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Wireless VoIP. C3 R94922096 謝明龍 R94922088 關尚儒. Outline. Problems to use V oIP on wireless network Voice over WLAN MAC method 802.11e Dual queue scheme VoIP and 802.11x standards. VoIP on Wireless Network. Wireless network – lower speed , noise

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Wireless voip

Wireless VoIP

C3

R94922096 謝明龍

R94922088 關尚儒


Outline
Outline

  • Problems to use VoIP on wireless network

  • Voice over WLAN

    • MAC method

      • 802.11e

      • Dual queue scheme

  • VoIP and 802.11x standards


Voip on wireless network
VoIP on Wireless Network

  • Wireless network – lower speed , noise

    • Upgrade physical speed , reduce noises (PHY)

    • Real-time packet prioritize (MAC)

  • 1AP-to-many Station

    • Upgrade the capacity of single AP

    • Admission control

  • Roaming

  • Mobile device power

  • Wireless security



802 11 supplements glossary
802.11 supplements glossary

  • 802.11a – 5GHz OFDM PHY layer

  • 802.11b – 2.4GHz CCK PHY layer

  • 802.11c – bridging tables

  • 802.11d – international roaming

  • 802.11e – quality of service MAC

  • 802.11f – inter-access point protocols

  • 802.11g – 2.4GHz OFDM PHY

  • 802.11h – European regulatory extensions

  • 802.11i – enhanced security

  • 802.11n – MIMO ODFM PHY


Phy 802 11n
PHY  802.11n

  • 2.4GHz+5GHz (a/b/g)

  • MIMO+OFDM

    • MIMO (Multiple-In, Multiple-Out)




Dual queue strategy1
Dual Queue Strategy

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

  • It is difficult to Upgrade (replace) the existing APs


Dual queue strategy2
Dual Queue Strategy

  • above 802.11 the MAC controller

    • Original NIC driver  FIFO queue

    • New NIC driver  RT + NRT queue

  • Strict priority queuing

  • Effect of MAC HW Queue



Voip and admission control
VOIP AND ADMISSION CONTROL

  • VoIP

    • codec  G.711

      • 64 kbps stream

      • 8-bit pulse coded modulation (PCM)

      • sampling rate : 8000 samples/second

    • A 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 and admission control1
VOIP AND ADMISSION CONTROL

