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Wireless VoIP

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Title: Wireless VoIP


1
Wireless VoIP
  • C3
  • R94922096 ???
  • R94922088 ???

2
Outline
  • Problems to use VoIP on wireless network
  • Voice over WLAN
  • MAC method
  • 802.11e
  • Dual queue scheme
  • VoIP and 802.11x standards

3
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

4
Voice over WLAN
5
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

6
802.11 standards
higher layers
supplements 802.11c and 802.11f
802.11 MAC
supplements 802.11d, 802.11e, 802.11i and 802.11h
802.11 PHY
supplements 802.11a, 802.11b and 802.11g

7
PHY ? 802.11n
  • 2.4GHz5GHz (a/b/g)
  • MIMOOFDM
  • MIMO (Multiple-In, Multiple-Out)

8
MIMO
9
IEEE 802.11 MAC
10
Hidden Node Problem
11
Dual Queue Strategy
12
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

13
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

14
Dual Queue Strategy
15
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

16
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

17
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

18
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

19
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.

20
COMPARATIVE PERFORMANCE EVALUATION
21
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

22
(No Transcript)
23
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

24
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

25
(No Transcript)
26
Observation
  • Effect of queue size

27
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

28
(No Transcript)
29
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

30
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

31
(No Transcript)
32
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

33
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

34
(No Transcript)
35
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
  • lt25ms

36
Brief Summary
  • Driver of the 802.11 MAC controller
  • Strict priority queuing
  • Bottleneck of TCP in WLAN ? downlink

37
VoIP and 802.11e QoS standards
38
Whats the difference between Wireless/Wired VoIP?
  • Mobility
  • Roaming
  • Security
  • Hidden UA
  • Quality of Service
  • Guarantee of voice quality

39
Hidden Node Problem
40
Quality of Service
  • QoS problems
  • 802.11e QoS standard
  • A non-standard solution
  • Dual Queue Strategy

41
QoS Problems
  • Dropped Packets
  • Delay
  • Jitter
  • Out-of-order Delivery
  • Error
  • VoIP requires strict limits on jitter and delay

42
Quality of Service
  • QoS problems
  • 802.11e QoS standard
  • A non-standard solution
  • Dual Queue Strategy

43
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

44
Coordination Function
  • For stations to decide which one has the right to
    deliver its packets
  • 802.11 DCF PCF
  • 802.11e EDCF HCF

45
Original 802.11 MAC
  • Distributed Coordination Function (DCF)
  • Point Coordination Function (PCF)

46
Distributed Coordination Function (DCF)
  • Share the medium between multiple stations
  • Rely on CSMA/CA and optional 802.11 RTS/CTS

47
How DCF works?
48
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

49
Original 802.11 MAC
  • Distributed Coordination Function (DCF)
  • Point Coordination Function (PCF)

50
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

51
How PCF works?
52
802.11 MAC Layer Framework
53
802.11e MAC Protocol Operation
  • Enhanced DCF (EDCF)
  • Hybrid Coordination Function (HCF)

54
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

55
802.11e MAC Protocol Operation
  • Enhanced DCF (EDCF)
  • Hybrid Coordination Function (HCF)

56
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

57
Whats the difference between Wireless/Wired VoIP?
  • Quality of Service
  • Security
  • Mobility

58
IEEE 802.11i
  • The draft standard was ratified on 24 June 2004
  • Supersede Wired Equivalent Privacy (WEP)
  • Wi-Fi Protected Access (WPA) is a subset
    implementation
  • And WPA2 is the full implementation

59
IEEE 802.11i (cont.)
  • 802.1X for authentication (entailing the use of
    EAP and an authentication server)
  • RSN for keeping track of associations
  • AES-based CCMP to provide confidentiality,
    integrity and origin authentication
  • Authentication process four-way handshake

60
The Four-Way Handshake
61
Whats the difference between Wireless/Wired VoIP?
  • Quality of Service
  • Security
  • Mobility

62
IEEE 802.11f 802.11r
  • 802.11f Inter-Access Point Protocol
  • 802.11r Fast roaming

63
Conclusion
64
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

65
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

66
Web Site References
  • http//www.ieee.or.com/Archive/80211/802_11e_QoS_f
    iles/frame.htm
  • http//en.wikipedia.org/wiki/IEEE_802.11
  • http//www.cs.nthu.edu.tw/nfhuang/chap13.htm13.1
  • http//www.eettaiwan.com/ART_8800360909_675327_3f3
    ffd7b_no.HTM
  • http//it.sohu.com/2003/12/11/09/article216750985.
    shtml
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