ServiceQuality of Service

QoS problemsQoS problems

802.11e QoS standard802.11e QoS standard

A non-standard solution –A non-standard solution –


QoS ProblemsQoS Problems

Dropped PacketsDropped PacketsDelayDelayJitterJitterOut-of-order DeliveryOut-of-order DeliveryErrorError

VoIP requires strict limits on jitter and VoIP requires strict limits on jitter and delay delay

Quality of ServiceQuality of Service

QoS problemsQoS problems

802.11e QoS standard802.11e QoS standard

A non-standard solution –A non-standard solution –


IEEE 802.11eIEEE 802.11e

A draft standard of July 2005A draft standard of July 2005

It defines a set of QoS enhancements for It defines a set of QoS enhancements for WLAN applicationsWLAN applications

and enhances the IEEE 802.11 Media and enhances the IEEE 802.11 Media Access Control (MAC) layerAccess Control (MAC) layer

Coordination FunctionCoordination Function

For stations to decide which one has the For stations to decide which one has the right to deliver its packetsright to deliver its packets

802.11: DCF & PCF802.11: DCF & PCF

802.11e: EDCF & HCF802.11e: EDCF & HCF

Original 802.11 MACOriginal 802.11 MAC

Distributed Coordination Function (DCF)Distributed Coordination Function (DCF)

Point Coordination Function (PCF)Point Coordination Function (PCF)

Distributed Coordination Function Distributed Coordination Function (DCF)(DCF)

Share the medium between multiple Share the medium between multiple stationsstations

Rely on CSMA/CA and optional 802.11 Rely on CSMA/CA and optional 802.11 RTS/CTSRTS/CTS

How DCF works?How DCF works?

DCF LimitationsDCF Limitations

When many collisions occur, the available When many collisions occur, the available bandwidth will be lowerbandwidth will be lower

No notion of high or low priority trafficNo notion of high or low priority traffic

A station may keep the mediumA station may keep the medium

If the station has a lower bitrate, all other If the station has a lower bitrate, all other stations will suffer from thatstations will suffer from that

No QoS guaranteesNo QoS guarantees

Original 802.11 MACOriginal 802.11 MAC

Distributed Coordination Function (DCF)Distributed Coordination Function (DCF)



Available only in "infrastructure" modeAvailable only in "infrastructure" mode

Optional mode, only very few APs or Wi-Fi Optional mode, only very few APs or Wi-Fi adapters actually implement itadapters actually implement it

Beacon frame, Contention Period, and CoBeacon frame, Contention Period, and Contention Free Periodntention Free Period

How PCF works?How PCF works?

802.11 MAC Layer Framework802.11 MAC Layer Framework

802.11e MAC Protocol Operation802.11e MAC Protocol Operation

Enhanced DCF (EDCF)Enhanced DCF (EDCF)

Hybrid Coordination Function (HCF)Hybrid Coordination Function (HCF)


Define Traffic ClassesDefine Traffic Classes

High priority traffic has a higher chance of being High priority traffic has a higher chance of being sent than low priority trafficsent than low priority traffic

A "best effort" QoSA "best effort" QoS

Simple to configure and implementSimple to configure and implement

802.11e MAC Protocol Operation802.11e MAC Protocol Operation


Hybrid Coordination Function (HCF)Hybrid Coordination Function (HCF)

Hybrid Coordination Function Hybrid Coordination Function (HCF)(HCF)

Works a lot like the PCFWorks a lot like the PCFMain difference with the PCF: Define the TMain difference with the PCF: Define the Traffic Classes (TC)raffic Classes (TC)Stations are given a Transmit Opportunity Stations are given a Transmit Opportunity (TXOP)(TXOP)TThe most advanced (and complex) he most advanced (and complex) coordination functioncoordination functionQoS can be configured with great precisioQoS can be configured with great precisionn

ConclusionConclusion

Paper References 1Paper References 1

Jeonggyun YuJeonggyun Yu,, Sunghyun Choi Sunghyun Choi,, Jaehwan Lee Jaehwan Lee, , “Enhancement of VoI“Enhancement of VoIP over IEEE 802.11 WLAN via Dual Queue Strategy”P over IEEE 802.11 WLAN via Dual Queue Strategy”Moncef Elaoud, David Famolari, and Ahbrajit GhoshMoncef Elaoud, David Famolari, and Ahbrajit Ghosh, , “Experimental “Experimental VoIP Capacity Measurements for 802.11b WLANs”VoIP Capacity Measurements for 802.11b WLANs”Mustafa ErgenMustafa Ergen, , “I-WLAN: Intelligent Wireless Local Area Networking“I-WLAN: Intelligent Wireless Local Area Networking””Gyung-Ho Hwang, Dong-Ho Cho,Gyung-Ho Hwang, Dong-Ho Cho, “New Access Scheme for VoIP P“New Access Scheme for VoIP Packets in IEEE 802.11e Wireless LANs”ackets in IEEE 802.11e Wireless LANs”Sai Shankar NSai Shankar N, , Javier del Prado PavonJavier del Prado Pavon, , Patrick WienertPatrick Wienert, , “Optimal p“Optimal packing of VoIP calls in an IEEE 802.11a/e WLAN in the presence of acking of VoIP calls in an IEEE 802.11a/e WLAN in the presence of QoS Constraints and Channel Errors”QoS Constraints and Channel Errors”

Paper Reference 2Paper Reference 2

Experimental VoIP capacity measurements for 802.11b WLANsEnhancement of VolP over IEEE 802.11 WLAN via dual queue strategyAn experimental study of throughput for UDP and VoIP traffic in IEEE 802.11b networksAdmission control for VoIP traffic in IEEE 802.11 networksHow well can the IEEE 802.11 wireless LAN support quality of service

Web Site ReferencesWeb Site References

http://www.ieee.or.com/Archive/80211/802_11e_http://www.ieee.or.com/Archive/80211/802_11e_QoS_files/frame.htmQoS_files/frame.htm

http://en.wikipedia.org/wiki/IEEE_802.11http://en.wikipedia.org/wiki/IEEE_802.11

http://www.cs.nthu.edu.tw/~nfhuang/chap13.htmhttp://www.cs.nthu.edu.tw/~nfhuang/chap13.htm#13.1#13.1

http://www.eettaiwan.com/ART_8800360909_67http://www.eettaiwan.com/ART_8800360909_675327_3f3ffd7b_no.HTM5327_3f3ffd7b_no.HTM

http://it.sohu.com/2003/12/11/09/article2167509http://it.sohu.com/2003/12/11/09/article216750985.shtml85.shtml

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Wireless VoIP