  • VoIP Admission Control

    • assumptions

      • ACK Packet transmitted with 2Mbps

      • Long PHY preamble

    • Packet transmission MAC

      • DIFS deference

      • Backoff

      • Packet transmission

      • SIFS deference

      • ACK transmission


Voip and admission control2
VOIP AND ADMISSION CONTROL

  • VoIP packet transmission time ≒ 981μs

    • VoIP MAC packet transmission time

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

    • ACK transmission time at 2 Mbits/s

      • 192-μs PLCP preamble/header + 14-byte ACK packet / 2Mbits/s = 248 μs

    • Average backoff duration

      • 31 (CWmin) * 20 μs (One Slot Time) / 2 = 310 μs


Voip and admission control3
VOIP AND ADMISSION CONTROL

  • Every VoIP sessioin

    • inter-active 2 senders

    • one voice packet transmitted every 20ms

  • Every 20ms time interval

    • 20 (= 20 ms / 981 μs) voice packets

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


Comparative performance evaluation
COMPARATIVE PERFORMANCE EVALUATION

  • Using the ns-2 simulator

    • 802.11b PHY

    • Traffic

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

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



Evaluation result
EVALUATION RESULT

  • Pure VoIP

  • Effect of VoIP with different TCP session numbers

  • Performance with Dual queue

  • Unfairness of NRT Packet

  • Effect of MAC HW Queue


Observation
Observation

  • Compare to our Evaluation

    • packet drop rate

  • 50 packets for the RT queue size

  • Downlink is disadvantaged

  • Simulation results are based on 11 Mbps


Evaluation result1
EVALUATION RESULT

  • Pure VoIP

  • Effect of VoIP with different TCP session numbers

  • Performance with Dual queue

  • Unfairness of NRT Packet

  • Effect of MAC HW Queue


Observation1
Observation

  • Effect of queue size


Evaluation result2
EVALUATION RESULT

  • Pure VoIP

  • Effect of VoIP with different TCP session numbers

  • Performance with Dual queue

  • Unfairness of NRT Packet

  • Effect of MAC HW Queue


Observation2
Observation

  • worst case delay 11ms

    • Queuing delay with the single queue

    • MAC HW queue wireless channel access

  • NRT queues

    • Size = 50 or 100  increase as the number of TCP flows increases

    • Size = 500  almost no change in delay


Evaluation result3
EVALUATION RESULT

  • Pure VoIP

  • Effect of VoIP with different TCP session numbers

  • Performance with Dual queue

  • Unfairness of NRT Packet

  • Effect of MAC HW Queue


Observation3
Observation

  • Unfairness

    • between upstream and downstream TCP flows with the queue sizes of 50 and 100

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


Evaluation result4
EVALUATION RESULT

  • Pure VoIP

  • Effect of VoIP with different TCP session numbers

  • Performance with Dual queue

  • Unfairness of NRT Packet

  • Effect of MAC HW Queue


Observation4
Observation

  • Delay of downlink voice packets

    • increases linearly proportional to the MAC HW queue size

  • Another 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 aceptable

    • <25ms


Brief summary
Brief Summary

  • Driver of the 802.11 MAC controller

  • Strict priority queuing

  • Bottleneck of TCP in WLAN  downlink



What s the difference between wireless wired voip
What’s the difference between Wireless/Wired VoIP?

  • Mobility

    • Roaming

  • Security

    • Hidden UA

  • Quality of Service

    • Guarantee of voice quality



Quality of service
Quality of Service

  • QoS problems

  • 802.11e QoS standard

  • A non-standard solution –

    Dual Queue Strategy


Qos problems
QoS Problems

  • Dropped Packets

  • Delay

  • Jitter

  • Out-of-order Delivery

  • Error

  • VoIP requires strict limits on jitter and delay


Quality of service1
Quality of Service

  • QoS problems

  • 802.11e QoS standard

  • A non-standard solution –

    Dual Queue Strategy


Ieee 802 11e
IEEE 802.11e

  • A draft standard of July 2005

  • It defines a set of QoS enhancements for WLAN applications

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


Coordination function
Coordination Function

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

  • 802.11: DCF & PCF

  • 802.11e: EDCF & HCF


Original 802 11 mac
Original 802.11 MAC

  • Distributed Coordination Function (DCF)

  • Point Coordination Function (PCF)


Distributed coordination function dcf
Distributed Coordination Function (DCF)

  • Share the medium between multiple stations

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



Dcf limitations
DCF Limitations

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

  • No notion of high or low priority traffic

  • A station may keep the medium

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

  • No QoS guarantees


Original 802 11 mac1
Original 802.11 MAC

  • Distributed Coordination Function (DCF)

  • Point Coordination Function (PCF)


Point coordination function pcf
Point Coordination Function (PCF)

  • Available only in "infrastructure" mode

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

  • Beacon frame, Contention Period, and Contention Free Period




802 11e mac protocol operation
802.11e MAC Protocol Operation

  • Enhanced DCF (EDCF)

  • Hybrid Coordination Function (HCF)


Enhanced dcf edcf
Enhanced DCF (EDCF)

  • Define Traffic Classes

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

  • A "best effort" QoS

  • Simple to configure and implement


802 11e mac protocol operation1
802.11e MAC Protocol Operation

  • Enhanced DCF (EDCF)

  • Hybrid Coordination Function (HCF)


Hybrid coordination function hcf
Hybrid Coordination Function (HCF)

  • Works a lot like the PCF

  • Main difference with the PCF: Define the Traffic Classes (TC)

  • Stations are given a Transmit Opportunity (TXOP)

  • The most advanced (and complex) coordination function

  • QoS can be configured with great precision



Paper references 1
Paper References 1

  • Jeonggyun Yu, Sunghyun Choi, Jaehwan Lee, “Enhancement of VoIP over IEEE 802.11 WLAN via Dual Queue Strategy”

  • Moncef Elaoud, David Famolari, and Ahbrajit Ghosh, “Experimental VoIP Capacity Measurements for 802.11b WLANs”

  • Mustafa Ergen, “I-WLAN: Intelligent Wireless Local Area Networking”

  • Gyung-Ho Hwang, Dong-Ho Cho,“New Access Scheme for VoIP Packets in IEEE 802.11e Wireless LANs”

  • Sai Shankar N, Javier del Prado Pavon, Patrick Wienert, “Optimal packing of VoIP calls in an IEEE 802.11a/e WLAN in the presence of QoS Constraints and Channel Errors”


Paper reference 2
Paper Reference 2

  • Experimental VoIP capacity measurements for 802.11b WLANs

  • Enhancement of VolP over IEEE 802.11 WLAN via dual queue strategy

  • An experimental study of throughput for UDP and VoIP traffic in IEEE 802.11b networks

  • Admission control for VoIP traffic in IEEE 802.11 networks

  • How well can the IEEE 802.11 wireless LAN support quality of service


Web site references
Web Site References

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

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

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

  • http://www.eettaiwan.com/ART_8800360909_675327_3f3ffd7b_no.HTM

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


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